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   4484篇
  免费   153篇
  国内免费   10篇
电工技术   71篇
综合类   29篇
化学工业   1346篇
金属工艺   112篇
机械仪表   87篇
建筑科学   274篇
矿业工程   8篇
能源动力   80篇
轻工业   354篇
水利工程   25篇
石油天然气   1篇
无线电   264篇
一般工业技术   826篇
冶金工业   609篇
原子能技术   39篇
自动化技术   522篇
  2022年   49篇
  2021年   55篇
  2020年   48篇
  2019年   57篇
  2018年   66篇
  2017年   57篇
  2016年   96篇
  2015年   82篇
  2014年   114篇
  2013年   208篇
  2012年   171篇
  2011年   257篇
  2010年   187篇
  2009年   169篇
  2008年   198篇
  2007年   189篇
  2006年   132篇
  2005年   160篇
  2004年   135篇
  2003年   106篇
  2002年   88篇
  2001年   87篇
  2000年   85篇
  1999年   91篇
  1998年   109篇
  1997年   93篇
  1996年   81篇
  1995年   79篇
  1994年   72篇
  1993年   79篇
  1992年   70篇
  1991年   53篇
  1990年   76篇
  1989年   47篇
  1988年   47篇
  1987年   53篇
  1986年   43篇
  1985年   67篇
  1984年   60篇
  1983年   49篇
  1982年   57篇
  1981年   45篇
  1979年   43篇
  1978年   45篇
  1977年   67篇
  1976年   45篇
  1975年   42篇
  1974年   56篇
  1972年   43篇
  1970年   40篇
排序方式: 共有4647条查询结果,搜索用时 15 毫秒
991.
A new allenic fatty acid, phlomic acid, 7,8-eicosadienoic acid or 20:2Δ7,8allene, has been observed in several genera of the Lamiaceae, subfamily Lamioideae. The occurrence of this fatty acid seems to be correlated with the presence of an unusual 20:1 acid, 20:1Δ9cis or 20:1n–11. Phlomic acid is apparently produced by chain-elongation of the major seed oil fatty acid, laballenic acid or 18:2Δ5,6allene.  相似文献   
992.
Unknown reaction rates make concentration control in laboratory recycle reactors a difficult task, particularly when gas chromatographs or other analytical equipment with long analysis times from part of the control system. For such time-delay systems, a model-based feedforward control technique is developed which uses some kind of learning linear mapping to provide estimates of the reaction rates. Regarding the number of time steps necessary to satisfy a new set point, in a variety of simulation studies, this technique has proven superior to similar but simpler control strategies.  相似文献   
993.
994.
995.
The new crystal structure information system DIAMOND is presented. It handles all kinds of crystallographic databases on PCs including SHELX files and Chemical Information Files (CIF’s). DIAMOND, because of its graphics capability, is a powerful tool for establishing structural relationships and for evaluating crystallographic data.  相似文献   
996.
Case-based reasoning is deemed an important technology to alleviate the bottleneck of knowledge acquisition in Artificial Intelligence (AI). In case-based reasoning, knowledge is represented in the form of particular cases with an appropriate similarity measure rather than any form of rules. The case-based reasoning paradigm adopts the view that an Al system is dynamically changing during its life-cycle which immediately leads to learning considerations. Within the present paper, we investigate the problem of case-based learning of indexable classes of formal languages. Prior to learning considerations, we study the problem of case-based representability and show that every indexable class is case-based representable with respect to a fixed similarity measure. Next, we investigate several models of case-based learning and systematically analyze their strengths as well as their limitations. Finally, the general approach to case-based learnability of indexable classes of formal languages is prototypically applied to so-called containmet decision lists, since they seem particularly tailored to case-based knowledge processing.  相似文献   
997.
In TM-rolling of strip and plate the mill parameters can be adjusted such that reversible temper embrittlement (RTE) happens. This leads, together with the TM-typical grain elongation, to a special fracture appearance which consists of sub-fracture (split, separation) formation starting from the main fracture plane. The lower toughness in the thickness direction is connected with a sloping shelf of the otherwise sigmoidal energy temperature curve of impact bending tests with ISO-V(CVN) specimens. It is shown how RTE can be avoided, namely by low phosphorus contents of the material and/or by low coiling temperatures at strip rolling. Accelerated cooling of plates can avoid RTE, but care must be taken not to produce plates with lower toughness.  相似文献   
998.
Information relating to piping damage in safety-relevant systems in German nuclear power plants with light water reactors (both pressurized water reactors (PWRs) and boiling water reactors (BWRs)) were analyzed with respect to the modes and the causes of damages. In general, the total range of observed piping damage is low. The incidents (82) in plants with PWRs affected mainly pipes with small diameters. Almost all damaged piping showed wall-penetrating cracks combined with leakages, which revealed the damage. Initial cracks at piping with larger diameters were discovered in isolated cases during in-service inspections. With regard to the incidents (71) in plants with BWRs, piping with small as well as large diameters was affected to different degrees. Wall-penetrating cracks combined with leakages were detected at piping with small diameters. For large-diameters pipes, cracks were indicated during in-service inspections and supplementary examinations. The results of the incident evaluations confirm the conservativeness of the safety concept chosen for the design of German nuclear power plants with light water reactors.  相似文献   
999.
Treatment of cotton cellulose with 3 M sodium hydroxide solution at 260°C and 280°C gave a mixture of carboxylic acids with a yield of > 95%. The identified 50 carboxylic acids included both hydroxy monocarboxylic acids and dicarboxylic acids; their routes of formation are discussed. Among the main compounds were lactic, glycolic, 2-hydroxy-2-methylpropanoic, 2-hydroxybutanoic, 3,4-dideoxypentonic, anhydroisosaccharinic, 2,3-dideoxypentaric, and 3,4-dideoxyhexaric acids. Technical utilisation of this kind of acid mixture requires further studies. Investigations of the cyclic compounds, formed in small amounts only, resulted in identification of mainly alkyl-substituted 2-cyclopenten-1-ones.  相似文献   
1000.
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