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   90232篇
  免费   1094篇
  国内免费   770篇
电工技术   2013篇
综合类   138篇
化学工业   13424篇
金属工艺   4447篇
机械仪表   4013篇
建筑科学   1889篇
矿业工程   755篇
能源动力   1966篇
轻工业   6719篇
水利工程   1170篇
石油天然气   3003篇
武器工业   52篇
无线电   8893篇
一般工业技术   20228篇
冶金工业   13943篇
原子能技术   2954篇
自动化技术   6489篇
  2022年   767篇
  2021年   1289篇
  2020年   997篇
  2019年   1208篇
  2018年   2405篇
  2017年   2480篇
  2016年   2782篇
  2015年   1542篇
  2014年   2440篇
  2013年   4686篇
  2012年   3420篇
  2011年   3748篇
  2010年   3274篇
  2009年   3669篇
  2008年   3600篇
  2007年   3481篇
  2006年   2909篇
  2005年   2335篇
  2004年   2072篇
  2003年   1895篇
  2002年   1815篇
  2001年   1794篇
  2000年   2038篇
  1999年   1869篇
  1998年   3969篇
  1997年   2879篇
  1996年   1980篇
  1995年   1541篇
  1994年   1343篇
  1993年   1363篇
  1992年   1007篇
  1991年   1062篇
  1990年   1090篇
  1989年   1055篇
  1988年   946篇
  1987年   879篇
  1986年   883篇
  1985年   948篇
  1984年   786篇
  1983年   773篇
  1982年   680篇
  1981年   693篇
  1980年   675篇
  1979年   659篇
  1978年   638篇
  1977年   779篇
  1976年   946篇
  1975年   588篇
  1974年   561篇
  1973年   547篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
51.
Protection of Metals and Physical Chemistry of Surfaces - In this work, a universal sorbent has been obtained that works according to the mechanisms of chemisorption and adsorption by impregnating...  相似文献   
52.
Multimedia Tools and Applications - Text-to-picture systems attempt to facilitate high-level, user-friendly communication between humans and computers while promoting understanding of natural...  相似文献   
53.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for...  相似文献   
54.
Strength of Materials - The paper addresses the investigation of high-strain rate compressive behavior of Al foams subjected to impact at the intermediate striking velocity ranged from 40 to...  相似文献   
55.
Potentiometric sensors with plasticized poly(vinyl chloride) membranes based on β-lactam–tetraalkylammonium ion associates sensitive to penicillin antibiotics are proposed. The physicochemical characteristics (solubility product constants and dissociation constants) of active membrane components and the electrode, transport, and selective properties of the membranes of liquidand solid-contact sensors have been studied. The quantitative characteristics of membrane transport (penetrability, ion flux, and transport rate) have been evaluated. The main charge carriers in the membranes and at the membrane/solution interface have been determined from the membrane transport characteristics. The potentiometric sensors are shown to be applicable to the determination of penicillin antibiotics in biological fluids (blood serum and oral fluid) from patients with urinary tract infection.  相似文献   
56.
The authors have developed a procedure and a test bench for studying evolution of various nature physical fields in modeling geomedium fracture by fluids. The test bench performs synchronous recording of macro- and micro-deformation, heat and acoustic emission induced in physical models of geomedium under loading to discontinuity. The experimental procedure has been trialed. The analysis of the synchronized test data allows a conclusion on the existence of time–space relationship between different nature physical fields induced during failure of solids.  相似文献   
57.
58.
59.
Formation and structural transformations of yttrium orthoferrite crystals have been studied using X-ray diffractometry, Mössbauer spectroscopy and transmission electron microscopy combined with electron microdiffraction. Said processes have been studied under heat treatment of glycine-nitrate combustion products. There have been identified formations of three structural yttrium orthoferrite modifications – amorphized hexagonal <h1>-YFeO3 (P63cm) and nanocrystalline hexagonal h2-YFeO3 (P63/mmc), as well as nanocrystalline orthorhombic o-YFeO3 (Pbnm), which are selectively formed depending on available three-dimensional confinements. Based on the analysis of changes in the fluid and size composition formulation, it has been proposed mechanism for formation and transformation of YFeO3 nanocrystals, including growth stage of h2-YFeO3 crystals due to amorphized phase of <h1>-YFeO3 up to critical size of about 15?nm and their subsequent transformation into orthorhombic form o-YFeO3.  相似文献   
60.
The occurrence and distributions of dibenzofurans (DBFs) and benzo[b]naphthofurans were investigated in crude oils from Niger Delta, Nigeria, by gas chromatography-mass spectrometry-mass spectrometry. The distribution of DBFs was characterized by the predominance of C2-dibenzofurans. 4-Methyldibenzofuran was the most abundant among the methyldibenzofurans isomers while dimethyldibenzofuran-2 (DMDBF-2), ethyldibenzofuran-1, DMDBF-3, and DMDBF-6 occurred in higher amounts when compared with other DMDBFs. Among the benzonaphthofurans, the abundance of benzo[b]naphtho[2,1-d]furan was higher than other isomers. The DBFs distributions in the oils were not affected by source facies and depositional environments. However, the DBFs concentrations increased with increasing maturity in oils from ADL and MJO oilfields.  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