全文获取类型
收费全文 | 6635篇 |
免费 | 370篇 |
专业分类
公路运输 | 1992篇 |
综合类 | 1894篇 |
水路运输 | 1934篇 |
铁路运输 | 1068篇 |
综合运输 | 117篇 |
出版年
2024年 | 31篇 |
2023年 | 41篇 |
2022年 | 122篇 |
2021年 | 183篇 |
2020年 | 227篇 |
2019年 | 161篇 |
2018年 | 118篇 |
2017年 | 166篇 |
2016年 | 138篇 |
2015年 | 258篇 |
2014年 | 509篇 |
2013年 | 415篇 |
2012年 | 639篇 |
2011年 | 672篇 |
2010年 | 502篇 |
2009年 | 400篇 |
2008年 | 414篇 |
2007年 | 568篇 |
2006年 | 472篇 |
2005年 | 293篇 |
2004年 | 173篇 |
2003年 | 113篇 |
2002年 | 72篇 |
2001年 | 73篇 |
2000年 | 37篇 |
1999年 | 27篇 |
1998年 | 21篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
排序方式: 共有7005条查询结果,搜索用时 250 毫秒
331.
332.
The fatigue strength of a 300 mm2 stranded copper conductor was investigated experimentally and by finite element (FE) analysis. An analytical model was also developed and validated. Wires taken from the outer layer of the conductor were fatigue tested in tension–tension loading and compared with similar data for wires taken from a 95 mm2 conductor. The wire cross section was deformed due to the compacting process that was applied during fabrication. When corrected for stress concentrations due to the deformation the data for the two sets of wire fell within the same scatter-band. Full scale testing was carried out in a specially designed rig with constant tensile load and reversed displacement controlled bending with a fixed curvature variation. The loading is a simulation of the loading of a power cable hanging from a floating vessel through a bellmouth. Conductors were tested in two states; dry and lubricated. A finite element model was established for the copper conductor. The model was formulated by a combination of elastic beam and beam-contact elements that included the effects of friction. The effect of local bending due to contact forces was included in the model. Two contact conditions were investigated; the point (trellis) contact between adjacent layers of wire and the inline contact within each layer and between the first layer (centre wire) and the second layer. The FE model was validated by a calibration test of a full scale conductor, and by sensitivity studies varying the size and the number of elements of the model. Fatigue analysis of the conductor was carried out, based on the S–N curve for individual wires. Taking into account the effects of friction and local bending, agreement was obtained between predicted and experimental fatigue strength of the conductor, for the FE model as well as the analytical model. 相似文献
333.
ABSTRACTA dynamic model for marginal cost pricing of port infrastructures links costs to system performance by combining a power-law function with time-dependent queueing analysis. Additionally, the model incorporates the marginal cost of capacity, including the effects of economies of scale. This allows the calculation of the marginal cost price under a dynamic framework. The model accounts for nonlinear behaviour of port demand, which is sensitive to price and service levels. The effects over time of cost and service levels on the port’s operational performance are quantified. The proposed model allows determining the optimal timing for capacity investment. The model is a starting point for the application of marginal cost pricing to ports. However, for practical application of such pricing method it is necessary to apply a system’s approach, as productivity and costs must be assessed at the terminal’s component level. This should allow the derivation of a marginal cost function at the terminal’s component level. 相似文献
334.
335.
《铁道标准设计通讯》2014,(8):81-84
针对一座外倾式非对称钢箱拱桥,通过利用桥梁结构专业软件Midas/civil建立其空间杆系有限元模型进行整体受力性能分析,探讨主要受力结构拱肋、吊杆以及钢箱主梁的力学特点;并通过外倾角的改变研究分析了吊杆内力随拱肋外倾角改变的变化规律,对于完善该类异型拱桥的设计理论、工程施工,确保结构安全、设计合理等方面都有一定的参考价值。 相似文献
336.
在岸边集装箱起重机起升机构和小车运行机构模型的基础上建立简化的单摆模型,通过对模型的受力分析建立非线性方程.同时在MATLAB的SIMUUNK环境下对此模型进行动态仿真,达到通过控制小车的驱动力来控制吊具的摆角的目的. 相似文献
337.
大型小水线面双体船纵向运动稳定性及纵向运动分析 总被引:1,自引:0,他引:1
以大型小水线面双体船为研究对象,观察其在静水中的纵向运动稳定性以及根据STF方法结合粘性修正方法预报其在波浪上的纵摇、垂荡运动等。首先根据ROUTH稳定性准则从定性角度观察其稳定性,然后从定量角度进行分析,给出其稳定性运动品质评价指标,并与配置稳定鳍后进行对比。最后给出配置稳定鳍后小水线面双体船的纵向运动预报。 相似文献
338.
基于ANSYSWorkbench的动车组水箱吊装结构强度分析 总被引:1,自引:0,他引:1
动车组车上吊装结构的设计是否合理将关系着动车组的安全运行,在对动车组车内水箱吊装结构模型合理简化的基础上,利用ANSYSWorkbench软件创建了其有限元模型,并依据标准EN12663,确定了其载荷工况,完成了对C型槽、滑块、联接螺栓的强度校核,其结果对水箱结构的设计及优化提供了参考. 相似文献
339.
对于桥梁静荷载试验,试验规范推荐的分级加载方法不能确保在分级加载过程中桥梁结构的多个控制截面同时是安全的。将所有加载车的加载位置比拟成一个广义的点,使得安全动态加载的问题转化成求解安全加载域边界的几何问题,从而很容易计算出安全加载路径。分析安全加载域的定义及计算。 相似文献
340.