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   278294篇
  免费   4401篇
  国内免费   1078篇
电工技术   4653篇
综合类   215篇
化学工业   42628篇
金属工艺   8718篇
机械仪表   7717篇
建筑科学   7896篇
矿业工程   866篇
能源动力   7868篇
轻工业   30315篇
水利工程   2322篇
石油天然气   2092篇
武器工业   5篇
无线电   35111篇
一般工业技术   50049篇
冶金工业   52863篇
原子能技术   3617篇
自动化技术   26838篇
  2021年   2174篇
  2020年   1592篇
  2019年   1982篇
  2018年   2978篇
  2017年   2947篇
  2016年   3341篇
  2015年   2523篇
  2014年   4223篇
  2013年   13565篇
  2012年   7641篇
  2011年   10814篇
  2010年   8320篇
  2009年   9321篇
  2008年   10023篇
  2007年   9929篇
  2006年   9179篇
  2005年   8285篇
  2004年   7920篇
  2003年   7775篇
  2002年   7265篇
  2001年   7515篇
  2000年   6719篇
  1999年   7271篇
  1998年   17025篇
  1997年   11889篇
  1996年   9118篇
  1995年   6998篇
  1994年   6189篇
  1993年   5999篇
  1992年   4411篇
  1991年   4047篇
  1990年   3956篇
  1989年   3753篇
  1988年   3613篇
  1987年   2986篇
  1986年   2825篇
  1985年   3592篇
  1984年   3240篇
  1983年   2936篇
  1982年   2696篇
  1981年   2674篇
  1980年   2478篇
  1979年   2385篇
  1978年   2184篇
  1977年   2420篇
  1976年   2969篇
  1975年   1825篇
  1974年   1707篇
  1973年   1783篇
  1972年   1312篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
141.
142.
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   
143.
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   
144.
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   
145.
Ozone measurement based on the optical absorption of visible light at 603 nm using polymer optical fibres is investigated and tested. Comparisons with a commercial UV based sensor demonstrate the ability of the visible based sensor to measure high concentrations over a range 27-127 mg/litre. A resolution of 5 mg/litre is also demonstrated for this sensor.  相似文献   
146.
There will always be a premium on innovation and original approaches to old problems. Engineers and designers are constantly urged to think outside the box. In space shuttle technician Arlene S. Reese's case, she decided to think outside the world of traditional, 2D drafting. Working under tough deadline pressures for a shuttle lighting installation project, Reese and her design team decided to blend digital photographs and 3D assemblies to show other contractors precisely where and how the job should be built. The result was a faster, more effective method for planning electrical projects that has earned awards for her team and continues to produce benefits for the National Aeronautics and Space Administration (NASA). Reese and the managers at NASA say the design method can apply to many architectural and engineering disciplines.  相似文献   
147.
148.
High cycle fatigue of bolted connections Extensive tests regarding the influences on the fatigue of bolt‐nut‐connections of preloading with torsion, of preloading with yielding, of loading with superimposed bending and of the tested lot are processed. These influences are not yet known according to VDI 2230. New testing devices were designed for these tests, which allow a far less expensive operation and may easily be used for bolts of diameters up to M100 and testing frequencies up to 1000 Hz. The validity of fatigue resistance according to VDI 2230 is specified with respect to the test results. The determined influence of the tested lots is unexpectedly high. The manufacturing process of bolts should be improved to minimize this influence.  相似文献   
149.
Bioavailability and Toxicity of Metal Nutrients during Anaerobic Digestion   总被引:1,自引:0,他引:1  
This paper investigates the effect of chelating agents on the bioavailability of Fe and Cu during anaerobic digestion. The results on metal speciation and methane production in anaerobic serum bottles showed that biomass was able to grow in the presence of citrate 1?mM and nitrilotriacetic acid (NTA) 1?mM, suggesting that the binding sites at the cell surface competed efficiently for the metals with the chelating agents added. The presence of free ethylenediaminetetraacetic acid 1?mM inhibited methanogenesis, and this seemed to be related to a loss in metal uptake capacity. Although the addition of soluble microbial products (SMP) did not change metal distribution in anaerobic systems, it caused an increase in the rate of methane production, and it is believed that direct uptake of Cu-SMP complexes was responsible for this increase. The best protection against Cu toxicity occurred when stoichiometric amounts of NTA, which should complex and solubilize most of the Cu, was added, and it is likely that NTA prevented lethal concentrations of Cu from being adsorbed onto the cell and hence internalized.  相似文献   
150.
Networkable Windows-based operating system devices present information security challenges to both vendors and users of such devices. This article highlights some of those threats and offers measures to improve the link between a firm's business strategy, its operational activities, and its information security strategy.  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