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   33579篇
  免费   4387篇
  国内免费   1983篇
电工技术   2125篇
综合类   2395篇
化学工业   6557篇
金属工艺   7515篇
机械仪表   1935篇
建筑科学   1810篇
矿业工程   1332篇
能源动力   860篇
轻工业   861篇
水利工程   364篇
石油天然气   1077篇
武器工业   425篇
无线电   2643篇
一般工业技术   4751篇
冶金工业   3425篇
原子能技术   237篇
自动化技术   1637篇
  2024年   195篇
  2023年   643篇
  2022年   1016篇
  2021年   1162篇
  2020年   1370篇
  2019年   1059篇
  2018年   994篇
  2017年   1379篇
  2016年   1355篇
  2015年   1436篇
  2014年   2020篇
  2013年   1945篇
  2012年   2401篇
  2011年   2620篇
  2010年   1878篇
  2009年   1935篇
  2008年   1723篇
  2007年   2266篇
  2006年   2171篇
  2005年   1700篇
  2004年   1510篇
  2003年   1331篇
  2002年   1149篇
  2001年   1006篇
  2000年   812篇
  1999年   591篇
  1998年   443篇
  1997年   317篇
  1996年   296篇
  1995年   233篇
  1994年   189篇
  1993年   153篇
  1992年   141篇
  1991年   123篇
  1990年   90篇
  1989年   98篇
  1988年   31篇
  1987年   24篇
  1986年   25篇
  1985年   18篇
  1984年   15篇
  1983年   13篇
  1982年   16篇
  1981年   15篇
  1980年   7篇
  1979年   8篇
  1977年   3篇
  1975年   7篇
  1974年   4篇
  1951年   5篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
The corrosion behavior of pure aluminum in inhibited and uninhibited 4 MKOH was investigated by means of hydrogen collection, polarization curve measurement and electrochemical impedance spectroscopy (EIS). The results showed that the corrosion of pure aluminum was greatly inhibited by the addition of ZnO and dimethyl amine epoxy propane (designated as DE). EIS and EDAX analyses revealed that ZnO produces its effect by depositing on the aluminum surface, which increases the overpotential of hydrogen evolution. It was also found that the addition of DE could greatly improve the deposition of zinc layers.  相似文献   
82.
One-sided auctions are used for market clearing in the spot markets for perishable goods because production cost in spot markets is already “sunk.” Moreover, the promptness and simplicity of one-sided auctions are beneficial for trading in perishable goods. However, sellers cannot participate in the price-making process in these auctions. A standard double auction market collects bids from traders and matches the higher bids of buyers and lower bids of sellers to find the most efficient allocation, assuming that the value of unsold items remains unchanged. Nevertheless, in the market for perishable goods, sellers suffer a loss when they fail to sell their goods, because their salvage values are lost when the goods perish. To solve this problem, we investigate the suitable design of an online double auction for perishable goods, where bids arrive dynamically with their time limits. Our market mechanism aims at improving the profitability of traders by reducing trade failures in the face of uncertainty of incoming/departing bids. We develop a heuristic market mechanism with an allocation policy that prioritizes bids of traders based on their time-criticality, and evaluate its performance experimentally using multi-agent simulation. We find out that our market mechanism realizes efficient and fair allocations among traders with approximately truthful behavior in different market situations.  相似文献   
83.
Preparation of Aluminum Nitride Powder from Aluminum Polynuclear Complexes   总被引:2,自引:0,他引:2  
AIN powder was synthesized from aluminum polynuclear complexes. Basic aluminum chloride and basic aluminum lactate were used as the aluminum polynuclear complexes. These starting materials and glucose were dissolved in water and mixed homogeneously. AIN powder was obtained by calcining after drying and precalcining at 800°C under nitrogen gas flow. Then excess carbon was removed by firing in air. Nitridation in the system was investigated and compared with that in the alumina–carbon black system. It was found that in our reaction system nitridation began and proceeded at lower calcination temperatures above 1200°C than in the alumina–carbon black system. Using aluminum polynuclear complexes, AIN was synthesized through the nitridation of γ-alumina and produced in a very fine and sharp particle size distribution.  相似文献   
84.
扩展双星树(T(n)n1,n2)是 n-1长路径的两端点分别联结 n1条悬挂边和 n2条悬挂边所得到的图。论文根据扩展双星树的结构特征,研究了扩展双星树的类Wiener指数,给出了一般计算公式。  相似文献   
85.
Indium tin oxide‐coated thin films (200 nm) are deposited on glass substrates by using R.f. sputtering technique. Here, we investigate the influence of new technique of treatment, which is called as “oil thermal annealing” on the nano‐structured indium tin oxide thin films at fixed temperature (150 °C) which improves adhesion strength, electrical conductivity and optical properties (transmittance) of the films. Oil thermal annealing is used to reduce inherent defects that may be introduced during the prepared thin film and cooling processes. Proposed technique is highly suitable for liquid crystal displays, solar cells and organic light emitting diodes, and many other display‐related applications.  相似文献   
86.
Proton exchanged ultrastable Y-type zeolite with silica/alumina = 40 showed a pronounced catalytic activity for the formation of ethyl methyl ketone directly from 1-butene and water. The formation rate of ethyl methyl ketone was much higher than those on MoO3-based catalysts in the oxidation of 1-butene by oxygen. It was suggested that the basic site necessary for the formation of ethyl ketone directly from 1-butene and water would be the pentacoordinated Al.  相似文献   
87.
A novel double suction shaft-less mini pump was developed for heat control of small energy systems in this study.The mini pump impeller with an exit diameter of 40 mm was combined with the motor rotor supported by the hybrid dynamic bearing.The specific speed of the pump was 125 min-1 m3 min-1 m.The hydraulic performance of the pump was investigated experimen-tally under four rotational speeds.From the test results,it was recognized that the pump could provide a flow discharge of 5 L/min and head of 1.5 m,w...  相似文献   
88.
工业纯铝在模拟海水中的电化学腐蚀行为   总被引:1,自引:0,他引:1  
为研究铝在海水中的腐蚀过程,采用电化学阻抗谱、浸泡试验、扫描电子显微镜研究工业纯铝在模拟海水中的腐蚀行为.结果表明:铝在模拟海水中发生点蚀的区域为富含Fe的晶间化合物处,点蚀半径随时间的增加而扩大.铝在模拟海水中的溶解曲线分为4个区间:活性溶解区、过渡区、过钝化区、钝化区.铝在模拟海水中,极化电位为过钝化区时,转移电阻R t随着电位的升高而变小,铝发生严重的点蚀;而极化电位为钝化区时,铝的转移电阻R t随着电位的升高基本不变,铝的溶解行为受到抑制.工业纯铝在模拟海水中发生点蚀的电位区间是-0.45~-0.65 V,钝化电位区间为-0.75~-0.85 V.  相似文献   
89.
为了解决目前煤矿瓦斯事故以及大量使用天然气的家庭安全、环境污染等问题,设计并开发了一种具有集成化、微型化的红外多气体检测系统,通过实验数据的测试对比和数据分析,这种系统达到了微功耗、微体积、宽量程、高分辨率等技术要求,且能集成多气体检测的微型检测系统.重点介绍了红外检测的光学原理,以及从单气体检测引入到集成多气体检测的设计思想和方法,并介绍了有关CAN总线的数据传输方式和无线数据通信方式在系统中的应用.  相似文献   
90.
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