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   457550篇
  免费   3252篇
  国内免费   732篇
电工技术   8570篇
综合类   416篇
化学工业   72598篇
金属工艺   18738篇
机械仪表   14886篇
建筑科学   10082篇
矿业工程   3435篇
能源动力   11701篇
轻工业   36786篇
水利工程   5623篇
石油天然气   11910篇
武器工业   29篇
无线电   48532篇
一般工业技术   93422篇
冶金工业   76594篇
原子能技术   11803篇
自动化技术   36409篇
  2021年   4553篇
  2020年   3576篇
  2019年   4650篇
  2018年   7397篇
  2017年   7493篇
  2016年   7989篇
  2015年   4888篇
  2014年   8276篇
  2013年   20850篇
  2012年   12700篇
  2011年   16818篇
  2010年   13560篇
  2009年   15095篇
  2008年   15211篇
  2007年   15032篇
  2006年   13068篇
  2005年   11787篇
  2004年   11225篇
  2003年   11009篇
  2002年   10603篇
  2001年   10330篇
  2000年   9833篇
  1999年   9596篇
  1998年   22150篇
  1997年   16073篇
  1996年   12544篇
  1995年   9660篇
  1994年   8678篇
  1993年   8523篇
  1992年   6691篇
  1991年   6531篇
  1990年   6380篇
  1989年   6222篇
  1988年   5970篇
  1987年   5389篇
  1986年   5242篇
  1985年   5887篇
  1984年   5376篇
  1983年   5182篇
  1982年   4628篇
  1981年   4738篇
  1980年   4510篇
  1979年   4588篇
  1978年   4495篇
  1977年   4927篇
  1976年   6134篇
  1975年   4111篇
  1974年   3878篇
  1973年   3986篇
  1972年   3406篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The results of a system analysis of the efficiency of nitrous oxide(N_2O) as a propellant component for small space vehicles(SSV) were presented. A criterion for mass efficiency of the SSV propulsion system(PS) is determined. The current global state-of-the-art of SSV PSs is shown. The application field of nitrous oxide in SSV PSs is calculated and mass efficiency of N_2O application is quantitatively determined. An overview of physical and chemical as well as operational properties of nitrous oxide as a promising, non-toxic component of rocket propellant is provided. Main physical and chemical constants of gaseous and liquid nitrous oxide; chemical properties of N_2O, thermal stability of N_2O, catalytic decomposition of N_2O, a mechanism of decomposition of N_2O, catalysts for decomposition of N_2O, ballast additives to N_2O, application of nitrous oxide, nitrous oxide as a rocket propellant, production of nitrous oxide, toxicity of nitrous oxide, fire hazard of N_2O, requirements to equipment when handling N_2O; storage and transportation of N_2O are considered. It is demonstrated that nitrous oxide is a chemical compound meeting the requirements to rocket propellants, including those related to the environmental friendliness of propellants. With 75 references.  相似文献   
2.
Search for conditions of conservation of fast ionic transport (FIT) in nanosystems of advanced superionic conductors (ASIC)[1-4] and synthesis of new types of device thin-film heterostructures on this basis is a fundamental scientific problem. ASICs (α-AgI, solid electrolytes of the family RbAg4I5, etc. ) are crystals with a record high level of ionic conductivity and a low value of activation energy E~0. 1 eV.  相似文献   
3.
根据实验室的试验结果,推荐应用浮选萃取联合工艺从水溶液中回收Mo(Ⅵ)。这一工艺包括制取以钼酸铵形式的商品,和对所有的有机试剂作再生处理。萃取Mo(Ⅵ)的准备系统,应包括在反萃取胺和用NaOH使水溶液碱化到pH=12以后,通过添加水溶液以使煤油、壬醇和AHII捕收剂按规定的比例进行混合等作业。对在萃取器中获得的混合液进行相分离后,有机溶液可用作泡沫浮选萃取Mo(Ⅵ)的萃取剂,而水溶液则加入到原始溶液中。  相似文献   
4.
Training and continuous education is today for the management of a mineral producing operation more important than ever before. The focus of education today in the field of mineral producing industry has not only to be dedicated versus the needs of the industry but also versus the importance of the ever increasing need of societal acceptance of industrial operations. Therefore it is expected that graduates from mining schools not only have a good knowledge of technical and economical subjects but also a good background for the realisation of environmental and safety targets for the people at work and in the neighbourhood of an operation. A strong request to the education and training at university level is therefore not only to deliver a broad knowledge but also the formation of a basis which allows to obtain authority for functions as “safety expert”, “Mine rescuer”, “waste disposal expert” and others. In the text the contents of the BSc study program “Natural resources” are reviewed and the training and education for a “Natural Resources Manager” together with the required continuous education is discussed.  相似文献   
5.
6.
7.
The procedure is proposed for calculating the characteristics of flow and heat exchange of coal-water fuels as applied to the pipeline hydraulic transport and heat-mass exchange in the apparatus of ecologically clean combustion in the objects of power engineering.  相似文献   
8.
Foundation of a university research cluster — Co-operation along the value creation chain from raw materials to components — Evidence of joint performance offers — Utilization of synergies — Integration of Christian Doppler Laboratories — Flexible arrangement of co-operations and networks  相似文献   
9.
10.
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