全文获取类型
收费全文 | 50289篇 |
免费 | 4882篇 |
国内免费 | 2799篇 |
专业分类
电工技术 | 3352篇 |
技术理论 | 3篇 |
综合类 | 3991篇 |
化学工业 | 7818篇 |
金属工艺 | 2627篇 |
机械仪表 | 2953篇 |
建筑科学 | 4343篇 |
矿业工程 | 1481篇 |
能源动力 | 1361篇 |
轻工业 | 4362篇 |
水利工程 | 1082篇 |
石油天然气 | 2555篇 |
武器工业 | 470篇 |
无线电 | 5890篇 |
一般工业技术 | 5799篇 |
冶金工业 | 2179篇 |
原子能技术 | 512篇 |
自动化技术 | 7192篇 |
出版年
2024年 | 355篇 |
2023年 | 1168篇 |
2022年 | 2049篇 |
2021年 | 2662篇 |
2020年 | 1905篇 |
2019年 | 1490篇 |
2018年 | 1683篇 |
2017年 | 1847篇 |
2016年 | 1560篇 |
2015年 | 2127篇 |
2014年 | 2613篇 |
2013年 | 3096篇 |
2012年 | 3228篇 |
2011年 | 3407篇 |
2010年 | 2877篇 |
2009年 | 2759篇 |
2008年 | 2773篇 |
2007年 | 2546篇 |
2006年 | 2563篇 |
2005年 | 2305篇 |
2004年 | 1580篇 |
2003年 | 1519篇 |
2002年 | 1568篇 |
2001年 | 1382篇 |
2000年 | 1101篇 |
1999年 | 1179篇 |
1998年 | 868篇 |
1997年 | 757篇 |
1996年 | 628篇 |
1995年 | 509篇 |
1994年 | 451篇 |
1993年 | 293篇 |
1992年 | 264篇 |
1991年 | 199篇 |
1990年 | 161篇 |
1989年 | 134篇 |
1988年 | 101篇 |
1987年 | 55篇 |
1986年 | 50篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1975年 | 3篇 |
1970年 | 4篇 |
1959年 | 4篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Mechanical properties characterization is needed in many industrial applications yet sufficient amount of material for fabricating standard-sized testing specimens is often not available. Techniques for testing miniaturized specimen must be adopted. Much effort has been made to develop techniques for impact, fracture toughness and tensile properties of sub-sized specimens. Work on the testing of fatigue properties is more limited. In this study, fatigue crack propagation behavior is evaluated from the growth of surface crack in a cylindrical rod under tension. Rods of various lengths and diameters were tested. As the size of the rod specimen is reduced, the fatigue crack growth rate tends to increase when correlated using the stress intensity factor range. This increase is explained largely by the decrease in the degree of premature crack closure in the small specimens. Valid fatigue crack growth data can be obtained among the specimens examined except on the crack growth on the surface of the smallest specimen, which has a length of 26 mm and diameter of 8 mm. Even so, valid data can still be elucidated on the latter specimen if the interior growth is considered. The dimensions of the latter specimen allow fatigue properties to be evaluated using broken remnants from impact or other test specimens. 相似文献
52.
Wafer-type piezoelectric transducers are effective transducers for the excitation and detection of ultrasonic Lamb waves in plate-like structures. Such transducers are, however, vulnerable to corrosion and physical damage when mounted in exposed locations. In this paper we describe an inductively coupled Lamb wave transducer that eliminates the need for direct electrical connections. Signals are coupled into and out of the transducer using two probe coils. In this paper we explore the operation of inductively coupled transducers both analytically and experimentally. Finite-element analysis is used to determine inductances and the coupling constant, and electrical circuit analysis to determine the transfer function and its dependence on the gap between the probe coils and the transducer. Experiments show that return signals of millivolt amplitude are obtained when the transducer is excited with 10-V amplitude pulses. These transducers are suitable for permanent mounting on structures to be monitored for cracks or flaws 相似文献
53.
54.
55.
电信服务营销渠道转型的必要性 总被引:5,自引:0,他引:5
分析了电信企业服务营销渠道的特点、旧有的服务营销渠道模式和存在的问题以及今后电信业和市场等方面发展的新需求,对电信服务营销渠道转型的必要性进行了探讨和研究,同时提供了一个可供参考的服务营销渠道价值评估体系架构,从量化服务营销渠道对电信企业贡献价值的角度论述了服务营销渠道转型的必要性。 相似文献
56.
本文详尽介绍了虚拟存储技术及其提供数据保护的方式,并重点论述了如何通过IP SAN的方式来实现数据的虚拟存储以及IP SAN的主要特点和优越性。 相似文献
57.
58.
Mechanical property-grain size relationships have been examined for squeeze cast Al-4.5% Cu alloy, for an aluminium alloy with a composition corresponding to wrought 7010, and for a magnesium alloy AZ91. The general trend of the results obtained showed that the tensile properties and the fatigue strength improved as grain size decreased and the reverse was found to be the case for the fatigue crack propagation resistance and fracture energy of these castings. However, the results also showed that no simple common relationship existed between grain size and the tensile properties of the different alloys. The results are discussed in respect of their microstructures. 相似文献
59.
基于S5933的PCI总线与8051的接口设计 总被引:3,自引:0,他引:3
简要介绍了PCI总线的特点,重点介绍了AMCC公司推出的S593X系列的高性能接口控制器,并通过实践给出基于S5933的PCI总线和8051的接口设计技术。 相似文献
60.