首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   409550篇
  免费   5015篇
  国内免费   1411篇
电工技术   7898篇
综合类   426篇
化学工业   61186篇
金属工艺   16860篇
机械仪表   12630篇
建筑科学   9938篇
矿业工程   1873篇
能源动力   10500篇
轻工业   36264篇
水利工程   4034篇
石油天然气   6595篇
武器工业   70篇
无线电   50707篇
一般工业技术   77814篇
冶金工业   75251篇
原子能技术   8869篇
自动化技术   35061篇
  2021年   3153篇
  2019年   3064篇
  2018年   5183篇
  2017年   5222篇
  2016年   5542篇
  2015年   3656篇
  2014年   6305篇
  2013年   18006篇
  2012年   10352篇
  2011年   14194篇
  2010年   11237篇
  2009年   12811篇
  2008年   13579篇
  2007年   13459篇
  2006年   11929篇
  2005年   11000篇
  2004年   10607篇
  2003年   10169篇
  2002年   9833篇
  2001年   9880篇
  2000年   9393篇
  1999年   9678篇
  1998年   23042篇
  1997年   16530篇
  1996年   12927篇
  1995年   10034篇
  1994年   8747篇
  1993年   8650篇
  1992年   6714篇
  1991年   6319篇
  1990年   6051篇
  1989年   5836篇
  1988年   5632篇
  1987年   4955篇
  1986年   4821篇
  1985年   5608篇
  1984年   5242篇
  1983年   4794篇
  1982年   4417篇
  1981年   4601篇
  1980年   4280篇
  1979年   4229篇
  1978年   4006篇
  1977年   4759篇
  1976年   5929篇
  1975年   3657篇
  1974年   3622篇
  1973年   3685篇
  1972年   3019篇
  1971年   2808篇
排序方式: 共有10000条查询结果,搜索用时 33 毫秒
991.
Summary.  Looking at rational mixture theories within the context of a new perspective, this work aims to put forward a proposal for an Eshelbian approach to the nonlinear mechanics of a constrained solid-fluid mixture, made up of an inhomogeneous poroelastic solid and an inviscid compressible fluid, which do not undergo any chemical reaction. Received July 26, 2001; revised May 15, 2002 Published online: January 16, 2003  相似文献   
992.
In this letter, we report new findings in the relation between channel hot-carrier (CHC) degradation and gate-oxide breakdown (BD) in short-channel nMOSFETS biased at V/sub G/>V/sub D/. We observe that the time-to-BD is strongly reduced in the hot carrier regime and that although the channel hot-electron injection into the oxide occurs mainly at the drain side, stress-induced leakage current (SILC) generation and oxide BD always occur at the source side. The results of these measurements indicate that not solely the energy of the injected electrons but also the oxide electric field is determinant in the oxide BD process.  相似文献   
993.
The distribution of ergosterol in different parts of shiitake mushrooms was studied in order to optimize the conversion of ergosterol to vitamin D2 during drying. The effect of moisture on the conversion of ergosterol to vitamin D2 was also investigated by adjusting the moisture content of fresh mushrooms to different levels in a large vacuum desiccator and subjecting them to UV irradiation at 290-320 nm wavelength, for 2 h. The moisture, ergosterol and vitamin D2 contents were determined using standard procedures. It was found that the ergosterol content on a dry matter basis of fresh shiitake mushroom was highest in the gills (10.6 ± 0.99 mg/g DM), followed by the cap or pileus (5.34 ± 0.64 mg/g DM) and was least in the stalk or stipe (2.97 ± 0.56). The moisture content had a marked influence on the conversion of ergosterol to vitamin D2, the best conversion taking place at a moisture content of about 70% on a wet basis.  相似文献   
994.
Web service conversation modeling: a cornerstone for e-business automation   总被引:1,自引:0,他引:1  
Web services are emerging as a promising technology for effectively automating interorganizational interactions. However, despite the growing interest, several issues remain to be addressed to provide Web services with benefits similar to what traditional middleware brings to intraorganizational application integration. We identify a framework that builds on current standards to help developers define extended service models and richer Web service abstractions. The framework's main feature is a conversation metamodel derived from our analysis of e-commerce portal sites.  相似文献   
995.
Dispersion–flocculation studies on a Goethite–clay system using flocculants were carried out as a function of flocculant concentrations, pH of slurry, time of agitation and dispersant dosage. Also, the effects of pH and polymer concentrations on the adsorption behaviour of the system were investigated. Results show that well flocculated goethite was preferentially obtained from 4% goethite/kaolinite clay suspensions, with 50 ppm causticised starch in the slurry at pH values of 3–11·5 and with 50 ppm polyacrylamide at pH values of 3–8. Good flocs were also obtained on flocculation of the goethite suspension with 50 ppm polyacrylamide at pH values of 5–7, while the kaolinite suspension did not respond to the same dosage of causticised starch in the same pH range. Results further reveal that for the goethite/kaolinite suspension, the best results was obtained with 50 ppm polyacrylamide at pH values of 7–10. Based on the data generated in the study, it was concluded that causticised starch is a better flocculant than polyacrylamide for goethite suspensions although polyacrylamide is an excellent flocculant for kaolinite suspensions.  相似文献   
996.
Algorithms are proposed that construct first integrals and Lyapunov functions for stability analysis of stationary solutions of differential equations describing mechanical systems of linked bodies.Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 138–148, January–February, 1992.  相似文献   
997.
998.
999.
This paper presents a method of solving planning problems that involve actions whose effects change according to the situations in which they are performed. The approach is an extension of the conventional planning methodology in which plans are constructed through an iterative process of scanning for goals that are not yet satisfied, inserting actions to achieve them, and introducing subgoals to these actions. This methodology was originally developed under the assumption that one would be dealing exclusively with actions that produce the same effects in every situation. The extension involves introducing additional subgoals to actions above and beyond the preconditions of execution normally introduced. These additional subgoals, called secondary preconditions, ensure that the actions are performed in contexts conducive to producing the effects we desire. This paper defines and analyzes secondary preconditions from a mathematically rigorous standpoint and demonstrates how they can be derived from regression operators.  相似文献   
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号