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   461250篇
  免费   5399篇
  国内免费   1211篇
电工技术   8679篇
综合类   579篇
化学工业   70774篇
金属工艺   18055篇
机械仪表   14381篇
建筑科学   10728篇
矿业工程   2320篇
能源动力   10740篇
轻工业   42873篇
水利工程   4668篇
石油天然气   8158篇
武器工业   98篇
无线电   54367篇
一般工业技术   86681篇
冶金工业   86137篇
原子能技术   10184篇
自动化技术   38438篇
  2021年   3760篇
  2019年   3651篇
  2018年   6274篇
  2017年   6276篇
  2016年   6654篇
  2015年   4204篇
  2014年   7188篇
  2013年   19821篇
  2012年   11561篇
  2011年   15732篇
  2010年   12462篇
  2009年   13930篇
  2008年   14853篇
  2007年   14910篇
  2006年   13444篇
  2005年   12058篇
  2004年   11632篇
  2003年   11324篇
  2002年   11072篇
  2001年   10942篇
  2000年   10563篇
  1999年   10569篇
  1998年   24925篇
  1997年   17749篇
  1996年   13926篇
  1995年   10858篇
  1994年   9686篇
  1993年   9459篇
  1992年   7509篇
  1991年   6978篇
  1990年   6995篇
  1989年   6663篇
  1988年   6419篇
  1987年   5613篇
  1986年   5559篇
  1985年   6421篇
  1984年   6085篇
  1983年   5485篇
  1982年   5186篇
  1981年   5376篇
  1980年   5080篇
  1979年   4905篇
  1978年   4798篇
  1977年   5479篇
  1976年   6877篇
  1975年   4338篇
  1974年   4196篇
  1973年   4341篇
  1972年   3549篇
  1971年   3295篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Thermogravimetry and pyrolysis in combination with gas chromatography and infrared spectroscopy were the experimental techniques applied to the thermal degradation of cinnamoylated poly(vinyl alcohol) samples, constituted from vinyl alcohol-vinyl cinnamate photocrosslinkable copolymers. The thermal decomposition products include gases, liquids and solids. The gases are formed from saturated and unsaturated volatile hydrocarbons C1? C4, carbon monoxide and carbon dioxide. The liquid fraction includes aromatic hydrocarbons and some oxygenated organic compounds. The solid product identified in the greatest amount was cinnamic acid. The content in the thermal decomposition products varies considerably both with copolymer composition and temperature.  相似文献   
952.
When sulphur dioxide inhibits the enzymic browning of catechol catalysed by mushroom tyrosinase, the main reaction product is 4-sulphocatechol. When assessed for its browning potential, this product appears to be unreactive and does not inhibit the enzyme.  相似文献   
953.
Ice observations, results, and conclusions are summarized for the March 1987 Labrador Ice Margin Experiment (LIMEX'87), an international oceanographic study conducted in the pack ice of the Grand Banks area off the coast of Newfoundland. Included are the ice extent, flow size and thickness, ice kinematics and rheology, ice microwave properties, oceanic properties under the ice, and penetration of swell into the ice  相似文献   
954.
In our one-semester course at the US Military Academy in New York, we educate roughly 800 undergraduates from nontechnical fields each year on intermediate-level IT skills. We place our students in an isolated virtual-computing environment, give them hands-on experience with a variety of attack vectors that hackers use to exploit vulnerabilities, and provide them with a multidimensional framework for understanding and mitigating risks. As a result of this educational experience, our students are better able to internalize the concepts we teach and end up with an increased realization of the actions required to protect crucial resources.  相似文献   
955.
956.
Currently, two motivators are effecting change in power systems education. First, the industry's transition to a more competitive environment is requiring changes in the content and pedagogy of power systems education. Second, engineering education as a whole is seeking to modify its curriculum to reflect a better balance between science and education in order to better meet the needs of industry. These curricular changes are largely a result of revised Accreditation Board for Engineering and Technology (ABET) accreditation requirements. In response to these changes, new curriculum and analysis tools were developed for a power systems capstone design course. The project integrates market economics and socio-political considerations with transient stability analysis and transmission planning. A power systems analysis package and an economic analysis tool were developed for use with this project. Student evaluations of the course in which the project was implemented indicate that the curriculum successfully addresses a broad range of ABET accreditation criteria.  相似文献   
957.
The electroplating of Ni-Cd alloy coatings was carried out from alkaline baths (pH 10). For comparison, electroplating of the parent metals, Ni and Cd, was performed individually under the same conditions. The cathodic current efficiency for codeposition was high and decreased with increasing current density. The codeposition process is an anomalous type of plating with Cd being the preferentially deposited metal. The Ni content in the deposits increased with increasing current density. This increase in Ni content improves the corrosion resistance and microhardness of the deposits. X-ray diffraction analysis showed that the deposits consist of a mixture of Ni, β, γ, γ1 phases.  相似文献   
958.
959.
960.
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