全文获取类型
收费全文 | 2474篇 |
免费 | 85篇 |
专业分类
公路运输 | 663篇 |
综合类 | 701篇 |
水路运输 | 623篇 |
铁路运输 | 498篇 |
综合运输 | 74篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 64篇 |
2021年 | 83篇 |
2020年 | 83篇 |
2019年 | 34篇 |
2018年 | 34篇 |
2017年 | 37篇 |
2016年 | 38篇 |
2015年 | 89篇 |
2014年 | 109篇 |
2013年 | 135篇 |
2012年 | 178篇 |
2011年 | 154篇 |
2010年 | 187篇 |
2009年 | 182篇 |
2008年 | 196篇 |
2007年 | 249篇 |
2006年 | 201篇 |
2005年 | 150篇 |
2004年 | 60篇 |
2003年 | 44篇 |
2002年 | 48篇 |
2001年 | 49篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 18篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1986年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有2559条查询结果,搜索用时 46 毫秒
211.
212.
213.
新建路隧道东线通风模拟分析 总被引:1,自引:0,他引:1
该文介绍了上海市新建路隧道东线通风系统和设计标准,运用SES软件模拟分析隧道通风效果,可供类似工程参考。 相似文献
214.
In this paper, we investigate the transient characteristics of combustion and emissions during engine start/stop operations
in hybrid electric vehicle (HEV) applications. Hydrocarbon (HC) emissions during the initial 2nd∼9th cycles are found to be significantly greater when the engine is quickly started under the original engine calibration mode.
Lower intake manifold absolute pressure (MAP) was also found to cause larger residual gas dilution and poor combustion, resulting
in a higher HC concentration when the cranking speed was increased. The post-catalyst HC concentration was found in the way
of initially decrease and then to increase again as the cranking speed was increased. A lowest concentration value was achieved
at a cranking speed of 1000 r/min. Engine shut-down by fuel cut-off was shown to produce lower emissions than shut-down by
ignition cut-off as one can avoid misfire of the last fuel injection cycle. The fuel deposited during the stop process seems
to impact engine restart enrichment mostly during the initial 0.7 s for this engine, whose performance is dominated by the
MAP transition characteristic and the time coefficient for fuel vaporization in this time period 相似文献
215.
The smoothed particle hydrodynamics (SPH), as a fully Lagrangian particle method, has been successfully applied to astrophysical problems and extended to elastic dynamics and computational fluid dynamics.High order derivatives have to be approximated when elastic dynamics problems are modeled. However, the approximation errors in SPH could lead to computational failure in the case that the order of derivative is high.A novel method was proposed in order to improve the accuracy of SPH method, which shows the relationship between the selected functions and their SPH approximations. The entire involved system was represented by a finite number of particles that carry individual mass and occupy individual space, and the integral interpolation was approximated by a summation interpolation. In addition, error comparison was made between SPH method with and without the present improvement. 相似文献
216.
Dong Hongli Jia Qiaoyan 《河北交通科技》2008,(1)
分析了影响车道功能划分的主要因素。以南京长江隧道为例介绍了确定隧道车道功能的计算方法,并给出了南京长江隧道车道划分模型。 相似文献
217.
混凝土施工裂缝的控制 总被引:1,自引:0,他引:1
在道路施工中混凝土经常会出现遇度裂缝,影响到结构的整体性和耐久性。在路面的使用过程中,温度变化对结构的应力状态具有显著影响。在大体积混凝土施工中,对温度应力及温度控制具有重要意义。从分析混凝土裂缝的产生原因入手,对温度应力的形成过程进行论述,从而提出控制混凝土裂缝的措施。 相似文献
218.
����ģʽ�ij��н�ͨ״̬�����������о� 总被引:1,自引:0,他引:1
首先选用较多的交通参数,设计提出了基于聚类方法的细粒度交通模式划分算法,将交通模式划分为较多的类别。结合实际数据,进行了实验,在四个路段参数的基础上,划分得到了十类交通模式。这其中都用到了模糊集合划分和定性推理。使用状态核确定一系列模式,随后系统状态被划分成若干个模式。提出了模式转移方程来描述在定性推理基础之上的状态转移,并从模式转移的角度进一步研究了系统的稳定性。一个城市交通系统的应用实例显示了本文提出方法的有效性,可以看出细粒度交通模式划分要比粗粒度有更多的优势,同时得出了聚类算法在细粒度交通模式划分中的劣势。 相似文献
219.
Shuqi Song Peng Han Dong Zou 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2018,56(1):113-127
The rail is modelled as a simply supported beam in the vehicle–track coupled dynamics. The beam is formulated by a partial differential equation that is transformed into an ordinary differential equation by the method of mode superposition for numerical calculation. However, the size of the matrix that is formed by the mode-superposition method increases significantly with track length, which limits the calculation efficiency. Some methods have been developed to solve this calculation issue, but they diminish the merits of the vehicle–track coupled dynamics, which would systematically investigate the dynamics of a vehicle and a track from the entire vehicle–track system. A new method is developed to resolve this contradiction. First, a theory based on a sliding window is established to improve the computational stability with respect to the length and the window-movement ratio. Then, two methods, namely finite element method analysis and an analytical solution, are used to verify the accuracy of the new method, which is highly efficient when used in a vertical half-vehicle–track coupled model to calculate the vehicle response when the vehicle moves on a long track. The results of the vehicle response calculated with and without the sliding window show good consistency. 相似文献
220.
Dongrun Liu Tianpei Cao Dong Chen Yupu Xiong 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2018,56(2):173-189
Assessment of the vibration of high-speed trains negotiating complex sections of terrain under strong wind conditions is very important for research into the operation safety and comfort of passengers on high-speed trains. To assess the vibration of high-speed trains negotiating complex sections of terrain under strong wind conditions, we performed a field measurement when the train passes through typical sections of complex terrain along the Lanzhou–Xinjiang high-speed railway in China. We selected the lateral vibration conditions, including the roll angle and lateral displacement of car-body gravity centre through two typical representative sections (embankment–tunnel–embankment and embankment–rectangular transition–cutting) for analysis. The results show that the severe car-swaying phenomenon occurs when the high-speed train moves through the test section, and the car-body lateral vibration characteristic is related significantly to the state of the terrain and topography along the railway. The main causes for this car-swaying phenomenon may be the transitions between different windproof structures, and the greater the scale of the transition region between different windproof structures or landform changes, the more obvious the car-swaying phenomenon becomes. The lateral vibration of the car-body is relatively steady when the train is running through terrain with minor changes in topography, such as the windbreak installed on the bridge and embankment, but the tail car sways more violently than the head car. When the vehicle runs from the windbreak installed on the embankment into the tunnel (or in the opposite direction), the tail car sways more intensely than the head car, and the head car runs relatively stable in the tunnel. 相似文献