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   1526469篇
  免费   24640篇
  国内免费   6987篇
电工技术   34254篇
综合类   6485篇
化学工业   271601篇
金属工艺   64115篇
机械仪表   42739篇
建筑科学   47064篇
矿业工程   11374篇
能源动力   50219篇
轻工业   117908篇
水利工程   15495篇
石油天然气   37288篇
武器工业   136篇
无线电   196398篇
一般工业技术   287954篇
冶金工业   170392篇
原子能技术   33794篇
自动化技术   170880篇
  2021年   15587篇
  2020年   11853篇
  2019年   14621篇
  2018年   14852篇
  2017年   14041篇
  2016年   21060篇
  2015年   17364篇
  2014年   28770篇
  2013年   87878篇
  2012年   36170篇
  2011年   48456篇
  2010年   42203篇
  2009年   50360篇
  2008年   45357篇
  2007年   42594篇
  2006年   45611篇
  2005年   39880篇
  2004年   42437篇
  2003年   42283篇
  2002年   41337篇
  2001年   38374篇
  2000年   36642篇
  1999年   35619篇
  1998年   46947篇
  1997年   40590篇
  1996年   36346篇
  1995年   31507篇
  1994年   29562篇
  1993年   29109篇
  1992年   26537篇
  1991年   23627篇
  1990年   23874篇
  1989年   22950篇
  1988年   21448篇
  1987年   19723篇
  1986年   19187篇
  1985年   22572篇
  1984年   22691篇
  1983年   20571篇
  1982年   19425篇
  1981年   19491篇
  1980年   18097篇
  1979年   18743篇
  1978年   17922篇
  1977年   17987篇
  1976年   19539篇
  1975年   16110篇
  1974年   15646篇
  1973年   15719篇
  1972年   13209篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
By using mathematical formulae developed in previous studies, certain pollution parameters of dye effluent obtained from reactive dyeing with a single dye can be predicted with good accuracy. In this study, the degree of pollution of reactive dyeing effluent using dye mixtures was also predicted by other approaches, such as linear and non-linear regression. The prediction accuracy was found to be satisfactory.  相似文献   
982.
展成式精密电火花加工机床   总被引:1,自引:0,他引:1  
研制了一种展成式精密电火花加工机床,它含有3个回转机构和4个直线移动机构,工件苡轴,工具电极苡轴和转台均可按需要回转,坐标工作台可作纵向和横向移动,工件头架可作轴向和竖向移动。可设置成多种复合运动方式和相应的结构布局,具有很丰富的加工功能,加工精度能达到微米级并实现电火花镜面加工。  相似文献   
983.
984.
985.
This study, which is based on responses from over 300 individuals in England and Wales, explores how a willingness to use a water-recycling system of specific configuration varies against a number of factors which are linked to system design, system scale, system context, and water-conservation behaviour. Findings show that there is broad willingness to accept in-house water recycling provided that public health is not compromised.  相似文献   
986.
Anguilla is a UK overseas (non-independent) territory in the Caribbean. It is a small middle-income island with a population of 13 000, and recent statistics indicate that it is more dependent on tourism than any other country or territory in the world. Rapid population growth and development have placed more emphasis on the need for human health and environmental protection. For the first time, a systematic water-quality monitoring programme has been developed, based on the realities of the local situation, e.g. low resource base, limited capabilities, dependence on household rainwater catchment, storage cisterns, and a poor water-supply network. Development of the programme incorporated the key themes of pragmatic, realistic, incremental, responsive, and consultative approaches.  相似文献   
987.
Cables to moving parts on a linear actuator in production machines, such as pick-and-place machines, are a source of unreliability owing to the possible breaking of a cable. They further reduce the positioning precision of the actuator owing to additional forces. Slotted waveguide systems for rail vehicles based on 2.4 GHz transmission frequency are well known, but transmitters/receivers and waveguides are bulky. The paper reports on the reduction in size of the equipment, adapted to 5.8 GHz using a commercial off-the-shelf RadioLan communication module. Further, the efficient termination of the wave-guide and a new way to reduce standing-wave effects is also discussed.  相似文献   
988.
We present uniaxial tensile test results for 30–50 nm thick freestanding aluminum films. Young’s modulus and ductility were found to decrease monotonically with grain size. Reverse Hall–Petch behavior was observed with no appreciable room temperature creep. Non-linear elasticity with small irreversible deformation was observed for 50 nm thick specimens.  相似文献   
989.
本文分析了目前制约我国城市可持续发展的最主要因素是低效率的土地利用方式 ,若使地上、地面、地下空间协调发展 ,合理科学的规划好地下空间 ,珍惜地下空间资源 ,健全地下空间法律法规 ,统一地下空间管理机构 ,则可高效率的利用土地。  相似文献   
990.
Following up on recent studies of the Zn-rich corners of the Zn-Fe-Ni and Zn-Fe-Si ternary systems, a 450 °C isothermal section of the Zn-Fe-Ni-Si quaternary phase diagram with the Zn composition being fixed at 93 at.% was determined experimentally using optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy (EDS), and x-ray diffractometry (XRD). FeSi was found to be in equilibrium with almost all phases in the section, including the T, ζ, Ni-δ, NiSi2, and FeSi2 phases, as well as the liquid phase (L). Silicon solubilities in the T, ζ, and Ni-δ phases were rather limited. However, the solubilities of Fe and Zn in the NiSi2 phase, at 4.5 at.% and 7.2 at.%, respectively, were appreciable. The existence of the (L+NiSi2+Ni-δ) three-phase equilibrium state apparently prevents other Ni-Si compounds from entering equilibrium with the liquid at 450 °C. No true quaternary compound was found in the study.  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