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   11017篇
  免费   116篇
  国内免费   9篇
电工技术   98篇
综合类   2篇
化学工业   1063篇
金属工艺   101篇
机械仪表   300篇
建筑科学   216篇
矿业工程   28篇
能源动力   130篇
轻工业   879篇
水利工程   107篇
石油天然气   15篇
无线电   863篇
一般工业技术   1034篇
冶金工业   5451篇
原子能技术   108篇
自动化技术   747篇
  2021年   69篇
  2020年   51篇
  2019年   61篇
  2018年   60篇
  2017年   83篇
  2016年   65篇
  2015年   47篇
  2014年   110篇
  2013年   319篇
  2012年   161篇
  2011年   259篇
  2010年   238篇
  2009年   231篇
  2008年   260篇
  2007年   242篇
  2006年   246篇
  2005年   219篇
  2004年   178篇
  2003年   201篇
  2002年   200篇
  2001年   162篇
  2000年   160篇
  1999年   256篇
  1998年   1420篇
  1997年   844篇
  1996年   663篇
  1995年   434篇
  1994年   363篇
  1993年   403篇
  1992年   143篇
  1991年   149篇
  1990年   162篇
  1989年   167篇
  1988年   172篇
  1987年   173篇
  1986年   138篇
  1985年   166篇
  1984年   94篇
  1983年   102篇
  1982年   84篇
  1981年   105篇
  1980年   97篇
  1979年   79篇
  1978年   79篇
  1977年   178篇
  1976年   390篇
  1975年   78篇
  1974年   71篇
  1973年   63篇
  1972年   54篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
A method of approximate channel identification is proposed that is based on a simplification of the correlation estimator. Despite the numerical simplification (no multiplications or additions are required, only comparisons and an accumulator), the performance of the proposed estimator is not significantly worse than that of the standard correlation estimator. A free (user selectable) parameter moves ‘smoothly’ from a situation with small sum‐squared channel estimation error but hard‐to‐identify channel peaks, to one with a larger sum‐squared estimation error but easy‐to‐identify channel peaks. The proposed estimator is shown to be biased and its behaviour is analysed in a number of situations. Applications of the proposed estimator to sparsity detection, symbol timing recovery and to the initialization of blind equalizers are suggested. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
32.
Any intelligent problem solving system should be able, given the known data on a case, to decide whether some item of information is true, false or unknown. In this paper the way in which various forms of commonsense reasoning can be integrated to provide such decisions is described. To this end three structural types of knowledge defined over data, and four strategies for exploiting these structures, are identified. ‘Decide-Status’ integrates the reasoning strategies into a task frame. This frame structure not only integrates the reasoning but also affords the appropriate facilities for providing strategic justifications for its conclusions, if required.  相似文献   
33.
Wastewater treatment technologies suitable for serving large populations are generally reliable and reasonably cost-effective, yet they are almost always financially inappropriate for small communities (< 2,000 p.e.). Comparative cost data suggests that waste stabilization ponds should be an attractive option for small communities, yet perceptions relating to land costs, climate and effluent quality have limited their application in the UK. This paper details typical UK land costs, climate and winter performance data for a pilot-scale waste stabilization pond with various upgrading technologies: system A, two tertiary maturation ponds in series; B, two tertiary maturation ponds in series followed by a reed bed channel; C, a control rock filter; D, an aerated rock filter; and E, a constructed wetland. System D was found to perform best, closely followed by system B.  相似文献   
34.
The results of Stan ton and Bairstow (1908) have been reanalyzed to yield information on the composition dependence of the low cycle impact fatigue properties of pearlitic plain carbon steels. It has been found that the energy absorbed per impact, Ei, and the number of impacts are failure, Nf, are related by the equation: In this equation q is determined by the carbon, manganese and silicon contents of the steel; Eo is the impact endurance limit; and C and D are constants. The curve represented by this equation intersects that representing the Johnson-Keller high cycle impact fatigue equation at a value of logeNf equal to 1/C. Thus, the transition from low to high cycle impact fatigue occurs at this value of logeNf.  相似文献   
35.
纽约州立大学Buffalo分校电子封装实验室正在为美国海军开发新型的功率电子封装,在一些极端苛刻的工作条件下(比如在军舰和战机上).它们能够解决大电流密度、高温和大的温度梯度所引起的种种问题。这类功率电子封装还有可能很快进入民用产品。  相似文献   
36.
Evaluative responses appear to involve 2 seemingly distinct sets of processes: those that are automatically activated and others that are more consciously controlled. Using functional magnetic resonance imaging, the authors investigated the brain systems associated with automatic and controlled evaluative processing. Participants made either evaluative (good-bad) or nonevaluative (past-present) judgments about famous names. Greater amygdala activity was observed for names rated as "bad" relative to those rated as "good," regardless of whether the task directly involved an evaluative judgment (good-bad) or not (past-present). Good-bad judgments resulted in greater medial and ventrolateral prefrontal cortex (PFC) activity than past-present judgments. Furthermore, there was greater ventrolateral PFC activity in good-bad judgments marked by greater ambivalence. Together, these findings indicate a neural distinction between processes engaged for automatic and controlled evaluation. Whereas automatic processes are sensitive to simple valence, controlled processes are sensitive to attitudinal complexity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
37.
38.
Over the past seven years, Columbia-Presbyterian Medical Center has been planning and implementing an integrated academic information management system. Accomplishments to date include establishing an institutional information architecture, installing a campus-wide network of workstations, recruiting the staff needed to develop and implement the system, and developing various applications. This paper presents the rationale and steps involved in these accomplishments, as well as data on use of the system so far.  相似文献   
39.
40.
Dapsone has clinical utility as an anti-inflammatory agent but the mechanism of this action remains unknown. We have previously reported that dapsone inhibits beta2 integrin (CD11b/CD18)-mediated adherence of human neutrophils in vitro and now describe studies designed to discover how dapsone-mediated inhibition of this neutrophil function occurs. Results indicate that dapsone interferes with the activation or function of the G-protein (Gi type) that initiates the signal transduction cascade common to chemotactic stimuli. They also show that dapsone-mediated suppression of this pathway inhibits the generation of second messengers essential to the activation of beta2 integrin molecules, as well as respiratory and secretory functions of neutrophils exposed to chemoattractants. We propose that the inhibition of chemoattractant-induced signal transduction by dapsone suppresses neutrophil recruitment and local production of toxic respiratory and secretory products in the affected skin of dermatitis herpetiformis and other neutrophilic dermatoses.  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