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   199668篇
  免费   2307篇
  国内免费   612篇
电工技术   3468篇
综合类   149篇
化学工业   28960篇
金属工艺   8049篇
机械仪表   6068篇
建筑科学   4811篇
矿业工程   1303篇
能源动力   5127篇
轻工业   17115篇
水利工程   2297篇
石油天然气   4040篇
武器工业   8篇
无线电   23066篇
一般工业技术   40012篇
冶金工业   37227篇
原子能技术   5086篇
自动化技术   15801篇
  2021年   1604篇
  2019年   1568篇
  2018年   2573篇
  2017年   2645篇
  2016年   2775篇
  2015年   1794篇
  2014年   3074篇
  2013年   8939篇
  2012年   5050篇
  2011年   7021篇
  2010年   5589篇
  2009年   6351篇
  2008年   6443篇
  2007年   6511篇
  2006年   5579篇
  2005年   5228篇
  2004年   5005篇
  2003年   4887篇
  2002年   4525篇
  2001年   4656篇
  2000年   4578篇
  1999年   4726篇
  1998年   11373篇
  1997年   8120篇
  1996年   6408篇
  1995年   4673篇
  1994年   4271篇
  1993年   4073篇
  1992年   3223篇
  1991年   3076篇
  1990年   2870篇
  1989年   2951篇
  1988年   2826篇
  1987年   2398篇
  1986年   2308篇
  1985年   2715篇
  1984年   2505篇
  1983年   2345篇
  1982年   2090篇
  1981年   2203篇
  1980年   2029篇
  1979年   2124篇
  1978年   2120篇
  1977年   2366篇
  1976年   3188篇
  1975年   1833篇
  1974年   1761篇
  1973年   1772篇
  1972年   1443篇
  1971年   1339篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Male weanling rats were subjected to standard 28-day PER trials following the outline by the AOAC (1984) except that the diets contained 8.5% protein (N × 6.25) as one of six wheat-based breakfast cereals, white flour, whole wheat flour or casein. One of the cereals was an extrusion puffed product, three were flaked and toasted cereals and two were extruded cereals. Of the two extruded cereals, one was lightly toasted and the other was more heavily toasted. Relative PER (R-PER) was lowest for the puffed cereal (- 15.3) and highest for the extruded-lightly toasted cereal (69.9). R-PER for the flaked cereals ranged from 1.7 to 16.3; the other extruded cereal had a R-PER of 2.8 and each of the two flours had a R-PER of 42.9.  相似文献   
992.
993.
994.
Ed W.B de Leer 《Water research》1985,19(11):1411-1419
In harbour sediment samples taken near an epichlorohydrin production plant, a series of highly chlorinated ethers and diethers were detected viz. three isomeric bis(dichloropropyl)ethers, several structurally closely related ethers with 9 carbon atoms (C9 ethers), a number of C12 ethers and diethers, and finally several C15 ethers. The formation of this new class of ether compounds can be explained on the basis of the chemistry of the addition of HOCl to allylchloride. After initial addition of Cl, a reactive intermediate is formed which may react with the product dichloropropanol, to give the C6 ethers, or may polymerize with the starting compound allylchloride followed by reaction with the product, to give the C9, C12 and C15 ethers.  相似文献   
995.
Summary Fourier transform infrared spectroscopy and birefringence measurements have been used to study the changes in molecular orientation which occur on drawing of plasticized as compared to pure polystyrene (PS) at a temperature T=Tg+Cte. No influence of plasticizers on orientation can be detected whatever the interactions between small molecules and PS chains are. Comparison with previous results obtained on PS-poly(vinylmethyl ether) compatible blends confirms the importance of the macromolecular nature of the second component to enhance the friction coefficient leading to higher level of chain orientation.  相似文献   
996.
997.
998.
999.
We describe planar buried heterostructure lasers which have low capacitance (lpF), large bandwidth (19GHz), high power (>20mW/facet) and high temperature operation (100°C). These lasers are very suitable for long-distance, highspeed digital and analogue signal transmission.  相似文献   
1000.
The possibility of long-term safe disposal of radioactive wastes based on their radiation and radiation-migration balance with the initial fuel component and taking account of the thermal, radiation, and elastic loads due to waste dispoasl on the natural medium is examined. The specific radiation and radiation-migration equivalence is established on the basis of the radiotoxicity of uranium and the components of the decay of uranium and individual radionuclides as well as the sum of the latter.  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