全文获取类型
收费全文 | 1782篇 |
免费 | 100篇 |
专业分类
公路运输 | 311篇 |
综合类 | 385篇 |
水路运输 | 382篇 |
铁路运输 | 738篇 |
综合运输 | 66篇 |
出版年
2024年 | 14篇 |
2023年 | 9篇 |
2022年 | 36篇 |
2021年 | 58篇 |
2020年 | 71篇 |
2019年 | 46篇 |
2018年 | 28篇 |
2017年 | 51篇 |
2016年 | 44篇 |
2015年 | 70篇 |
2014年 | 138篇 |
2013年 | 96篇 |
2012年 | 171篇 |
2011年 | 170篇 |
2010年 | 105篇 |
2009年 | 93篇 |
2008年 | 115篇 |
2007年 | 150篇 |
2006年 | 131篇 |
2005年 | 104篇 |
2004年 | 65篇 |
2003年 | 36篇 |
2002年 | 23篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1985年 | 2篇 |
排序方式: 共有1882条查询结果,搜索用时 0 毫秒
591.
This study reviews the literature on air cargo operations and compares theoretical studies with the practical problems of airlines, freight forwarders, and terminal service providers. In particular, we review studies in which mathematical models were used to identify the essential characteristics of air cargo operations, such as the intrinsic differences from passenger operations, and to explore the service processes in air cargo operations. The typical models used in previous studies are summarized. We then highlight the insightful findings from an industrial interview and present the gaps between previous research and practical realities. We finally discuss the new research opportunities of air cargo operations according to the gaps. 相似文献
592.
The link transmission model (LTM) has great potential for simulating traffic flow in large-scale networks since it is much more efficient and accurate than the Cell Transmission Model (CTM). However, there lack general continuous formulations of LTM, and there has been no systematic study on its analytical properties such as stationary states and stability of network traffic flow. In this study we attempt to fill the gaps. First we apply the Hopf–Lax formula to derive Newell’s simplified kinematic wave model with given boundary cumulative flows and the triangular fundamental diagram. We then apply the Hopf–Lax formula to define link demand and supply functions, as well as link queue and vacancy functions, and present two continuous formulations of LTM, by incorporating boundary demands and supplies as well as invariant macroscopic junction models. With continuous LTM, we define and solve the stationary states in a road network. We also apply LTM to directly derive a Poincaré map to analyze the stability of stationary states in a diverge-merge network. Finally we present an example to show that LTM is not well-defined with non-invariant junction models. We can see that Newell’s model and continuous LTM complement each other and provide an alternative formulation of the network kinematic wave theory. This study paves the way for further extensions, analyses, and applications of LTM in the future. 相似文献
593.
Our daily driving experience and empirical observations suggest that traffic patterns in a road network are relatively stationary during peak periods. In numerous transportation network studies, there has been an implicit conjecture that stationary states exist in a network when origin demands, route choice proportions, and destination supplies are constant. In this study, we first rigorously formulate the conjecture within the framework of a network kinematic wave theory with an invariant junction model. After defining stationary states, we derive a system of algebraic equations in 3-tuples of stationary link flow-rates, demands, and supplies. We then introduce a new definition of junction critical demand levels based on effective demands and supplies. With a map in critical demand levels, we show that its fixed points and, therefore, stationary states exist with the help of Brouwer’s fixed point theorem. For two simple road networks, we show that the map is well-defined and can be used to solve stationary states with a brute-force method. Finally we summarize the study and present some future extensions and applications. 相似文献
594.
595.
596.
为使消磁时消磁线圈上的能量能够回馈到消磁电源、提高能源利用率,提出基于超级电容和锂电池混合供电的消磁电源控制策略。
通过研究消磁线圈强耦合工况下的电气特性,引入超级电容和锂电池混合供电的消磁电源系统。将消磁线圈电流的变化分为上升、保持、下降(能量回馈)3个阶段,在消磁线圈电流变化的不同阶段,控制相应功率器件的开通和关断。借助Matlab/Simulink进行仿真,分析仿真结果,以验证基于超级电容和锂电池混合供电系统的能量回馈控制策略的可行性。
仿真结果表明,流经各消磁线圈的总电流值可以快速上升至消磁额定电流值,并稳定在额定值附近,且超调量较小。
超级电容和锂电池混合供电的消磁电源系统能够将消磁线圈上的能量回馈至超级电容中,减少整套消磁系统的能源损耗。
597.
598.
《铁道标准设计通讯》2017,(8):1-5
为了确定铁路线路技术标准与运量水平之间的耦合关系,分析运量水平主导线路主要技术标准类项目特性和线路技术标准主导运量水平类项目特性,从供需平衡角度出发,得出运量构成机制和线路标准条件从能力供给到运量诱发的质变条件。 相似文献
599.
600.