全文获取类型
收费全文 | 2645篇 |
免费 | 152篇 |
专业分类
公路运输 | 777篇 |
综合类 | 880篇 |
水路运输 | 548篇 |
铁路运输 | 464篇 |
综合运输 | 128篇 |
出版年
2024年 | 8篇 |
2023年 | 18篇 |
2022年 | 41篇 |
2021年 | 66篇 |
2020年 | 102篇 |
2019年 | 65篇 |
2018年 | 54篇 |
2017年 | 60篇 |
2016年 | 80篇 |
2015年 | 95篇 |
2014年 | 204篇 |
2013年 | 161篇 |
2012年 | 254篇 |
2011年 | 240篇 |
2010年 | 187篇 |
2009年 | 163篇 |
2008年 | 161篇 |
2007年 | 195篇 |
2006年 | 199篇 |
2005年 | 117篇 |
2004年 | 63篇 |
2003年 | 69篇 |
2002年 | 36篇 |
2001年 | 44篇 |
2000年 | 30篇 |
1999年 | 6篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 17篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
排序方式: 共有2797条查询结果,搜索用时 15 毫秒
881.
全电力推进系统相对于传统推进系统具有明显优势,是目前船舶推进技术的研究热点之一。全电力推进技术正在经历由交流组网技术向直流组网技术过渡的过程。在比较直流组网技术相对于交流组网技术的优势后,详细介绍目前几种流行的已经得到实船验证的直流组网技术路线,并对其异同点进行比较。分析结果表明,直流组网技术明显优于交流组网技术,不同的直流组网技术路线本身也会对系统的性能产生巨大的影响,特别是异步发电机+全控整流器的方案相对于其他的直流组网技术路线具有明显的优势。 相似文献
882.
为了研究空冷器管道系统的流体均配问题,引入多孔介质模型,应用Fluent对空冷器的管道系统进行了数值模拟研究。结果表明:空冷器的压降越大,管道系统的流体分配越均匀;分流集合管与汇流集合管中的压力分布在一定程度上决定了管道系统的流体分配;分流集合管与汇流集合管中流体的流动方向相反有利于管道系统的流体均配,当二者的流体流动方向相同时,沿流动方向各支管流量依次增加。管道系统结构优化后,流体分配更均。 相似文献
883.
H. Nozaki 《International Journal of Automotive Technology》2008,9(3):307-315
Because Formula cars are lighter than ordinary cars, the optimal settings for this type of car are thought to be different
from those of a ordinary car. The front and rear weight distribution ratio of a vehicle is an important parameter that exerts
a significant influence on critical cornering. The tendency of a ordinary car to under-steer during critical cornering is
determined by the front and rear weight distribution ratio of the vehicle. Specifically, when the front of an ordinary FR
(front-engine, rear wheel drive) vehicle is slightly heavier than the rear, the car tends to understeer during critical cornering.
However, the optimal weight distribution ratio for critical cornering is not obvious for a formula car because of its lightness.
This observation was investigated using a driving course similar to a real driving course to perform a maximum speed cornering
simulations. It was found that a front to rear weight distribution ratio of 40:60 resulted in the fastest lap time. This ratio
also gave the best results in the maximum-speed driving experiment performed using a driving simulator. Moreover, the maximum
lateral acceleration during turning, the driving force, and the load movement of the inside and outside wheels was calculated
using experimental driving force data and the concept of a tire friction circle. As a result, driving mechanics have been
determined for a vehicle having a front/rear weight distribution ratio of 40:60 while traveling at maximum speed. 相似文献
884.
J. -S. Jo S. -H. You J. Y. Joeng K. I. Lee K. Yi 《International Journal of Automotive Technology》2008,9(5):571-576
The Vehicle stability control system is an active safety system designed to prevent accidents from occurring and to stabilize
dynamic maneuvers of a vehicle by generating an artificial yaw moment using differential brakes. In this paper, in order to
enhance vehicle steerability, lateral stability, and roll stability, each reference yaw rate is designed and combined into
a target yaw rate depending on the driving situation. A yaw rate controller is designed to track the target yaw rate based
on sliding mode control theory. To generate the total yaw moment required from the proposed yaw rate controller, each brake
pressure is properly distributed with effective control wheel decision. Estimators are developed to identify the roll angle
and body sideslip angle of a vehicle based on the simplified roll dynamics model and parameter adaptation approach. The performance
of the proposed vehicle stability control system and estimation algorithms is verified with simulation results and experimental
results. 相似文献
885.
Fatigue design approach for the spot-welded T-type member using a simulated single spot-welded joint
In order to develop a fatigue design method for actual railroad car and commercial vehicle body structures using the fatigue
data of simulated single spot-welded lap joints, we first analyzed the stress distribution and evaluated fatigue strength
of spot-welded T-type members that are the components of actual railroad car and commercial vehicle body structures. Next,
fatigue design approach of these members using the fatigue data of single spot-welded lap joints was investigated. From our
results, we found that, even though there was a quantitative difference of fatigue strength between the single spot-welded
joint and the actual members over the same number of fatigue cycles, through the use of appropriate correction, the fatigue
design criterion of actual spot-welded members, such as those used in railroad car and commercial vehicle body, can be predicted
using the fatigue strength of single spot-welded joint. 相似文献
886.
比拟正交异性板法,即G-M法,是目前确定桥梁荷载横向分布系数的一种常用方法。但是该方法计算过程繁冗,具有重复性,而且它所用到的计算图表粗略,每次所查读的影响系数K0和K1值都是估读,误差较大。该文通过运用多种计算机软件,整合G-M法的计算过程,使之快捷准确。并举例说明,可供桥梁设计人员参考。 相似文献
887.
广州市轨道交通4号线[区间7标]高架桥跨度为25,27.5,30,32.5 m预应力简支箱梁,重点介绍了预制节段箱梁施工中关键技术、预制节段箱梁拼装和架设施工工艺。 相似文献
888.
889.
SHEN Chao WEI Jianfeng GUO Hongzong JIANG Keqiang LIU Tengai QIAN Zhendong ZHANG Lei 《中南公路工程》2008,(5)
在介绍国内外立转开启式桥梁桥面铺装研究现状的基础上,从轻质铺装材料开发和薄型铺装结构研究、基于大悬臂结构和界面接触特性的力学性能数值模拟、黏结层材料试验3个方面阐述了立转开启式桥梁桥面铺装研究的关键技术和难点。 相似文献
890.
行人穿越机动车流的平均临界间隙分析方法 总被引:1,自引:0,他引:1
通过研究行人穿越机动车流的平均临界间隙.对所观测的行人穿越间隙数据进行归纳分析,得出可接受穿越间隙的正态分布函数N(4.86,1.72),并通过三种不同的方法逐一计算出平均临界间隙,可为今后的行人延误时间、通行能力以及与车辆之间的冲突分析研究提供解决方案。 相似文献