全文获取类型
收费全文 | 4434篇 |
免费 | 103篇 |
专业分类
公路运输 | 1477篇 |
综合类 | 685篇 |
水路运输 | 1228篇 |
铁路运输 | 534篇 |
综合运输 | 613篇 |
出版年
2023年 | 18篇 |
2022年 | 59篇 |
2021年 | 83篇 |
2020年 | 57篇 |
2019年 | 47篇 |
2018年 | 98篇 |
2017年 | 112篇 |
2016年 | 211篇 |
2015年 | 93篇 |
2014年 | 132篇 |
2013年 | 372篇 |
2012年 | 264篇 |
2011年 | 381篇 |
2010年 | 367篇 |
2009年 | 280篇 |
2008年 | 325篇 |
2007年 | 304篇 |
2006年 | 240篇 |
2005年 | 189篇 |
2004年 | 91篇 |
2003年 | 91篇 |
2002年 | 49篇 |
2001年 | 67篇 |
2000年 | 75篇 |
1999年 | 28篇 |
1998年 | 33篇 |
1997年 | 42篇 |
1996年 | 43篇 |
1995年 | 45篇 |
1994年 | 16篇 |
1993年 | 25篇 |
1992年 | 26篇 |
1991年 | 14篇 |
1990年 | 28篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 18篇 |
1982年 | 16篇 |
1981年 | 21篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1975年 | 16篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有4537条查询结果,搜索用时 31 毫秒
891.
S.T.H. Jansen J.J.M. Van Oosten 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1995,24(4):343-363
In the scope of the European Prometheus project a passenger car with active rear wheel steering was developed by TNO in cooperation with PSA. During development and engineering of the rear wheel steering system simulation tools have been used to reduce development costs. This paper describes the evaluation of different simulation models, from simple to complex, with results of full vehicle driving tests. The optimal balance for model complexity and accuracy was achieved with a 2-dimensional model with an added roll degree of freedom. The results show that validation using time responses can give ambiguous and inaccurate results, and that frequency response functions are much more usable in validation. 相似文献
892.
G. Roos R. Rollet R.F.C. Kriens 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1997,27(4):267-283
Numerical design of vehicles having optimal straight line stability on undulating road surfaces requires an accurate vehicle model based on knowledge of the relevant phenomena. Therefore, vehicle behavior on undulating straight roads has been analyzed and modeled. Measurements on a flat road surface have shown that the dedicated vehicle model yields accurate simulation results of the steering response to medium steering wheel angle inputs. In addition, the model has been validated by measuring two vehicle responses during normal driving on an undulating straight road: viz. the responses to the small steering wheel angle input and to the input by the global inclination of the road surface. 相似文献
893.
介绍了绘制正弦线电流的开关模式单相半控桥整流器,用它来获得功率因数补偿并保持直流环节电压的恒定.在该整流器中使用4个有源开关,以便在交流端电压上产生单极脉宽调制(PWM)电压波形.与中性点箝位变流器(NPC)相比,该整流器没有箝位二极管也能实现三点式PWM控制.控制电路采用两个控制回路:外部控制回路用比例积分电压控制器调整直流环节电压,采用相位闭环电路产生与电源电压同相的正弦波形来实现功率因数补偿.在内部控制回路中,用基于载波的电流控制器跟踪线电流信号.为补偿由于负载变化所引起的中点电压,控制电路采用中点电压补偿器.该整流器的交流侧可产生3个电压电平,并用计算机仿真与试验结果验证了控制算法的有效性. 相似文献
894.
895.
896.
The dynamic response of flat horizontal plates vibrating in air and under water has been investigated experimentally and analytically. The effect of the boundary conditions and the depth of submergence of the plates has been studied. Excellent agreement was obtained between the analytical solution and the experimental results. An approximate expression for the evaluation of the modal added masses for rectangular plates has been derived. This can be used to estimate the natural frequencies of plating constituting the internal structure within the cargo spaces in tankers and liquid cargo carriers. 相似文献
897.
Deregulation of U.S. Airline Industry may have lowered systematic risk because pricing freedom and route flexibility improved airline management reaction to various economic conditions. Reduced systematic risk offers lower cost of equity capital for the industry as a whole as well as for individual carriers. Previous research has had mixed results in identifying a relationship between deregulation and airline industry cost of capital. This study plots airline industry Beta coefficients across the years 1963 to 1987 and clears up previously conflicting research findings. Beta coefficients had been falling since the fuel crisis of 1974 and continued to fall through 1980. Fluctuations since deregulation have been relatively minor and systematic risk has leveled off at a significantly lower value than before deregulation. Studies which concentrate on the fluctuation in Beta since 1978 are dependent on the exact time period of analysis, and their conclusions that deregulation raised or lowered systematic risk are likewise suspect. A broader view of systematic risk changes in the deregulatory era shows airline Betas peaking from 1971 to 1973 and a gradual decrease as deregulation was being discussed, implemented, and legally mandated. This gradual decline from 1974 to 1980 may be attributed to such factors as fuel prices, interest rates, general inflation as well as deregulation. In any case systematic risk of the U.S. Airline industry has been lower since deregulation than in decades before. 相似文献
898.
以某新建大型工程为例阐述人工挖孔桩的施工工艺、施工过程中应注意的问题,并重点介绍了钻孔取芯试验、单桩竖向抗压静载试验、低应变动力检测等方法在人工挖孔桩质量检测中的综合运用。 相似文献
899.
At transit terminals where two routes interchange passengers, total system costs may be reduced by allowing some “slack” time in the vehicle schedules to decrease the probability of missed connections. Transfer cost functions are formulated and used to determine optimal slack time for simple systems with transfers between one bus route and one rail line. Some analytic results are derived for empirical discrete and Gumbel distributions of bus arrival times. Relations between the optimal slack times and headways, transfer volumes, passenger time values, bus operating costs, and standard deviations of bus and train arrivals are also developed numerically using normally distributed arrivals. However, the proposed numerical approach can optimize slack times for any observed arrival distributions. The results provide some guidelines on desirable slack times and show that schedule coordination between the two routes is not worth attempting when standard deviations of arrivals exceed certain levels. Possible extensions of this work are suggested in the last section. 相似文献
900.