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   102879篇
  免费   2098篇
  国内免费   554篇
电工技术   1162篇
综合类   2391篇
化学工业   16157篇
金属工艺   5218篇
机械仪表   3625篇
建筑科学   2873篇
矿业工程   586篇
能源动力   2496篇
轻工业   5478篇
水利工程   1474篇
石油天然气   700篇
武器工业   8篇
无线电   11282篇
一般工业技术   19748篇
冶金工业   3544篇
原子能技术   413篇
自动化技术   28376篇
  2024年   85篇
  2023年   433篇
  2022年   958篇
  2021年   1347篇
  2020年   1092篇
  2019年   1144篇
  2018年   15410篇
  2017年   14154篇
  2016年   10874篇
  2015年   1283篇
  2014年   1308篇
  2013年   2101篇
  2012年   4328篇
  2011年   10607篇
  2010年   9068篇
  2009年   6317篇
  2008年   7339篇
  2007年   8258篇
  2006年   576篇
  2005年   1538篇
  2004年   1412篇
  2003年   1412篇
  2002年   768篇
  2001年   246篇
  2000年   329篇
  1999年   210篇
  1998年   307篇
  1997年   249篇
  1996年   211篇
  1995年   157篇
  1994年   115篇
  1993年   117篇
  1992年   97篇
  1991年   83篇
  1990年   69篇
  1989年   74篇
  1988年   78篇
  1987年   51篇
  1986年   60篇
  1985年   70篇
  1984年   75篇
  1983年   68篇
  1982年   47篇
  1980年   47篇
  1976年   57篇
  1968年   52篇
  1966年   44篇
  1965年   44篇
  1955年   64篇
  1954年   70篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
This paper addresses scientists’ behaviour regarding the patenting of knowledge produced in universities and other public sector research organisations (PSROs). Recent years have witnessed a rapid growth in patenting and licensing activities by PSROs. We argue that the whole process depends to a certain extent on scientists’ willingness to disclose their inventions. Given this assumption, we conduct research into individual behaviour in order to understand scientists’ views concerning the patenting of their research results. Data from a questionnaire survey of Portuguese researchers from nine PSROs in life sciences and biotechnology is presented and analysed and complemented with in-depth interviews. The results reveal that overall the scientists surveyed show a low propensity to become involved in patenting and licensing activities, despite the fact that the majority had no “ethical” objections to the disclosure of their inventions and the commercial exploitation of these. Perceptions about the impacts of these activities on certain fundamental aspects of knowledge production and dissemination are however divergent. This may account for the low participation levels. Furthermore, most scientists perceived the personal benefits deriving from this type of activity to be low. Similarly, the majority also believed that there are many difficulties associated with the patenting process and that they receive limited support from their organisations, which lack the proper competences and structures to assist with patenting and licensing.  相似文献   
142.
143.
144.
145.
146.
147.
148.
149.
Titanium oxides were reduced to metallic titanium using the liquid calcium floating on the molten CaCl2. A part of Ca dissolved into CaCl2 and reacted with TiO2 settled below CaCl2. The by-product CaO also dissolved by about 20 mol pct into CaCl2, which was effective in reducing the oxygen concentration in the obtained Ti particles. The compositional region in the Ca-CaCl2-CaO system was examined for the less oxygen contamination in Ti and the better handling in leaching. A large amount of the residual calcium oxidized the titanium powder in leaching. The metallic Ti powder less than 1000 mass ppm oxygen could be obtained only for 3.6 ks using 5 to 7 mol pct Ca-CaCl2 at 1173 K. The powder was slightly sintered like sponge, and contained approximately 1500 ppm Ca. The anatase phae, the intermediate product in the refining process of TiO2, could be also supplied as raw material as well as rutile.  相似文献   
150.
The corrosion behaviour of nitrogen-containing austenitic stainless steel in methanol containing different concentrations of H2SO4, HCl, LiCl and H2SO4 + HCl has been investigated using a potentiostatic polarization method. The cathodic reaction in the H2SO4, HCl and H2SO4 + HCl solutions was proton reduction whereas in the neutral LiCl solution, oxygen reduction was the predominant cathodic reaction. Active, passive and transpassive behaviours were observed only for higher concentrations of H2SO4 (0.01–2.0 M) due to the inherent water content. A cathodic loop, characterized by measured negative current in the anodic region, was also observed in solutions, in which the concentration of H2SO4 was 1.0 M or higher. The relative stability of the passive films decreased as the H2SO4 concentration increased, and thus the steel suffered from mild pitting corrosion. In the chloride environment, the rate of corrosion increased as the Cl ion concentration increased. The presence of acid along with Cl ions enhanced corrosion, and the corrosion rate increased significantly. The steel suffered from mild intergranular corrosion in acidic chloride solutions of methanol. In the H2SO4 + HCl solutions, passive films were only formed when the H2SO4 to HCl concentration ratio was greater than ∼10:1.  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