首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2252篇
  免费   14篇
公路运输   667篇
综合类   77篇
水路运输   748篇
铁路运输   72篇
综合运输   702篇
  2022年   32篇
  2021年   16篇
  2020年   22篇
  2019年   20篇
  2018年   60篇
  2017年   55篇
  2016年   73篇
  2015年   23篇
  2014年   75篇
  2013年   352篇
  2012年   118篇
  2011年   123篇
  2010年   104篇
  2009年   100篇
  2008年   101篇
  2007年   72篇
  2006年   49篇
  2005年   52篇
  2004年   32篇
  2003年   45篇
  2002年   37篇
  2001年   43篇
  2000年   28篇
  1999年   34篇
  1998年   54篇
  1997年   35篇
  1996年   44篇
  1995年   35篇
  1994年   23篇
  1993年   27篇
  1992年   30篇
  1991年   18篇
  1990年   19篇
  1989年   20篇
  1988年   19篇
  1987年   17篇
  1986年   17篇
  1985年   16篇
  1984年   17篇
  1983年   11篇
  1982年   18篇
  1981年   23篇
  1980年   24篇
  1979年   24篇
  1978年   15篇
  1977年   17篇
  1976年   16篇
  1975年   25篇
  1974年   12篇
  1973年   12篇
排序方式: 共有2266条查询结果,搜索用时 15 毫秒
31.
The hot stamping process has been used in the automotive industry to reduce the weight of the body-in-white and to increase passenger safety via improved crashworthiness. However, defects such as fracture and wrinkle occur when hot stamping is performed using a conventional drawing or forming method. In this study, a channel-type indirect blank holder (CIBH) is proposed to develop a high-strength center pillar in form-type hot stamping, so that the aforementioned drawbacks are overcome. This type of blank holder plays an important role in reducing severe wrinkling at the flange; such wrinkling leads to folding after the completion of form-type hot-stamping. First, we investigated the effect of the channel shape on the indirect blank holding force by using a simplified two-dimensional plane-strain stamping process. Second, we selected the slope angle and corner radius of the channel as the main shape parameters by finite element analysis and artificial neural network (ANN). It is known that fracture at the hot formed wall and wrinkle at the flange are significantly affected by the slope angle of the channel, and the appropriate value for eliminating fracture and wrinkle is determined to be 99°. By performing hot stamping using a form die with the selected channel, we can manufacture a high-strength center pillar without wrinkle and fracture.  相似文献   
32.
33.
Results of vehicle crosswind research involving both full-scale driver-vehicle tests and associated analyses are presented. The paper focuses on experimental crosswind testing of several different vehicle configurations and a group of seven drivers. A test procedure, which utilized wind-generating fans arranged in alternating directions to provide a crosswind “gauntlet”, is introduced and described. Driver preferences for certain basic chassis and aerodynamic properties are demonstrated and linked to elementary system responses measured during the crosswind gauntlet tests. Based on these experimental findings and confirming analytical results, a two-stage vehicle design process is then recommended for predicting and analyzing the crosswind sensitivity of a particular vehicle or new design.  相似文献   
34.
In previous publications the author has described a so-called first-order theory for the motion of a railway vehicle wheelset on a tangent track. In the present report the geometrical aspect of this theory is further evaluated and a method for solving the constraint equations between the coordinates of the wheelset is indicated.  相似文献   
35.
The control behaviour of motorcycle riders is studied by means of a simulation model for the ridermotorcycle system, which stresses the control actions of the riders. The rider model describes the major steering torque control as well as the rider's own body control actions. This simulation model is applied to a single lane change maneuver and the results of this simulation are compared with the experiments in order to examine its validity.  相似文献   
36.
In regard to the belt and pulley system of a metal V-belt CVT, the characteristics of the ratio changing speed is obtained by experiments. It is summarized in a practical and simple experimental equation. By using this equation a simulation model is developed to analyze the response of a vehicle with a metal V-belt CVT to a rapid pulley ratio change. The simulation results are in reasonable agreements with experimental results.  相似文献   
37.
An Anti-Lock Brake System (ABS) system is developed for motorcycles using different control laws to improve the safety during emergent braking conditions. The mechanical design problem is first investigated so as to modify a scooter to be equipped with the proposed ABS brake system and to set up experimental test stand. For ABS control, the slip control, P1R3, and P2R4 methods are used to implement the controller using an Intel 80196KC single chip microcomputer. The hard-ware-in-the-loop (HITL) simulation is also performed in PC to check the performance in various road conditions including dry and wet roads. It is found experimentally that both P1R3 and P2R4 can both achieve ABS function, but P2R4 performs more desirably than P1R3 method.  相似文献   
38.
39.
For railway vehicles having coned wheels mounted on solid axles, there is a conflict between the stability of lateral deviations from the motion along the track and the ability to steer round curves. A general theory is developed for the two-axle vehicle in which there is a lack of symmetry, fore-and-aft, both of the interwheelset structure and of the equivalent conicities of the wheelsets. It is shown that whilst parameters can be selected which provide static and dynamic stability and perfect steering for both directions of motion, there is a lightly damped mode of oscillation for any practical configuration and the significance of this is discussed.  相似文献   
40.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号