全文获取类型
收费全文 | 636篇 |
免费 | 16篇 |
专业分类
公路运输 | 68篇 |
综合类 | 125篇 |
水路运输 | 180篇 |
铁路运输 | 272篇 |
综合运输 | 7篇 |
出版年
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 3篇 |
2017年 | 16篇 |
2016年 | 14篇 |
2015年 | 14篇 |
2014年 | 54篇 |
2013年 | 23篇 |
2012年 | 59篇 |
2011年 | 51篇 |
2010年 | 38篇 |
2009年 | 48篇 |
2008年 | 49篇 |
2007年 | 54篇 |
2006年 | 56篇 |
2005年 | 14篇 |
2004年 | 22篇 |
2003年 | 11篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有652条查询结果,搜索用时 15 毫秒
521.
522.
针对城市路网中区域性的大范围交通拥堵问题,提出了基于宏观基本图(Macroscopic Fundamental Diagram,MFD)的多子区协调控制策略,以提升路网的整体运行效益.该策略将城市区域路网划分为多个子区,每个子区的交通流又划分为内部流和转移流,综合两者建立了基于MFD的多子区交通流模型,并给出了对各子区交通流诱导时的边界约束条件;通过调节子区边界控制输入,设计了边界反馈控制器对各子区转移流进行动态诱导,继而进行了迭代分析,以判断其是否满足边界约束,并对控制器进行了Lyapunov稳定性分析.仿真结果表明,所提策略使城市区域路网中各子区车辆总数渐近收敛于设定值,且整体平均流量提高了约11%,大范围交通拥堵状况得到明显缓解. 相似文献
523.
李维波方鹏潘峻锋郝春昊张忠田 《中国舰船研究》2022,(5):268-277
[Objective]In order to reduce the switching frequency of an intermediate frequency inverter power supply, ensure the quality of the output waveform and realize digitalization easily, a SPWM sampling method based on a tangent-secant midpoint approximation is proposed. [Methods]It is proven by deduction that the quantitative relationship of the natural sampling method can be approximated, and a Matlab/Simulink simulation model is built. The algorithm is designed and applied to an intermediate frequency inverter device, and the correctness of the proposed method is verified in the two aspects of simulation and experiment. [Results]The simulation results show that the total harmonic distortion (THD) of the output waveform based on the tangent-secant midpoint approximation method is 2.64%, lower than the 3.99% of the symmetrical regular sampling method. The waveform quality of the tangent-secant midpoint approximation method is obviously better than that of the symmetrical regular sampling method, as it not only reduces the switching frequency but also takes into account the requirements of THD. [Conclusions]SPWM sampling based on tangent-secant midpoint approximation is applied to the intermediate frequency power supply and is able to effectively overcome the shortcomings of the low-quality output waveform and high switching frequency of the symmetrical regular sampling method. Both theoretical analysis and engineering practice verify the rationality and correctness of the proposed method, and it can be widely extended to the field of intermediate frequency power supply installation. © 2022 Journal of Clinical Hepatology. All rights reserved. 相似文献
524.
为解决车下设备箱在生产过程中需耗费大量工时进行焊接矫形的问题,提出一种基于铆接结构车下设备箱的设计,并通过有限元仿真计算进行验证,为城市轨道交通车下设备箱的研发提供一种设计新思路。 相似文献
525.
526.
527.
《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2012,50(4):375-388
When driving in curves, how do drivers use the force appearing on the steering wheel? As it carries information related to lateral acceleration, this force could be necessary for drivers to tune their internal model of vehicle dynamics; alternatively, being opposed to the drivers' efforts, it could just help them stabilize the steering wheel position. To assess these two hypotheses, we designed an experiment on a motion-based driving simulator. The steering characteristics of the vehicle were modified in the course of driving, unknown to drivers. Results obtained with standard drivers showed a surprisingly wide range of adaptation, except for exaggerated modifications of the steering force feedback. A two-level driver model, combining a preview of vehicle dynamics and a neuromuscular steering control, reproduces these experimental results qualitatively and indicates that adaptation occurs at the haptic level rather than in the internal model of vehicle dynamics. This effect is related to other theories on the manual control of dynamics systems, wherein force feedback characteristics are abstracted at the position control level. This research also illustrates the use of driving simulation for the study of driver behavior and future intelligent steering assistance systems. 相似文献
528.
529.
该系统以TI公司的DSP芯片TMS320LF2407A为基础,形成了具有高速数据采集和实时数据处理功能的硬件平台,在此平台上通过应用SVPWM算法,FFT算法和数字PID算法等数字处理技术,采用闭环控制,形成了具有良好人机交互界面和通信功能的全数字化SVPWM三相逆变器系统。该系统具有很好的动稳态性能。 相似文献
530.