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   467842篇
  免费   7136篇
  国内免费   2429篇
电工技术   9104篇
综合类   1109篇
化学工业   69113篇
金属工艺   17782篇
机械仪表   13659篇
建筑科学   12931篇
矿业工程   1291篇
能源动力   12819篇
轻工业   48743篇
水利工程   3725篇
石油天然气   3895篇
武器工业   80篇
无线电   59723篇
一般工业技术   83995篇
冶金工业   91686篇
原子能技术   6608篇
自动化技术   41144篇
  2021年   3600篇
  2020年   2594篇
  2019年   3165篇
  2018年   4813篇
  2017年   4791篇
  2016年   5266篇
  2015年   4195篇
  2014年   6839篇
  2013年   21765篇
  2012年   11777篇
  2011年   16646篇
  2010年   13200篇
  2009年   14697篇
  2008年   15605篇
  2007年   15565篇
  2006年   14538篇
  2005年   13242篇
  2004年   12555篇
  2003年   12462篇
  2002年   11893篇
  2001年   12399篇
  2000年   11175篇
  1999年   12486篇
  1998年   31016篇
  1997年   21580篇
  1996年   16498篇
  1995年   12357篇
  1994年   10900篇
  1993年   10587篇
  1992年   7510篇
  1991年   7201篇
  1990年   6646篇
  1989年   6369篇
  1988年   6253篇
  1987年   5124篇
  1986年   5018篇
  1985年   6110篇
  1984年   5492篇
  1983年   4953篇
  1982年   4608篇
  1981年   4672篇
  1980年   4349篇
  1979年   4019篇
  1978年   3834篇
  1977年   4692篇
  1976年   6523篇
  1975年   3247篇
  1974年   3061篇
  1973年   3110篇
  1972年   2441篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture.  相似文献   
43.
The purpose of this paper is to introduce a new I DDQ measurement technique based on active successive approximations, called ASA-I DDQ. This technique has unique features facilitating a speed-up in I DDQ measurement. Experimental results suggest that a significant speed-up factor (up to 4) can be obtained over the QuiC-Mon technique. Such a speed-up is a key element in the replacement of single-threshold I DDQ testing since it amplifies the effectiveness of post-processing techniques.  相似文献   
44.
45.
The current Internet and wireless networks are harsh environments for transporting high-bandwidth multimedia data. We examine the technical issues involved, and describe an end-to-end solution to support a Web-based learn-on-demand system that operates in a wireless campus environment.  相似文献   
46.
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented.  相似文献   
47.
48.
49.
50.
Accurate and reliable decision making in oncological prognosis can help in the planning of suitable surgery and therapy, and generally, improve patient management through the different stages of the disease. In recent years, several prognostic markers have been used as indicators of disease progression in oncology. However, the rapid increase in the discovery of novel prognostic markers resulting from the development in medical technology, has dictated the need for developing reliable methods for extracting clinically significant markers where complex and nonlinear interactions between these markers naturally exist. The aim of this paper is to investigate the fuzzy k-nearest neighbor (FK-NN) classifier as a fuzzy logic method that provides a certainty degree for prognostic decision and assessment of the markers, and to compare it with: 1) logistic regression as a statistical method and 2) multilayer feedforward backpropagation neural networks an artificial neural-network tool, the latter two techniques having been widely used for oncological prognosis. In order to achieve this aim, breast and prostate cancer data sets are considered as benchmarks for this analysis. The overall results obtained indicate that the FK-NN-based method yields the highest predictive accuracy, and that it has produced a more reliable prognostic marker model than both the statistical and artificial neural-network-based methods.  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