为探究影响我国沿海港口外贸货物吞吐量的因素,以及这些因素的影响因金融危机的爆发而发生的变化,建立基于贸易引力模型的我国沿海港口外贸货物吞吐量影响因素的向量自回归(Vector Auto Regression,VAR)模型,研究金融危机爆发前后交通...为探究影响我国沿海港口外贸货物吞吐量的因素,以及这些因素的影响因金融危机的爆发而发生的变化,建立基于贸易引力模型的我国沿海港口外贸货物吞吐量影响因素的向量自回归(Vector Auto Regression,VAR)模型,研究金融危机爆发前后交通运输固定投资、人民币实际有效汇率、外商直接投资、世界经济状况和国内经济状况对我国沿海港口外贸货物吞吐量的影响.由方差分解分析发现:对交通运输体系固定投资的增加在金融危机后较之金融危机之前更能提高沿海港口外贸货物吞吐量;人民币实际有效汇率和外商直接投资的波动在金融危机之前、后对沿海港口外贸货物吞吐量均不构成显著影响;金融危机后世界经济的复苏明显提高沿海港口外贸货物吞吐量;我国国内经济状况对沿海港口外贸货物吞吐量的影响在金融危机后大幅削弱.展开更多
The ultrastructure of the vegetative cells of Nostoc flagelliforme Born. et Flah. was investigated with high pressure freezing and freeze substitution technique and compared with the results obtained by using conv...The ultrastructure of the vegetative cells of Nostoc flagelliforme Born. et Flah. was investigated with high pressure freezing and freeze substitution technique and compared with the results obtained by using conventional preparation methods. During the processes of chemical fixation, dehydration and embedding, the cell structures might be more artificially modified than that obtained from high pressure freezing and freeze substitution. With the present method, the sheath of N. flagelliforme could be well penetrated and no extra big space could exist between the cell and the sheath. The cell protoplasm rarely shrinked. Some fine structures of cell inclusions and unit membranes became visualized. Many bacteria were harbored in the sheath. In addition, the presence of big vacuoles in the cell of N. flagelliforme as well as the presence of bacteria in the sheath shown in the present preparation for cyanobacteria has not been described so far in the literature.展开更多
Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples...Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples were prepared with high pressure freezing and freeze substitution techniques. The ultrastructure of dense cell was similar to that of sieve element at its early developmental stage. With the concurrent agglutination of chromatin in the nucleus, the abnormal location of organelles and the high density of cytoplasm, the ultrastructural characteristics in die dense cells of the nectariferous tissue and in the sieve element are matched with those of the programmed cell death in animal and plant reported in recent years. The disorganization of nucleus and most organelles in the differentiation of sieve elements and dense cells is closely associated with the transportation and modification of pre-nectar and the transference of nectar. This suggests that the cytological changes in sieve element and nectariferous tissue are closely associated with the nectary functional activities.展开更多
文摘为探究影响我国沿海港口外贸货物吞吐量的因素,以及这些因素的影响因金融危机的爆发而发生的变化,建立基于贸易引力模型的我国沿海港口外贸货物吞吐量影响因素的向量自回归(Vector Auto Regression,VAR)模型,研究金融危机爆发前后交通运输固定投资、人民币实际有效汇率、外商直接投资、世界经济状况和国内经济状况对我国沿海港口外贸货物吞吐量的影响.由方差分解分析发现:对交通运输体系固定投资的增加在金融危机后较之金融危机之前更能提高沿海港口外贸货物吞吐量;人民币实际有效汇率和外商直接投资的波动在金融危机之前、后对沿海港口外贸货物吞吐量均不构成显著影响;金融危机后世界经济的复苏明显提高沿海港口外贸货物吞吐量;我国国内经济状况对沿海港口外贸货物吞吐量的影响在金融危机后大幅削弱.
文摘The ultrastructure of the vegetative cells of Nostoc flagelliforme Born. et Flah. was investigated with high pressure freezing and freeze substitution technique and compared with the results obtained by using conventional preparation methods. During the processes of chemical fixation, dehydration and embedding, the cell structures might be more artificially modified than that obtained from high pressure freezing and freeze substitution. With the present method, the sheath of N. flagelliforme could be well penetrated and no extra big space could exist between the cell and the sheath. The cell protoplasm rarely shrinked. Some fine structures of cell inclusions and unit membranes became visualized. Many bacteria were harbored in the sheath. In addition, the presence of big vacuoles in the cell of N. flagelliforme as well as the presence of bacteria in the sheath shown in the present preparation for cyanobacteria has not been described so far in the literature.
文摘Ultrastructural changes in the sieve element and dense cells of nectariferous tissue during the development of floral nectary in Arabidopsis thaliana L. were investigated with transmission electron microscopy. Samples were prepared with high pressure freezing and freeze substitution techniques. The ultrastructure of dense cell was similar to that of sieve element at its early developmental stage. With the concurrent agglutination of chromatin in the nucleus, the abnormal location of organelles and the high density of cytoplasm, the ultrastructural characteristics in die dense cells of the nectariferous tissue and in the sieve element are matched with those of the programmed cell death in animal and plant reported in recent years. The disorganization of nucleus and most organelles in the differentiation of sieve elements and dense cells is closely associated with the transportation and modification of pre-nectar and the transference of nectar. This suggests that the cytological changes in sieve element and nectariferous tissue are closely associated with the nectary functional activities.
