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   255603篇
  免费   1962篇
  国内免费   893篇
电工技术   4352篇
综合类   205篇
化学工业   37341篇
金属工艺   8244篇
机械仪表   7275篇
建筑科学   6822篇
矿业工程   541篇
能源动力   7312篇
轻工业   29040篇
水利工程   2234篇
石油天然气   1854篇
武器工业   6篇
无线电   33644篇
一般工业技术   46473篇
冶金工业   46456篇
原子能技术   3368篇
自动化技术   23291篇
  2021年   1899篇
  2020年   1552篇
  2019年   1905篇
  2018年   2573篇
  2017年   2598篇
  2016年   2938篇
  2015年   2204篇
  2014年   3679篇
  2013年   11974篇
  2012年   6781篇
  2011年   9680篇
  2010年   7461篇
  2009年   8404篇
  2008年   8929篇
  2007年   8943篇
  2006年   8303篇
  2005年   7507篇
  2004年   7218篇
  2003年   7103篇
  2002年   6599篇
  2001年   7028篇
  2000年   6338篇
  1999年   6845篇
  1998年   16393篇
  1997年   11385篇
  1996年   8604篇
  1995年   6561篇
  1994年   5724篇
  1993年   5583篇
  1992年   4011篇
  1991年   3790篇
  1990年   3555篇
  1989年   3380篇
  1988年   3283篇
  1987年   2594篇
  1986年   2487篇
  1985年   3157篇
  1984年   2797篇
  1983年   2559篇
  1982年   2344篇
  1981年   2390篇
  1980年   2205篇
  1979年   2048篇
  1978年   1879篇
  1977年   2176篇
  1976年   2724篇
  1975年   1584篇
  1974年   1489篇
  1973年   1558篇
  1972年   1144篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Bizhanov  A. M.  Aubertot  C. 《Metallurgist》2021,65(7-8):699-712
Metallurgist - The article describes the concept of partially replacing the sinter in a blast furnace charge with extrusion briquettes to form the basis for sintering and briquetting synergy. The...  相似文献   
32.
33.
34.
The scheduling of maintenance for water distribution systems is a complex task encompassing a wide range of alternatives. The methodology presented in this paper can consider the major piping alternatives of replacing and cleaning, and relining. It also considers the potential of pumping improvements while accounting for the costs of maintenance, failure and operations for a multiple-period planning horizon. To solve the problem a nonlinear optimization model is linked with a network simulation model. The application showed that the procedure can determine solutions in reasonable times.  相似文献   
35.
The provision of countryside recreation facilities at a local level is likely to receive increasing attention during the next decade. As an integral part of the assessment of the quality of present provision within the Congleton District of Cheshire (U.K.) five site surveys were made. Each site provides different facilities for recreation and interview questions were designed to investigate the background of the visitors and the nature of the interplay between site and visitor. The analysis of answers attempts to illustrate those aspects of this interrelationship, which may be important during the consideration of future provision of recreation sites and their management.  相似文献   
36.
Feasibility of a waste material, flyash, as a material for purification of wastewater containing Lissamine Red has been studied. Effects of time and concentration, temperature and pH on the removal of the dye have been studied. Lower concentrations favour the uptake of dye from water and the maximum removal was observed at a dye concentration of 20 mgL m 1 , 30°C, pH of 7 and adsorbent particle size of 53 µm. Dynamics of the uptake was studied using Lagergren's equation. The mass transfer coefficient was found to be 0.05 cmmin m 1 at a concentration of 20 mgL m 1 , 30°C and 53 µm particle size.  相似文献   
37.
Responses to hydrocarbon stress of four tropical plants Panicum maximum, Zea mays, Centrosema sp. and Pueraria sp. grown in crude oil contaminated soils (1%, 5% and 10% w/w) were evaluated in a green house. Plants’ percentage survival, shoot heights, biomass development, and phytotoxicity susceptibility were used as indicators of growth, stress response and hydrocarbon tolerance. Relative to control, shoot heights and biomass of plants reduced with increasing hydrocarbon concentration, but 1% w/w oil-in-soil, stimulated shoot heights (5.9% and 6.4%) and weights (21.9% and 2.3%) in P. maximum and Centrosema sp. respectively. P. maximum tolerated the contaminant stress with biomass yields of 113% and 57% of control respectively in 1% and 10% w/w oil-in-soil. All the plants had 100% survival in 1% w/w, but considerably reduced survival in 10% w/w oil-in-soil. These results show that P. maximum has great potential for phytoremediation of petroleum contaminated soil.  相似文献   
38.
39.
40.
对PPP项目市场需求风险的影响因素、分担偏好、参与者的管理能力等问题进行探讨,以实例提出PPP项目市场需求风险完全由政府承担、政府与私人投资者共同承担及私人投资者承担的三种模式。在此基础上提出风险分担中政府所应承担的责任,以及市场分担与项目竞争强度的关系等观点,以期为政府后续PPP项目市场需求风险的管理提供参考和借鉴。  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