期刊文献+
共找到86篇文章
< 1 2 5 >
每页显示 20 50 100
Change analysis of rice area and production in China during the past three decades 被引量:16
1
作者 LIU Zhenhuan LI Zhengguo +5 位作者 TANG Pengqin LI Zhipeng WU Wenbin YANG Peng YOU Liangzhi TANG Huajun 《Journal of Geographical Sciences》 SCIE CSCD 2013年第6期1005-1018,共14页
Rice's spatial-temporal distributions, which are critical for agricultural, environ- mental and food security research, are affected by natural conditions as well as socio-eco- nomic developments. Based on multi-sour... Rice's spatial-temporal distributions, which are critical for agricultural, environ- mental and food security research, are affected by natural conditions as well as socio-eco- nomic developments. Based on multi-source data, an effective model named the Spatial Production Allocation Model (SPAM) which integrates arable land distribution, administrative unit statistics of crop data, agricultural irrigation data and crop suitability data, was used to get a series of spatial distributions of rice area and production with 10-km pixels at a national scale -it was applied from the early 1980s onwards and used to analyze the pattern of spatial and temporal changes. The results show that significant changes occurred in rice in China during 1980-2010. Overall, more than 50% of the rice area decreased, while nearly 70% of rice production increased in the change region during 1980-2010. Spatially, most of the increased area and production were in Northeast China, especially, in Jilin and Heilongjiang; most of the decreased area and production were located in Southeast China, especially, in regions of rapidly urbanization in Guangdong, Fujian and Zhejiang. Thus, the centroid of rice area was moved northeast approximately 230 km since 1980, and rice production about 320 km, which means rice production moved northeastward faster than rice area because of the significant rice yield increase in Northeast China. The results also show that rice area change had a decisive impact on rice production change. About 54.5% of the increase in rice pro- duction is due to the expansion of sown area, while around 83.2% of the decrease in rice production is due to contraction of rice area. This implies that rice production increase may be due to area expansion and other non-area factors, but reduced rice production could largely be attributed to rice area decrease. 展开更多
关键词 rice distribution spatial production allocation model spatial-temporal changes China
原文传递
Spatio-temporal dynamics of maize cropping system in Northeast China between 1980 and 2010 by using spatial production allocation model 被引量:13
2
作者 TAN Jieyang YANG Peng +6 位作者 LIU Zhenhuan WU Wenbin ZHANG Li LI Zhipeng YOU Liangzhi TANG Huajun LI Zhengguo 《Journal of Geographical Sciences》 SCIE CSCD 2014年第3期397-410,共14页
Understanding crop patterns and their changes on regional scale is a critical re- quirement for projecting agro-ecosystem dynamics. However, tools and methods for mapping the distribution of crop area and yield are st... Understanding crop patterns and their changes on regional scale is a critical re- quirement for projecting agro-ecosystem dynamics. However, tools and methods for mapping the distribution of crop area and yield are still lacking. Based on the cross-entropy theory, a spatial production allocation model (SPAM) has been developed for presenting spa- tio-temporal dynamics of maize cropping system in Northeast China during 1980-2010. The simulated results indicated that (1) maize sown area expanded northwards to 48~N before 2000, after that the increased sown area mainly occurred in the central and southern parts of Northeast China. Meanwhile, maize also expanded eastwards to 127°E and lower elevation (less than 100 m) as well as higher elevation (mainly distributed between 200 m and 350 m); (2) maize yield has been greatly promoted for most planted area of Northeast China, espe- cially in the planted zone between 42°N and 48°N, while the yield increase was relatively homogeneous without obvious longitudinal variations for whole region; (3) maize planting density increased gradually to a moderately high level over the investigated period, which reflected the trend of aggregation of maize cultivation driven by market demand. 展开更多
关键词 spring maize spatial production allocation model spatio-temporal pattern Northeast China
原文传递
Feeding Effect of Triticale Fodder as Replacement of Straw on Production Performance of Dairy Cows 被引量:2
3
作者 Nathu Ram Sarker Mohammad Asaduzzaman +4 位作者 Khan Shahidul Huque Mohammad Toyebur Rahman NazrulIslam Mohammad Enamul Haque Stephen R. Waadington 《Journal of Agricultural Science and Technology(A)》 2013年第1期72-82,共11页
Twenty lactating cows of two to five parity having an average live weight of 290.00 to 330.00 kg and an average milk production of 4.54 kg/head/day to 4.66 kg/head/day were selected from the Central Cattle breeding St... Twenty lactating cows of two to five parity having an average live weight of 290.00 to 330.00 kg and an average milk production of 4.54 kg/head/day to 4.66 kg/head/day were selected from the Central Cattle breeding Station and Dairy Farm. The four dietary treatment were: SlooTo (Straw 100: Triticale 0 as control); $5oT5o (Straw 50: Triticale 50); $25T75 (Straw 25: Triticale 75) and SoTloo (Straw 0: Triticale 100). It was observed that the roughage dry matter intake (DMI) (2.61 ~ 0.07 kg) in percent live weight was significantly (P 〈 0.05) higher in $25T75 and the lowest (1.76 ~ 0.018 kg) in the control group (SlooTo) and the differences were significant among the dietary treatments except $5oT5o and SoTloo. The total DMI was significantly (P 〈 0.05) higher in SoT^oo (13.36 i 0.13 kg) followed by $25T75, $5oT5o and SlooTo, respectively. The digestibility of crude protein (CP) was slightly higher in $25T75 (75.48 ~ 0.96) compared to SoTtoo (75.31 ~ 1.45) and the difference was non-significant (P 〉 0.05). Milk production was significantly (P 〈 0.05) the highest in $5oT5o and the lowest in SlooTo followed by SoTloo, $25T75, respectively. The percent increased in milk yield was also the highest in $5oT5o (67.68%) and the lowest in SlooTo (28.85%). The 4% fat corrected milk was also significantly (P 〈 0.05) higher in $5oT5o followed by SoTloo, $25T75 and SlooTo, respectively. Therefore, it can be concluded that triticale and straw at a ratio of 50:50 may be fed for better production performance of dairy cows. 展开更多
关键词 Triticale green fodder production performance REPLACEMENT milk yield.
在线阅读 下载PDF
Effects of Supplementing Various Linoleic to α-linolenic Acid Ratios and Vitamin A on Production Performance and Egg Characteristics of Laying Hens during Summer Months 被引量:1
4
作者 S.Ahmad M.Yousaf +5 位作者 Z.Kamran M.U.Sohail M.N.Tahir K.C.Koutoulis A.Manzoor 《Journal of Zoological Research》 2019年第1期1-9,共9页
In the present feeding trial,responses of laying hens that were kept at high ambient temperature and Fed with various dietary ratios of linoleic acid(LNA)toα-linolenic acid(ALA)and vitamin A levels on production perf... In the present feeding trial,responses of laying hens that were kept at high ambient temperature and Fed with various dietary ratios of linoleic acid(LNA)toα-linolenic acid(ALA)and vitamin A levels on production performance and egg quality traits were evaluated.A total of 360 Leghorn laying hens at 40th week of age(average initial body weight;1.79±0.23 kg)were fed with various combinations of canola oil and linseed oil containing diets to achieve LNA to ALA dietary ratios of 20:1,10:1,4:1,2:1,1:1 and 1:2,each supplemented with 3000 or 10000 IU of vitamin A/kg of diet.The experiment was designed as a 6×2 factorial Completely Randomized Design that continued for 12 weeks.Feed intake,body weight gain,egg production and egg quality traits were recorded during the trial.Decreasing dietary LNA to ALA ratio or increasing poly unsaturated fatty acids(PUFA)in the diet decreased(P<0.05)body weight gain and yolk percentage in laying hens.Feed intake,hen-day and hen-housed egg production,feed conversion ratio(FCR)per dozen of eggs and shell quality remained unaffected(P>0.05)by dietary treatments.Feed conversion ratio per kg eggs,egg weight and egg-shell thickness showed a curvilinear(P<0.05)response to decreasing dietary LNA to ALA ratio.Although the dietary ratio of LNA to ALA of 4:1 or less could produce eggs by the hens with desirable quantities of n-6 and n-3 PUFA–that are characteristics of functional diets–the performance of laying hens in terms of body weight gain and egg-yolk percentage was slightly compromised.Therefore,a 4:1 or 2:1 LNA to ALA combination can make a borderline between the production traits and the feed economics. 展开更多
关键词 EGG quality FATTY ACIDS Hot climate Layers performance VITAMIN A
在线阅读 下载PDF
Life cycle greenhouse gas emissions from five contrasting rice production systems in the tropics
5
作者 Pradeep K.DASH Pratap BHATTACHARYYA +3 位作者 Soumya R.PADHY Amaresh K.NAYAK Annie POONAM Sangita MOHANTY 《Pedosphere》 SCIE CAS CSCD 2023年第6期960-971,共12页
Carbon footprint (CF) quantification of major rice production systems (RPSs) is a prerequisite for developing strategies for climate change mitigation in agriculture. Total life cycle greenhouse gas emissions (LC-GHGs... Carbon footprint (CF) quantification of major rice production systems (RPSs) is a prerequisite for developing strategies for climate change mitigation in agriculture. Total life cycle greenhouse gas emissions (LC-GHGs) from rice production to consumption might provide precise CFs for RPSs. Therefore, we assessed three segments (pre-farm, on-farm, and post-farm) of LC-GHGs under five major contrasting RPSs, i.e., aerobic rice (AR), shallow lowland rice(SLR), system of rice intensification (SRI), deep water rice (DWR), and zero-tilled direct-seeded rice (ZTR), in India to determine the corresponding CFs.Carbon footprint was the lowest for ZTR, while LC-GHGs were the lowest for AR. Therefore, AR is an adequate option for short-term reduction of GHG emissions. However, ZTR might be promoted by incentives as a long-term strategy. Among segmental LC-GHGs, on-farm GHG emissions contributed less than the other two segmental GHG emissions. The post-farm (i.e., farm gate to consumption) segment contributed the largest proportion (54%–69%) of total LC-GHGs, followed by pre-farm (i.e., cradle to farm) segment (21%–27%) and on-farm operation (11%–23%). These findings suggest that post-farm components that contribute to maximum GHG emissions must be scientifically tackled with proactive policy initiatives. However, the data of this segment are limited and scattered. Therefore, real-time assessment of GHG emissions during post-farm operation and input transportation from cradle to farm requires more precise quantification. Although CF in SRI was higher, this system had the potential to achieve higher yields and better soil carbon storage. Therefore,SRI may be encouraged from the perspectives of food security and long-term sustainability by reducing GHG emissions by three to four times. 展开更多
关键词 carbon-equivalent emission carbon footprint climate change mitigation global warming management practice soil carbon stock:
原文传递
Study on Feeding Effect of Different Levels of Protein and Energy on Production Performance of Pregnant Mother and Neo-Natal Calves
6
作者 Nathu Ram Sarker Muhammad Khaiml Bashar Sheik Mohammad Jahangir Hossain Mohammed Khorshed Alam and Khan Shahidul Huque 《Journal of Agricultural Science and Technology(A)》 2015年第2期81-89,共9页
The present study was undertaken to assess feeding effect on productive and reproductive performances of pre-natal and post-natal Red Chittagong Cattle (RCC) cows under on-station condition. A total of 16 pregnant R... The present study was undertaken to assess feeding effect on productive and reproductive performances of pre-natal and post-natal Red Chittagong Cattle (RCC) cows under on-station condition. A total of 16 pregnant RCC cows having pregnancy 6-7 months and between 1-3 parities was selected for the study and was allocated randomly into four dietary treatment groups. There are four type diets, i.e., To (standard diet according to National Research Council (NRC), 1995), T1 (5% below standard diet), T2 (5% above standard diet), T3 (10% above standard diet) and a control treatment T4 (maintained as farm practice). The energy and protein requirements of experimental cows were determined as per standard developed by NRC. The results revealed that crude protein (CP) and metabolizable energy (ME, MJ/day) requirements among cows of different dietary groups were not significantly different, although CP requirements between T1 and T3 differed significantly. Total dry mater (DM) and ME intake differed significantly (P 〈 0.001) among cows of different dietary groups, but DM intake was significantly lower for cows in farm practice group Z4 compared to the cows of other dietary groups. The total CP intake had no significant variation (P 〉 0.05) among cows of all dietary groups, but CP intake from roughage varied significantly (P 〈 0.001). Final live weight and total live weight gain had no significant variation for cows of all groups, but there were significant (P 〈 0.05) variation for daily weight gain. Daily weight gain of cows for first four dietary groups were significantly (P 〈 0.05) higher than cows of farm practice groups T4. Weight of calf from birth to 90 days and daily weight gain calves under different dietary groups showed that there were no significant (P 〉 0.05) variation of calf birth weights for all dietary groups, although lower birth weight was found in farm practice groups T4. Gestation length and postpartum heat period of cows of different dietary treatment groups revealed that there was no significant (P 〉 0.05) variation for those traits among cows of different dietary treatment groups, although there seems to be shorter postpartum heat for cows in dietary group T2 and longer period in farm practice group T4. Total and daily milk yield up to 30 days and 90 days of cows had no significant (P 〉 0.05) effect for different dietary treatment groups, although there seems to be slightly better milk production performance for dietary T2 and To, respectively for 30 days and 90 days total and daily milk yield. There were no significant (P 〉 0.05) changes of total and daily weight gain of cows for all dietary groups, however cows of standard dietary group To performed slightly better than those of cows of other dietary groups. Milk composition of cows of different dietary treatment groups showed that there was no significant (P 〉 0.05) variation on milk composition for cows of different dietary groups. Post-natal body condition score (BCS) for the 1st, 3rd and 4th months differed significantly (P 〈 0.05) among different dietary groups, while not found significant difference on the 2nd month. Therefore, it may be concluded that pre-natal feeding has significant effect on body weight gain, birth weight of calves and milk production of dairy cows. Hence, it is suggested that better nutrition may be provided during pre-natal period to harvest good quality of calves and higher milk yield from post-natal period. 展开更多
关键词 Pre-natal POST-NATAL postpartum heat period gestation length milk yield.
在线阅读 下载PDF
Mono Ethanol Amine (MEA) Pulping of Wheat Straw: An Environmentally Friendly Suggestion for the Fluff Pulp Production
7
作者 Saeed Ismaeilimoghadam Saeed Mahdavi +2 位作者 Mehdi Pourhashemi Afsaneh Shahraki Mehdi Jonoobi 《Journal of Renewable Materials》 EI CAS 2024年第10期1771-1789,共19页
This research aimed to investigate the effect of pulping conditions and refining intensities of wheat straw to be recommended for fluff pulp production.For this purpose,mono ethanol amine(MEA)was selected as a de-lign... This research aimed to investigate the effect of pulping conditions and refining intensities of wheat straw to be recommended for fluff pulp production.For this purpose,mono ethanol amine(MEA)was selected as a de-lignification agent at three levels of 50:50,25:75,and 15:85(MEA/water,W/V%),and soda-AQ 14 W/V%was used as a reference pulping.To investigate the optimal refining intensity,the obtained pulp was passed through a single disk laboratory refiner from 0 to 6 times and in two different consistencies(1.5 and 2.5 W/V%).Total yield,kappa number,ash content,and the Schopper-Riegler(SR°)freeness of the prepared pulps were investigated.Finally,hand sheets with a targeted basic weight of 70 g/m^(2) were made according to the related standards.The hand sheets were characterized using Fourier transform infrared(FTIR)spectroscopy and a field emission scanning electron microscope(FE-SEM).Sheet density,brightness,and mechanical properties such as burst,tensile,and tear indices were also investigated.The FE-SEM photographs showed that the texture of the hand sheet became denser as the refining intensity increased.External fibrillation on the surface of the fibers was also observed,especially on those refined with 2.5%consistency.The results of the chemical composition of wheat straw indicated that wheat straw containing a high percentage of holocellulose is an excellent candidate for the production of fluff pulp.The total yield and kappa number of MEA pulps increased with the decrease in MEA concentration.FTIR results indicated the presence of a peak related to amino groups in the pulp related to MEA pulp.The results also indicated that the mechanical properties of the papers,except for the tear index,were enhanced as the intensity of refining and the pulp consistency during refining increased. 展开更多
关键词 Wheat straw mono ethanol amine fluff pulp CELLULOSE
在线阅读 下载PDF
Buccal DNA global methylation and cognitive performance in stunted children under five years of age
8
作者 Ahmad Rusdan Handoyo Utomo Yusnita Yusnita +8 位作者 Siti Maulidya Sari Octaviani Indrasari Ranakusuma Sunu Bagaskara Wening Sari Yulia Suciati Anggi Puspa Nur Hidayati Silviatun Nihayah Catur Anggono Putro Neni Nurainy 《Journal of Biomedical Research》 2025年第2期146-154,共9页
The prevalence of stunting in Indonesian children under five years of age is approximately 20%.Chronic maternal malnutrition contributes to the risk of stunting by affecting global DNA methylation.In the present study... The prevalence of stunting in Indonesian children under five years of age is approximately 20%.Chronic maternal malnutrition contributes to the risk of stunting by affecting global DNA methylation.In the present study,we aimed to evaluate the levels of 5-methyl-cytosine(5mC)as a surrogate marker of global DNA methylation in buccal swabs and its potential association with the risk of stunting and cognitive performance.The levels of 5mC were measured using an enzyme-linked immunosorbent assay.The Wechsler Preschool and Primary Scale of Intelligence(WPPSI)was used to measure cognitive function.Buccal swab DNA samples and anthropometric data were collected from a total of 231 children aged zero to five years.In this cross-sectional cohort,the prevalence of stunting was 37%in 138 children aged zero to two years and 30%in 93 children aged over two years.The univariable analysis revealed that the levels of 5mC in buccal swab DNA were significantly lower in severely stunted children(median,2.84;interquartile range[IQR],2.39–4.62)and children aged less than two years(median,2.81;IQR,2.53–4.62)than those in normal children(median,3.75;IQR,2.80–4.74;P-value,0.028)and children aged over four years(median,4.01;IQR,3.39–4.87;P-value<0.001),respectively.We also found that the average cognitive scores tended to be low in boys and stunted children,although the differences were not statistically significant.Furthermore,the levels of 5mC found in buccal swab and mouthwash DNA were not associated with cognitive scores. 展开更多
关键词 global DNA methylation 5mC ELISA STUNTING COGNITIVE
暂未订购
Long-Range Admixture Linkage Disequilibrium and Allelic Responses of Sub1 and TPP7 under Consecutive Stress in Rice Validated Through Mendelian Randomization
9
作者 Sabarinathan SELVARAJ Parameswaran CHIDAMBARANATHAN +8 位作者 Goutam Kumar DASH Priyadarsini SANGHAMITRA Kishor Pundlik JEUGHALE Cayalvizhi BALASUBRAMANIASAI Devraj LENKA Basavantraya Navadagi DEVANNA Seenichamy Rathinam PRABHUKARTHIKEYAN Sanghamitra SAMANTARAY Amaresh Kumar NAYAK 《Rice science》 2025年第5期704-716,I0095-I0117,共36页
Consecutive stresses,such as initial submergence during germination followed by water deficit during the seedling stage,pose significant challenges to direct-seeded rice cultivation.By Linkage disequilibrium analysis,... Consecutive stresses,such as initial submergence during germination followed by water deficit during the seedling stage,pose significant challenges to direct-seeded rice cultivation.By Linkage disequilibrium analysis,Sub1 and Dro1(Δbp:10 Mb),as well as Sub1 and TPP7(Δbp:6 Mb)were identified to exhibit long-range linkage disequilibrium(LRLD).Meta-QTL analysis further revealed that Sub1 and TPP7 co-segregated for tolerance to submergence at the germination and seedling stages.Based on this,we hypothesized that LRLD might influence plant responses to consecutive stresses.To test this hypothesis,we developed a structured recombinant inbred line population from a cross between Bhalum 2 and Nagina 22,with alleles(Sub1 and TPP7)in linkage equilibrium.Mendelian randomization analysis validated that the parental alleles,rather than the recombinant alleles of Sub1 and TPP7,significantly influenced 13 out of 41 traits under consecutive stress conditions.Additionally,16 minor additive effect QTLs were detected between the genomic regions,spanning Sub1 and TPP7 for various traits.A single allele difference between these genomic regions enhanced crown root number,root dry weight,and specific root area by 11.45%,15.69%,and 33.15%,respectively,under flooded germination conditions.Candidate gene analysis identified WAK79 and MRLK59 as regulators of stress responses during flooded germination,recovery,and subsequent water deficit conditions.These findings highlight the critical role of parental allele combinations and genomic regions between Sub1 and TPP7 in regulating the stress responses under consecutive stresses.Favourable haplotypes derived from these alleles can be utilized to improve stress resilience in direct-seeded rice. 展开更多
关键词 anaerobic germination consecutive stress long-range linkage disequilibrium RICE water deficit Mendelian randomization
在线阅读 下载PDF
Layer-by-layer tear film measurement in patients with dry eye and meibomian gland dysfunction
10
作者 Reiko Arita Gaku Takeuchi +2 位作者 Kiyofumi Sasai Masatsugu Nakamura Masahiro Akiba 《International Journal of Ophthalmology(English edition)》 2025年第11期2057-2064,共8页
AIM:To evaluate parameters measured using the tear film imager(TFI)prototype,a new technology that enables to quantify the tear film thickness of lipid and mucoaqueous layers.METHODS:In this cross-sectional study,pati... AIM:To evaluate parameters measured using the tear film imager(TFI)prototype,a new technology that enables to quantify the tear film thickness of lipid and mucoaqueous layers.METHODS:In this cross-sectional study,patients with dry eye,meibomian gland dysfunction(MGD),and non-dry eye/MGD from February 2020 to January 2021 were analyzed.Quantified TFI outputs included lipid layer thickness(LLT),mucoaqueous layer thickness(MALT),MALT rate of change(MALTR),and lipid breakup time.Two other interferometry devices,LipiView2 and DR-1α,were used for comparison.TFI outputs and other clinical parameters were analyzed using correlation coefficients.Each patient underwent one or several study visits.Baseline values of three device outputs,other clinical parameters,and their changes were examined.RESULTS:This study involved 28 patients(8 patients with dry eyes,13 with MGD,and 7 with non-dry eye/MGD).Baseline TFI,LipiView2,and DR-1αvalues were associated with various clinical parameters.The LLT values estimated using TFI had a correlation with the plugging score in the upper eyelid(r=−0.42).Several TFI values have correlated better than LipiView2 and DR-1α,particularly with questionnaire scores.MALTR by TFI revealed a correlation between standardized patient evaluation on eye dryness(SPEED)and dry eye-related quality of life score(DEQS)scores(r=0.59,0.43),respectively.CONCLUSION:TFI enabled to quantify the LLT and MALT separately over time and shows the moderate correlations between TFI measurements and clinical parameters,which yields the potential for TFI to serve as a complementary tool for assessing dry eye and MGD. 展开更多
关键词 dry eye lipid layer thickness meibomian gland dysfunction mucoaqueous layer thickness tear film imager
原文传递
近30年中国水稻种植区域与产量时空变化分析 被引量:133
11
作者 刘珍环 李正国 +5 位作者 唐鹏钦 李志鹏 吴文斌 杨鹏 游良志 唐华俊 《地理学报》 EI CSCD 北大核心 2013年第5期680-693,共14页
通过综合80年代初以来的农作物面积与产量统计、耕地分布、农业灌溉分布以及作物生长适宜性分布等多源数据,利用基于交叉信息熵原理的作物空间分配模型(Spatial Production Allocation Model,SPAM),获得了我国10km像元尺度的水稻分布信... 通过综合80年代初以来的农作物面积与产量统计、耕地分布、农业灌溉分布以及作物生长适宜性分布等多源数据,利用基于交叉信息熵原理的作物空间分配模型(Spatial Production Allocation Model,SPAM),获得了我国10km像元尺度的水稻分布信息。在此基础上,重点分析了80年代初以来水稻种植面积与产量的时空变化特征。总体来看,在全国水稻种植区域内发生变化的地区中有超过50%的地区水稻种植面积出现缩减态势,但仍有近70%的地区水稻产量在增加。空间变化来看,种植面积缩减主要发生在东南沿海的广东、福建和浙江等省,而增加主要出现在东北地区的吉林和黑龙江等省,我国水稻种植重心因此向东北方向迁移约230km,产量重心向东北迁移约320km。同时,研究还发现我国水稻种植面积变化对产量增减具有重要影响,其中产量增加表现为面积与非面积因素的共同作用,数据显示种植面积扩展对水稻增产的平均贡献率约54.5%,而在产量减少的区域,面积缩减对减产的贡献率高达80%以上。 展开更多
关键词 水稻 作物空间分配模型 时空变化 中国
原文传递
不同上部刚度对木框架剪力墙受力性能影响的试验研究 被引量:13
12
作者 刘雁 Ni Chun +2 位作者 卢文胜 吕西林 周定国 《土木工程学报》 EI CSCD 北大核心 2008年第11期63-70,共8页
木框架剪力墙试验研究时,荷载传递梁的刚度对木框架剪力墙的破坏模式以及侧向荷载承载力有直接的影响,当木框架剪力墙墙端以及墙中洞口边未采用墙端锚栓时,这种影响更甚。当墙顶连接铰接荷载传递梁时,在水平荷载作用下,木框架剪力墙的... 木框架剪力墙试验研究时,荷载传递梁的刚度对木框架剪力墙的破坏模式以及侧向荷载承载力有直接的影响,当木框架剪力墙墙端以及墙中洞口边未采用墙端锚栓时,这种影响更甚。当墙顶连接铰接荷载传递梁时,在水平荷载作用下,木框架剪力墙的墙端易于被上拔而与墙基础分离,此时试验所得到的木框架剪力墙的侧向荷载承载力接近于下限值;反之,刚性荷载传递梁所得到的木框架剪力墙的侧向荷载承载力接近于上限值。主要通过22片墙体的试验研究来了解上层墙体、楼盖刚度对下层木框架剪力墙受力性能的影响。其中16片为6m长2.44m高的单层足尺木框架剪力墙,墙顶一半采用铰接荷载传递梁一半采用刚性荷载传递梁,4片为足尺典型二层墙体,另外2片为增加了墙端锚栓的单层足尺木框架剪力墙。对试验结果从初始刚度、极限荷载、极限位移、能量耗散以及锚栓内力等方面进行分析,最后形成了采用刚性荷载传递梁和二层墙体均能增加墙体侧向荷载承载力的结论。 展开更多
关键词 木框架剪力墙 受力性能 刚度
原文传递
基于作物空间分配模型的东北三省春玉米时空分布特征 被引量:16
13
作者 谭杰扬 李正国 +6 位作者 杨鹏 刘珍环 李志鹏 张莉 吴文斌 游良志 唐华俊 《地理学报》 EI CSCD 北大核心 2014年第3期353-364,共12页
利用1980.2010年东北三省分县玉米播种面积与产量统计、耕地分布、农业灌溉分布以及作物适宜性分布等多源数据,结合基于交叉信息熵原理的作物空间分配模型(SpatialProductionAllocationModel,SPAMl,在5’×5’的像元尺度模拟... 利用1980.2010年东北三省分县玉米播种面积与产量统计、耕地分布、农业灌溉分布以及作物适宜性分布等多源数据,结合基于交叉信息熵原理的作物空间分配模型(SpatialProductionAllocationModel,SPAMl,在5’×5’的像元尺度模拟了春玉米种植面积与产量的时空分布,并重点分析了两者在纬向、经向,以及高程上的时空变化规律。结果显示:(1)玉米种植面积在2000年前向北扩展至北纬44°-48°间,2000年后在中南部出现大规模发展(北纬42°-44°),并进一步向东扩展至东经1230127。间,同时还表现为向低海拔(高程100m以下)和较高海拔(高程200~350m)扩展的态势;(2)单产在纬向上的增加区主要集中在北纬42°-48°,经向上的单产增加则相对均匀,高程上单产提升区主要集中在海拔350m以下。(3)像元内玉米种植比例整体上由中低种植比例为主逐步演变为中高比例占据主体,并且中高种植比例像元对应的玉米单产水平整体上较高,反映了市场经济驱动下的玉米种植集聚化和规模化的发展趋势。 展开更多
关键词 春玉米 作物空间分配模型 时空变化 东北三省
原文传递
利用染色体步移PCR检测辐射松的单核苷酸多态性 被引量:4
14
作者 李伟 李慧 +1 位作者 陈晓阳 WU Harry 《西北植物学报》 CAS CSCD 北大核心 2007年第8期1571-1576,共6页
用染色体步移技术(chromosome walking)的基本原理以辐射松(Pinus radiata)肌动蛋白基因(actin)为例,利用获得的EST序列设计定向引物,向上游和下游进行了染色体序列的步移.获得了包括启动子、5′端非编码区和编码区及3′端非编码区辐射... 用染色体步移技术(chromosome walking)的基本原理以辐射松(Pinus radiata)肌动蛋白基因(actin)为例,利用获得的EST序列设计定向引物,向上游和下游进行了染色体序列的步移.获得了包括启动子、5′端非编码区和编码区及3′端非编码区辐射松肌动蛋白基因基因组序列2154 bp.通过对200株不同辐射松个体进行PCR扩增及测序,共获得了21个SNPs,其中启动子区域3个,编码区15个,3′端非编码区4个.实验结果为今后染色体步移技术在基因非编码区SNP的检测提供了理论与技术参考. 展开更多
关键词 染色体步移 PCR 辐射松 单核苷酸多态性
在线阅读 下载PDF
功率因数校正的数字控制技术应用研究 被引量:8
15
作者 陈新 Charlie Wu W Hutchings 《南京航空航天大学学报》 EI CAS CSCD 北大核心 2007年第2期164-170,共7页
以单管Boost型PFC电路作为研究对象,分别针对电流断续、电流临界连续和电流连续3种工作模态,详细讨论了数字控制PFC的实现方法和设计过程,并分别给出了样机实验结果;此外,结合M C 56F 8013的外设资源特点,给出了基于DSP的PFC详细的系统... 以单管Boost型PFC电路作为研究对象,分别针对电流断续、电流临界连续和电流连续3种工作模态,详细讨论了数字控制PFC的实现方法和设计过程,并分别给出了样机实验结果;此外,结合M C 56F 8013的外设资源特点,给出了基于DSP的PFC详细的系统接口设计,包括PWM控制策略和同步控制AD采样环节。对PFC的数字控制方案进行了系统研究,提供了不同工作模式下的完整数字控制解决方案,为功率因数的数字控制技术应用提供了较好的参考作用。 展开更多
关键词 数字信号处理 功率因数校正 数字控制 PI控制
在线阅读 下载PDF
基于DSC控制的移相全桥DC/DC变换器 被引量:6
16
作者 陈新 Charlie WU WHut chings 《电力电子技术》 CSCD 北大核心 2006年第5期38-41,共4页
数字控制由于高集成度带来的低成本、设计沿继性、控制灵活等优点而应用逐渐广泛,电力电子应用逐渐朝着高频化方向发展,这也对高频开关电源的数字控制提出了要求。利用Freescale新型号数字信号控制器(DigitalSingnalController,DSC)MC56... 数字控制由于高集成度带来的低成本、设计沿继性、控制灵活等优点而应用逐渐广泛,电力电子应用逐渐朝着高频化方向发展,这也对高频开关电源的数字控制提出了要求。利用Freescale新型号数字信号控制器(DigitalSingnalController,DSC)MC56F8323的高性能特性,完成了基于DSC的带同步整流的高频软开关移相全桥变换器的数字控制,描述了DSC产生软件移相控制策略,并给出了详细的数字控制系统设计和软件结构设计,最后用一台500W实验样机验证了数字控制所带来的优良的系统性能。 展开更多
关键词 变换器 移相全桥 数字控制/数字信号控制器 数字信号处理器
在线阅读 下载PDF
DROLOXIFENE枸橼酸盐的工艺改进及其新的生物活性
17
作者 陈瑛 夏鹏 +3 位作者 张倩 郑云红 夏奕 杨征宇 《药学学报》 CAS CSCD 北大核心 2000年第12期902-905,共4页
目的 探索droloxifene的合成方法 ,并对其新的生物活性进行研究。方法和结果 以甲氧基苯和苯乙酸为原料 ,经酰氯化、付 克反应、烷基化、去甲基化、醚化、格氏加成、消除脱水、构型转化及成盐共 9步反应 ,得droloxifene枸橼酸盐 ,8... 目的 探索droloxifene的合成方法 ,并对其新的生物活性进行研究。方法和结果 以甲氧基苯和苯乙酸为原料 ,经酰氯化、付 克反应、烷基化、去甲基化、醚化、格氏加成、消除脱水、构型转化及成盐共 9步反应 ,得droloxifene枸橼酸盐 ,8步收率 14 7% (9 2 % [1] )。生物活性实验发现其具有缓解肿瘤细胞多药耐药性和诱导黄体细胞凋亡的两种新的生物活性。结论 本文对droloxifene的合成工艺进行了改进 ,反应步骤缩短两步 ,异构体分离、转化方法简便 ,原料及试剂易得 ,操作简便。两种新的生物活性的发现对新药研究及扩大临床应用提供了实验依据。 展开更多
关键词 DROLOXIFENE 枸橼酸盐 抗癌药 生物活性
在线阅读 下载PDF
Antioxidant activity and identification of bioactive compounds from leaves of Anthocephalus cadamba by ultra-performance liquid chromatography/electrospray ionization quadrupole time of flight mass spectrometry 被引量:8
18
作者 Madhu Chandel Upendra Sharma +2 位作者 Neeraj Kumar Bikram Singh Satwinderjeet Kaur 《Asian Pacific Journal of Tropical Medicine》 SCIE CAS 2012年第12期977-985,共9页
Objective:To evaluate the antioxidant potential of different extract/fractions of Anthocephalus cadamba(A.cadamba)(Roxb.) Miq.(Rubiaceae) and study the tentative identification of their active constituents.Metho... Objective:To evaluate the antioxidant potential of different extract/fractions of Anthocephalus cadamba(A.cadamba)(Roxb.) Miq.(Rubiaceae) and study the tentative identification of their active constituents.Methods:The extract/fractions were screened for antioxidant activity using various in vitro assays viz.DPPH assay,ABTS assay,superoxide anion radical scavenging assay, reducing power assay and plasmid DNA nicking assay.Total phenolic content of extract/fractions was determined by colorimetric method.An ultra-performance LC-electrospray-quadrupoletime of flight mass spectrometry method was used to analyse the active constituents of extract/ fractions of A.cadamba.Results:The ethyl acetate fraction was found to be most active fraction in all the assays as compared to other extract/fractions.The IC<sub>50</sub> value of ethyl acetate fraction (ETAC fraction) was 21.24μg/mL,1.12μg/mL,9.68μg/mL and S7.81μg/mL in DPPH assay, ABTS assay,reducing power assay and superoxide scavenging assay respectively.All the extract/ fractions also showed the potential to protect the plasmid DNA(pBR322) against the attack of hydroxyl radicals generated by Fenton’s reagent.The bioactive compounds were identified by UPLC-ESI-QTOF-MS,by comparing the mass andλ<sub>max</sub> with literature values.Conclusions:The potential of the extract/fractions to scavenge different free radicals in different systems indicated that they may be useful therapeutic agents for treating radical-related pathologic damage. 展开更多
关键词 Anthocephalus cadamba ANTIOXIDANT ACTIVITY UPLC-ESI-QTOF-MS
暂未订购
Gas chromatography-mass spectrometry analysis of essential oils from five parts of Chaihu(Radix Bupleuri Chinensis) 被引量:11
19
作者 Jie Meng Xingfu Chen +5 位作者 Wenyu Yang Jiuhua Song Yu Zhang Zhifei Li Xingwang Yang Zhanguo Yang 《Journal of Traditional Chinese Medicine》 SCIE CAS CSCD 2014年第6期741-748,共8页
OBJECTIVE: To analyze the essential oils from flowers, leaves, stems, roots, and fruits of Chaihu(Radix Bupleuri Chinensis).METHODS: We extracted essential oils from different parts of Chaihu(Radix Bupleuri Chinensis)... OBJECTIVE: To analyze the essential oils from flowers, leaves, stems, roots, and fruits of Chaihu(Radix Bupleuri Chinensis).METHODS: We extracted essential oils from different parts of Chaihu(Radix Bupleuri Chinensis) using a steam distillation method. The essential oils were analyzed by gas chromatography-mass spectrometry(GC-MS). Data were collected in full scan mode(m/z 60-600). Volatile components were identified based on their retention indices and by comparing their mass spectra with those in the National Institute of Standards and Technology 2005 database assisted by tandem mass spectrometry information. The relative content of each constituent wasdetermined by area normalization.RESULTS: We identified 111 components, of which12 were common to all 5 parts, 30 were found only in roots, 14 were found only in flowers, 6 were found only in leaves, 4 were found only in stems,and 17 were found only in fruits.CONCLUSION: Our results show that the stems,flowers, leaves, and fruits of Chaihu(Radix Bupleuri Chinensis)contain a high concentration of essential oils, and that the exact composition of the essential oils differs among the plant parts. To develop new medicines and make full use of the Chaihu(Radix Bupleuri Chinensis)resource, it is important to characterize the essential oils from different parts of the plant. In future research, it will be important to determine the pharmacological effects of the various components and the essential oil mixtures. 展开更多
关键词 Gas chromatography-mass spectrome-try Oils volatile Chaihu (Radix Bupleuri Chinensis)
原文传递
Effect of Fiber Loadings and Treatment on Dynamic Mechanical, Thermal and Flammability Properties of Pineapple Leaf Fiber and Kenaf Phenolic Composites 被引量:6
20
作者 M.Asim M.Jawaid +1 位作者 M.Nasir N.Saba 《Journal of Renewable Materials》 SCIE 2018年第4期383-393,共11页
This study deals with the analysis of dynamic mechanical,thermal and flammability properties of treated and untreated pineapple leaf fiber(PALF)and kenaf fiber(KF)phenolic composites.Results indicated that storage mod... This study deals with the analysis of dynamic mechanical,thermal and flammability properties of treated and untreated pineapple leaf fiber(PALF)and kenaf fiber(KF)phenolic composites.Results indicated that storage modulus was decreased for all composites with increases in temperature and pattern of slopes for all composites,having almost the same values of E′at glass transition temperature(Tg).The peak of the loss modulus of pure phenolic composites was shown to be much less.After the addition of kenaf/PALF,peaks were higher and shifted towards a high temperature.The Tan delta peak height was low for pure phenolic composites and maximum for 60%PALF phenolic composites.Cole-Cole analysis was carried out to understand the phase behavior of the composite samples.Thermogravimetric analysis(TGA)results indicated that pure phenolic composites have better thermal stability than PALF and kenaf phenolic composites.Vertical and horizontal UL-94 tests were conducted and showed pure phenolic resin is highly fire resistant.The overall results showed that treated KF composites enhanced the dynamic mechanical and thermal properties among all PALF/KF composites. 展开更多
关键词 Pineapple leaf FIBER KENAF FIBER PHENOLIC resin DYNAMIC MECHANICAL analysis thermogravimetric analysis FLAMMABILITY
在线阅读 下载PDF
上一页 1 2 5 下一页 到第
使用帮助 返回顶部