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   325673篇
  免费   4529篇
  国内免费   992篇
电工技术   5547篇
综合类   787篇
化学工业   49802篇
金属工艺   12443篇
机械仪表   9439篇
建筑科学   7756篇
矿业工程   2220篇
能源动力   7147篇
轻工业   27746篇
水利工程   3746篇
石油天然气   7135篇
武器工业   20篇
无线电   33197篇
一般工业技术   60224篇
冶金工业   69154篇
原子能技术   7704篇
自动化技术   27127篇
  2021年   2208篇
  2018年   4151篇
  2017年   4322篇
  2016年   4963篇
  2015年   3263篇
  2014年   4673篇
  2013年   12501篇
  2012年   8837篇
  2011年   11565篇
  2010年   8224篇
  2009年   9394篇
  2008年   9545篇
  2007年   9437篇
  2006年   8390篇
  2005年   10507篇
  2004年   9277篇
  2003年   8536篇
  2002年   7452篇
  2001年   7225篇
  2000年   6439篇
  1999年   6754篇
  1998年   19763篇
  1997年   14120篇
  1996年   10607篇
  1995年   7694篇
  1994年   6795篇
  1993年   6708篇
  1992年   4679篇
  1991年   4686篇
  1990年   4530篇
  1989年   4521篇
  1988年   4477篇
  1987年   3780篇
  1986年   3755篇
  1985年   4300篇
  1984年   4023篇
  1983年   3688篇
  1982年   3532篇
  1981年   3724篇
  1980年   3592篇
  1979年   3416篇
  1978年   3531篇
  1977年   4457篇
  1976年   6195篇
  1975年   3241篇
  1974年   3038篇
  1973年   3062篇
  1972年   2681篇
  1971年   2507篇
  1970年   2134篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Application of brown titanium dioxide (TiO2-x) and its modified composite forms in the photocatalytic decomposition of organic pollutants in the environment is a promising way to provide solutions for environmental redemption. Herein, we report the synthesis of effective and stable TiO2-x nanoparticles with g-C3N4, RGO, and multiwalled carbon nanotubes (CNTs) using a simple hydrothermal method. Among all the as-synthesized samples, excellent photocatalytic degradation activity was observed for RGO-TiO2-x nanocomposite with high rate constants of 0.075 min?1, 0.083 min?1 and 0.093 min?1 for methylene blue, rhodamine-B, and rosebengal dyes under UV–Visible light irradiation, respectively. The altered bandgap (1.8 eV) and the large surface area of RGO-TiO2-x nanocomposite impacts on both absorption of visible light and efficiency of photogenerated charge electron (e?)/hole (h+) pair separation. This resulted in enhanced photocatalytic property of carbon-based TiO2-x nanocomposites. A systematic study on the influence of different carbon nanostructures on the photocatalytic activity of brown TiO2-x is carried out.  相似文献   
82.
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical...  相似文献   
83.
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   
84.
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   
85.
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   
86.
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   
87.
We deal with the mathematical model of the incremental degradation of the internal coating (e.g. a polymeric material) of a metallic pipe in which a fluid flows relatively fast. The fluid drags solid impurities so that longitudinal scratches, inaccessible to any direct inspection procedure, are produced on the coating. Time evolution of this kind of defects can be reconstructed from the knowledge of a sequence of temperature maps of the external surface. The time-varying orthogonal section of this damaged interface is determined as a function of time and polar angle through the identification of a suitable effective heat transfer coefficient by means of Thin Plate Approximation.  相似文献   
88.
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   
89.
90.
The failure of frontline antibiotics in the clinic is one of the most serious threats to human health and requires a multitude of novel therapeutics and innovative approaches to treatment so as to curtail the growing crisis. In addition to traditional resistance mechanisms resulting in the lack of efficacy of many antibiotics, most chronic and recurring infections are further made tolerant to antibiotic action by the presence of biofilms. Herein, we report an expanded set of 5-benzylidene-4-oxazolidinones that are able to inhibit the formation of Staphylococcus aureus biofilms, disperse preformed biofilms, and, in combination with common antibiotics, are able to significantly reduce the bacterial load in a robust collagen-matrix model of biofilm infection.  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