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   648924篇
  免费   8738篇
  国内免费   1920篇
电工技术   11605篇
综合类   497篇
化学工业   100178篇
金属工艺   23924篇
机械仪表   18747篇
建筑科学   17213篇
矿业工程   2632篇
能源动力   16471篇
轻工业   63572篇
水利工程   6075篇
石油天然气   8740篇
武器工业   31篇
无线电   78009篇
一般工业技术   122633篇
冶金工业   119957篇
原子能技术   11914篇
自动化技术   57384篇
  2021年   4703篇
  2019年   4395篇
  2018年   7385篇
  2017年   7425篇
  2016年   7916篇
  2015年   5818篇
  2014年   9538篇
  2013年   29474篇
  2012年   16088篇
  2011年   22324篇
  2010年   17603篇
  2009年   19979篇
  2008年   21030篇
  2007年   21165篇
  2006年   18828篇
  2005年   17493篇
  2004年   16751篇
  2003年   16343篇
  2002年   15974篇
  2001年   15908篇
  2000年   14881篇
  1999年   15460篇
  1998年   36144篇
  1997年   26502篇
  1996年   20735篇
  1995年   16058篇
  1994年   14367篇
  1993年   13930篇
  1992年   10525篇
  1991年   10222篇
  1990年   9748篇
  1989年   9524篇
  1988年   9225篇
  1987年   7808篇
  1986年   7771篇
  1985年   9254篇
  1984年   8799篇
  1983年   7796篇
  1982年   7336篇
  1981年   7425篇
  1980年   7053篇
  1979年   6883篇
  1978年   6676篇
  1977年   7922篇
  1976年   10483篇
  1975年   5807篇
  1974年   5551篇
  1973年   5465篇
  1972年   4633篇
  1971年   4167篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A team of faculty members at the University of Denver changed the learning environment in key courses in the Department of Engineering from predominately teacher centered to student centered. Through this funded project new grading methods were implemented, classrooms were renovated and wired with studio layouts to facilitate learning, the Engineering Circuits Laboratory was rewired and instrumented for automated data acquisition and reporting, and two new pedagogical approaches were developed. At the onset of the project, six goals were established related to student learning. The introduction of industry standard hardware and software provided students with unprecedented hands‐on experience and project related activities stimulated faculty innovations in other current and future courses. Assessment results indicate that the new grading system improved the clarity of expectations for students before assignments were given resulting in increased reported motivation for learning in many courses. Even though course GPAs did not always reflect higher achievement on graded work, faculty members firmly believe that deeper understanding was achieved because more complex material was assimilated.  相似文献   
992.
993.
The results of a comparative numerical investigation of three types of resonator systems of a cyclotron for acceleration of negative hydrogen and deuterium ions up to maximum energy 30 and 15 MeV, respectively, are presented. It is shown that a vertical system with two half-wave resonators excited in-phase has the smallest active losses and the smallest differential of the amplitude of the accelerating voltage along the edge of the dees and is effective for accelerating particles at dual working frequencies.  相似文献   
994.
Andrei Nikolaevich Kolmogorov was the foremost contributor to the mathematical and philosophical foundations of probability in the twentieth century, and his thinking on the topic is still potent today. In this article we first review the three stages of Kolmogorov's work on the foundations of probability: (1) his formulation of measure-theoretic probability, 1933; (2) his frequentist theory of probability, 1963; and (3) his algorithmic theory of randomness, 1965–1987. We also discuss another approach to the foundations of probability, based on martingales, which Kolmogorov did not consider.  相似文献   
995.
Abstract The purpose of this exploratory study was to investigate the influence of two individual characteristics (Web experience and academic focus) of adolescents on the Web perception, using off-line questionnaires (a Lickert response scale) constituted on the basis of a series of interviews. Questions concerned: perceptions about the nature of information found in the Web; 'strategies' of access to the interesting Internet sites and the reliability of different information resources (libraries, television, Web, etc.). Results lead to the assumption that adolescents with high Web experience became more critical, less confident and less enthusiastic than adolescents with low Web experience and that, in some dimensions, perceptions of literature students are different to those of science students. Even if some interesting results were obtained, further research is needed to explore users' perceptions related to individuals' characteristics and to determine the generalisability of the influences identified in this exploratory study.  相似文献   
996.
This paper introduces the quality of sagacity measure in the extended variable precision rough sets model - VPRSl,u. The need for this measure is a direct consequence of the use of the associated l and u values. Moreover, different levels of miss-classification are allowed in the classification of objects to a decision class or its compliment. This measure attempts to take this into account, by acknowledging the classification of an object to the compliment of a decision class, as an appropriate (if not optimum) classification of that object. A consequence of the analysis is a discussion of the notion of open and closed worlds in VPRSl,u.  相似文献   
997.
The bisymmetry property is studied for operators defined on a finite chain. In particular, a characterization of all bisymmetric, commutative and smooth binary operators is given. It is deduced from this characterization that bisymmetry and associativity are equivalent for finite chains, under these additional conditions.  相似文献   
998.
This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100-150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
999.
1000.
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