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   699882篇
  免费   7865篇
  国内免费   1511篇
电工技术   12829篇
综合类   572篇
化学工业   109118篇
金属工艺   28420篇
机械仪表   22260篇
建筑科学   16114篇
矿业工程   5082篇
能源动力   18066篇
轻工业   57106篇
水利工程   8318篇
石油天然气   16714篇
武器工业   43篇
无线电   75565篇
一般工业技术   141571篇
冶金工业   122965篇
原子能技术   17127篇
自动化技术   57388篇
  2021年   6471篇
  2019年   6195篇
  2018年   10645篇
  2017年   10867篇
  2016年   11393篇
  2015年   7149篇
  2014年   12134篇
  2013年   32232篇
  2012年   18924篇
  2011年   25576篇
  2010年   20603篇
  2009年   22989篇
  2008年   23223篇
  2007年   22998篇
  2006年   19906篇
  2005年   18133篇
  2004年   17315篇
  2003年   16931篇
  2002年   16195篇
  2001年   15870篇
  2000年   15341篇
  1999年   15262篇
  1998年   35972篇
  1997年   25950篇
  1996年   20279篇
  1995年   15384篇
  1994年   13937篇
  1993年   13577篇
  1992年   10490篇
  1991年   10154篇
  1990年   9911篇
  1989年   9705篇
  1988年   9346篇
  1987年   8358篇
  1986年   8091篇
  1985年   9274篇
  1984年   8447篇
  1983年   8046篇
  1982年   7187篇
  1981年   7390篇
  1980年   6989篇
  1979年   7143篇
  1978年   7027篇
  1977年   7851篇
  1976年   10012篇
  1975年   6262篇
  1974年   6030篇
  1973年   6106篇
  1972年   5171篇
  1971年   4863篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
The worldwide proliferation of fraudulent materials has brought about the need for a new approach to the control of purchased material quality. Nuclear power, defense, aerospace and many other industries are affected by the supply of poor quality clones that presume to be original replacement parts. Safety considerations abound as these highly defective materials are used in systems that are critical to the preservation of human lives. Commonly utilized quality assurance programs have not effectively stopped the influx of fraudulent materials. These programs fail to concentrate inspection efforts on materials and inspection attributes that would effectively prevent the acceptance of fraudulent materials. herein a solution is presented to this problem in the form of an expert system application. Information commonly available in industry is formulated into a knowledge based system wherein advisories are given to the user regarding key purchased material receipt inspection strategies.  相似文献   
982.
983.
Self-pulsation at 45 GHz repetition frequency has been demonstrated in 1.5 /spl mu/m monolithic single-section quantum dot Fabry-Perot semiconductor lasers without saturable absorber. The mode-beating exhibits a narrow linewidth below 100 kHz, demonstrating high phase correlation between these modes. Such modelocked lasers open ways to low timing-jitter components for clock recovery or millimetre-wave generation in wireless transmission applications.  相似文献   
984.
The kinetics of electronic processes in vidicon phototargets based on semiconductor-insulator structures with a narrow-gap semiconductor is considered taking into account charge drain in the insulator layer and relaxation of the nonequilibrium depletion region in the semiconductor layer. The integration time, threshold sensitivity, and resolution at various intensities of incident radiation are estimated.  相似文献   
985.
986.
Ellagic acid (2, 3, 7, 8‐tetrahydroxy(1)benzopyrano(5, 4, 3‐cde)(1)benzopyran‐5, 10‐dione) was selected as a model pollutant which is present in the tannic fraction of cork processing wastewater. The ultrafiltration of aqueous ellagic acid solutions through three membranes was studied in tangential UF laboratory equipment. Two of the membranes were polyethersulfone (Biomax10K and Biomax5K, with MWCO of 10000 and 5000 Da, respectively), and the third made of regenerated cellulose (Ultracel5K, with MWCO of 5000 Da). The water hydraulic permeability was evaluated for each membrane. The evolution of the permeate flow rate with processing time was followed, and the influence of the main operating variables (feed flow rate, trans‐membrane pressure and nature of the membranes) on the permeate flux was also established. According to the hypothesis of the film theory, the intrinsic and apparent rejection coefficients, as well as the mass transfer coefficients, were also determined, and the values obtained were discussed as a function of the operating conditions used.  相似文献   
987.
988.
989.
This article presents the development of a ceramic micro heat exchanger. Starting from its geometrical design, results obtained from a simplified simulation of the heat exchanger efficiency will be given. The alumina microcomponents were manufactured by a rapid prototyping process chain. Here, stereolithography was combined with a low‐pressure injection molding process for the rapid and precise manufacturing of ceramic components down to the micrometer range. A micro heat exchanger, joined from sintered components using a glass solder, was applied as a prototype and checked for its performance at a system pressure of 8 bar.  相似文献   
990.
The main purpose of this study was to evaluate the performance of the electrochemical oxidation process as a post-treatment for the effluents of a bench-scale UASB reactor treating simulated wastewater from an unbleached pulp plant. The oxidation process was performed using a single compartment cell with two plates as electrodes. The anode was made of Ti/Ru0.3Ti0.7O2 and the cathode of stainless steel. The following variables were evaluated: current density (75, 150 and 225 mA cm(-2)) and recirculation flow rate in the electrochemical cell (0.22, 0.45 and 0.90 L h(-1)). The increase in current density from 75 to 225 mA cm(-2) did not increased the color removal efficiency for the tested flow rates, 0.22, 0.45 and 0.90 L h(-1), however the energy consumption increased significantly. The results indicated the technical feasibility of the electrochemical treatment as post-treatment for UASB reactors treating wastewaters from pulp and paper plants.  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