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   1776507篇
  免费   47823篇
  国内免费   17303篇
电工技术   49054篇
技术理论   31篇
综合类   23293篇
化学工业   313907篇
金属工艺   79337篇
机械仪表   60149篇
建筑科学   68062篇
矿业工程   20793篇
能源动力   57496篇
轻工业   126501篇
水利工程   20014篇
石油天然气   56017篇
武器工业   2377篇
无线电   224629篇
一般工业技术   313416篇
冶金工业   188233篇
原子能技术   36582篇
自动化技术   201742篇
  2022年   14695篇
  2021年   26059篇
  2020年   19631篇
  2019年   21133篇
  2018年   23161篇
  2017年   23638篇
  2016年   28582篇
  2015年   27901篇
  2014年   41645篇
  2013年   102884篇
  2012年   52235篇
  2011年   65947篇
  2010年   58127篇
  2009年   65693篇
  2008年   59086篇
  2007年   55949篇
  2006年   59514篇
  2005年   52558篇
  2004年   49595篇
  2003年   48384篇
  2002年   46832篇
  2001年   43391篇
  2000年   42419篇
  1999年   42972篇
  1998年   55124篇
  1997年   46684篇
  1996年   41869篇
  1995年   35739篇
  1994年   32937篇
  1993年   31728篇
  1992年   28135篇
  1991年   24816篇
  1990年   24787篇
  1989年   23670篇
  1988年   21893篇
  1987年   19938篇
  1986年   19233篇
  1985年   22425篇
  1984年   22424篇
  1983年   20360篇
  1982年   19410篇
  1981年   19481篇
  1980年   18094篇
  1979年   18531篇
  1978年   17745篇
  1977年   17632篇
  1976年   18688篇
  1975年   15965篇
  1974年   15456篇
  1973年   15553篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Microsystem Technologies -  相似文献   
992.
A device able to electrokinetically concentrate cationic samples has many potential medical and industrial applications, but until now has remained undeveloped due to the lack of a commercial anion-permselective material leading to a prohibitively complex fabrication procedure. Herein, a novel multiscale-porous anion exchange membrane (MP-AEM) that enables the convenient and scalable electrokinetic concentration of cationic species is proposed. A mechanically enhanced multiscale-porous structure with a solid framework is realized by adopting polyester resin as an additive to overcome the intrinsic limitations of the AEM material. The scalable MP-AEM-embedded electrokinetic concentrator is devised based on the peculiar properties of the MP-AEM that for allow both ion and fluid transport. With the MP-AEM, the concentrator is fabricated in a highly streamlined manner consisting only of a simple insertion and assembly. The concentration performance of the MP-AEM-embedded electrokinetic concentrator is demonstrated with a positively charged fluorescent dye and a fluorescein-labeled protein, and the results show enrichment factors of 250 and 500, respectively. The MP-AEM makes cationic electrokinetic concentration more accessible and scalable, thereby enabling further progress in a wide range of fields.  相似文献   
993.
Programming and Computer Software - Modern computer systems often include specialized processors that are programmed in domain-specific languages. The compiler-in-the-loop technology, which assumes...  相似文献   
994.
Wireless Personal Communications - This paper considers half-duplex cooperative spectrum sharing scheme where both primary and secondary systems mutually cooperate with each other to exploit...  相似文献   
995.
This paper considers a novel distributed iterative learning consensus control algorithm based on neural networks for the control of heterogeneous nonlinear multiagent systems. The system's unknown nonlinear function is approximated by suitable neural networks; the approximation error is countered by a robust term in the control. Two types of control algorithms, both of which utilize distributed learning laws, are provided to achieve consensus. In the provided control algorithms, the desired reference is considered to be an unknown factor and then estimated using the associated learning laws. The consensus convergence is proven by the composite energy function method. A numerical simulation is ultimately presented to demonstrate the efficacy of the proposed control schemes.  相似文献   
996.
997.
Hydrogen fuel is a promising alternative to fossil fuels because of its energy content, clean nature, and fuel efficiency. However, it is not readily available. Most current producion processes are very energy intensive and emit carbon dioxide. Therefore, this article reviews technological options for hydrogen production that are eco-friendly and generate clean hydrogen fuel. Biological methods, such different fermentation processes and photolysis are discussed together with the required substrates and the process efficiency.  相似文献   
998.
999.
1000.
This study addresses the thermo‐diffusion and the diffusion‐thermo phenomena in a semi‐infinite absorbent channel whose walls are contracting/expanding, with heat source/sink effects. The governing partial differential equations with suitable boundary conditions are transformed to a system of dimensionless ordinary differential equations. An analytic solution of the problem has been found using a technique called homotopy analysis method (HAM). HAM gives consistently valid answers to the problem over an extensive variety of parameters and also provides better accuracy. To validate the analytical results, a comparison has been presented with a numerical solution calculated by using the parallel shooting method. The effects of dimensionless parameters, that is, deformation parameter, Reynolds number, Soret and Dufour numbers, and heat source/sink parameter on the expressions of velocity, temperature, and concentration profiles are analyzed graphically to understand the physics of the deformable channel. It has been noted that the velocity across the channel is higher for the expanding channel, as compared to that for the contracting channel. Also the Soret and Dufour number increases the temperature of the fluid, and decreases the concentration. The temperature profile has an increasing behavior in the case of heat source, and a decreasing behavior in the case of heat sink.  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