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   1508311篇
  免费   27644篇
  国内免费   8221篇
电工技术   35658篇
综合类   8018篇
化学工业   271695篇
金属工艺   65124篇
机械仪表   42927篇
建筑科学   46914篇
矿业工程   12000篇
能源动力   50663篇
轻工业   114077篇
水利工程   15392篇
石油天然气   38015篇
武器工业   454篇
无线电   197127篇
一般工业技术   283583篇
冶金工业   157638篇
原子能技术   34173篇
自动化技术   170718篇
  2021年   16278篇
  2020年   12350篇
  2019年   15000篇
  2018年   15558篇
  2017年   14820篇
  2016年   21433篇
  2015年   17895篇
  2014年   29470篇
  2013年   88755篇
  2012年   36246篇
  2011年   48290篇
  2010年   43085篇
  2009年   51579篇
  2008年   45083篇
  2007年   42264篇
  2006年   45334篇
  2005年   39529篇
  2004年   41765篇
  2003年   41516篇
  2002年   40628篇
  2001年   37447篇
  2000年   35880篇
  1999年   34606篇
  1998年   42636篇
  1997年   37895篇
  1996年   34623篇
  1995年   30362篇
  1994年   28585篇
  1993年   28349篇
  1992年   26217篇
  1991年   23310篇
  1990年   23619篇
  1989年   22705篇
  1988年   21276篇
  1987年   19481篇
  1986年   18930篇
  1985年   22306篇
  1984年   22448篇
  1983年   20455篇
  1982年   19311篇
  1981年   19414篇
  1980年   18010篇
  1979年   18638篇
  1978年   17791篇
  1977年   17607篇
  1976年   18624篇
  1975年   16050篇
  1974年   15601篇
  1973年   15658篇
  1972年   13160篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
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   
162.
The process of electrodeposition can be described in terms of a reaction-diffusion partial differential equation (PDE) system that models the dynamics of the morphology profile and the chemical composition. Here we fit such a model to the different patterns present in a range of electrodeposited and electrochemically modified alloys using PDE constrained optimization. Experiments with simulated data show how the parameter space of the model can be divided into zones corresponding to the different physical patterns by examining the structure of an appropriate cost function. We then use real data to demonstrate how numerical optimization of the cost function can allow the model to fit the rich variety of patterns arising in experiments. The computational technique developed provides a potential tool for tuning experimental parameters to produce desired patterns.  相似文献   
163.
Orduna-Malea  Enrique  Aytac  Selenay  Tran  Clara Y. 《Scientometrics》2019,121(1):433-450
Scientometrics - The purpose of this study is to ascertain the suitability of GS’s url-based method as a valid approximation of universities’ academic output measures, taking into...  相似文献   
164.
International Journal of Computer Vision - Anticipating future situations from streaming sensor data is a key perception challenge for mobile robotics and automated vehicles. We address the problem...  相似文献   
165.
Measurement Techniques - A comparative analysis of the results of estimation of measurement uncertainty is conducted. The results are obtained by a method described in the Handbook on the...  相似文献   
166.
Mobile Networks and Applications - Public cloud system offers Infrastructure-as-a-Service (IaaS) to deliver the computational resources on demand. Resource requirements of a cloud environment are...  相似文献   
167.
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical...  相似文献   
168.
Strength of Materials - Creep constitutive equations have been derived for the materials that exhibit the properties of orthotropy (transversal isotropy) and transient creep under cyclic loading. A...  相似文献   
169.
170.
Journal of Communications Technology and Electronics - Approximate formulas for calculating the coefficient of reflection from an artificial magnetic conductor (AMC) based on a capacitive lattice...  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