全文获取类型
收费全文 | 4101篇 |
免费 | 76篇 |
专业分类
公路运输 | 1162篇 |
综合类 | 1001篇 |
水路运输 | 1114篇 |
铁路运输 | 747篇 |
综合运输 | 153篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 66篇 |
2021年 | 139篇 |
2020年 | 91篇 |
2019年 | 27篇 |
2018年 | 42篇 |
2017年 | 36篇 |
2016年 | 59篇 |
2015年 | 73篇 |
2014年 | 127篇 |
2013年 | 216篇 |
2012年 | 279篇 |
2011年 | 287篇 |
2010年 | 328篇 |
2009年 | 339篇 |
2008年 | 303篇 |
2007年 | 420篇 |
2006年 | 406篇 |
2005年 | 263篇 |
2004年 | 85篇 |
2003年 | 78篇 |
2002年 | 67篇 |
2001年 | 95篇 |
2000年 | 80篇 |
1999年 | 49篇 |
1998年 | 43篇 |
1997年 | 31篇 |
1996年 | 35篇 |
1995年 | 19篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
排序方式: 共有4177条查询结果,搜索用时 15 毫秒
991.
Zhong Chang Liu Xing Yuan Jing Tian Yong Qiang Han Kai Bo Yu Peng Kun Teng 《International Journal of Automotive Technology》2018,19(5):783-794
The object of this paper is to reduce soot emissions under typical 5s transient conditions of constant speed and increasing torque. And effects of fuel injection timing on combustion and emissions parameters were experimentally and numerically studied in a regulated two-stage turbocharged diesel engine with a turbine bypass valve (TBV). The test results indicated that: the smaller TBV opening could improve deterioration of smoke emissions and BSFC at medium and heavy loads. Afterward, the full-stage injection timing (FSIT) strategies (delaying injection timing during the entire transient process) could reduce soot and NOX emissions simultaneously. However, when TBV opening became larger, smoke emissions and BSFC were deteriorated gradually. Moreover, the sectional-stage injection timing (SSIT) strategies (advancing injection timing from 10 % load to a preset load and delaying injection timing from the preset load to 100 % load) could markedly reduce soot emissions by 75.8 % with TBV opening 20 %; the degradation of fuel consumption could be effectively suppressed. Finally, coupling the SSIT strategies with the TBV control strategies could significantly improve the transient performance. 相似文献
992.
Xia Xin Xiong Lu Hou Yuye Teng Guowen Yu Zhuoping 《International Journal of Automotive Technology》2017,18(6):993-1006
In this work, the reference model modification strategy for vehicle stability control based on driver's intention recognition under emergent obstacle avoidance situation was proposed. First the conflicts between the driver's emergency alignment (EA) intention and vehicle response characteristics were analyzed in critical emergent obstacle avoidance situation. Second combining steering wheel angle and its speed, the driver's EA intention was recognized. The reference model modification strategy based on steering operation index (SOI) was presented. Then a LQR model following controller with tire cornering stiffness adaption was used to generate direct yaw moment for tracking modified reference yaw rate and reference sideslip angle. Finally based on the four-in-wheel-motor-drive (FIWMD) electric vehicles (EV), double lane change and slalom tests were conducted to compare the results using modified reference model with the results using normal reference model. The experimental tests have proved the effectiveness of the reference model modification strategy based on driver's intention recognition. 相似文献
993.
994.
重庆枢纽北左、北右联络线隧道与既有蔡东联络线双碑隧道水平最小净距只有7 m,设计采用控制爆破施工,要求既有隧道爆破振速不大于5 cm/s,施工难度极大。为减少施工对既有隧道的影响,通过试爆获得振动衰减规律,验证开挖方式的可行性,利用试爆结果,完善了最终的爆破方案,并在正式施工中得到了成功应用,保证了重庆枢纽联络线隧道开挖工程的安全高效完成。 相似文献
995.
由于汽车的普及,车内的空气质量引发消费者越来越多的关注。糟糕的车内空气质量会增大人们罹患某种特定疾病的概率,因此控制与减少车内空气污染成为汽车生产设计商所追求的目标。微颗粒污染物,即PM2.5是车内空气污染物的重要来源之一。负离子因能有效沉降空气中的微颗粒,成为车内快速去除微颗粒污染的重要手段。在文章中,我们通过在车内进行微颗粒沉降实验,记录微颗粒物浓度在负离子仪以及车内空调内/外循环净化模式下的变化,并通过SPSS与MATLAB对污染物浓度进行数学建模分析。结果表明:单独使用负离子仪器并无法有效降低车内空气的颗粒浓度,而必须配合车内空气循环系统。在负离子作用下,结合车内空气循环系统,微颗粒浓度迅速下降,下降速度与空气交换速度和微颗粒在空气中的迁移速度相关。 相似文献
996.
997.
998.
Caihong Huang Jing Zeng 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2018,56(12):1922-1944
This paper focuses on revealing the dynamic behaviour of a hydraulic yaw damper under very small excitation conditions. First, the measured yaw damper movement is presented when a train experiences unstable motions. It shows that the yaw damper is characterized by very small harmonic movement between 0.5 and 2?mm. Following this, a simplified physical model of the yaw damper is developed which has the ability to reproduce its dynamic performance in the range of operating conditions, and then suitably validated with experimental results. At last, the dynamic behaviour of the yaw damper under very small amplitudes is investigated by comparing with its static behaviour, and the dynamic stiffness and damping in terms of key parameters are studied. It is concluded that there is a great difference in the damper performance between dynamic and static conditions which is caused by the internal damper flexibility under small amplitudes. The percentage of entrapped air in oil, rubber attachment stiffness, and leakage flow have a great effect on the dynamic behaviour of the yaw damper related to the dynamic stiffness and damping. The effect is even more remarkable for smaller amplitudes regarding the dissolved air in oil. Oil leakage has a greater impact on dynamic damping than dynamic stiffness. The series stiffness of the yaw damper is mainly provided by the spring effect of the oil when the rubber attachment stiffness reached a certain limit, and an additional increase in rubber attachment stiffness becomes useless to further enhance the overall stiffness of the damper. 相似文献
999.
1000.
介绍了新研制的广范围时间继电器,对船舶辅锅炉点火程序控制系统方面的改进和广范围时间继电器的使用功能及其优点。 相似文献