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   445232篇
  免费   4100篇
  国内免费   648篇
电工技术   7551篇
综合类   340篇
化学工业   71994篇
金属工艺   21665篇
机械仪表   15360篇
建筑科学   9034篇
矿业工程   4524篇
能源动力   8484篇
轻工业   32628篇
水利工程   6032篇
石油天然气   15375篇
武器工业   55篇
无线电   41079篇
一般工业技术   96701篇
冶金工业   71738篇
原子能技术   14692篇
自动化技术   32728篇
  2021年   4241篇
  2019年   4089篇
  2018年   7532篇
  2017年   7775篇
  2016年   8233篇
  2015年   4637篇
  2014年   8060篇
  2013年   18399篇
  2012年   11956篇
  2011年   15420篇
  2010年   12393篇
  2009年   13730篇
  2008年   14238篇
  2007年   14095篇
  2006年   11963篇
  2005年   10491篇
  2004年   10242篇
  2003年   9919篇
  2002年   9908篇
  2001年   9632篇
  2000年   9442篇
  1999年   8853篇
  1998年   18663篇
  1997年   13816篇
  1996年   10629篇
  1995年   8473篇
  1994年   7705篇
  1993年   7718篇
  1992年   6379篇
  1991年   6195篇
  1990年   6453篇
  1989年   6261篇
  1988年   6018篇
  1987年   5631篇
  1986年   5583篇
  1985年   6138篇
  1984年   5927篇
  1983年   5565篇
  1982年   5251篇
  1981年   5348篇
  1980年   5274篇
  1979年   5381篇
  1978年   5569篇
  1977年   5881篇
  1976年   7093篇
  1975年   5033篇
  1974年   5038篇
  1973年   5155篇
  1972年   4495篇
  1971年   4144篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In this work, a quantitative analysis is applied to resolve the newly reported polarity-dependent charge-to-breakdown (Q/sub BD/) data from thick oxides of 6.8 nm down to ultrathin oxides of 1.9 nm. Three independent sets of Q/sub BD/ data, i.e., n/sup +/poly/NFET stressed under inversion and accumulation, and p/sup +/ poly/PFET under accumulation are carefully investigated. The Q/sub BD/ degradation observed for p-type anodes, either poly-Si or Si-substrate, can be nicely understood with the framework of maximum energy released by injected electrons. Thus, this work provides a universal and quantitative account for a variety of experimental observations in the time-to-breakdown (T/sub BD/) and Q/sub BD/ polarity-dependence of oxide breakdown.  相似文献   
102.
'Software defined radio' (SDR) is a technology that will appear in future generations of mobile phones, i.e. following the third-generation mobile phone technology that is currently being defined and developed. Early versions of 'pragmatic' SDR will allow the terminal to be reconfigured at any level of its protocol stack. Ultimately, the 'pure' SDR technology will allow a mobile phone or terminal to have its air interface software configured or reconfigured by other software (or software parameters) that have been downloaded to the terminal, e.g. over the air, or from a remote server via the Internet and one's personal computer (PC). A number of security issues arise with downloaded code that implements the air interface functions, and these may not be obvious simply from looking at the way PC software is updated on-line today. This paper starts with an outline of the code that allows a mobile phone to operate over a particular air interface. This sets the baseline for a discussion of the security issues surrounding the change of this code from one that is fixed and downloaded once only, to code that is reconfigurable during the life of a product.  相似文献   
103.
104.
105.
106.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 111–113, August, 1989.  相似文献   
107.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 14–15, February, 1989.  相似文献   
108.
109.
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   
110.
Results of a numerical investigation of heat and mass transfer at the initial stage of fire within a building in combustion of kerosene, carried out with the use of a three-dimensional mathematical field model, are presented. A comparison of the distribution of the averaged temperatures and velocities along the vertical axis of the convective column and of the mass rates of gas flows through an open opening with the experimental data has been made. Substantial three-dimensional inhomogeneities of the velocities and the temperatures in the near-ceiling layer have been revealed. It has been established that near the opening there is a critical separation zone which influences significantly the parameters of natural gas transfer.  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