全文获取类型
收费全文 | 15644篇 |
免费 | 1218篇 |
国内免费 | 1167篇 |
专业分类
电工技术 | 574篇 |
技术理论 | 1篇 |
综合类 | 2193篇 |
化学工业 | 677篇 |
金属工艺 | 172篇 |
机械仪表 | 730篇 |
建筑科学 | 1451篇 |
矿业工程 | 324篇 |
能源动力 | 365篇 |
轻工业 | 383篇 |
水利工程 | 418篇 |
石油天然气 | 263篇 |
武器工业 | 62篇 |
无线电 | 912篇 |
一般工业技术 | 1804篇 |
冶金工业 | 738篇 |
原子能技术 | 83篇 |
自动化技术 | 6879篇 |
出版年
2024年 | 36篇 |
2023年 | 99篇 |
2022年 | 180篇 |
2021年 | 231篇 |
2020年 | 331篇 |
2019年 | 340篇 |
2018年 | 332篇 |
2017年 | 428篇 |
2016年 | 513篇 |
2015年 | 509篇 |
2014年 | 1073篇 |
2013年 | 1101篇 |
2012年 | 1222篇 |
2011年 | 1078篇 |
2010年 | 902篇 |
2009年 | 1071篇 |
2008年 | 1078篇 |
2007年 | 1111篇 |
2006年 | 972篇 |
2005年 | 882篇 |
2004年 | 678篇 |
2003年 | 605篇 |
2002年 | 480篇 |
2001年 | 485篇 |
2000年 | 398篇 |
1999年 | 322篇 |
1998年 | 246篇 |
1997年 | 193篇 |
1996年 | 160篇 |
1995年 | 150篇 |
1994年 | 126篇 |
1993年 | 107篇 |
1992年 | 89篇 |
1991年 | 74篇 |
1990年 | 73篇 |
1989年 | 79篇 |
1988年 | 59篇 |
1987年 | 29篇 |
1986年 | 19篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1979年 | 8篇 |
1964年 | 8篇 |
1963年 | 9篇 |
1961年 | 8篇 |
1957年 | 7篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
针对铜鼓县小水电站联网时存在的问题及其不利影响进行了分析,井提出了改进途径,指出小水电站的联网改造应立足安全,争取效益。 相似文献
22.
This paper formulates the pickup and delivery problem, also known as the dial-a-ride problem, as an integer program. Its polyhedral structure is explored and four classes of valid inequalities developed. The results of a branch-and-cut algorithm based on these constraints are presented. 相似文献
23.
We study the application of the geographic nearest neighbor approach to two problems. The first problem is the construction of an approximately minimum length rectilinear Steiner tree for a set ofn points in the plane. For this problem, we introduce a variation of a subgraph of sizeO(n) used by YaO [31] for constructing minimum spanning trees. Using this subgraph, we improve the running times of the heuristics discussed by Bern [6] fromO(n
2
log
n) toO(n log2
n). The second problem is the construction of a rectilinear minimum spanning tree for a set ofn noncrossing line segments in the plane. We present an optimalO(n logn) algorithm for this problem. The rectilinear minimum spanning tree for a set of points can thus be computed optimally without using the Voronoi diagram. This algorithm can also be extended to obtain a rectilinear minimum spanning tree for a set of nonintersecting simple polygons.The results in this paper are a part of Y. C. Yee's Ph.D. thesis done at SUNY at Albany. He was supported in part by NSF Grants IRI-8703430 and CCR-8805782. S. S. Ravi was supported in part by NSF Grants DCI-86-03318 and CCR-89-05296. 相似文献
24.
陈金强 《数字社区&智能家居》2007,(9):1460-1461
中等职业学校一般开设VB、VC及数据库等涉及程序设计的计算机课程。本文拟就程序设计中一题多解的教学方法进行探讨。 相似文献
25.
Mulcahy Nicholas J.; Call Josep; Dunbar Robin I. M. 《Canadian Metallurgical Quarterly》2005,119(1):23
Two important elements in problem solving are the abilities to encode relevant task features and to combine multiple actions to achieve the goal. The authors investigated these 2 elements in a task in which gorillas (Gorilla gorilla) and orangutans (Pongo pygmaeus) had to use a tool to retrieve an out-of-reach reward. Subjects were able to select tools of an appropriate length to reach the reward even when the position of the reward and tools were not simultaneously visible. When presented with tools that were too short to retrieve the reward, subjects were more likely to refuse to use them than when tools were the appropriate length. Subjects were proficient at using tools in sequence to retrieve the reward. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
26.
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
27.
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
28.
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
29.
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
30.
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