全文获取类型
收费全文 | 989篇 |
免费 | 53篇 |
专业分类
公路运输 | 232篇 |
综合类 | 352篇 |
水路运输 | 234篇 |
铁路运输 | 184篇 |
综合运输 | 40篇 |
出版年
2024年 | 10篇 |
2023年 | 6篇 |
2022年 | 22篇 |
2021年 | 32篇 |
2020年 | 29篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 24篇 |
2016年 | 20篇 |
2015年 | 41篇 |
2014年 | 92篇 |
2013年 | 68篇 |
2012年 | 97篇 |
2011年 | 91篇 |
2010年 | 77篇 |
2009年 | 60篇 |
2008年 | 54篇 |
2007年 | 80篇 |
2006年 | 57篇 |
2005年 | 34篇 |
2004年 | 20篇 |
2003年 | 24篇 |
2002年 | 11篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有1042条查询结果,搜索用时 438 毫秒
491.
492.
详细介绍了隧道内CRTSⅡ型双块式无砟轨道施工过程中的一些关键技术,如CPIII点测设技术、支脚安装精调技术、轨枕振动嵌入技术等,这些关键技术能为客运专线无砟轨道施工提供一些有益的参考。 相似文献
493.
依据矩量法对偶极子天线和单线行波天线进行分析,将其分为多个小段,分别计算各段上的电流,然后根据电流分布计算出远场和近场的场强波瓣图,从近场随距离的明显变化得出天线近场分析的必要性. 相似文献
494.
495.
《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2012,50(2):251-279
A sensitivity analysis has been performed to assess the influence of the inertial properties of railway vehicles on their dynamic behaviour. To do this, 216 dynamic simulations were performed modifying, one at a time, the masses, moments of inertia and heights of the centre of gravity of the carbody, the bogie and the wheelset. Three values were assigned to each parameter, corresponding to the percentiles 10, 50 and 90 of a data set stored in a database of railway vehicles. After processing the results of these simulations, the analysed parameters were sorted by increasing influence. It was also found which of these parameters could be estimated with a lesser degree of accuracy for future simulations without appreciably affecting the simulation results. In general terms, it was concluded that the most sensitive inertial properties are the mass and the vertical moment of inertia, and the least sensitive ones the longitudinal and lateral moments of inertia. 相似文献
496.
《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2012,50(7):992-1015
We set out to answer the question: At what hitch angle does it become impossible for a vehicle and trailer to continue to backing up without getting into a jackknife? Jackknifing during backing up of trailers occurs when the hitch angle increases to a point such that the vehicle and trailer fold together about the hitch point like a jackknife. If the backward motion is continued, the jackknife effect progressively worsens, until the vehicle and trailer are in physical contact with each other. Jackknifing can result in traffic disruptions and wasted time, and can potentially cause damage or personal injury. Our goal is to analytically determine the ‘critical hitch angle’ (θcr), the hitch angle threshold beyond which a continued reverse motion causes an inescapable jackknifing. In this paper, we provide a formal definition of θcr for slow backing up of vehicle–trailer systems on a level solid surface, beyond which the vehicle must stop backing up and revert to forward motion in order to escape from jackknifing. The critical hitch angle is sub-categorised into Absolute (θcr, a) and Directional (θcr, d) critical hitch angles depending on the operating constraints and vehicle steering objectives. One solution for θcr is posed as a numerical solution to the steady-state conditions of the dynamic equations. The effects of such hitch angle limitations are demonstrated through simulation. Also, a warning system making use of the θcr is proposed. Such warning systems can assist drivers in avoiding jackknifing while backing up a vehicle–trailer system. 相似文献
497.
498.
499.
计算了z=4,6时的一维单峰幅度非对称映象的两个标度因子δ和a值。结果表明,它们都具有振荡行为,即交替地收敛到各自的两个常数c_1、c_2和d_1、d_2。对于固定的z值,c_1·c_2=δ~2,d_1·d_2=a~2。在聚点a~*处有c_1=c_2=δ,d_1=d_2=a。这里δ,a及a~*是一维单峰对称映象中相同z值下的标度因子值和聚点值。 相似文献
500.