全文获取类型
收费全文 | 1655篇 |
免费 | 60篇 |
专业分类
公路运输 | 570篇 |
综合类 | 383篇 |
水路运输 | 338篇 |
铁路运输 | 366篇 |
综合运输 | 58篇 |
出版年
2024年 | 5篇 |
2023年 | 5篇 |
2022年 | 31篇 |
2021年 | 42篇 |
2020年 | 54篇 |
2019年 | 44篇 |
2018年 | 55篇 |
2017年 | 66篇 |
2016年 | 73篇 |
2015年 | 65篇 |
2014年 | 86篇 |
2013年 | 57篇 |
2012年 | 261篇 |
2011年 | 112篇 |
2010年 | 68篇 |
2009年 | 69篇 |
2008年 | 78篇 |
2007年 | 139篇 |
2006年 | 91篇 |
2005年 | 74篇 |
2004年 | 67篇 |
2003年 | 42篇 |
2002年 | 24篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1715条查询结果,搜索用时 328 毫秒
211.
212.
《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2012,50(8):1321-1338
In order to study the dynamic behaviours of locomotives under saturated adhesion, the stability and characteristics of stick–slip vibration are analysed using the concepts of mean and dynamic slip rates. The longitudinal vibration phenomenon of the wheelset when stick–slip occurs is put forward and its formation mechanism is made clear innovatively. The stick–slip vibration is a dynamic process between the stick and the slip states. The decreasing of mean and dynamic slip rates is conducive to its stability, which depends on the W/R adhesion damping. The torsion vibration of the driving system and the longitudinal vibration of the wheelset are coupled through the longitudinal tangential force when the wheelset alternates between the stick and the slip states. The longitudinal oscillation frequencies of the wheelset are integral multiples of the natural frequency of torsion vibration of the driving system. A train dynamic model integrated with an electromechanical and a control system is established to simulate the stick–slip vibration phenomenon under saturated adhesion to verify the theoretical analysis. The results show that increases of the longitudinal axle guidance stiffness and the motor suspension stiffness are beneficial to the stick–slip vibration stability and the locomotive's traction ability. The optimised matching of the longitudinal axle guidance stiffness and the motor suspension stiffness are helpful to avoid longitudinal resonance when the stick–slip vibration occurs. 相似文献
213.
214.
《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2012,50(12):1687-1704
This paper presents a feedback-feedforward steering controller that simultaneously maintains vehicle stability at the limits of handling while minimising lateral path tracking deviation. The design begins by considering the performance of a baseline controller with a lookahead feedback scheme and a feedforward algorithm based on a nonlinear vehicle handling diagram. While this initial design exhibits desirable stability properties at the limits of handling, the steady-state path deviation increases significantly at highway speeds. Results from both linear and nonlinear analyses indicate that lateral path tracking deviations are minimised when vehicle sideslip is held tangent to the desired path at all times. Analytical results show that directly incorporating this sideslip tangency condition into the steering feedback dramatically improves lateral path tracking, but at the expense of poor closed-loop stability margins. However, incorporating the desired sideslip behaviour into the feedforward loop creates a robust steering controller capable of accurate path tracking and oversteer correction at the physical limits of tyre friction. Experimental data collected from an Audi TTS test vehicle driving at the handling limits on a full length race circuit demonstrates the improved performance of the final controller design. 相似文献
215.
《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2012,50(11):1517-1540
Proper rail geometry in the crossing part is essential for reducing damage on the nose rail. To improve the dynamic behaviour of turnout crossings, a numerical optimisation approach to minimise rolling contact fatigue (RCF) damage and wear in the crossing panel by varying the nose rail shape is presented in the paper. The rail geometry is parameterised by defining several control cross-sections along the crossing. The dynamic vehicle–turnout interaction as a function of crossing geometry is analysed using the VI-Rail package. In formulation of the optimisation problem a combined weighted objective function is used consisting of the normal contact pressure and the energy dissipation along the crossing responsible for RCF and wear, respectively. The multi-objective optimisation problem is solved by adapting the multipoint approximation method and a number of compromised solutions have been found for various sets of weight coefficients. Dynamic behaviour of the crossing has been significantly improved after optimisations. Comparing with the reference design, the heights of the nose rail are notably increased in the beginning of the crossing; the nominal thicknesses of the nose rail are also changed. All the optimum designs work well under different track conditions. 相似文献
216.
217.
基于地面力学理论和液压传动理论,对采用不同同步方式的单泵多马达液压行走系统的动力学问题进行了研究。建立了行走系统的动力学模型,对比了行走系统的牵引力、速度和传动效率。结果表明:在单泵多马达液压行走系统同步方式中,电子防滑技术的性能优于同步分流和自有分流技术。 相似文献
218.
219.
管路系统的辐射噪声在军事上已成为衡量现代鱼雷总体先进程度的重要标志之一。针对鱼雷海水管路脉动压力大、引发辐射噪声显著的特点,本文利用流体力学(CFD)软件进行分析,得出流体速度与管壁压力随入口流量的变化规律,总结了引起脉动压力变化的原因。理论分析和仿真实验结果表明:管路设计中应避免使用弯管,减小压力脉动。 相似文献
220.
研究了斜拉桥发生索梁耦合共振的机理与条件,充分考虑了拉索振动的几何非线性、垂度与桥面刚度的影响,建立了索梁耦合振动的数值计算模型.计算结果表明,拉索发生大幅振动与斜拉桥主梁的刚度以及拉索本身的振动特性有关,拉索可能在主梁振动的作用下发生1∶1的主共振或2∶1的主参数共振.根据计算结果讨论了这两种共振的性质,提出了抑制索梁耦合共振的方法. 相似文献