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   583250篇
  免费   6991篇
  国内免费   1125篇
电工技术   10793篇
综合类   497篇
化学工业   93750篇
金属工艺   23802篇
机械仪表   19053篇
建筑科学   12853篇
矿业工程   4354篇
能源动力   15669篇
轻工业   46800篇
水利工程   7075篇
石油天然气   15034篇
武器工业   40篇
无线电   62298篇
一般工业技术   119883篇
冶金工业   96695篇
原子能技术   14792篇
自动化技术   47978篇
  2022年   4651篇
  2021年   6551篇
  2020年   4857篇
  2019年   6156篇
  2018年   10320篇
  2017年   10303篇
  2016年   10674篇
  2015年   6572篇
  2014年   10984篇
  2013年   27436篇
  2012年   16565篇
  2011年   21998篇
  2010年   17715篇
  2009年   19499篇
  2008年   19666篇
  2007年   19259篇
  2006年   16665篇
  2005年   15039篇
  2004年   14225篇
  2003年   13886篇
  2002年   13393篇
  2001年   12981篇
  2000年   12450篇
  1999年   12136篇
  1998年   27857篇
  1997年   20204篇
  1996年   15791篇
  1995年   12124篇
  1994年   10976篇
  1993年   10714篇
  1992年   8408篇
  1991年   8195篇
  1990年   8069篇
  1989年   7837篇
  1988年   7532篇
  1987年   6814篇
  1986年   6591篇
  1985年   7461篇
  1984年   6761篇
  1983年   6493篇
  1982年   5826篇
  1981年   5953篇
  1980年   5672篇
  1979年   5761篇
  1978年   5686篇
  1977年   6198篇
  1976年   7713篇
  1975年   5115篇
  1974年   4907篇
  1973年   4988篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films.  相似文献   
103.
Poly(vinyl alcohol) is crosslinked in dilute solution (c=0.1 wt%) with glutaraldehyde. The reaction product is characterized by viscometry and gel permeation chromatography (g.p.c.). The intrinsic viscosity decreases with increasing degree of crosslinking and does not depend on temperature. G.p.c. reveals that the reaction product is not homogeneous, but consists of a mixture of particles with different sizes, possibly both intra- and intermolecularly crosslinked molecules. The intramolecularly crosslinked molecules are smaller in size than the initial polymer molecules and their size depends on the degree of crosslinking. They possess a narrow particle size distribution even if the initial polymer sample had a broad molecular weight distribution.  相似文献   
104.
105.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 111–113, August, 1989.  相似文献   
106.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 14–15, February, 1989.  相似文献   
107.
We investigate the saturation effects of power broadening, Stark shifting, and population transfer on Stokes conversion in stimulated Raman scattering. We do not make the usual rotating wave approximation because the detuning from the next electronic state is assumed to be in the optical regime. Retaining the counter-rotating terms allows an exact determination of the pump and Stokes indexes of refraction. Steady-state solutions for the Stokes intensity and phase are obtained and the effects of making the rotating wave approximation (RWA) are discussed. Finally, we examine the behavior of these solutions for Stokes conversion in hydrogen gas when geometric propagation is appropriate.  相似文献   
108.
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment.  相似文献   
109.
110.
Consideration was given to the decision making procedures based on the fuzzy messages of experts whose preferences on the set of collective decisions can also be fuzzy.  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