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   15653篇
  免费   1209篇
  国内免费   1167篇
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
  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 0 毫秒
51.
Data from 296 sibling pairs (mean ages 10 and 13 years), their primary caregivers, and census records were used to test the hypothesis that African American children's likelihood of developing conduct problems associated with harsh parenting, a lack of nurturant-involved parenting, and exposure to an older sibling's deviance-prone attitudes and behavior would be amplified among families residing in disadvantaged neighborhoods. A latent construct representing harsh-inconsistent parenting and low levels of nurturant-involved parenting was positively associated with younger siblings' conduct disorder symptoms, as were older siblings' problematic attitudes and behavior. These associations were strongest among families residing in the most disadvantaged neighborhoods. Future research and prevention programs should focus on the specific neighborhood processes associated with increased vulnerability for behavior problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
52.
A new approach to study ergodicity of filtering processes is presented. It is based on the vanishing discount approach to discounted functional of filtering process. We show that limit superior of the Cesaro averages of the functionals is the same for all initial conditions from which the uniqueness of invariant measures of filtering processes follows. The approach is based on certain assumption for which we provide a sufficient condition using concavity arguments. In addition we show the existence of solutions to the Poisson equation corresponding to filtering process with concave functional. The assumptions are then extended to the controlled case and using similar concave arguments we obtain the existence of solutions to the Bellman equation corresponding to partially observed average cost per unit time problem.  相似文献   
53.
Many problems in geophysics, acoustics, elasticity theory, cancer treatment, food process control and electrodynamics involve study of wave field synthesis (WFS) in some form or another. In the present work, modelling of wave propagation phenomena is studied as a static problem, using finite element method and treating time as an additional spatial dimension. In particular, WFS problems are analysed using discrete methods. It is shown that a fully finite element-based scheme is very natural and effective method for the solution of such problems. Distributed WFS in the context of two-dimensional problems is outlined and incorporation of any geometric or material non-linearities is shown to be straightforward. This has significant implications for problems in geophysics or biological media, where material inhomogeneities are quite prevalent. Numerical results are presented for several problems referring to media with material inhomogeneities and predefined absorption profiles. The method can be extended to three-dimensional problems involving anisotropic media properties in a relatively straightforward manner. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
54.
This article is the twenty-fourth of a series of articles discussing various open research problems in automated reasoning. The problem proposed for research asks one to find an appropriate theory for modulating across argument and across literal boundaries. Because demodulation has proved so useful—is most cases, even crucial—to automated reasoning, extending this concept to permit canonicalization to be applied at the predicate and at the clause and subclause levels merits exploration. For evaluating a proposed solution to this research problem, we suggest problems from mathematics, logic, program verification, database inquiry, and the world of puzzles.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   
55.
The concept of combinatorial objects is formalized. It allows strict definition of a combinatorial optimization problem (COP). An efficient metaheuristic method to solve COPs (H-method) is considered. It includes stochastic local search algorithms as a built-in procedure. A parallel implementation of the H-method is set forth and analyzed. The results from a numerical experiment and solution of some well-known COPs on personal computers and on the SKIT cluster supercomputer are presented. The study was supported by INTAS (Project 06-1000017-8909). __________ Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 70–79, November–December 2007.  相似文献   
56.
The efficiency characteristics of multicast key distribution schemes based on (v, b, r, λ)-designs are investigated. The stability and connectivity of such designs are estimated. These estimates generalize and enhance the well-known estimates for the efficiency characteristics of multicast key distribution schemes based on incomplete block designs. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 100–111, May–June 2007.  相似文献   
57.
A pseudohyperbolic problem of optimal control of intratumoral drug distribution is formulated. It takes into account the heterogeneity of tumor tissues and effects of convection diffusion in a fissured porous medium. A mathematical model constructed and the corresponding optimal control problem are shown to be correct. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 147–154, November–December 2007.  相似文献   
58.
《中华人民共和国煤炭法》亟待修订   总被引:1,自引:0,他引:1  
当前,由于《煤炭法》颁布的时代背景发生很大变化,该法已经不能适应形势发展和实际工作的需要。该法存在的主要问题包括煤炭开采市场准入门槛设置过低、对煤炭生产开发规划规定过分原则等。我们应以科学发展观为指导,按照市场经济规律的要求,针对存在的问题尽快对《煤炭法》进行修订和完善。  相似文献   
59.
An N-superconcentrator is a directed, acyclic graph with N input nodes and N output nodes such that every subset of the inputs and every subset of the outputs of same cardinality can be connected by node-disjoint paths. It is known that linear-size and bounded-degree superconcentrators exist. Here it is proved that such superconcentrators exist (by a random construction of certain expander graphs as building blocks) having density 28 (where the density is the number of edges divided by N). The best known density before this paper was 34.2 [U. Schöning, Construction of expanders and superconcentrators using Kolmogorov complexity, J. Random Structures Algorithms 17 (2000) 64-77] or 33 [L.A. Bassalygo, Personal communication, 2004].  相似文献   
60.
大坝安全监测信息发布应随着计算机网络和软件技术的发展,逐渐走向网络化。随着微软ASP.Net 2.0的发布,开发基于Net的大坝安全监测信息W eb发布条件更加成熟。文章对W eb开发主要功能数据查询、图形绘制、报表制作及系统优化等主要技术问题进行了探讨,可供科研院所、水库大坝管理部门参考。  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