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   175982篇
  免费   2502篇
  国内免费   687篇
电工技术   3411篇
综合类   199篇
化学工业   29388篇
金属工艺   6262篇
机械仪表   5358篇
建筑科学   5487篇
矿业工程   653篇
能源动力   4515篇
轻工业   18861篇
水利工程   1329篇
石油天然气   834篇
武器工业   5篇
无线电   22062篇
一般工业技术   32473篇
冶金工业   29230篇
原子能技术   2569篇
自动化技术   16535篇
  2021年   1151篇
  2019年   1145篇
  2018年   1469篇
  2017年   1475篇
  2016年   1720篇
  2015年   1418篇
  2014年   2351篇
  2013年   8034篇
  2012年   4044篇
  2011年   5705篇
  2010年   4427篇
  2009年   5041篇
  2008年   5679篇
  2007年   5853篇
  2006年   5233篇
  2005年   4874篇
  2004年   4683篇
  2003年   4533篇
  2002年   4547篇
  2001年   4420篇
  2000年   4088篇
  1999年   4087篇
  1998年   7035篇
  1997年   5611篇
  1996年   4884篇
  1995年   4101篇
  1994年   3773篇
  1993年   3581篇
  1992年   3178篇
  1991年   2930篇
  1990年   2992篇
  1989年   2966篇
  1988年   2759篇
  1987年   2540篇
  1986年   2434篇
  1985年   2942篇
  1984年   2736篇
  1983年   2546篇
  1982年   2398篇
  1981年   2261篇
  1980年   2118篇
  1979年   2197篇
  1978年   2035篇
  1977年   2295篇
  1976年   2761篇
  1975年   1803篇
  1974年   1621篇
  1973年   1653篇
  1972年   1342篇
  1971年   1214篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This paper describesMicroScope, a framework for developing analysis tools for Lisp programs. MicroScope uses a knowledge-intensive approach for program representation and analysis. The analysis tools share a common object oriented program database, and a common Prolog inference engine. The use of Prolog and a declarative representation for programs permits sharing of information, and provides high bandwidth communication between diverse analysis tools. It also supports program specification and debugging activities in the same framework. Extensions to Prolog to support analysis are described, and two tools, theCritic and theExpector, are presented.This work supported in part by Hewlett-Packard Company, the National Science foundation Under Grant Number MCS81-21750 and the Defense Advanced Research Projects Agency under contract number DAAK11-84-K-0017.  相似文献   
62.
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   
63.
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   
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