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   203574篇
  免费   2288篇
  国内免费   655篇
电工技术   4133篇
综合类   131篇
化学工业   27834篇
金属工艺   7691篇
机械仪表   5624篇
建筑科学   4155篇
矿业工程   753篇
能源动力   5087篇
轻工业   14899篇
水利工程   1758篇
石油天然气   2925篇
武器工业   9篇
无线电   27928篇
一般工业技术   38596篇
冶金工业   46104篇
原子能技术   3611篇
自动化技术   15279篇
  2021年   1476篇
  2020年   1136篇
  2019年   1461篇
  2018年   2389篇
  2017年   2332篇
  2016年   2385篇
  2015年   1632篇
  2014年   2826篇
  2013年   8378篇
  2012年   4684篇
  2011年   6386篇
  2010年   5141篇
  2009年   5991篇
  2008年   6353篇
  2007年   6349篇
  2006年   5786篇
  2005年   5395篇
  2004年   5328篇
  2003年   5169篇
  2002年   4966篇
  2001年   5359篇
  2000年   4982篇
  1999年   5509篇
  1998年   15812篇
  1997年   10442篇
  1996年   8046篇
  1995年   5870篇
  1994年   5086篇
  1993年   5098篇
  1992年   3441篇
  1991年   3319篇
  1990年   3263篇
  1989年   3095篇
  1988年   2823篇
  1987年   2274篇
  1986年   2351篇
  1985年   2670篇
  1984年   2359篇
  1983年   2118篇
  1982年   1957篇
  1981年   2097篇
  1980年   1839篇
  1979年   1702篇
  1978年   1682篇
  1977年   2059篇
  1976年   2746篇
  1975年   1439篇
  1974年   1395篇
  1973年   1339篇
  1972年   1130篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Summary The current article deals with the initial developments of the use of a continuous plug flow reactor using an original heterogeneous catalyst system for the living coordinated anionic polymerization of certain oxygenated rings. This reactor is designed in order to maintain the essential characteristics of the original batch system. One of the pertinent parameters considered here is the residence time of the reactants inside the reactor. The column has been used to investigate ethylene oxide and -caprolactone oligomerization. Initial experiments have pointed out how the molecular weights can depend on the flow rate for a fixed bed length. Some theoretical problems relative to the reactive column are discussed in order to investigate more in depth the properties of this original continuous process and to model it to find the optimal working conditions.  相似文献   
952.
Flavor and oxidative stabilities were studied by organoleptic evaluation and chemical analysis of three different samples of soybean oil: unhydrogented (I); hydrogenated with nickel catalyst (II); and hydrogenated with copper-chromium catalyst (III). Analyses for these oils were: I II III iodine Value 138 109 113 Linolenate, % 8.3 3.3 0.4 Each oil was deodorized with the addition of either citric acid alone or citric acid plus BHA and BHT antioxidants. Addition of antioxidants did not improve the flavor stabilities of the oils in accelerated storage tests but did improve the flavor stabilities of II and III in light exposure tests. All three oils that received the same additive treatment had equivalent flavor stability in both accelerated storage and light exposure tests. However, both hydrogenation and antioxidant treatment improved oxidative stability as measured by the Active Oxygen Method. There was good correlation between flavor score and the logarithm of the peroxide value determined at the time of tasting. Presented at the AOCS Meeting, New York, May 1977.  相似文献   
953.
954.
Total lipid and phospholipid contents of liver, skin and depot fat from yearling hen turkeys have been studied. Liver lipid averaged 88.5 mg/g wet tissue; skin, 385.0 and depot fat, 753.5. Phospholipids comprised 32.05% of total lipid of liver, but only 0.81% of skin and 0.46% of depot fat. Fatty acids of liver differed from those of skin or depot fat by larger amounts of 16∶0, 18∶0, 20∶4, 22∶0 and 24∶0, and smaller amounts of 16∶1, 18∶1, 18∶2, 18∶3 and 20∶0. Similarity existed between skin and depot fat. Journal Paper No. J-6473 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 1696.  相似文献   
955.
Thin layer chromatography was adapted for direct quantitative estimation of sucrose esters of palmitic acid. Urea-phosphoric acid spray was used to detect the sucrose moiety of the various esters. The photometrically metermined density density of each spot on the thin layer plate was found to be proportional to its sucrose content. Ester content was then obtained by multiplying sucrose found by the factor, mol. wt. ester/mol. wt. sucrose. Ester mixtures were prepared by interesterifying sucrose with various proportions of methyl palmitate in dimethylformamide solution. Positional isomers were observed at each level of substitution but could not be adequately separated from each other for quantitative evaluation. Presented at the AOCS Meeting, Minneapolis, October 1969. So. Utiliz. Res. Dev. Div., ARS, USDA.  相似文献   
956.
Temperature dependence of KIC values for Si3N4 bodies sintered at high pressures without additives was studied from room temperature to 1400°C. Little change in KK was found in this range.  相似文献   
957.
The matrix concept was used to characterize the chromatographic rules in the elution of molecular species of triglyceride. To prove the hypothesis experimentally, cacao butter, palm oil, linseed oil, olive oil, rapeseed oil and triglyceride of “Ogonori” (Gracilaria verrucosa) were examined. A matrix model was suggested to help determine the individual molecular species of naturally occurring triglycerides.  相似文献   
958.
959.
960.

The 10th Five-Year Plan — A Five-Year Plan For Product Quality And Production Efficiency

The main task of the man-made fibre industry is to improve the quality of its products  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