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   1422篇
  免费   28篇
  国内免费   2篇
电工技术   3篇
化学工业   167篇
金属工艺   11篇
机械仪表   11篇
建筑科学   19篇
矿业工程   2篇
能源动力   14篇
轻工业   152篇
水利工程   8篇
石油天然气   10篇
无线电   30篇
一般工业技术   83篇
冶金工业   902篇
自动化技术   40篇
  2023年   7篇
  2022年   25篇
  2021年   33篇
  2020年   20篇
  2019年   24篇
  2018年   30篇
  2017年   28篇
  2016年   25篇
  2015年   15篇
  2014年   24篇
  2013年   21篇
  2012年   24篇
  2011年   35篇
  2010年   19篇
  2009年   35篇
  2008年   23篇
  2007年   29篇
  2006年   18篇
  2005年   10篇
  2004年   12篇
  2003年   10篇
  2002年   15篇
  2001年   10篇
  2000年   9篇
  1999年   28篇
  1998年   249篇
  1997年   152篇
  1996年   113篇
  1995年   62篇
  1994年   42篇
  1993年   55篇
  1992年   8篇
  1991年   14篇
  1990年   6篇
  1989年   11篇
  1988年   13篇
  1987年   5篇
  1986年   12篇
  1985年   16篇
  1984年   4篇
  1983年   2篇
  1982年   15篇
  1981年   9篇
  1980年   9篇
  1979年   3篇
  1978年   4篇
  1977年   25篇
  1976年   91篇
  1974年   1篇
  1955年   1篇
排序方式: 共有1452条查询结果,搜索用时 15 毫秒
81.
In computer and electronic manufacturing, it is very important to be able to automatically check whether the surface mounted devices (SMD) are correctly placed on the printed circuit boards. The inspection of these boards has to be done on a shop floor, where statistical characteristics of the noise vary so much that, in essence, we only have interval estimates for this noise.We show that under this interval uncertainty, the optimal image processing technique consists of using Haar wavelets. Wavelets indeed lead to much better results than previously used Fourier transform techniques.On a more fundamental level, our result is a step towards solving an important problem related to wavelets: that wavelet transforms often empirically work much better than other methods, but there are very few theoretical explanations of this efficiency. Our results shows that, probably, such a theoretical explanation can be obtained if we take interval uncertainty into consideration.  相似文献   
82.
83.
Small amounts of Li2O result in sintering in the AIN-Y2O3-CaO and AIN-CaO systems at firing temperatures <1600°C. The effect is ascribed to reduction of the liquidus temperature. Furthermore, Li2O is removed by volatization at temperatures from 1300° to 1600°C, and its content decreases several ppm from the initial 0.3 wt%. Li2O-doped AIN specimens containing Y2O3 and CaO additives are well densified by firing at 1600°C for 6 h, and their thermal conductivity is 135 W.m−1.K−1.The effect of Li2O addition on sintering and thermal conductivity also is discussed through thermo-dynamic considerations.  相似文献   
84.
85.
86.
Analysis of amino acids is complicated by treatment with ampicillin. High voltage electrophoresis, which is convenient for the qualitative assessment of metabolic diseases, yields smears of ampicillin that mask the bands of citrulline, homocitrulline, phenylalanine, cystine, and homocystine. The addition of penicillinase prior to high voltage electrophoresis eliminates ampicillin and other penicillins and reveals these key amino acids.  相似文献   
87.
88.
89.
SUMMARY Poly(amide-ester)s, poly(amide-carbonate)s and poly(amide-thiocarbonate)s derived from the diphenols-amides N-(2,6-dibromo-4-nitrophenyl)-4,4-bis(4-hydroxyphenyl)-pentanamide (I) and N-(2,6-diiodo-4-nitrophenyl)-4,4-bis(4-hydroxyphenyl)-pentanamide (II) and terephthaloyl chloride (a), isophthaloyl chloride (b), and adipoyl chloride (c), and phosgene (d) and thiophosgene (e) respectively, have been synthesized under phase transfer conditions using several quaternary ammonium salts as phase transfer catalysts. Benzyltriethylammonium chloride (BTEAC) was effective in practically all cases due to the hydrophilicity of this catalyst. Poly(amido-ester)s derived from II and aromatic diacids were insoluble in all the organic solvents, and the effectivity of the process was evaluated by the increase of the yields with respect to the essays without catalysts. Received: 26 January 1999/Revised version: 17 May 1999/Accepted: 17 May 1999  相似文献   
90.
Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were used in 2 replicated 4 × 4 Latin squares to quantify effects of supplementing protein as urea, solvent soybean meal (SSBM), cottonseed meal (CSM), or canola meal (CM) on omasal nutrient flows and microbial protein synthesis. All diets contained (% of dry matter) 21% alfalfa silage and 35% corn silage plus 1) 2% urea plus 41% high-moisture shelled corn (HMSC), 2) 12% SSBM plus 31% HMSC, 3) 14% CSM plus 29% HMSC, or 4) 16% CM plus 27% HMSC. Crude protein was equal across diets, averaging 16.6%. The CSM diet supplied the least rumen-degraded protein and the most rumen-undegraded protein. Microbial nonammonia N flow was similar among the true protein supplements but was 14% lower in cows fed urea. In vivo ruminal passage rate, degradation rate, and estimated escape for the 3 true proteins were, respectively, 0.044/h, 0.105/h, and 29% for SSBM; 0.051/h, 0.050/h, and 51% for CSM; and 0.039/h, 0.081/h, and 34% for CM. This indicated that CSM protein was less degraded because of both a faster passage rate and slower degradation rate. Omasal flow of individual AA, branched-chain AA, essential AA, nonessential AA, and total AA all were lower in cows fed urea compared with one of the true protein supplements. Among the 3 diets supplemented with true protein, omasal flow of Arg was greatest on CSM, and omasal flow of His was greatest on CSM, intermediate on CM, and lowest on SSBM. Lower flows of AA and microbial nonammonia N explained lower yields of milk yield and milk components observed on the urea diet in the companion lactation trial. These results clearly showed that supplementation with true protein was necessary to obtain sufficient microbial protein and rumen-undegraded protein to meet the metabolizable AA requirements of high-producing dairy cows.  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