全文获取类型
收费全文 | 2280篇 |
免费 | 8篇 |
专业分类
公路运输 | 325篇 |
综合类 | 764篇 |
水路运输 | 752篇 |
铁路运输 | 75篇 |
综合运输 | 372篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 6篇 |
2018年 | 336篇 |
2017年 | 296篇 |
2016年 | 254篇 |
2015年 | 18篇 |
2014年 | 11篇 |
2013年 | 19篇 |
2012年 | 87篇 |
2011年 | 232篇 |
2010年 | 244篇 |
2009年 | 73篇 |
2008年 | 200篇 |
2007年 | 162篇 |
2006年 | 25篇 |
2005年 | 79篇 |
2004年 | 50篇 |
2003年 | 75篇 |
2002年 | 23篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有2288条查询结果,搜索用时 453 毫秒
11.
The micro-structure on hard-brittle chip materials (HBCMs) surface can produce predominant functions and features. The micro-grinding with diamond wheel micro-tip is an efficient method to machine microstructure on HBCMs. However, different HBCMs and crystal orientation may have a significant influence on the micro-grinding performance. In this paper, the micro-grinding performance along different crystal orientation of HBCMs is investigated. First, a dressed 600# diamond grinding wheel is used to micro-grind micro-structure on HBCMs. Then, the experiment of micro-grinding force test is completed. Finally, the quality of microgroove, the grinding ratio and the micro-grinding force are investigated and they are related to the crystal orientation of HBCMs. It is shown that the stronger resistance to the micro-crack propagation has the best quality of microgroove and the smallest grinding ratio. Moreover, the hardest single-crystal SiC has the best machinability and the micro-grinding force is 38.9%, 10.8% and 46.8% less than the one of sapphire, single-crystal Si and quartz glass, respectively. The direction to micro-grind easily is the crystal orientation 〈10\(\overline 1 \)0〉 for single-crystal SiC and sapphire. In addition, the micro-grinding force increases with the increase of the micro-grinding depth and feed rate and decreases with the increase of the grinding wheel speed. 相似文献
12.
Among several post quantum primitives proposed in the past few decades, lattice-based cryptography is considered as the most promising one, due to its underlying rich combinatorial structure, and the worst-case to average-case reductions. The first lattice-based group signature scheme with verifier-local revocation(VLR) is treated as the first quantum-resistant scheme supported member revocation, and was put forward by Langlois et al. This VLR group signature(VLR-GS) has group public key size of O(nm log N log q), and a signature size of O(tm log N log q log β). Nguyen et al. constructed a simple efficient group signature from lattice, with significant advantages in bit-size of both the group public key and the signature. Based on their work, we present a VLR-GS scheme with group public key size of O(nm log q) and signature size of O(tm log q). Our group signature has notable advantages: support of membership revocation, and short in both the public key size and the signature size. 相似文献
13.
通过对某条提速线路曲线段的轨温及横向位移进行现场测试,分析了曲线段轨道结构在轨温变化时对轨排横向位移变化的影响.分析结果表明:在轨温较低的情况下,列车荷载激扰等随机因素是轨排横向位移的主因;在轨温较高时,轨排横向位移的主因则是轨道温度力.曲线段轨排横向位移的波形差异性较大,在日常工务养护中应以缓圆点附近的曲线作为养护重点. 相似文献
14.
15.
16.
17.
18.
电子节气门技术的发展现状及趋势 总被引:26,自引:0,他引:26
简要回顾了发动机电喷系统中电子节气门的由来及发展;论述了最新电子节气门产品的系统组成、工作原理、功能及其优点,并对其进一步的发展趋势作了分析探讨。 相似文献
19.
介绍现场机械设备液压系统维护中的配管设计,包括配管设计要求、主要技术性能参数、油管的选用以及设计要点。以一实例对配管设计不当而产生故障的原因进行分析,并提出改进措施。 相似文献
20.
With the development of vehicle gearbox to high-power-density and high-speed, how to predict and optimize the dynamic characteristics of vehicle gearbox becomes increasingly prominent. Aiming at the vehicle gearbox, this paper comprehensively and deeply studies the dynamic characteristics under the multi-boundary conditions. The generation mechanism of the multi-source excitations triggering the gearbox vibration is analyzed firstly. The vibration transfer path of the gearbox is explored. Secondly, the engine excitation, the gear meshing excitation and the bearing support load are numerically calculated. According to the finite element method, a fluid-solid coupling finite element model of the gearbox body is established to predict the gearbox dynamic responses based on the Galerkin method and the Hamiltonian variational principle. Finally, the effects of the excitation condition, oil height and reinforcement forms on the vibration responses of the gearbox body are thoroughly studied by simulation. The analysis indicates that it not only helps to modify and improve the method of forecasting the gearbox dynamic response, and also provides the theoretical and technical guidance for the gearbox design and optimization. 相似文献