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   596476篇
  免费   7244篇
  国内免费   1062篇
电工技术   10822篇
综合类   494篇
化学工业   95734篇
金属工艺   23951篇
机械仪表   19131篇
建筑科学   14245篇
矿业工程   4418篇
能源动力   15316篇
轻工业   48057篇
水利工程   7296篇
石油天然气   15060篇
武器工业   42篇
无线电   62317篇
一般工业技术   121136篇
冶金工业   100585篇
原子能技术   14898篇
自动化技术   51280篇
  2021年   6024篇
  2020年   4400篇
  2019年   5796篇
  2018年   9837篇
  2017年   9990篇
  2016年   10538篇
  2015年   6651篇
  2014年   11101篇
  2013年   28141篇
  2012年   17164篇
  2011年   22748篇
  2010年   18320篇
  2009年   20097篇
  2008年   20522篇
  2007年   20210篇
  2006年   17543篇
  2005年   15881篇
  2004年   14956篇
  2003年   14589篇
  2002年   14093篇
  2001年   13411篇
  2000年   12755篇
  1999年   12499篇
  1998年   28128篇
  1997年   20507篇
  1996年   16066篇
  1995年   12456篇
  1994年   11261篇
  1993年   11019篇
  1992年   8715篇
  1991年   8337篇
  1990年   8308篇
  1989年   8070篇
  1988年   7732篇
  1987年   7037篇
  1986年   6787篇
  1985年   7743篇
  1984年   7037篇
  1983年   6692篇
  1982年   6021篇
  1981年   6131篇
  1980年   5849篇
  1979年   5947篇
  1978年   5883篇
  1977年   6366篇
  1976年   7871篇
  1975年   5274篇
  1974年   5057篇
  1973年   5124篇
  1972年   4381篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
93.
94.
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   
95.
96.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 111–113, August, 1989.  相似文献   
97.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 14–15, February, 1989.  相似文献   
98.
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   
99.
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   
100.
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