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   1564631篇
  免费   24793篇
  国内免费   7028篇
电工技术   34611篇
综合类   6455篇
化学工业   274092篇
金属工艺   64977篇
机械仪表   44183篇
建筑科学   47345篇
矿业工程   11557篇
能源动力   50399篇
轻工业   119860篇
水利工程   15725篇
石油天然气   37836篇
武器工业   150篇
无线电   198037篇
一般工业技术   292146篇
冶金工业   193408篇
原子能技术   34235篇
自动化技术   171436篇
  2021年   15609篇
  2020年   11968篇
  2019年   14707篇
  2018年   17161篇
  2017年   16487篇
  2016年   22062篇
  2015年   17551篇
  2014年   28790篇
  2013年   88086篇
  2012年   37061篇
  2011年   50642篇
  2010年   43931篇
  2009年   51842篇
  2008年   46919篇
  2007年   44296篇
  2006年   45876篇
  2005年   40875篇
  2004年   42777篇
  2003年   42525篇
  2002年   41360篇
  2001年   38518篇
  2000年   36728篇
  1999年   36379篇
  1998年   54833篇
  1997年   45155篇
  1996年   39057篇
  1995年   32874篇
  1994年   30510篇
  1993年   30464篇
  1992年   26681篇
  1991年   23775篇
  1990年   24072篇
  1989年   23158篇
  1988年   21651篇
  1987年   19920篇
  1986年   19234篇
  1985年   22544篇
  1984年   22508篇
  1983年   20456篇
  1982年   19442篇
  1981年   19612篇
  1980年   18202篇
  1979年   18621篇
  1978年   17908篇
  1977年   18074篇
  1976年   19712篇
  1975年   16070篇
  1974年   15543篇
  1973年   15659篇
  1972年   13122篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
995.
The concept of the integrated services digital network (ISDN) could revolutionize information management. The purpose of the ISDN is to provide a worldwide network that offers end-to-end digital connectivity supporting a wide variety of communications services. ISDN subscribers will have direct access to a high-speed digital pipeline capable of supporting simultaneous voice, data, facsimile, and various other services and calling features.  相似文献   
996.
Blends of lard with eight separate fats or oils (70:30 w/w) were prepared and used as the fat component of meat batters. After cooking, the batters were analyzed for water and fat exudation and gel strength. None differed significantly from the control of 100% lard. Positive correlation coefficients, however, were significant between percent monounsaturated triglycerides and water exudation, polyunsaturated triglycerides and fat exudation and saturated triglycerides and gel strength. Addition of lecithin, cholesterol or methyl palmitate to the lard increased fat exudation and decreased gel strength. Sodium laurate had the opposite effect whether added to the lard or to the aqueous phase.  相似文献   
997.
A narrow linewidth has been obtained in a new 1.5 ?m distributed feedback laser integrated monolithically with a tunable external cavity. The linewidth of 18 MHz has been achieved by tuning the current in the external cavity, and the FM response was flat from 100 kHz to 500 MHz.  相似文献   
998.
Modeling and CW operation of a quasi-three-level 946 nm Nd: YAG laser   总被引:18,自引:0,他引:18  
A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds4I9/2in Nd3+,4I15/2in Er3+,5I8in Ho3+and3H6in Tm3+. It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the4F3/2-4I9/2transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.  相似文献   
999.
A novel typed of hybrid-mode feed horn is presented. It comprises a hollow conical dielectric waveguide whose outer surface is metallized, and whose inner surface is coated with circumferentially oriented conducting strips. It may be designed to have mimimal cross polarization at two arbitrarily separated frequencies, as for a dual depth corrugated horn. Compared to the corrugated horn, it has the potential of lower weight and lower price. Small horns will have some cross polarization due to undesired radiation from the fields transmitted within the dielectric.  相似文献   
1000.
An algorithm for construction of the reachability domain by the given time instant ? for a nonlinear third order system under the condition of preliminary approach to a predefined point is proposed. All possible cases of location of this point in the motion plane of the system for different values of the time instant ? are studied.  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