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   234604篇
  免费   3923篇
  国内免费   693篇
电工技术   3992篇
综合类   390篇
化学工业   36649篇
金属工艺   11100篇
机械仪表   7659篇
建筑科学   4807篇
矿业工程   2316篇
能源动力   5099篇
轻工业   16832篇
水利工程   3141篇
石油天然气   7856篇
武器工业   32篇
无线电   22998篇
一般工业技术   50401篇
冶金工业   41605篇
原子能技术   6783篇
自动化技术   17560篇
  2021年   2659篇
  2020年   2046篇
  2019年   2410篇
  2018年   4551篇
  2017年   4500篇
  2016年   4875篇
  2015年   3026篇
  2014年   4678篇
  2013年   10458篇
  2012年   7009篇
  2011年   8526篇
  2010年   6968篇
  2009年   7541篇
  2008年   7814篇
  2007年   7622篇
  2006年   6396篇
  2005年   5777篇
  2004年   5124篇
  2003年   5012篇
  2002年   4796篇
  2001年   4822篇
  2000年   4512篇
  1999年   4641篇
  1998年   12417篇
  1997年   8530篇
  1996年   6457篇
  1995年   4717篇
  1994年   4087篇
  1993年   4272篇
  1992年   3156篇
  1991年   3187篇
  1990年   3041篇
  1989年   3025篇
  1988年   3012篇
  1987年   2680篇
  1986年   2706篇
  1985年   3079篇
  1984年   2871篇
  1983年   2722篇
  1982年   2438篇
  1981年   2445篇
  1980年   2518篇
  1979年   2476篇
  1978年   2493篇
  1977年   2709篇
  1976年   3366篇
  1975年   2277篇
  1974年   2153篇
  1973年   2278篇
  1972年   1982篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Power Technology and Engineering - The major results from the survey and geotechnical monitoring during the leveling of the model foundation of the Zagorsk PSP-2 in test site No. 3 are presented....  相似文献   
92.
Chorismate and isochorismate constitute branch-point intermediates in the biosynthesis of many aromatic metabolites in microorganisms and plants. To obtain unnatural compounds, we modified the route to menaquinone in Escherichia coli. We propose a model for the binding of isochorismate to the active site of MenD ((1R,2S, 5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-3-ene-1-carboxylate (SEPHCHC) synthase) that explains the outcome of the native reaction with α-ketoglutarate. We have rationally designed variants of MenD for the conversion of several isochorismate analogues. The double-variant Asn117Arg–Leu478Thr preferentially converts (5S,6S)-5,6-dihydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHD), the hydrolysis product of isochorismate, with a >70-fold higher ratio than that for the wild type. The single-variant Arg107Ile uses (5S,6S)-6-amino-5-hydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHA) as substrate with >6-fold conversion compared to wild-type MenD. The novel compounds have been made accessible in vivo (up to 5.3 g L−1). Unexpectedly, as the identified residues such as Arg107 are highly conserved (>94 %), some of the designed variations can be found in wild-type SEPHCHC synthases from other bacteria (Arg107Lys, 0.3 %). This raises the question for the possible natural occurrence of as yet unexplored branches of the shikimate pathway.  相似文献   
93.
Journal of Communications Technology and Electronics - Approximate formulas for calculating the coefficient of reflection from an artificial magnetic conductor (AMC) based on a capacitive lattice...  相似文献   
94.
The chromium (Cr) evaporation behavior of several different types of iron (Fe)-based AFA alloys and benchmark Cr2O3-forming Fe-based 310 and Ni-based 625 alloys was investigated for 500 h exposures at 800 °C to 900 °C in air with 10% H2O. The Cr evaporation rates from alumina-forming austenitic (AFA) alloys were ~5 to 35 times lower than that of the Cr2O3-forming alloys depending on alloy and temperature. The Cr evaporation behavior was correlated with extensive characterization of the chemistry and microstructure of the oxide scales, which also revealed a degree of quartz tube Si contamination during the test. Long-term oxidation kinetics were also assessed at 800 to 1000 °C for up to 10,000 h in air with 10% H2O to provide further guidance for SOFC BOP component alloy selection.  相似文献   
95.
Power Technology and Engineering - The monitoring of hydraulic structures as high-risk facilities is discussed. Monitoring should ensure the reliability and functioning of a hydraulic structure...  相似文献   
96.
Theoretical Foundations of Chemical Engineering - A choline chloride–sulfosalicylic acid deep eutectic solvent (DES) is proposed for dissolving the oxides Co(II), Cu(II), Zn(II), Fe(III),...  相似文献   
97.
Atomic Energy - The results of calculations and experimental determination of the neutronics characteristics of the IRT-T research reactor are presented. The IRT-T reactor is a pool reactor with...  相似文献   
98.
Journal of Inorganic and Organometallic Polymers and Materials - The reaction of potassium tetracyanocupprate(I) with triethyltin bromide in presence of phenanthroline (Phen) and quinoxaline (Qox)...  相似文献   
99.
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   
100.
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