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   507671篇
  免费   88666篇
  国内免费   55416篇
电工技术   44604篇
技术理论   57篇
综合类   39220篇
化学工业   78392篇
金属工艺   40863篇
机械仪表   27635篇
建筑科学   37574篇
矿业工程   23194篇
能源动力   17738篇
轻工业   39017篇
水利工程   12627篇
石油天然气   33254篇
武器工业   6260篇
无线电   64318篇
一般工业技术   67982篇
冶金工业   24664篇
原子能技术   4630篇
自动化技术   89724篇
  2024年   3808篇
  2023年   9251篇
  2022年   13497篇
  2021年   17800篇
  2020年   17979篇
  2019年   25232篇
  2018年   27782篇
  2017年   29870篇
  2016年   28743篇
  2015年   30830篇
  2014年   33237篇
  2013年   35720篇
  2012年   35978篇
  2011年   34579篇
  2010年   30256篇
  2009年   26415篇
  2008年   24384篇
  2007年   23131篇
  2006年   23140篇
  2005年   20703篇
  2004年   17426篇
  2003年   15009篇
  2002年   13751篇
  2001年   12468篇
  2000年   12545篇
  1999年   13650篇
  1998年   11764篇
  1997年   9994篇
  1996年   9470篇
  1995年   8459篇
  1994年   7017篇
  1993年   5545篇
  1992年   4855篇
  1991年   3668篇
  1990年   2886篇
  1989年   2526篇
  1988年   2039篇
  1987年   987篇
  1986年   797篇
  1985年   536篇
  1984年   374篇
  1983年   290篇
  1982年   338篇
  1981年   267篇
  1980年   220篇
  1976年   303篇
  1975年   233篇
  1972年   252篇
  1971年   141篇
  1960年   208篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
981.
Since the late 1980s, the eight-component model of the comprehensive school health program (CSHP), has been adopted widely in the United States and internationally. While it is acknowledged that the eight program elements should be delivered in a coordinated, interactive manner, numerous issues regarding how this integration best can be achieved, including who at the school level should have this responsibility and how the eight components relate conceptually and logistically, have not been addressed adequately. In essence, a CSHP transforms several solo performers into an orchestra. This article proposes the school health coordinator as an essential element in the eight-component model of the CSHP--the maestro, without whom there can be no symphony. The coordinator's principal responsibilities include administration, integration of personnel and programs, evaluation, and direct intervention. Three program elements--staff wellness, healthy environment, and community/family involvement--are subsumed within the coordinator's role, effectively reducing the number of program elements from eight to five. Potential benefits in addition to issues regarding feasibility of the SHC, are discussed and studies examining the effectiveness of the SHC model are recommended.  相似文献   
982.
直接斜率波前复原算法的控制效果分析   总被引:7,自引:0,他引:7  
建立自适应光学系统功率谱抑制函数的概念,分析了采用直接斜率波前复原算法的自适应当光学系统的控制效果,理论分析与61单元自适应光学系统上的实验结果表明,直接斜率波前复原算法将导致控制效果下降。  相似文献   
983.
984.
A new optimization model is discussed for the design of cellular manufacturing systems. It is based on an integer programming formulation that updates some other models by eliminating redundant machine assignment and cost coefficients dependent on cell configuration. To reduce computational burdens, a simplified integer programming model and a decomposition algorithm are proposed. Several computer solutions were performed to evaluate the performance of the new model. The computational results are discussed.  相似文献   
985.
986.
提出差动光栅概念,举例说明差动光栅在光纤面板刀口响应测试和材料形变自动监测系统等精密测试中的应用。  相似文献   
987.
Endogenous prostacyclin (PGI2; epoprostenol) is a potent endothelium-derived pulmonary vasodilator. However, the effects of exogenous PGI2 on isolated arteries could be either relaxant or contractile, depending on the species and organ studied. The present study investigated the distal pathways involved in the PGI2-induced contraction in rat intrapulmonary artery (PA) and relaxation in lamb PA. When vessels were precontracted with 30 mM K+, PGI2 (1 microM) induced relaxation in lamb PA but caused contraction in rat PA. Use of 30 mM K+, phenylephrine, serotonin, angiotensin II, or hypoxia to precontract the vessels did not alter the contractile effect of PGI2 in rat PA. Nevertheless, PGI2 produced a mild relaxation in rat PA precontracted by U-46619, a thromboxane A2 (TxA2)-receptor agonist, whereas the TxA2-receptor blocker SQ-29548 (0.1-0.5 microM) abolished the contractile response in rat PA. These data suggest that PGI2-induced contraction is mediated by activation of TxA2 receptors. The PGI2-induced modest relaxation in rat PA, which was only observed when TxA2 receptors were blocked by SQ-29548, suggests that the PGI2-mediated vasorelaxant pathway is diminished in these vessels. Simultaneous application of forskolin, an adenylate cyclase activator, and rolipram, a phosphodiesterase inhibitor, caused similar relaxation in both rat and lamb PA. This suggests that the adenosine 3',5'-cyclic monophosphate-dependent relaxing pathway is intact in rat PA and is comparable to that in lamb PA. On the basis of these data, we conclude that the pathways responsible for the paradoxical effects of PGI2 on rat and lamb PA are located upstream of the adenosine 3',5'-cyclic monophosphate-dependent relaxing pathway and that a paucity of PGI2 receptors in rat PA may be responsible.  相似文献   
988.
A necessary and sufficient condition for the union of an arbitrary family of fuzzy subgroups of a group to be a fuzzy group has been proposed. The criterion which gives a cut of the unit interval is called the Schnittaxiom. It has been applied successfully to investigate fuzzy subgroupness of arbitrary unions of homomorphic images and preimages.  相似文献   
989.
面向对象机器翻译知识库IMT—KB的设计与实现   总被引:1,自引:0,他引:1  
机器翻译知识库是机译系统的重要组成部分,针对传统机译知识库的不足之处,本文提出一种面向对象的机译知识体系结构,同时给出这种具有层次性和模块性机译知识库的存储组织和管理机制。  相似文献   
990.
An analytical method is presented for calculating the resonant frequency andQ-factor of a superconducting dielectric disk resonator operating in millimeter-wave regime with whispering-gallery mode. Resonant frequency shift due to the optical generation of quasi-particles in superconducting film is investigated as a function of photon flux. An optically tunable resonant frequency of about 500 MHz is estimated, and good agreement is found between numerical results and experimental ones.  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