排序方式: 共有59条查询结果,搜索用时 15 毫秒
51.
52.
Compared with the extensive research on logistics network infrastructures (LNIs) in the developed world, empirical research
is still scarce in China. In this paper the theory of LNIs is firstly overviewed. Then a new evaluation index system for LNIs
is set up which contains factors that reflect the economic development level, transportation accessibility and turnover volume
of freight traffic. An empirical study is carried out by using data envelopment analysis (DEA) and principal component analysis
(PCA) approach to classify LNIs into 4 clusters for 25 cities in the Yangtze River Delta Region of China. According to the
characteristics of the 4 clusters, suggestions are proposed for improving their LNIs. Finally, after comparing different LNIs
of 25 cities in the Yangtze River Delta Region of China, this paper proposes that different LNIs including hub, central distribution
center or cross docking center, regional distribution center or distribution center should be built reasonably in order to
meet the customer’s requirement in the four different cluster cities. 相似文献
53.
本文介绍了强迫电流滞后高频开关SPWM三相整流器,采用绝缘栅晶体管作为主电路的开关元件,其控制采用电流滞后控制方法。这种整流方式功率因数可达到1,具有正弦的输入电流与可调的输出直流电压,并具有双向工转换的能力,且控制简单,响应时间快。 相似文献
54.
55.
56.
57.
58.
59.