全文获取类型
收费全文 | 11453篇 |
免费 | 936篇 |
国内免费 | 636篇 |
专业分类
电工技术 | 960篇 |
综合类 | 924篇 |
化学工业 | 1597篇 |
金属工艺 | 976篇 |
机械仪表 | 2272篇 |
建筑科学 | 646篇 |
矿业工程 | 307篇 |
能源动力 | 453篇 |
轻工业 | 690篇 |
水利工程 | 209篇 |
石油天然气 | 325篇 |
武器工业 | 118篇 |
无线电 | 912篇 |
一般工业技术 | 1720篇 |
冶金工业 | 419篇 |
原子能技术 | 79篇 |
自动化技术 | 418篇 |
出版年
2024年 | 42篇 |
2023年 | 190篇 |
2022年 | 295篇 |
2021年 | 339篇 |
2020年 | 421篇 |
2019年 | 326篇 |
2018年 | 332篇 |
2017年 | 385篇 |
2016年 | 401篇 |
2015年 | 451篇 |
2014年 | 679篇 |
2013年 | 840篇 |
2012年 | 730篇 |
2011年 | 801篇 |
2010年 | 556篇 |
2009年 | 633篇 |
2008年 | 575篇 |
2007年 | 766篇 |
2006年 | 693篇 |
2005年 | 546篇 |
2004年 | 460篇 |
2003年 | 396篇 |
2002年 | 348篇 |
2001年 | 299篇 |
2000年 | 248篇 |
1999年 | 197篇 |
1998年 | 213篇 |
1997年 | 180篇 |
1996年 | 136篇 |
1995年 | 112篇 |
1994年 | 97篇 |
1993年 | 60篇 |
1992年 | 64篇 |
1991年 | 45篇 |
1990年 | 38篇 |
1989年 | 25篇 |
1988年 | 24篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1959年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
用有限元模拟拱坝坝体、非连续接触单元模拟坝肩,计算了在设计地震荷载作用下小湾拱坝坝肩残余位移和坝体应力。以拉应力达到坝体混凝土抗拉强度为控制标准,得出坝肩岩体的动力稳定安全系数。计算结果表明,小湾拱坝坝肩仍具有一定的安全度。 相似文献
992.
电接触可靠性研究中的几个热点问题分析 总被引:1,自引:1,他引:0
根据电接触理论的发展过程,并结合煤矿生产现状对目前国内外电接触可靠性研究中的几个热点问题进行了分析。 相似文献
993.
We report measurement of the electrical resistivityρ(T) and point contact differential conductance (dI/dV) for icosahedral Al70Pd30 −x
(x=7,9 and 11) at low temperatures. Below 10 K, forx=11,ρ(T) follows a logT dependence. All the three compositions show a sharp minimum in the differential conductance near zero bias. Magnitude of
the dip in the point contact conductance increases as the Mn concentration increases. The dip near zero bias also follows
a logV dependence forV < 30 mV. 相似文献
994.
J. DAHLBERG B. ALFREDSSON 《Fatigue & Fracture of Engineering Materials & Structures》2005,28(7):599-613
A hardened steel cylinder was repeatedly pressed against a flat case‐hardened steel specimen that was equally wide as the cylinder was long. Some contact end effects were noted as a result of limited plastic deformation. A strain gauge on the contact surface, just outside the contact and oriented perpendicular to the cylinder detected a surface strain when the cylinder was loaded. The non‐zero surface strain was the result of boundary effects of the finite specimen. Four different types of contact fatigue cracks developed in and below the specimen contact surface. The cracks were named lateral, median, contact end and edge cracks. Changes in the measured surface strain values could be used to determine when the lateral and edge cracks developed. The order in which all four crack types typically developed was determined from optical crack observation at test termination, strain measurements and stress computations. Numerical computations using finite‐element (FE) analyses were used to verify the surface strain behaviour due to loading and cracking; to verify contact end effects; crack locations and crack orientation by aid of the Findley multi‐axial fatigue criterion. 相似文献
995.
S. Reaz Ahmed S. K. Deb Nath M. Wahhaj Uddin 《International journal for numerical methods in engineering》2005,64(6):729-750
Optimum design of tire‐tread sections is an important practical issue. However, useful study of the problem that can suggest a reliable guideline for determining the optimum tread sections had hardly been made in the past. The present paper describes a new analysis of the state of stresses in tire‐tread sections in contact with the road surface, taking special care of the boundary conditions. Based on the analysis, a method is proposed to determine the optimum tread shapes for avoiding lateral slippage between tires and roads. The displacement potential function formulation, an ideal mathematical model for the practical stress problems, has been used in conjunction with finite‐difference method of solution. For the present analysis, lateral slipping in absence of frictional resistance as well as the no‐slip conditions of the tire‐tread contact surface have been considered along with a large number of tread aspect ratios. The present computational approach proves to be a powerful tool for determining the optimum tread shapes for avoiding the lateral slippage of tire‐treads. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
996.
S. G. Jia P. Liu F. Z. Ren B. H. Tian M. S. Zheng G. S. Zhou 《Metals and Materials International》2005,11(1):71-76
Cu−Ag−Zr alloy has an excellent combination of mechanical strength and electrical conductivity, and is a promising contact
wire material for high-speed electrified railways. An investigation of the electritrobological behavior of Cu−Ag−Zr wire is
presented here. Wear tests are conducted under laboratory conditions with a specified sliding wear tester that simulated train
motion under an electrical current applied across the sliding interface. The Cu−Ag−Zr alloy wire is slid against a copper-based
powder metallurgy strip used in railway systems under unlubricated conditions. Worn surfaces of the Cu−Ag−Zr alloy wire are
analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDS). Within the studied range of electrical
current, normal pressure, and sliding speed, the wear rate increases with increasing electrical current and sliding distance.
Adhesive wear, abrasive wear, and electrical erosion are the dominant mechanisms during the electrical sliding processes.
Compared with a Cu−Ag contact wire under the same test conditions, the Cu−Ag−Zr alloy wire has much better wear resistance. 相似文献
997.
介绍了SSJ-11A型静态时间继电器的应用及构造原理,探讨了时间继电器延时接点瞬动的可能原因,举例说明了SSJ-11A型时间继电器延时接点瞬动的检测方法. 相似文献
998.
999.
The arc erosion experiments on five kinds of silver-based contact materials,AgZnO (10), AgSnO2 (8.5) In2O3 (4), AgCdO (12), AgNi(10), AgWC(12)C(3) were carried out according to different breaking times, breaking currents, and making pressures. Then based on the theoretical analysis and the photographs taken by scanning electronic microscope with EDAX analyzer, the crack morphology was studied scientifically. Three types of cracks, which are cavity cracks, grain boundaries (or phase boundaries) slipping cracks, and thermal stress cracks, were put forward under arc and making pressure through establishing their physical models and discussing their formation mechanisms. 相似文献
1000.
简要介绍了Cu-Cr合金触头材料的结构特点及其优良性能.叙述了Cu—Cr合金制备技术的进展,重点介绍了触头材料的几种制备工艺,并比较了各种制备工艺的优缺点及其应用范围,最后展望了触头材料的发展趋势. 相似文献