全文获取类型
收费全文 | 898篇 |
免费 | 37篇 |
专业分类
公路运输 | 260篇 |
综合类 | 252篇 |
水路运输 | 222篇 |
铁路运输 | 148篇 |
综合运输 | 53篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 30篇 |
2021年 | 36篇 |
2020年 | 24篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 15篇 |
2015年 | 29篇 |
2014年 | 29篇 |
2013年 | 52篇 |
2012年 | 43篇 |
2011年 | 73篇 |
2010年 | 66篇 |
2009年 | 79篇 |
2008年 | 47篇 |
2007年 | 71篇 |
2006年 | 55篇 |
2005年 | 50篇 |
2004年 | 26篇 |
2003年 | 34篇 |
2002年 | 35篇 |
2001年 | 27篇 |
2000年 | 13篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有935条查询结果,搜索用时 0 毫秒
341.
342.
343.
Abstract Existing origin constrained and doubly constrained gravity models have not been compared, theoretically or empirically, in terms of their forecasting power. Due to the newly advanced technology of intelligent transport systems, the expanded data presently available have made various models more comparable in terms of forecasting power. This paper uses archived automatic passenger counting (APC) data for urban rail in the Seoul metropolitan area. The APC data contains information about each trip's origin, destination, ticket type, fare, and distance on a daily basis. The objective of this paper is to compare the goodness-of-fit of aggregate and disaggregate gravity modeling using these data. A Hyman aggregate gravity model is used as the aggregate model without the spatial effect. The disaggregate model adopts a multinomial logit as the destination choice model with the spatial effect. In general, while the formulation of aggregate and disaggregate gravity model models are similar, the calibration and parameter estimation methods of the two models are different. As a result, this empirical study demonstrates that the variation in goodness-of-fit and forecasting power largely depends on the estimation method and selected variables. The forecasting power of the disaggregate modeling approach outperforms that of the aggregate model. This paper further confirms that spatial arrangement plays important roles in gravity modeling. 相似文献
344.
345.
对纤维增强聚合物(FRP)格栅加筋混凝土梁的弯曲行为和破坏模式进行了试验研究。采用复合材料制备了3条纵向肋和4条纵向肋2种不同构造的平面正交格栅,埋入混凝土梁,并对加筋混凝土梁进行四点弯曲试验。结果显示,在本研究采用的混凝土梁尺寸条件下,3根纵向肋的复合材料格栅加筋梁以弯曲破坏模式为主,而4根纵向肋的格栅加筋梁则以局部剪切破坏模式为主。试验结果表明,3根纵向肋的格栅充分发挥了复合材料的抗拉特性,具有更高的加筋效率。 相似文献
346.
航测机为高质量地完成航拍和重力测量任务,把飞行员从繁重的飞行操纵中解脱出来,需要在飞机上安装自动驾驶仪系统,使飞机在自动驾驶仪的控制下完成定高和定向飞行。阐述APS-65自动驾驶仪系统的组成、功能和特点,对航测机上安装APS-65自动驾驶仪系统过程中遇到的问题进行分析,并提出处理措施。 相似文献
347.
由于大气干扰的影响,雷达平台很难按照理想轨迹飞行,因此对SAR轨迹偏离下的三维场景回波模拟研究具有现实意义,但此方面在国内研究较少.文中基于SAR轨迹偏离条件下的回波信号模型,提出了适合此模式的SAR回波模拟频域算法,推导了SAR回波频域模拟公式,分析了算法的性能及应用范围,给出了仿真结果和结论,证明了所提算法的有效性和可行性. 相似文献
348.
349.
S. B. Han Y. H. Chang E. Y. Lee Y. J. Chung B. Suh 《International Journal of Automotive Technology》2010,11(1):105-110
Hybrids combine a combustion engine with an electric motor and battery. The two technologies can be combined to reduce fuel
consumption and exhaust emissions. This paper presents the concept of hybrid electric vehicles (HEVs) applied to truck or
van vehicles with diesel engines. The simulation results from the advanced vehicle simulator (ADVISOR) demonstrate that the
required power may be properly shared between the internal combustion engine and electric motor. The simulation can also be
used to prove that the technique is useful for improvements in driving performance; additionally, the technique is suitable
for hybrid electric vehicles, allowing for good fuel economy and low emissions performance. 相似文献
350.
B. H. Lee J. H. Song Y. J. Chang C. H. Jeon 《International Journal of Automotive Technology》2010,11(6):783-791
The diesel combustion process is highly dependent on fuel injection parameters, and understanding fuel spray development is
essential for proper control of the process. One of the critical factors for controlling the rate of mixing of fuel and air
is the number of injector holes in a diesel engine. This study was intended to explore the behavior of the formation of spray
mixtures, combustion, and emissions as a function of the number of injector hole changes; from this work, we propose an optimal
number of holes for superior emissions and engine performance in diesel engine applications. The results show that increasing
the number of holes significantly influences evaporation, atomization, and combustion. However, when the number of holes exceeds
a certain threshold, there is an adverse effect on combustion and emissions due to a lack of the air entrainment required
for the achievement of a stoichiometric mixture. 相似文献