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   172566篇
  免费   3493篇
  国内免费   1603篇
电工技术   4159篇
技术理论   4篇
综合类   1573篇
化学工业   27997篇
金属工艺   7003篇
机械仪表   6123篇
建筑科学   5951篇
矿业工程   933篇
能源动力   4442篇
轻工业   18588篇
水利工程   1472篇
石油天然气   1930篇
武器工业   125篇
无线电   22836篇
一般工业技术   31437篇
冶金工业   24722篇
原子能技术   2554篇
自动化技术   15813篇
  2021年   1559篇
  2020年   1145篇
  2019年   1380篇
  2018年   1657篇
  2017年   1801篇
  2016年   1808篇
  2015年   1819篇
  2014年   2718篇
  2013年   7737篇
  2012年   4436篇
  2011年   5914篇
  2010年   4816篇
  2009年   5377篇
  2008年   5768篇
  2007年   6014篇
  2006年   5417篇
  2005年   5093篇
  2004年   4667篇
  2003年   4544篇
  2002年   4604篇
  2001年   4529篇
  2000年   4258篇
  1999年   4319篇
  1998年   7118篇
  1997年   5635篇
  1996年   4833篇
  1995年   4041篇
  1994年   3651篇
  1993年   3379篇
  1992年   2940篇
  1991年   2814篇
  1990年   2706篇
  1989年   2712篇
  1988年   2512篇
  1987年   2195篇
  1986年   2134篇
  1985年   2570篇
  1984年   2329篇
  1983年   2200篇
  1982年   2074篇
  1981年   1999篇
  1980年   1864篇
  1979年   1875篇
  1978年   1770篇
  1977年   2085篇
  1976年   2562篇
  1975年   1583篇
  1974年   1430篇
  1973年   1453篇
  1972年   1196篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
61.
Some of the factors affecting cloud point determination of palm oleins are described. These are the type of container used, method of stirring, rate of stirring and bath temperature. The repeatability and reproducibility standard deviations of the method are determined from collaborative trials. Recommendations for the test are made to reduce the large variations among laboratories.  相似文献   
62.
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   
63.
An innovative method for modelling biological processes under anaerobic conditions is presented and discussed. The method is based on titrimetric and off-gas measurements. Titrimetric data is recorded as the addition rate of hydroxyl ions or protons that is required to maintain pH in a bioreactor at a constant level. An off-gas analysis arrangement measures, among other things, the transfer rate of carbon dioxide. The integration of these signals results in a continuous signal which is solely related to the biological reactions. When coupled with a mathematical model of the biological reactions, the signal allows a detailed characterisation of these reactions, which would otherwise be difficult to achieve. Two applications of the method to the enhanced biological phosphorus removal processes are presented and discussed to demonstrate the principle and effectiveness of the method.  相似文献   
64.
The US Centers for Disease Control and Prevention (CDC) created the Public Health Information Network to advance fully capable, interoperable information systems in public health organizations. PHIN prioritizes public health information systems' functional requirements, capabilities, performance measures, and operational characteristics while letting the architects of those systems choose enabling approaches, methods, and concepts to meet the requirements. PHIN also provides a certification process for public health administrators to evaluate their information infrastructure's quality. The certification process is important because affected organizations often depend on certification for continued funding.  相似文献   
65.
66.
The IBM RISC System/6000, a superscalar microprocessor, is presented. The architecture of this processor has its instruction set specifically designed for a superscalar machine containing three independent units-branch, fixed-point, and floating-point. The design also emphasizes high-performance floating-point operations. The design principles are to offer maximum overlap of the three functional units, avoid dead cycles, and define instructions that can (for the most part) be completed at a rate of one per cycle. The branch cycle, fixed- and floating-point units, cache management, and performance are described. Benchmark results are given  相似文献   
67.
A Rate-Control vaginal device was developed which overcomes the low bioavailability and unpredictable Q - t1/2 type release and absorption rate profiles of flurogestone acetate delivered by the currently marketed Syncro-Mate pessary.

The in vitro release and vaginal absorption profiles from the Rate-Control vaginal device were run simultaneously, a linear Q - t relationship was obtained with a significant improvement in bioavailability. A mathematical model was developed to correlate the in vitro drug release and the vaginal absorption profiles of flurogestone acetate from the vaginal devices.

The design, development and the simultaneous release and absorption profiles of flurogestone acetate from this new vaginal device were outlined and discussed.  相似文献   
68.
Ion-beam sputter-deposited alloy films of Co/sub 74/Fe/sub 6/B/sub 15/Si/sub 5/ and Fe/sub 75/Ni/sub 5/B/sub 15/Si/sub 5/ were examined for their magnetic and structural properties. Films were characterized by ferromagnetic resonance, vibrating sample magnetometry, and extended X-ray absorption fine structure (EXAFS) analysis. Using atomic parameters deduced from EXAFS modeling and fitting procedures, magnetic properties were calculated with no adjustable parameters. Correlation between perpendicular FMR measurements and EXAFS first-shell modeling suggests a low-temperature formation of cobalt-borides in the Co/sub 74/Fe/sub 6/B/sub 15/Si/sub 5/ alloy. Annealed Fe/sub 75/Ni/sub 5/B/sub 15/Si/sub 5/ samples did not display evidence of structural and/or magnetic instabilities until the onset of long-range crystallization near T/sub ann/=400 degrees C.<>  相似文献   
69.
A Brachiaria breeding project is being conducted at CIAT, Colombia to combine acid soil adaptation of B. decumbens with other favourable traits of Brachiaria species that are less adapted to acid soils. Micro-PIXE was applied to investigate nutrient uptake and distribution in root tips of different species grown in hydroponic culture under control and simulated acid soil stress conditions. Different sample measurement approaches were evaluated, including: (1) linear scans with single point measurements along the root axis; (2) mapping of whole root tips; and (3) mapping of root cross sections. Different tissue types could be distinguished on the base of differences in nutrient concentrations and/or Al stress. Al, if supplied under nutrient stress conditions, increased P accumulation in the central vascular tissue of the meristematic and elongation zone of B. decumbens and B. brizantha. Furthermore, a negative correlation was found between Al and Cl accumulation in the root cap of B. decumbens.  相似文献   
70.
A new method is presented for arbitrarily assigning the closed-loop poles of a linear multi-input/multi-output system using linear output feedback. The method employs a new notion of rank-one system representations and involves the use of state transformation matrices which preserve such representations while reducing the degree of the feedforward matrix  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