首页 | 官方网站   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   1557570篇
  免费   24529篇
  国内免费   7047篇
工业技术   1589146篇
  2021年   15567篇
  2020年   11877篇
  2019年   14654篇
  2018年   18501篇
  2017年   18300篇
  2016年   22637篇
  2015年   17518篇
  2014年   28649篇
  2013年   87918篇
  2012年   37211篇
  2011年   51890篇
  2010年   45345篇
  2009年   53325篇
  2008年   47741篇
  2007年   45606篇
  2006年   45798篇
  2005年   41634篇
  2004年   42941篇
  2003年   42625篇
  2002年   41427篇
  2001年   37969篇
  2000年   36336篇
  1999年   35452篇
  1998年   49187篇
  1997年   41955篇
  1996年   37014篇
  1995年   31760篇
  1994年   29575篇
  1993年   29413篇
  1992年   26447篇
  1991年   23605篇
  1990年   23957篇
  1989年   23041篇
  1988年   21548篇
  1987年   19794篇
  1986年   19154篇
  1985年   22502篇
  1984年   22488篇
  1983年   20482篇
  1982年   19389篇
  1981年   19461篇
  1980年   18099篇
  1979年   18613篇
  1978年   17841篇
  1977年   17806篇
  1976年   18965篇
  1975年   16093篇
  1974年   15568篇
  1973年   15682篇
  1972年   13149篇
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
992.
993.
994.
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   
995.
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   
996.
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   
997.
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   
998.
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   
999.
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   
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-23

京公网安备 11010802026262号