全文获取类型
收费全文 | 500391篇 |
免费 | 52261篇 |
国内免费 | 39804篇 |
专业分类
电工技术 | 55924篇 |
技术理论 | 59篇 |
综合类 | 54554篇 |
化学工业 | 69110篇 |
金属工艺 | 19370篇 |
机械仪表 | 30760篇 |
建筑科学 | 46800篇 |
矿业工程 | 19429篇 |
能源动力 | 15611篇 |
轻工业 | 28842篇 |
水利工程 | 17735篇 |
石油天然气 | 17769篇 |
武器工业 | 5143篇 |
无线电 | 52165篇 |
一般工业技术 | 41445篇 |
冶金工业 | 20870篇 |
原子能技术 | 6266篇 |
自动化技术 | 90604篇 |
出版年
2024年 | 2199篇 |
2023年 | 6753篇 |
2022年 | 12254篇 |
2021年 | 14415篇 |
2020年 | 14776篇 |
2019年 | 12675篇 |
2018年 | 11900篇 |
2017年 | 15384篇 |
2016年 | 17370篇 |
2015年 | 19547篇 |
2014年 | 27588篇 |
2013年 | 28619篇 |
2012年 | 35447篇 |
2011年 | 38419篇 |
2010年 | 29247篇 |
2009年 | 30065篇 |
2008年 | 29965篇 |
2007年 | 36642篇 |
2006年 | 34437篇 |
2005年 | 29664篇 |
2004年 | 25071篇 |
2003年 | 21401篇 |
2002年 | 17160篇 |
2001年 | 14106篇 |
2000年 | 11893篇 |
1999年 | 9744篇 |
1998年 | 7518篇 |
1997年 | 6400篇 |
1996年 | 5665篇 |
1995年 | 4769篇 |
1994年 | 4137篇 |
1993年 | 3084篇 |
1992年 | 2703篇 |
1991年 | 2079篇 |
1990年 | 1774篇 |
1989年 | 1481篇 |
1988年 | 1165篇 |
1987年 | 778篇 |
1986年 | 593篇 |
1985年 | 586篇 |
1984年 | 554篇 |
1983年 | 393篇 |
1982年 | 428篇 |
1981年 | 276篇 |
1980年 | 237篇 |
1979年 | 160篇 |
1978年 | 91篇 |
1977年 | 108篇 |
1976年 | 71篇 |
1975年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The space-time distribution of the basic kinetic parameters of a plasma is experimentally determined under conditions of expansion of plasma clusters and jets into vacuum. It is demonstrated that the dynamics and structure of plasmoids injected by pulsed erosion plasma accelerators of the electrothermal type are characterized by two successive stages or two modes of acceleration, namely, the Joule heating of electrons in the initial region of the path and the collisionless expansion of rarefied plasma. 相似文献
992.
993.
M. A. Fatykhov 《High Temperature》2004,42(4):621-628
The paper gives the results of experimental investigations of the initial pressure gradient of bituminous oil and the time dependences of variation of the temperature in a formation model and of the well production rate in a microwave-frequency electromagnetic field. The effect of strong decay of the non-Newtonian properties of bituminous oil is revealed. The nonuniformity of temperature distribution over the formation thickness is demonstrated, which depends on the initial production rate of the well and on the duration of stimulation of the bottom-hole zone of formation. 相似文献
994.
995.
The Simulation of Impact Loads on Beam-type Structures using a Pseudo-dynamic Procedure 总被引:5,自引:0,他引:5
F. J. Q. Melo J. A. O. Carneiro P. P. Camanho C. L. Tavares A. A. Fernandes 《Strain》2004,40(1):13-23
Abstract: This study proposes an alternate method for the analysis of beams with solid cross-section or built as a framed structure and subjected to transverse impact loads from an external striker. The procedure used in the analysis is a combination of two essential tools using pseudo-dynamic techniques. The method reported here involves only one degree of freedom for the structure modelling and assumes an elastic contact between an external striker and the beam structure, which in reality does not happen. As only one degree of freedom is considered in the analysis, some important limitations are inherent to the method proposed here. Essentially, there is the difficulty of modelling the displacement field associated with the transient structure behaviour accurately, as a consequence of fast-rate impact loads. Another difficulty faced by the method refers to a local structure behaviour associated with contact loads. The present method can deal with large displacements in transversely loaded beams associated to a collapse mechanism having a simple geometry and defined with precision from a single parameter. This ensures reasonable accuracy in the evaluation of the strain energy absorbing capacity of transversely impacted beam structures using a single degree of freedom model in a pseudo-dynamic procedure. 相似文献
996.
We study low-frequency vibrations of a vibroprotective system of solid bodies formed by a roller damper and a moving load-carrying body under the action of external harmonic excitations. The dynamic equations of combined motion of the working body of the damper over the hinged roller without sliding and the load-carrying body are deduced and numerically analyzed. A new procedure is proposed for the evaluation of the optimal parameters of adjustment of roller dampers in nonlinear systems. 相似文献
997.
A problem of deformation of a curved shell loaded by internal pressure, axial force, and temperature difference is discussed. Physical equations are derived whereby the displacements and angles of rotation of the line of centers of mass of cross sections of a shell are related to loading parameters. A general constitutive set of equations for a curved element during its deformation is given. Using a method of initial parameters, an analytical solution is obtained for the differential equations for displacements and angles of rotation of the center line allowing for the action of distributed forces and moments. 相似文献
998.
通过对黑岱沟露天煤矿运输设备出动率调查,初步分析了目前主要运输设备的现状以及存在问题的原因和影响因素,就加大预防性维修的比重,实行全面的预防性维修制度提出了一些看法。 相似文献
999.
Doratha E Drake 《Information Processing Letters》2003,85(4):211-213
We present a linear time approximation algorithm with a performance ratio of 1/2 for finding a maximum weight matching in an arbitrary graph. Such a result is already known and is due to Preis [STACS'99, Lecture Notes in Comput. Sci., Vol. 1563, 1999, pp. 259-269]. Our algorithm uses a new approach which is much simpler than the one given by Preis and needs no amortized analysis for its running time. 相似文献
1000.
研究了显色剂 4 ( 2 噻唑偶氮 ) 5 二甲氨基苯胺 (简称TADMA)与铑 的显色反应。结果表明 ,在 pH3 2~ 4 8范围内 ,铑 与TADMA反应形成 1∶2红色络合物 ,加入无机酸后色泽加深 ,络合物的表观摩尔吸光系数为 1 2 1× 10 5,铑质量浓度在 0~ 0 92 μg/mL范围内服从比尔定律。本方法操作简便 ,灵敏度高 ,选择性好 ,常见金属离子在一定范围内无干扰 ,用于催化剂中微量铑的测定 ,结果满意 相似文献