全文获取类型
收费全文 | 1279篇 |
免费 | 6篇 |
专业分类
公路运输 | 592篇 |
综合类 | 113篇 |
水路运输 | 272篇 |
铁路运输 | 64篇 |
综合运输 | 244篇 |
出版年
2023年 | 21篇 |
2022年 | 37篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 78篇 |
2017年 | 71篇 |
2016年 | 155篇 |
2015年 | 12篇 |
2014年 | 19篇 |
2013年 | 31篇 |
2012年 | 89篇 |
2011年 | 187篇 |
2010年 | 160篇 |
2009年 | 54篇 |
2008年 | 112篇 |
2007年 | 72篇 |
2006年 | 22篇 |
2005年 | 32篇 |
2004年 | 18篇 |
2003年 | 25篇 |
2002年 | 9篇 |
2001年 | 10篇 |
2000年 | 14篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有1285条查询结果,搜索用时 31 毫秒
891.
892.
893.
894.
895.
制备一种玄武岩纤维/铝合金层合板复合结构,通过试验和仿真,探讨该复合结构的拉伸、压缩、剪切、弯曲和抗冲击特性。采用连续壳单元模拟纤维层,建立低速冲击仿真模型,从能量吸收、接触力和层合板损伤程度3个方面,研究铺层结构和冲击载荷角度对纤维金属层合板抗冲击性能的影响。最后,将纤维金属层合板应用于发动机罩外板,进行发动机罩静态刚度和行人头部碰撞仿真分析。结果表明,与原发动机罩相比,纤维金属层合板发动机罩的弯曲刚度和扭转刚度均有不同程度提高,行人头部保护性能得到改善。 相似文献
896.
汽车驱动桥发响原因分析 总被引:1,自引:0,他引:1
汽车驱动桥发响,是目前汽车生产、使用维修中存在的问题之一(在单、双级驱动桥中都有发生)。它直接影响到汽车的高速行驶和驱动桥使用寿命。本文以JN150车的八部发响驱动桥为研究对象,对其进行了观察、检测、分析,找出并排除了引起发响的因素,并重新装好驱动桥,使汽车正常运行。 相似文献
897.
阐述中低速磁浮系统这一新交通系统的基本原理和特点,提出中低速磁浮系统的适用范围.深圳中低速磁浮8号线项目的应用研究表明,中低速磁浮系统是解决城市交通问题的绿色途径. 相似文献
898.
N. L. Azad A. Mozaffari J. K. Hedrick 《International Journal of Automotive Technology》2017,18(2):195-207
In this paper, a gain scheduled linear quadratic tracking system (LQTS) tuned optimally by an evolutionary strategy (ES) is devised to reduce the total tailpipe hydrocarbon (HC) emissions of an automotive engine over the coldstart period. As the engine’s behavior during coldstart operations is nonlinear, the system dynamics is clearly analyzed and represented by a number of separate linear models generated based on a coldstart model verified by experimental data. An independent LQTS is then implemented for each of these linear models. In this way, several control laws are created, and the corresponding gains are calculated for each of the independent control laws. ES is then used to tune the adjustable parameters of LQTSs to calculate the control inputs, namely air/fuel ratio (AFR) and spark timing (Δ), such that the resulting exhaust gas temperature (T exh) and engine-out HC emissions (HC raw) be close to a set of optimum profiles. This enables the controller reduce the cumulative tailpipe hydrocarbon emissions (HC cum) to the highest possible extent. To demonstrate the acceptable performance of the proposed controller, an optimal controller derived from the Pontryagin’s minimum principle (PMP) is also taken into account. Based on the results of the conducted comparative study, it is shown that the proposed control technique has a very good performance, and also, can be easily used for real-time applications, as it consumes a remarkably trivial computational time for calculating the controlling commands. 相似文献
899.
Z. C. Kan D. M. Lou Z. Z. Cao Z. Y. Hu S. Liu Z. H. Yang 《International Journal of Automotive Technology》2017,18(2):209-217
Altitude has a significant effect on combustion of heavy-duty diesel engines, especially during cold start. An experimental study on a heavy-duty diesel engine operating at different altitudes was conducted. Tests were based on a direct injection (DI) turbocharged diesel engine with intake and exhaust pressure controlled by the plateau simulation test system to stimulate altitude conditions including 0 m, 1000 m, 2000 m, 3000 m and 4000 m. Results indicated that the compression and expansion resistance moment reduced and the speed increased during the cranking period. The peak pressure of several cycles was increased during the start-up period; however, the expansion pressure dropped more and the indicated mean effective pressure (IMEP) reduced as the altitude rose. While at an altitude of over 2000 m, the peak pressure fluctuated obviously during the start-up period. The higher the altitude was, the more the fluctuation amplitude and cycle number increased and combustion instability enhanced, which resulted the start-up period time increasing at high altitude. When the altitude rose, the cycle-to-cycle variation of the peak pressure and speed fluctuation increased during the idle, the ignition and CA50 were delayed and the combustion duration was shortened. The effect of altitude on combustion characteristics of the diesel engine was more significant during the start-up period than during its idle period. 相似文献
900.
Nowadays, the selective catalytic reduction (SCR) is a promising solution to fulfill stringent nitrogen oxide (NOX) emission standards enforced by worldwide regulation bodies for lean burning engines. However, in the practical operation, urea deposits occur under unfavorable conditions, which bring about a failure of urea dosing strategy, affect the SCR system de-NOx performance and lowering the fuel economy by increasing the engine back pressure. This paper will present 3D deposit model, which can be used to predict the deposit position. Furthermore, a model-based controls strategy and calibration are designed. The comparison test results of both engine emission tests and vehicle field tests shows there is significant deposits improvement with the embedded model. 相似文献