全文获取类型
收费全文 | 3315篇 |
免费 | 234篇 |
专业分类
公路运输 | 870篇 |
综合类 | 1060篇 |
水路运输 | 747篇 |
铁路运输 | 766篇 |
综合运输 | 106篇 |
出版年
2024年 | 16篇 |
2023年 | 25篇 |
2022年 | 98篇 |
2021年 | 108篇 |
2020年 | 127篇 |
2019年 | 105篇 |
2018年 | 88篇 |
2017年 | 87篇 |
2016年 | 84篇 |
2015年 | 104篇 |
2014年 | 205篇 |
2013年 | 180篇 |
2012年 | 284篇 |
2011年 | 327篇 |
2010年 | 241篇 |
2009年 | 221篇 |
2008年 | 232篇 |
2007年 | 276篇 |
2006年 | 226篇 |
2005年 | 171篇 |
2004年 | 84篇 |
2003年 | 65篇 |
2002年 | 40篇 |
2001年 | 51篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 14篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有3549条查询结果,搜索用时 31 毫秒
961.
962.
风载是综合集成桅杆复合材料天线罩所受的主要载荷之一,研究天线罩的风载特性将对复合材料天线罩的结构设计具有重要指导意义。采用试验和数值模拟的方法对倾斜侧壁正八边形天线罩的风载特性进行研究,分析天线罩表面平均压力系数和脉动压力系数的周向分布规律,以及Strouhal数(St数)随雷诺数(Re数)和风向角的变化规律,并将计算结果与试验结果进行比较分析。研究结果表明:平均压力系数和脉动压力系数沿周向分布变化较大,不同风向角下St数随Re的增加趋于稳定值,平均压力系数和脉动压力系数计算值与试验值基本相近。 相似文献
963.
为提高设备运行效率,节约人力成本,一些集装箱码头开创了"一拖双挂"技术。介绍集装箱码头牵引车"一拖双挂"技术项目背景和发展情况。分析该项目节能原理,阐述车型选定、实施方案、技术创新点等。该项目取得良好节能效益、经济效益、社会效益。 相似文献
964.
To investigate the stability and mechanical characteristics of a type of heavy haul coupler with restoring bumpstop, the geometry and force states of couplers were analysed at different yaw angles and the longitudinal forces. The structural characteristics of this coupler were summarised. To aid in the investigation, a multi-body dynamics model with four heavy haul locomotives and three detailed couplers was established to simulate the process of emergency braking. In addition, the coupler yaw instability and lateral forces were tested in order to investigate the effect of relevant parameters on the locomotive's wheelset lateral forces. The results show that only when the bumpstop force exceeds half of the coupler longitudinal compression force, can the follower be rotated and the yaw angle of the coupler increase. The bumpstop preload is the most important stabilising factor. The coupler lateral force is constant when the coupler longitudinal force is smaller than the critical values of 2000, 1400 and 1150 kN at coupler free angles of 7°, 8° and 9°, respectively, for operation on straight track. The coupler free angle and the locomotive's lateral clearance of the secondary stopper are important in decreasing the wheelset lateral forces of the locomotive. It is advised that a smaller locomotive's secondary lateral suspension stiffness, a free clearance of 35 mm and an elastic clearance of 15 mm from the secondary lateral stopper be selected. If the coupler's free angle is less than the self-stabilising angle which is 5.5° for operation on straight track, the coupler is stable no matter how great the longitudinal force is. The wheelset lateral forces are allowed at the coupler longitudinal force of 2500 kN when the free angle is 6°. These studies establish meaningful improvements for the stability of couplers and match the heavy haul locomotive with its suspension parameters. 相似文献
965.
《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2012,50(7):1085-1102
The paper presents a curving adaptive cruise control (ACC) system that is coordinated with a direct yaw-moment control (DYC) system and gives consideration to both longitudinal car-following capability and lateral stability on curved roads. A model including vehicle longitudinal and lateral dynamics is built first, which is as discrete as the predictive model of the system controller. Then, a cost function is determined to reflect the contradictions between vehicle longitudinal and lateral dynamics. Meanwhile, some I/O constraints are formulated with a driver permissible longitudinal car-following range and the road adhesion condition. After that, desired longitudinal acceleration and desired yaw moment are obtained by a linear matrix inequality based robust constrained state feedback method. Finally, driver-in-the-loop tests on a driving simulator are conducted and the results show that the developed control system provides significant benefits in weakening the impact of DYC on ACC longitudinal car-following capability while also improving lateral stability. 相似文献
966.
967.
968.
969.
现有的安全距离模型是基于纵向相对车速或减速度值建立的,没有考虑移动目标的横向运动特性。本文利用移动目标横穿马路的速度、相对位置,建立横向安全距离模型,并提出一种基于横向安全距离模型的主动避障算法。首先,根据横向移动目标横穿马路的速度、相对位置和自车的制动距离建立横向安全距离模型,设计主动避障算法。接着,为计及路面条件对制动效果的影响,引入当前行驶路面估算的附着系数峰值估算最大制动减速度,约束目标避障减速度,并调整制动强度,以适应不同路况的安全避障行驶。最后,以典型横向移动目标骑行者作为研究对象,通过PreScan/Simulink/CarSim联合仿真验证避障算法的有效性。结果表明:基于横向安全距离模型的主动避障算法能有效避免与骑行者碰撞,提高行车的主动安全性。 相似文献