全文获取类型
收费全文 | 28817篇 |
免费 | 2689篇 |
国内免费 | 1971篇 |
专业分类
电工技术 | 1049篇 |
技术理论 | 1篇 |
综合类 | 4002篇 |
化学工业 | 900篇 |
金属工艺 | 568篇 |
机械仪表 | 1676篇 |
建筑科学 | 6380篇 |
矿业工程 | 633篇 |
能源动力 | 448篇 |
轻工业 | 749篇 |
水利工程 | 576篇 |
石油天然气 | 369篇 |
武器工业 | 164篇 |
无线电 | 1930篇 |
一般工业技术 | 2644篇 |
冶金工业 | 993篇 |
原子能技术 | 96篇 |
自动化技术 | 10299篇 |
出版年
2024年 | 80篇 |
2023年 | 182篇 |
2022年 | 410篇 |
2021年 | 482篇 |
2020年 | 655篇 |
2019年 | 570篇 |
2018年 | 582篇 |
2017年 | 754篇 |
2016年 | 900篇 |
2015年 | 955篇 |
2014年 | 2018篇 |
2013年 | 1867篇 |
2012年 | 2357篇 |
2011年 | 2393篇 |
2010年 | 1959篇 |
2009年 | 2147篇 |
2008年 | 2070篇 |
2007年 | 2228篇 |
2006年 | 1835篇 |
2005年 | 1621篇 |
2004年 | 1227篇 |
2003年 | 1083篇 |
2002年 | 861篇 |
2001年 | 812篇 |
2000年 | 660篇 |
1999年 | 524篇 |
1998年 | 389篇 |
1997年 | 308篇 |
1996年 | 252篇 |
1995年 | 219篇 |
1994年 | 189篇 |
1993年 | 144篇 |
1992年 | 117篇 |
1991年 | 98篇 |
1990年 | 98篇 |
1989年 | 95篇 |
1988年 | 82篇 |
1987年 | 40篇 |
1986年 | 22篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 8篇 |
1964年 | 8篇 |
1963年 | 9篇 |
1961年 | 8篇 |
1958年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Larry Wos 《Journal of Automated Reasoning》1987,3(4):433-435
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
32.
33.
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
34.
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
35.
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
36.
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
37.
Cooper M. Lynne; Wood Phillip K.; Orcutt Holly K.; Albino Austin 《Canadian Metallurgical Quarterly》2003,84(2):390
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
38.
姜志明 《石油化工管理干部学院学报》2003,(4):61-62
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
39.
40.
Fadwa T. Eljack Ahmed F. Abdelhady Mario R. Eden Frederico B. Gabriel Xiaoyun Qin Mahmoud M. El-Halwagi 《Computers & Chemical Engineering》2005,29(11-12):2304
Decoupling the constitutive equations from the balance and constraint equations allows for reformulating a conventional forward problem into two reverse problems. The first reverse problem is the reverse of a simulation problem, where the process model is solved in terms of the constitutive (synthesis/design) variables instead of the process variables, thus providing the synthesis/design targets. The second reverse problem (reverse property prediction) solves the constitutive equations to identify unit operations, operating conditions and/or products by matching the synthesis/design targets. Visualization of the problem is achieved by employing recently developed property clustering techniques, which allows a high-dimensional problem to be visualized in two or three dimensions. The clusters by definition satisfy intra-stream and inter-stream conservation through linear “mixing” rules, which allows for the development of consistent additive rules along with their ternary representation. 相似文献