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   3854篇
  免费   31篇
  国内免费   1篇
电工技术   30篇
化学工业   317篇
金属工艺   27篇
机械仪表   35篇
建筑科学   116篇
矿业工程   6篇
能源动力   48篇
轻工业   245篇
水利工程   42篇
石油天然气   12篇
无线电   177篇
一般工业技术   308篇
冶金工业   2160篇
原子能技术   24篇
自动化技术   339篇
  2022年   16篇
  2021年   17篇
  2019年   22篇
  2018年   22篇
  2017年   19篇
  2016年   29篇
  2015年   22篇
  2014年   40篇
  2013年   101篇
  2012年   71篇
  2011年   85篇
  2010年   63篇
  2009年   92篇
  2008年   83篇
  2007年   85篇
  2006年   79篇
  2005年   61篇
  2004年   75篇
  2003年   78篇
  2002年   58篇
  2001年   62篇
  2000年   53篇
  1999年   91篇
  1998年   591篇
  1997年   353篇
  1996年   257篇
  1995年   178篇
  1994年   115篇
  1993年   153篇
  1992年   53篇
  1991年   58篇
  1990年   61篇
  1989年   58篇
  1988年   41篇
  1987年   46篇
  1986年   48篇
  1985年   56篇
  1984年   36篇
  1983年   31篇
  1982年   31篇
  1981年   28篇
  1980年   33篇
  1979年   16篇
  1978年   15篇
  1977年   51篇
  1976年   101篇
  1975年   21篇
  1974年   18篇
  1973年   21篇
  1972年   14篇
排序方式: 共有3886条查询结果,搜索用时 31 毫秒
11.
12.
13.
Meeting a person with AIDS in the classroom was evaluated to determine if it had an impact on students' perceived susceptibility to HIV infection and attitudes toward persons with AIDS. The meeting was incorporated into the Grade 9 AIDS education program of a school district in Nova Scotia. Four schools participated in this study. Two schools were randomly assigned to the treatment group, which met the person with AIDS, and the remaining two schools formed the comparison group. Measures of the two attitudinal variables were collected using a self-report questionnaire that was administered both prior to and two weeks after the educational intervention. Meeting a person with AIDS in the classroom had no measurable impact on students perceived susceptibility to HIV infection nor on their attitudes toward persons with AIDS. Suggestions for using the educational intervention more effectively and for further research are made.  相似文献   
14.
15.
MAN is but a part of the universe; his capabilities make him a significant link, in the cycle of life. To ensure this life, man must live in harmony with his environment. Recently, a disharmony has been discovered which could have grave effects upon the existence of man. It appears that man in his great thrust forward is destroying his own environment. The gravity of this threat to man's own existence carries some intrinsic problems of its own: man must allow his reason rather than his emotion to take command.  相似文献   
16.
17.
Various educational programs have been developed and found to be effective in the self-management of arthritis. This study reexamined the effectiveness of one such program, "Bone Up On Arthritis" (BUOA), when the program was delivered by a community-based service organization to a sample of persons (N = 154) who differed widely in disease type and demographic characteristics. Arthritis Foundation staff implemented BUOA at four national sites; data were collected and analyzed by University of Michigan nurse researchers. Investigators found improved scores on all outcome measures (self-care behavior, helplessness, pain, dysfunction, and depression). These findings suggest that "Bone Up" is an effective nursing intervention in multiple organizational and community environments and for diverse patient populations.  相似文献   
18.
19.
We analyze generalization in XCSF and introduce three improvements. We begin by showing that the types of generalizations evolved by XCSF can be influenced by the input range. To explain these results we present a theoretical analysis of the convergence of classifier weights in XCSF which highlights a broader issue. In XCSF, because of the mathematical properties of the Widrow-Hoff update, the convergence of classifier weights in a given subspace can be slow when the spread of the eigenvalues of the autocorrelation matrix associated with each classifier is large. As a major consequence, the system's accuracy pressure may act before classifier weights are adequately updated, so that XCSF may evolve piecewise constant approximations, instead of the intended, and more efficient, piecewise linear ones. We propose three different ways to update classifier weights in XCSF so as to increase the generalization capabilities of XCSF: one based on a condition-based normalization of the inputs, one based on linear least squares, and one based on the recursive version of linear least squares. Through a series of experiments we show that while all three approaches significantly improve XCSF, least squares approaches appear to be best performing and most robust. Finally we show how XCSF can be extended to include polynomial approximations.  相似文献   
20.
We show that restricting a number of characterizations of the complexity classPto be positive (in natural ways) results in the same class of (monotone) problems, which we denote byposP. By a well-known result of Razborov,posPis a proper subclass of the class of monotone problems inP. We exhibit complete problems forposPvia weak logical reductions, as we do for other logically defined classes of problems. Our work is a continuation of research undertaken by Grigni and Sipser, and subsequently Stewart; indeed, we introduce the notion of a positive deterministic Turing machine and consequently solve a problem posed by Grigni and Sipser.  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