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   426625篇
  免费   6265篇
  国内免费   1408篇
电工技术   7839篇
综合类   339篇
化学工业   62536篇
金属工艺   17125篇
机械仪表   13889篇
建筑科学   9889篇
矿业工程   2324篇
能源动力   12292篇
轻工业   30183篇
水利工程   4533篇
石油天然气   8056篇
武器工业   19篇
无线电   50964篇
一般工业技术   86693篇
冶金工业   80931篇
原子能技术   9477篇
自动化技术   37209篇
  2021年   4044篇
  2020年   3227篇
  2019年   4159篇
  2018年   6915篇
  2017年   6932篇
  2016年   7387篇
  2015年   4726篇
  2014年   7783篇
  2013年   21958篇
  2012年   12502篇
  2011年   16650篇
  2010年   13202篇
  2009年   14871篇
  2008年   15356篇
  2007年   15133篇
  2006年   13567篇
  2005年   12172篇
  2004年   11464篇
  2003年   11220篇
  2002年   10331篇
  2001年   9870篇
  2000年   9014篇
  1999年   9501篇
  1998年   24299篇
  1997年   16630篇
  1996年   12783篇
  1995年   9919篇
  1994年   8749篇
  1993年   8783篇
  1992年   6424篇
  1991年   5926篇
  1990年   6022篇
  1989年   5639篇
  1988年   5316篇
  1987年   4737篇
  1986年   4596篇
  1985年   5245篇
  1984年   4824篇
  1983年   4357篇
  1982年   4023篇
  1981年   4089篇
  1980年   3720篇
  1979年   3638篇
  1978年   3611篇
  1977年   4005篇
  1976年   5076篇
  1975年   3130篇
  1974年   2863篇
  1973年   2968篇
  1972年   2412篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
41.
Telecommunication Systems - Energy saving in User Equipment (UE) is one of the important issues for limited sources of power in the device. It is critical for the UE to maximize its energy...  相似文献   
42.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
43.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  相似文献   
44.
45.
46.
Mixing by gas injection is an operation used in industrial processes such as wastewater treatment, metallurgy, or methanization in which pressurized gas is injected into a fluid in order to reduce concentrations and temperatures gradients. This study demonstrates how the CFD toolbox OpenFOAM can be used to simulate such flows. Experimental measurements and observations have been performed on a pilot-scale reactor where pressurized air is injected in a yield stress fluid. The volume of fluid method and an adaptive mesh with refinement at the interface have been used to track the gas inclusions. The numerical model accuracy has been assessed by comparing experimental and numerical results related to the bubble's frequency, dimensions, and rising velocities as well as the fluid recirculation, yielded, and unyielded regions in the tank. The influence of injection parameters such as the injection flow rate and the fluid rheological parameters has been quantified.  相似文献   
47.
Cybernetics and Systems Analysis - The authors propose a method for solving the problem of approach of controlled objects in dynamic game problems with a terminal payoff function. The method is...  相似文献   
48.
Journal of Computer and Systems Sciences International - Engineering systems contain actuators with force limits, so the level and rate saturation nonlinearities are often found in control systems....  相似文献   
49.
Cybernetics and Systems Analysis - The paper examines prerequisites and assumptions of the classical Bass innovation diffusion model with the aim of applying it in modeling of relevant stochastic...  相似文献   
50.
Suzuki-Miyaura (S-M) is regarded the most powerful way for synthesis biaryls, triaryls, or incorporating of substituted aryl moieties in organic preparation by the cross-coupling of aryl boronic acid with aryl halides using the Pd catalyst. This work reports the combining of the hydrothermal and microwave-assisted protocol to convert the glucose to magnetic carbon spheres (Fe3O4-CSPs) decorated with Pd nanoparticles (NPs) as the catalyst for Suzuki-Miyaura cross-coupling reactions. The physicochemical properties in the produced composite were examined using FESEM, HRTEM, nitrogen isotherms, Raman spectroscopy, FTIR, XPS, and XRD. The as-fabricated composite Pd/Fe3O4-CSPs is mostly spherical with a core–shell structure and possesses a great surface area of 253.2 m2·g-1. Its catalytic performance demonstrates that the composite has excellent stability and high tolerance Suzuki-Miyaura cross-coupling reactions in 30 min at 80 ℃. Both activated and deactivated aryl halides provided excellent yield. The as-fabricated catalyst was recycled for up to four catalytic cycles without a substantial decline in performance. Moreover, this research offers a facile roadmap for synthesizing Pd/Fe3O4-CSPs composites and promoting the practical implementation of Pd/Fe3O4-CSPs catalysts for organic transformation processes.  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