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   12168篇
  免费   320篇
  国内免费   16篇
电工技术   131篇
综合类   18篇
化学工业   2573篇
金属工艺   202篇
机械仪表   209篇
建筑科学   637篇
矿业工程   64篇
能源动力   271篇
轻工业   1159篇
水利工程   136篇
石油天然气   52篇
无线电   822篇
一般工业技术   1795篇
冶金工业   2841篇
原子能技术   116篇
自动化技术   1478篇
  2022年   126篇
  2021年   192篇
  2020年   159篇
  2019年   144篇
  2018年   174篇
  2017年   174篇
  2016年   221篇
  2015年   175篇
  2014年   268篇
  2013年   682篇
  2012年   468篇
  2011年   586篇
  2010年   435篇
  2009年   457篇
  2008年   523篇
  2007年   517篇
  2006年   431篇
  2005年   346篇
  2004年   328篇
  2003年   341篇
  2002年   305篇
  2001年   210篇
  2000年   186篇
  1999年   214篇
  1998年   245篇
  1997年   194篇
  1996年   167篇
  1995年   195篇
  1994年   171篇
  1993年   176篇
  1992年   161篇
  1991年   117篇
  1990年   150篇
  1989年   167篇
  1988年   142篇
  1987年   146篇
  1986年   143篇
  1985年   191篇
  1984年   168篇
  1983年   155篇
  1982年   160篇
  1981年   162篇
  1980年   120篇
  1979年   158篇
  1978年   153篇
  1977年   138篇
  1976年   122篇
  1975年   126篇
  1974年   116篇
  1973年   122篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
A method for the rapid, simultaneous determination of protein, fat, carbohydrate, non-protein nitrogen and total solids in milk and liquid dairy products by infrared reflectance spectroscopy is presented. The method is calibrated against known standards obtained by conventional, time-consuming wet chemical methods but, once calibrated, can be operated routinely by non-skilled personnel. The method is sensitive and accurate down to 0·5% w/v and can be applied to most liquid samples without any need for prior preparation.  相似文献   
23.
Although the banking industry plays a central role in the world economy and has traditionally been an innovative user of information technology, banks are struggling to develop mature Internet strategies. A model used to analyze the type of Internet activities among a sample of banks as well as their level of sophistication and customization is useful not only for revealing unexploited opportunities in the banking sector but also for guiding the strategy-building process of organizations in other industries.  相似文献   
24.
Computer science often faces the criticism that it isn't actual science. Doing science means using the scientific method, which includes reporting results so that others can repeat and verify them. The problem with the computer science community is the lack of shared terms with precise semantics. When a researcher reports phenomenal results that can't be replicated, the author might be viewed as a brilliant alchemist, but such works undermine claims of being "science."  相似文献   
25.
The oligosaccharide component compositions of a series of non-reducing oligosaccharides extracted from the roots of Arnica montana L. has been determined by gel permeation chromatography (g.p.c.). The range of oligosaccharides present was found to extend beyond the octasaccharide previously reported. with 16% to 19% of the oligosaccharides having a degree of polymerisation of between 11 and 19 and almost 3% having a degree of polymerisation greater than 20. The chromatographic behaviour of this series of oligosaccharides is compared with that observed for series of D-gluco-oligosaccharides.  相似文献   
26.
Summary In A Logic Covering Undefinedness in Program Proofs [1], Barringer, Cheng and Jones present a 3-valued logic designed for Program-Verification and Computer Science applications in general. In this paper we want to add some the oretical background to their arguments for the need for such a system.  相似文献   
27.
28.
A theoretical investigation of a catalytic porous-wall reactor in which gaseous and liquid reactants approach each other from opposite sides of the catalyst is undertaken. Equations for the annular liquid-channel are coupled with those for the catalytic wall and solved numerically and analytically using a simplified model. For the model reaction under study, the main design and operation parameters which affect reactor performance are the Thiele modulus, Peclet number, width of the liquid channel and the inlet concentration of the reactant in the liquid phase.

The effect of reactor configuration is peculiar to the cylindrical geometry because the thickness and relative location of the catalytic wall as well as the selection of the liquid and gas channels can influence the reactor performance. Thin-walled catalyst tubes have larger effectiveness factors and as the tube radius approaches that of the reactor, conversion in the reactor increases especially when the liquid is saturated with the gaseous reactant. Concentration of the liquid reactant in the feed has a significant effect if the reactant is depleted at some point inside the catalyst wall. Since the reaction zone width can be adjusted by changing the feed composition, this might have important implications with respect to selectivity.  相似文献   
29.
The work reported here represents initial attempts to develop a complete kinetic and mechanistic understanding of the reaction chemistry of H2S under coal liquefaction conditions, using both model systems and coal. Hydrogen sulphide was found to promote/catalyse the transfer of hydrogen from tetralin to 2-hydroxyquinoline (2-HOQ). The presence of H2S can increase the rate of hydrogen transfer from tetralin to 2-HOQ by a factor of 10 compared with the same reaction run in the absence of H2S. The energy of activation for hydrogen transfer was found to decrease by ≈5 kcal mol−1 in the presence of H2S. The presence of H2S was also found to promote loss of oxygen from 2-HOQ to form small amounts of quinoline. No evidence of CC or CN bond cleavage in 2-HOQ was noted under any of the reaction conditions studied. These results suggest that the presence of H2S reduces the temperatures necessary to promote effective hydrogen transfer from tetralin by 50–75 °C. Moreover, they imply that similar effects occur in H2S-promoted coal liquefaction.  相似文献   
30.
We present a fully automatic arm and hand tracker that detects joint positions over continuous sign language video sequences of more than an hour in length. To achieve this, we make contributions in four areas: (i) we show that the overlaid signer can be separated from the background TV broadcast using co-segmentation over all frames with a layered model; (ii) we show that joint positions (shoulders, elbows, wrists) can be predicted per-frame using a random forest regressor given only this segmentation and a colour model; (iii) we show that the random forest can be trained from an existing semi-automatic, but computationally expensive, tracker; and, (iv) introduce an evaluator to assess whether the predicted joint positions are correct for each frame. The method is applied to 20 signing footage videos with changing background, challenging imaging conditions, and for different signers. Our framework outperforms the state-of-the-art long term tracker by Buehler et al. (International Journal of Computer Vision 95:180–197, 2011), does not require the manual annotation of that work, and, after automatic initialisation, performs tracking in real-time. We also achieve superior joint localisation results to those obtained using the pose estimation method of Yang and Ramanan  (Proceedings of the IEEE conference on computer vision and pattern recognition, 2011).  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