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   476741篇
  免费   5618篇
  国内免费   1572篇
电工技术   9222篇
综合类   516篇
化学工业   68370篇
金属工艺   18241篇
机械仪表   14792篇
建筑科学   11475篇
矿业工程   1836篇
能源动力   12709篇
轻工业   39960篇
水利工程   4431篇
石油天然气   6540篇
武器工业   80篇
无线电   63223篇
一般工业技术   92246篇
冶金工业   90410篇
原子能技术   9518篇
自动化技术   40362篇
  2021年   3882篇
  2020年   2894篇
  2019年   3639篇
  2018年   6214篇
  2017年   6304篇
  2016年   6605篇
  2015年   4232篇
  2014年   7405篇
  2013年   21303篇
  2012年   11746篇
  2011年   16165篇
  2010年   12842篇
  2009年   14572篇
  2008年   15603篇
  2007年   15487篇
  2006年   13956篇
  2005年   12507篇
  2004年   12110篇
  2003年   12214篇
  2002年   11423篇
  2001年   11850篇
  2000年   11189篇
  1999年   11736篇
  1998年   29043篇
  1997年   20403篇
  1996年   15788篇
  1995年   12144篇
  1994年   10813篇
  1993年   10702篇
  1992年   7967篇
  1991年   7576篇
  1990年   7320篇
  1989年   6891篇
  1988年   6655篇
  1987年   5777篇
  1986年   5609篇
  1985年   6378篇
  1984年   5901篇
  1983年   5476篇
  1982年   5135篇
  1981年   5082篇
  1980年   4876篇
  1979年   4646篇
  1978年   4309篇
  1977年   5206篇
  1976年   6783篇
  1975年   3863篇
  1974年   3776篇
  1973年   3773篇
  1972年   3130篇
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
991.
992.
Since the natural estrogens 17 beta-estradiol (E2) and estron (E1), and the synthetic estrogen 17 alpha-ethynyl estradiol (EE2) have strong endocrine disrupting effects and the tendency to persist in effluent from wastewater treatment plants, effective measures are needed to remove them from wastewater. In this research, to gain an understanding of the characteristics of estrogen decomposition by ozonation, experiments were conducted using effluent from an actual wastewater treatment plant. In this experiment, estrogen was added to effluent at a concentration of 200 ng/l and 20 ng/l before the ozonation experiments. The results showed 90% or more of estrogen concentration and estrogenic activity of E2, El and EE2 to be removed at an ozone dose of 1 mg/l. At an ozone dose of 3 mg/l, the estrogen concentration and estrogenic activity of E2, El and EE2 in the treated water fell below the detection limit. The removal rate was not influenced by the kind of estrogen. No generation of byproducts with estrogenic activity was observed. The authors conclude that estrogen in secondary treated wastewater can be almost entirely removed at the practical ozone dose rate applied for the purpose of disinfection, which is up to about 5 mg/l.  相似文献   
993.
This paper presents a fiber-optic vehicle axle detector for roadways. It is based on a fiber-optic Michelson interferometer that is mounted directly into the road surface. The fully dielectric design allows for remote operation of the sensor via a long section of optical fiber. A simple signal-processing scheme of the output signals has been adopted that allows for reliable detection of commercial and personal vehicles.  相似文献   
994.
The current work presents the procedure of designing and carrying out measurements of radiation emission from an air-traffic surveillance radar. The system requirements are first given, and then the equipment used is described. The steps to determine the operating characteristics of the radar are specified in detail. The necessary methods for manual power measurements and calculations are next explained. Since the final measurement system was fully automated, its main features (topology, protocol of operation) are also given. Finally, some measurement results taken during the initial phase of system operation are presented and discussed.  相似文献   
995.
The phase diagrams of ternary liquid systems tetradecane-n-octanol (or cyclohexanone)-lanthanide(III) nitrate solvates with tri-n-butyl phosphate [Ln(NO3)3(TBP)3, Ln = La, Ce, Pr, or Sm] at T = 298.15 K were studied. These diagrams contain areas of homogeneous solutions and an area of separation into two liquid phases (I, II). Phases I and II are enriched in tetradecane and Ln(NO3)3(TBP)3, respectively. n-Octanol and cyclohexanone mainly pass into phase II.  相似文献   
996.
997.
Studied the effects of variations in base rate (BR) information and temporal context on predictions of violence and hindsight bias (HB). 270 undergraduates estimated the likelihood of violent offenders committing another violent offense based upon fictitious case history information. Ss were given 1 of 2 population BRs of the likelihood of reoffending (30% or 70%) and a recidivism estimation question that was phrased either predictively, predictively with a given outcome of either recidivism or no recidivism, or postdictively. Although different offenders were perceived as differentially likely to reoffend, estimated likelihood of recidivism was affected by neither BR nor temporal phrasing of the estimation task. A 2nd study of 182 undergraduates, using shorter case histories, also found no BR effect. HB effects were weak and inconsistent in both studies. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
998.
999.
Algorithms are proposed that construct first integrals and Lyapunov functions for stability analysis of stationary solutions of differential equations describing mechanical systems of linked bodies.Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 138–148, January–February, 1992.  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