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   442501篇
  免费   5589篇
  国内免费   1626篇
电工技术   7156篇
综合类   2542篇
化学工业   67293篇
金属工艺   21516篇
机械仪表   14399篇
建筑科学   10176篇
矿业工程   3362篇
能源动力   10005篇
轻工业   31181篇
水利工程   5572篇
石油天然气   10270篇
武器工业   24篇
无线电   48122篇
一般工业技术   89515篇
冶金工业   66636篇
原子能技术   10198篇
自动化技术   51749篇
  2021年   3188篇
  2019年   3086篇
  2018年   19402篇
  2017年   18331篇
  2016年   15457篇
  2015年   4170篇
  2014年   6333篇
  2013年   15887篇
  2012年   12637篇
  2011年   21815篇
  2010年   18271篇
  2009年   16995篇
  2008年   18324篇
  2007年   19090篇
  2006年   10133篇
  2005年   10402篇
  2004年   9719篇
  2003年   9347篇
  2002年   8568篇
  2001年   8213篇
  2000年   7855篇
  1999年   7898篇
  1998年   19627篇
  1997年   13895篇
  1996年   10664篇
  1995年   8044篇
  1994年   6939篇
  1993年   7095篇
  1992年   5293篇
  1991年   5279篇
  1990年   5038篇
  1989年   4999篇
  1988年   5015篇
  1987年   4363篇
  1986年   4403篇
  1985年   4971篇
  1984年   4632篇
  1983年   4343篇
  1982年   3957篇
  1981年   3971篇
  1980年   3904篇
  1979年   3931篇
  1978年   3915篇
  1977年   4330篇
  1976年   5292篇
  1975年   3515篇
  1974年   3382篇
  1973年   3519篇
  1972年   3060篇
  1971年   2790篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Zusammenfassung Dieser Artikel beschreibt einige Erfahrungen und typische Problemstellungen mit Textmining in der Medizin und gibt einen Einblick in aktuelle und zukünftige Herausforderungen in Forschung & Entwicklung. Interessant ist n?mlich, dass auch im ,,Multimedia-Zeitalter“ die meiste Information immer noch als ,,Text“ vorliegt. Mithilfe von statistischen und linguistischen Verfahren wird mit sogenannter ,,Textmining-Software“ versucht, aus Freitexten Information ,,heraus zu schürfen“ (deshalb ,,Textmining“). Allerdings ist es damit noch nicht genug. Der n?chste Schritt besteht darin, die Information sowohl nutzbar als auch brauchbar zu machen. Die jeweiligen End-Benutzerinnen und End-Benutzer müssen in die Lage versetzt werden, auf der Basis der gewonnenen Information deren Wissen zu erweitern. In unserem konkreten Fall sollen damit Entscheidungen im Rahmen ?rztlichen Handelns unterstützt werden. Probleml?sungen in diesem Bereich erfordern eine holistische Sicht- und Herangehensweise. Daher wird es immer wichtiger, Erkenntnisse aus Informatik und Psychologie zusammenflie?en zu lassen und auf systemischer Ebene technologisch umzusetzen.  相似文献   
992.
In the present work, the prospects and trends of solid electrolyte membrane reactors (SEMRs) towards hydrogen production, are discussed. Initially, an overview of the principles, the properties and the techniques related to the usage of the SEMRs, are presented. In the following, a literature survey covering earlier and recent developments of the various methods (e.g. reforming or partial oxidation or dehydrogenation of hydrocarbons, steam electrolysis) employed in the SEMRs for the production of hydrogen, is performed. Finally, the current status of this research field is analyzed and future research topics are proposed.  相似文献   
993.
The Bahrain International Circuit (BIC) is considered as one of the best international racing car track in terms of technical aspects and architectural quality. Two Formula 1 races have been hosted in the Kingdom of Bahrain, in 2004 and 2005, at BIC. The BIC had recently won the award of the best international racing car circuit.  相似文献   
994.
Polymer Injection Forming (PIF) and Polymer Injection-Compression Forming (PICF) are new manufacturing technologies for sheet metal-polymer macro-composites, which result from the combination of injection moulding and sheet metal forming. In these processes, a metal blank is formed inside an injection mould by using the pressure of the molten polymer that, after cooling, permanently bonds to the metal sheet creating a fully finished product in only one production step. This paper presents a calibrated multi-physics numerical model of the processes that proves to be suitable to investigate the mutual metal-polymer interactions and to provide a reliable tool in designing the process as well as its control.  相似文献   
995.
The effect of the oxygen partial pressure on the spinodal decomposition in the Ba2YCu3O6—Ba2YCu3O7 system has been studied. A decrease in the oxygen partial pressure was found to increase the decomposition rate. The most probable cause of the effect consists in the decrease of oxygen concentration in the near-boundary regions of grains.  相似文献   
996.
The optical properties of bismuth telluride crystals doped with donor-and acceptor-type impurities are studied. The fact that energy corresponding to the resonance frequency of plasma oscillations of free charge carriers (plasmons) approaches the band-gap energy is detected in the infrared spectral region, where the main elementary excitations in the electronic system of these materials are observed. The mentioned approach of energies varies the intensity of electron-plasmon interaction, which affects the recombination processes in the materials widely used for the fabrication of thermoelectric energy converters.  相似文献   
997.
A successive approximation technique that is based on the conventional line-by-line-addressing is proposed. A large number of gray shades can be displayed without flicker by using low-cost liquid crystal display drivers that are designed to drive the pixels to either ON or OFF states in bilevel displays.  相似文献   
998.
A digital position-sensitive X-ray imaging scintillation detector has been designed for the MEDIANA medical diagnostic station of the Kurchatov Synchrotron Radiation Center (the Kurchatov Institute). A single-crystal CsI(Tl) scintillator 8 mm thick is used as a screen with approximately 100% detection efficiency for X rays with energies as high as 100 keV. A CCD matrix of dimensions 1024 × 1024 pixels is the photodetector. The spatial resolution is five line pairs per mm in a field of vision of 35 × 35 mm for 100-keV X rays.  相似文献   
999.
A novel reversible addition-fragmentation chain transfer (RAFT) reagent bearing triphenylamine (TPA) group, 4-diphenylamino-dithiobenzoic acid benzyl ester (DDABE), was designed and synthesized. It was used in the RAFT polymerizations of styrene (St) and methyl acrylate (MA) to prepare end-functionalized polymers. The results of the polymerization showed that the RAFT polymerizations could be well controlled using DDABE as the RAFT agent. Number-average molecular weight (Mn,GPC) increased linearly with monomer conversion, and molecular weight distributions were relatively narrow (PDI< 1.50). The results of chain-extension reaction, 1H NMR spectra and UV/Vis spectra confirmed that most of the polymers chains were end-capped by the functional triphenylamine (TPA) groups. The effect of feed molar ratios of St/DDABE/AIBN on polymerization was investigated.  相似文献   
1000.
The cellulose solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) was successfully applied as reaction medium for the synthesis of allyl cellulose by conversion of the polymer with allyl chloride in the presence of solid NaOH. Samples with degree of substitution from 0.50 to 2.98 were accessible by varying the molar ratio anhydroglucose unit:allyl chloride:NaOH and reaction time. DMSO/TBAF was found to be an efficient reaction medium for the preparation of highly functionalized samples from spruce sulfite pulp with degree of polymerization of about 500 even in a scale of 50 g. The allyl cellulose samples were characterized by means of FTIR- and NMR spectroscopy. Size exclusion chromatography revealed negligible polymer degradation during synthesis and purification of the samples.  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