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   244600篇
  免费   2964篇
  国内免费   1243篇
电工技术   4836篇
综合类   264篇
化学工业   35558篇
金属工艺   10870篇
机械仪表   7075篇
建筑科学   6337篇
矿业工程   485篇
能源动力   6299篇
轻工业   24213篇
水利工程   1849篇
石油天然气   1336篇
武器工业   3篇
无线电   31125篇
一般工业技术   45040篇
冶金工业   50499篇
原子能技术   3877篇
自动化技术   19141篇
  2021年   1572篇
  2019年   1427篇
  2018年   2330篇
  2017年   2235篇
  2016年   2455篇
  2015年   1914篇
  2014年   3170篇
  2013年   10841篇
  2012年   5471篇
  2011年   7820篇
  2010年   6305篇
  2009年   7001篇
  2008年   7591篇
  2007年   7681篇
  2006年   7078篇
  2005年   6545篇
  2004年   6274篇
  2003年   6287篇
  2002年   6263篇
  2001年   6388篇
  2000年   5820篇
  1999年   6446篇
  1998年   16648篇
  1997年   11651篇
  1996年   8995篇
  1995年   6726篇
  1994年   5934篇
  1993年   5755篇
  1992年   4073篇
  1991年   4013篇
  1990年   3598篇
  1989年   3518篇
  1988年   3455篇
  1987年   2923篇
  1986年   2849篇
  1985年   3430篇
  1984年   3061篇
  1983年   2759篇
  1982年   2567篇
  1981年   2587篇
  1980年   2447篇
  1979年   2292篇
  1978年   2238篇
  1977年   2822篇
  1976年   4201篇
  1975年   1909篇
  1974年   1805篇
  1973年   1789篇
  1972年   1465篇
  1971年   1322篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
From visual data exploration to visual data mining: a survey   总被引:8,自引:0,他引:8  
We survey work on the different uses of graphical mapping and interaction techniques for visual data mining of large data sets represented as table data. Basic terminology related to data mining, data sets, and visualization is introduced. Previous work on information visualization is reviewed in light of different categorizations of techniques and systems. The role of interaction techniques is discussed, in addition to work addressing the question of selecting and evaluating visualization techniques. We review some representative work on the use of information visualization techniques in the context of mining data. This includes both visual data exploration and visually expressing the outcome of specific mining algorithms. We also review recent innovative approaches that attempt to integrate visualization into the DM/KDD process, using it to enhance user interaction and comprehension.  相似文献   
192.
A new supported liquid membrane (SLM) system was prepared for the selective transport of bismuth ions from the aqueous feed into the aqueous permeate phase. The support of the SLM was a thin porous polypropylene or polyvinylidene fluoride membrane impregnated with diisooctyldithiophosphinic acid (Cyanex 301) as mobile carrier in 4‐chloroacetophenon as organic solvent. Cyanex 301 acts as a highly selective carrier for the uphill transport of bismuth ions through the SLM. In the presence of HNO3 as a metal ion acceptor in the strip solution, the transport of bismuth ions into the strip side reached 70 % of the initial feed concentration after 3.5 hours. The selectivity and efficiency of bismuth transport from aqueous solutions containing different mixtures of cations were investigated. In the presence of P2O72– ions as suitable masking agent in the feed solution, the interfering effects of other cations were completely eliminated. The selective transport of bismuth through SLM is superior to liquid‐liquid extraction or through bulk liquid membranes. This is due to the high efficiency. The SLM reduces the solvent requirements, combines extraction and stripping operations in a single process and allows the use of highly selective extractants. The system may be applied to samples containing very low bismuth concentrations.  相似文献   
193.
As a result of shrinking fossil fuels, biomass as a regenerative energy source gains importance. To realize biomass projects it is essential to investigate in convenient thermal procedures. On this evidence an analysis and evaluation of diverse gasification technologies with different boundary conditions and diverse biomasses are indispensable. Form and kind of the biomass as well as the type of the gasification plant cause different compositions of the product gas. The gasifiers show advantages and disadvantages concerning the biomass and the produced gas quality, depending on reactor type, kind of heat supply, gasification medium, and the pressure ratio in the reactor. As the ideal gasifier for different biomass is presently not available, it will be shown, which biomass is suitable for fixed bed or fluidized bed gasifiers.  相似文献   
194.
Alphorn, a software environment for programming distributed computer systems, is described. Programs running on different computers, possibly of different types and running different operating systems, communicate in a client-server relationship by means of remote procedure calls. This efficient construct structures programs neatly. The paper covers distributed process control, Alphorn's object-based programming style, remote procedure calls, the service interface language, configuration, runtime and debugging, and fault tolerance support  相似文献   
195.
A calorimeter of 25 bismuth germanate (BGO) crystals equipped with silicon photodiode readout has been tested at the CERN SPS in the energy range 1–50 GeV. The response for electrons has been shown to be linear in this energy range and the rms resolution obtained ( ) is approximately 1%, for E > 4 GeV. The electron/pion separation was found to be better than 1:500 in the energy range 1–20 GeV. Data on lateral and longitudinal shower development were compared with the results of a Monte Carlo simulation using the SLAC-EGS program and found to be in good agreement.  相似文献   
196.
197.
198.
The benefits of adhesively bonded structures are well known. However, the most significant factor limiting the extensive application of metal bonding in primary aerospace structures is the prevailing lack of confidence in its long term durability under hostile environmental conditions.1,2  相似文献   
199.
200.
This paper focuses on tracking, reconstruction and motion estimation of a well-defined MEMS optical switch from a microscopic view. For out-of-view reconstruction, a homography capable of transforming feature points and feature lines between a microscopic image and a CAD model of the switch is implemented. The homography between two sequential microscopic images is decomposed and factorized for motion estimation. Optical flow has also been explored to provide rough estimations of rotation centre and angle. The paper also illustrates motion parameter optimization principles to deal with uncertainty inherent in micro world. After non-linear optimization, estimation accuracy for rotation angle and rotation centre can reach 0.06° and pixel level, respectively.  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