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   595302篇
  免费   7414篇
  国内免费   1038篇
电工技术   10827篇
综合类   528篇
化学工业   96044篇
金属工艺   23898篇
机械仪表   19009篇
建筑科学   14246篇
矿业工程   4392篇
能源动力   15210篇
轻工业   48031篇
水利工程   7180篇
石油天然气   15109篇
武器工业   42篇
无线电   62396篇
一般工业技术   121301篇
冶金工业   100169篇
原子能技术   14894篇
自动化技术   50478篇
  2021年   6067篇
  2020年   4445篇
  2019年   5779篇
  2018年   9827篇
  2017年   10013篇
  2016年   10655篇
  2015年   6746篇
  2014年   11142篇
  2013年   27821篇
  2012年   17195篇
  2011年   22905篇
  2010年   18317篇
  2009年   20136篇
  2008年   20567篇
  2007年   20178篇
  2006年   17521篇
  2005年   15805篇
  2004年   14946篇
  2003年   14506篇
  2002年   14016篇
  2001年   13335篇
  2000年   12790篇
  1999年   12503篇
  1998年   28193篇
  1997年   20472篇
  1996年   16073篇
  1995年   12427篇
  1994年   11258篇
  1993年   11018篇
  1992年   8686篇
  1991年   8331篇
  1990年   8294篇
  1989年   8067篇
  1988年   7732篇
  1987年   7000篇
  1986年   6786篇
  1985年   7668篇
  1984年   6942篇
  1983年   6657篇
  1982年   5996篇
  1981年   6090篇
  1980年   5781篇
  1979年   5891篇
  1978年   5817篇
  1977年   6310篇
  1976年   7829篇
  1975年   5232篇
  1974年   5008篇
  1973年   5078篇
  1972年   4338篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 111–113, August, 1989.  相似文献   
122.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 14–15, February, 1989.  相似文献   
123.
The effect of secondary scattering that is produced by the induced current in an infinitely long, finitely conducting wire over a plane, finitely conducting earth from an incident electromagnetic pulse is investigated. This is accomplished by finding the field of a Hertzian dipole over the earth and identifying the part that is due to secondary scattering. Frequency-domain results for the overall induced current require that certain infinite integrals be numerically evaluated. Fourier inversion to the time domain in turn requires the numerical evaluation of another infinite integral. When the results are compared to those obtained when secondary scattering is ignored, it is found that secondary scattering slightly increases the current for the case of broadside incidence and reduces it for the case of grazing incidence by as much as two orders of magnitude. Peak currents are much smaller than previously thought. These general results hold for all of the earth parameters that were used in the study  相似文献   
124.
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   
125.
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   
126.
127.
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   
128.
129.
130.
The paper describes new experimental evidence on the effects of fast neutron irradiation on the nucleation of bubbles in superheated demineralized water during sudden depressurization. The experimental range covered strating pressures of (0.33–6.0) MPa. It was shown that fast neutron irradiation causes significant increases in the bubble formation for specified conditions of pressure, temperature and rate of blowdown. A mechanistic interpretation of the measurements based on a thermodynamic model was included, and comparison was made, in terms of void fraction, with the experimental results.  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