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   397539篇
  免费   5419篇
  国内免费   1527篇
电工技术   7081篇
综合类   286篇
化学工业   60135篇
金属工艺   14636篇
机械仪表   11469篇
建筑科学   10352篇
矿业工程   1372篇
能源动力   11033篇
轻工业   41159篇
水利工程   3581篇
石油天然气   4855篇
武器工业   6篇
无线电   49080篇
一般工业技术   73452篇
冶金工业   74061篇
原子能技术   7045篇
自动化技术   34882篇
  2021年   2849篇
  2019年   2667篇
  2018年   4276篇
  2017年   4284篇
  2016年   4680篇
  2015年   3440篇
  2014年   5814篇
  2013年   18349篇
  2012年   10342篇
  2011年   14627篇
  2010年   11406篇
  2009年   13086篇
  2008年   13486篇
  2007年   13545篇
  2006年   12189篇
  2005年   11219篇
  2004年   10716篇
  2003年   10390篇
  2002年   9841篇
  2001年   10258篇
  2000年   9448篇
  1999年   10039篇
  1998年   24470篇
  1997年   17248篇
  1996年   13104篇
  1995年   10045篇
  1994年   8605篇
  1993年   8473篇
  1992年   6172篇
  1991年   5901篇
  1990年   5608篇
  1989年   5441篇
  1988年   5312篇
  1987年   4472篇
  1986年   4308篇
  1985年   5189篇
  1984年   4702篇
  1983年   4345篇
  1982年   3990篇
  1981年   4104篇
  1980年   3787篇
  1979年   3644篇
  1978年   3445篇
  1977年   4036篇
  1976年   5138篇
  1975年   2976篇
  1974年   2907篇
  1973年   2989篇
  1972年   2380篇
  1971年   2192篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
81.
'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   
82.
83.
84.
This paper describes a sequential tripping strategy used in a wide area back-up protection expert system (BPES) to combat situations in which protection relays have maloperated or information is missing. The BPES is an innovative back-up protection scheme designed to prevent the occurrence of widespread blackouts. The BPES evaluates the certainty that transmission lines are likely to be affected by the fault and uses a sequential tripping strategy to isolate the fault if a firm decision is not available due to maloperated relays and/or missing information. The mode of analysis and the sequential tripping strategy ensures that the BPES will clear a fault at minimum risk to the network. An example is included to demonstrate how the certainty factor based sequential tripping strategy is employed by the BPES to clear a fault which occurred on the South Western part of the UK National Grid System  相似文献   
85.
Eliminating the adoption barrier   总被引:1,自引:0,他引:1  
Krueger  C. 《Software, IEEE》2002,19(4):29-31
  相似文献   
86.
87.
The separate contributions of impellers and stators to suction are studied by means of interaction models. From these, suction can be predicted when interchangeable components are used in any combination, and in either direction of impeller rotation. Methods are devised by which numerical values of the impeller and stator terms can be simply assigned. The resulting model provides good agreement with experiment. The influence of variability in component geometry is reflected in the model parameters. Possible applications of the model are suggested.  相似文献   
88.
89.
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   
90.
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