全文获取类型
收费全文 | 3864篇 |
免费 | 66篇 |
专业分类
公路运输 | 1082篇 |
综合类 | 944篇 |
水路运输 | 1047篇 |
铁路运输 | 715篇 |
综合运输 | 142篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 58篇 |
2021年 | 124篇 |
2020年 | 83篇 |
2019年 | 25篇 |
2018年 | 33篇 |
2017年 | 32篇 |
2016年 | 56篇 |
2015年 | 67篇 |
2014年 | 113篇 |
2013年 | 195篇 |
2012年 | 260篇 |
2011年 | 272篇 |
2010年 | 311篇 |
2009年 | 314篇 |
2008年 | 292篇 |
2007年 | 411篇 |
2006年 | 386篇 |
2005年 | 251篇 |
2004年 | 79篇 |
2003年 | 73篇 |
2002年 | 65篇 |
2001年 | 91篇 |
2000年 | 74篇 |
1999年 | 49篇 |
1998年 | 39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3930条查询结果,搜索用时 31 毫秒
991.
992.
连续梁桥是中等跨径桥梁中常用的一种桥梁结构,预应力混凝土连续梁桥是其主要结构形式,它具有接缝少、刚度好、行车平顺舒适等优点,其中,预应力是连续梁施工的重点和难点。以新建太中银铁路跨石中高速公路特大桥连续梁施工为例,对影响预应力部分施工的关键要素进行简要阐述。 相似文献
993.
A. Boukehili Y. T. Zhang Q. Zhao C. Q. Ni H. F. Su G. J. Huang 《International Journal of Automotive Technology》2012,13(6):987-998
The power management strategy in many hybrid vehicles is based on expert rules and thresholds. These rule-based strategies can result in good efficiency in term of fuel economy and emissions if their thresholds and rules are accurate. However, due to the complexity and the non-linearity of the hybrid powertrain, determining accurate thresholds and rules is neither explicit nor straightforward, and experts in most cases fail to define these thresholds and rules with enough accuracy. Based on this fact, the objective of this paper is to propose a method to improve this rule-based strategy by refining its thresholds and rules. To achieve this, we used an optimization method (dynamic programming) to calculate the optimal power management, determine the optimal control signals, and extract efficient thresholds and rules that can be used in real time. Finally, simulation results for the three strategies (optimal, simple and refined strategy) are shown and discussed. 相似文献
994.
Nonlinear interactions among incident wave, tank-sloshing and floating body coupling motion are investigated. The fully nonlinear sloshing and body-surface nonlinear free surface hydrodynamics is simulated using a Non-Uniform Rational B-Spline (NURBS) higher-order panel method in time domain based on the potential theory. A robust and stable improved iterative procedure (Yan and Ma, 2007) for floating bodies is used for calculating the time derivative of velocity potential and floating body motion. An energy dissipation condition based on linear theory adopted by Huang (2011) is developed to consider flow viscosity effects of sloshing flow in nonlinear model. A two-dimensional tank model test was performed to identify its validity. The present nonlinear coupling sway motion results are subsequently compared with the corresponding Rognebakke and Faltinsen (2003)’s experimental results, showing fair agreement. Thus, the numerical approach presented in this paper is expected to be very efficient and realistic in evaluating the coupling effects of nonlinear sloshing and body motion. 相似文献
995.
The computational fluid dynamics(CFD) method is used to numerically simulate a propeller wake flow field in open water.A sub-domain hybrid mesh method was adopted in this paper.The computation domain was separated into two sub-domains,in which tetrahedral elements were used in the inner domain to match the complicated geometry of the propeller,while hexahedral elements were used in the outer domain.The mesh was locally refined on the propeller surface and near the wake flow field,and a size function was used to control the growth rate of the grid.Sections at different axial location were used to study the spatial evolution of the propeller wake in the region ranging from the disc to one propeller diameter(D) downstream.The numerical results show that the axial velocity fluctuates along the wake flow;radial velocity,which is closely related to vortices,attenuates strongly.The trailing vortices interact with the tip vortex at the blades’ trailing edge and then separate.The strength of the vortex shrinks rapidly,and the radius decreases 20% at one diameter downstream. 相似文献
996.
997.
为一台可变气门正时(VVT)发动机的配气相位调节器开发了一套可变气门正时机构的测试系统,完成了机油控制阀(OCV)工质流量特性的测试.分析了VVT动态响应特性的测试原理.借助该测试系统,测得不同的OCV、转速、温度和压力时相位器的动态响应曲线.最后进行了相位器泄漏量的测试. 相似文献
998.
建立了变速器齿轮与齿轮轴系统的有限元模型,并对其进行有限元分析,以计算齿轮轴变形和轮齿接触应力,分析变速器齿轮轴变形对齿面接触状态的影响.通过与经典方法计算结果的比较,表明所建立的齿轮与齿轮轴系统有限元模型,不但可准确计算齿轮轴变形和齿面接触应力,且能综合分析齿轮轴变形对齿面接触区域的载荷分布、轮齿间载荷分配和齿面接触应力的影响,为更全面、精确分析变速器齿轮的齿面接触状态和载荷分布,预测齿轮疲劳寿命提供依据. 相似文献
999.
探讨某款燃料电池轿车碰撞结构安全设计的思路,阐述其具体设计,并借助有限元法对该车模型进行了碰撞模拟,根据模拟结果进行了改进设计,并验证改进设计的有效性.结果表明改进后的碰撞结构安全设计可行、有效. 相似文献
1000.