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   18040篇
  免费   1511篇
  国内免费   1339篇
电工技术   744篇
技术理论   1篇
综合类   2505篇
化学工业   719篇
金属工艺   198篇
机械仪表   852篇
建筑科学   1596篇
矿业工程   358篇
能源动力   378篇
轻工业   424篇
水利工程   448篇
石油天然气   298篇
武器工业   87篇
无线电   1215篇
一般工业技术   2103篇
冶金工业   783篇
原子能技术   93篇
自动化技术   8088篇
  2024年   58篇
  2023年   148篇
  2022年   266篇
  2021年   307篇
  2020年   404篇
  2019年   425篇
  2018年   410篇
  2017年   521篇
  2016年   605篇
  2015年   605篇
  2014年   1257篇
  2013年   1295篇
  2012年   1405篇
  2011年   1248篇
  2010年   1043篇
  2009年   1218篇
  2008年   1209篇
  2007年   1263篇
  2006年   1079篇
  2005年   1001篇
  2004年   766篇
  2003年   681篇
  2002年   558篇
  2001年   546篇
  2000年   438篇
  1999年   361篇
  1998年   277篇
  1997年   221篇
  1996年   183篇
  1995年   170篇
  1994年   139篇
  1993年   119篇
  1992年   100篇
  1991年   84篇
  1990年   78篇
  1989年   85篇
  1988年   65篇
  1987年   29篇
  1986年   20篇
  1985年   20篇
  1984年   19篇
  1983年   20篇
  1982年   14篇
  1981年   14篇
  1980年   9篇
  1979年   12篇
  1964年   8篇
  1963年   9篇
  1961年   8篇
  1957年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
This article is the fourth of a series of articles discussing various open research problems in automated reasoning. The problem proposed for research focuses on finding criteria that would enable an automated reasoning program to expand or contract definitions wisely. For evaluating a proposed solution to this research problem, we include suggestions concerning possible test problems.This work was supported by the Applied Mathematical Sciences subprogram of the Office of Energy Research, U.S. Department of Energy, under contract W-31-109-Eng-38.  相似文献   
52.
New quadratic models are proposed to improve the upper-bound estimates in the maximum weighted cut problem. They are found by two original methods for deriving redundant quadratic constraints. A well-known linear model is shown to follow from the models proposed. Recommendations on how to develop its strengthened analogs are given. This study is partially sponsored from the grant UM2-2574-KV-03 (CRDF Cooperative Grants Program). __________ Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 63—75, January–February 2006.  相似文献   
53.
An optimal control problem with nonsmooth performance criterion described by a system of ordinary differential equations is considered. Necessary first-order optimality conditions are obtained.  相似文献   
54.
介绍了二次盐水及离子膜电解工序的主要设备和流程,对二次盐水及离子膜电解工序运行中出现的问题进行了分析,并提出了解决措施。  相似文献   
55.
The authors present a theory for understanding risk for problem drinking among reservation-dwelling American Indians. The theory offers an overall framework for understanding the risk process for this group. It considers the distinction between factors that influence mean levels of American Indian problem drinking and factors that influence individual differences in American Indian drinking. It proposes important contextual differences between reservation-dwelling American Indians and Caucasians that may help explain the higher mean levels of American Indian problem drinking. The theory further holds that, within the high mean level of problem drinking characteristic of many American Indian reservations, individual differences in problem drinking can be explained by very similar personality and learning factors as those that influence problem-drinking levels for other ethnic groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
This paper presents a new concept for symmetric boundary element method (SBEM) applicable to 2-D steady-state and transit potential problems. Two kinds of SBEM formulations are derived. Symmetry is obtained simply through matrix manipulation, and no hypersingularity appears. Therefore, SBEM is much easier than the traditional symmetric Galerkin BEM. Compared with the traditional asymmetric BEM, the present SBEM can reduce the computational cost for time domain problems only. However, when applied to BEM/FEM coupling procedure, SBEM can reduce the computational cost for both steady-state and time domain problems. Three numerical examples are included to illustrate the effectiveness and accuracy of the present formulations.  相似文献   
57.
Longitudinal data from a representative sample of 1,978 Black and White adolescents were used to examine the role of personality in multiple risk or problem behaviors. Results indicate that covariation among diverse behaviors (educational underachievement, delinquent behavior, substance use, sexual behavior) can be adequately modeled by a single higher order factor, and that impulsivity and avoidance coping serve as generalized risk factors for involvement in these behaviors. Whereas none of the personality variables examined explained change in problem behaviors once established, avoidance coping prospectively predicted involvement among a subgroup of adolescents with little or no prior involvement. Results suggest that dysfunctional styles of regulating emotions and emotionally driven behaviors are core features of risky or problem behaviors during adolescence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
58.
关于建立纺织用染化料生态安全性评价体系的设想   总被引:2,自引:1,他引:1  
从可持续发展战略和“绿色”、环保、生态等方面的需要提出关于建立纺织用染化料生态安全性评价体系的意义,并建议了列入安全性评价体系的项目及实施办法,同时也提出了需要解决的问题。  相似文献   
59.
从辩证关系角度详细阐述了类似于北京燕化建筑工程公司这样的国有施工企业走向市场过程中应关注的企业定位、利益相关性、竞争策略与公平性、自我保护与內涵发展等问题,以促进国有施工企业的改革与发展。  相似文献   
60.
多部件设备维修问题研究及遗传算法求解   总被引:1,自引:0,他引:1  
合理组织设备维修,缩短设备维修时间是生产运营管理的一个重要环节。本文探讨了多部件设备维修的有效组织问题。考虑到维修工人对拆分后设备的不同部分具有不同的维修效率,提出了一种基于维修时间优化的决策方法,将其与经典指派方法进行了比较;进一步地,对这一NP-hard问题设计了遗传算法,通过数值例子讨论了其求解有效性。  相似文献   
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