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   4716篇
  免费   441篇
  国内免费   48篇
电工技术   110篇
综合类   18篇
化学工业   1467篇
金属工艺   159篇
机械仪表   209篇
建筑科学   197篇
矿业工程   16篇
能源动力   294篇
轻工业   505篇
水利工程   81篇
石油天然气   78篇
武器工业   5篇
无线电   383篇
一般工业技术   769篇
冶金工业   141篇
原子能技术   33篇
自动化技术   740篇
  2024年   20篇
  2023年   80篇
  2022年   132篇
  2021年   346篇
  2020年   290篇
  2019年   350篇
  2018年   425篇
  2017年   409篇
  2016年   382篇
  2015年   206篇
  2014年   363篇
  2013年   549篇
  2012年   363篇
  2011年   381篇
  2010年   246篇
  2009年   198篇
  2008年   121篇
  2007年   82篇
  2006年   66篇
  2005年   32篇
  2004年   23篇
  2003年   24篇
  2002年   16篇
  2001年   8篇
  2000年   9篇
  1999年   5篇
  1998年   13篇
  1997年   6篇
  1996年   10篇
  1995年   7篇
  1994年   4篇
  1993年   3篇
  1992年   3篇
  1991年   4篇
  1990年   4篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1983年   4篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1976年   3篇
  1975年   1篇
  1974年   1篇
排序方式: 共有5205条查询结果,搜索用时 31 毫秒
171.
172.
173.
Parameter extraction of the five-parameter single-diode model of solar cells and modules from experimental data is a challenging problem. These parameters are evaluated from a set of nonlinear equations that cannot be solved analytically. On the other hand, a numerical solution of such equations needs a suitable initial guess to converge to a solution. This paper presents a new set of approximate analytical solutions for the parameters of a five-parameter single-diode model of photovoltaic (PV) cells and modules. The proposed solutions provide a good initial point which guarantees numerical analysis convergence. The proposed technique needs only a few data from the PV current-voltage characteristics, i.e. open circuit voltage Voc, short circuit current Isc and maximum power point current and voltage Im; Vm making it a fast and low cost parameter determination technique. The accuracy of the presented theoretical I–V curves is verified by experimental data.  相似文献   
174.
Neural Computing and Applications - Nowadays, one of the problems in current authentication, authorization and accounting (AAA) model is lack of accurate roadmap of access management in integrated...  相似文献   
175.
Graphene oxide was chemically functionalized with a modifier synthesized from coupling reaction of ethylenediamine and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid in low and high graft densities. Then, the modified graphenes were used in grafting from reversible addition-fragmentation chain transfer polymerization of styrene. Successful synthesis and grafting of modifier was approved by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy (FTIR). Also, FTIR, X-ray photo electron spectroscopy, and Raman spectroscopy were used to confirm the successful grafting of modifier moieties. Molecular weight and polydispersity index of attached polystyrene chains were studied by size exclusion chromatography. Thermogravimetric analysis was used to investigate the degradation temperatures, char contents, and graft ratios. Weight ratio of modifier in modified graphenes is calculated to be 4.93 × 10?2 and 12.23 × 10?2 for low and high graft densities. Also, molar ratio of modifier is 121.22 and 300.71 μmol/g respectively. Scanning electron and transmission electron microscopies show that graphite layers with flat surface were wrinkled during the oxidation process and also polystyrene-grafted graphenes are observed as opaque layers.  相似文献   
176.
177.
Journal of Porous Materials - The development of theranostic nanostructures is one of the most advanced branches of pharmaceutical and medical sciences in the world today. Due to the unique...  相似文献   
178.
Applied Intelligence - 3D Speckle tracking techniques are used to quantify cardiac deformation in 3D echocardiographic images. Elastic image registration methods are successful in solving 3D...  相似文献   
179.
Multimedia Tools and Applications - Video games are changing how we interact and communicate with each other. They can provide an authentic and collaborative platform for building new communities...  相似文献   
180.
The sphericity and size of ammonium perchlorate (AP) particles significantly influence the properties of composite propellants. As the AP particles become more spherical, the accumulation coefficient increases, the viscosity during casting decreases, and the particle loading and burning rate increase. Hence, the production of micronized AP particles with an average size between 1 and 20 μm is important to increase the loading percentage of AP in the composite propellant. Here, the Taguchi experimental design was used to optimize the solvent-antisolvent crystallization (SAC) process for the preparation of micronized AP particles with higher sphericity. SAC parameters such as the type of antisolvent, the solvent-to-antisolvent ratio, the antisolvent temperature, the stirring speed, and the retention time were investigated at four levels. The type of antisolvent and the solvent-to-antisolvent ratio were found to mainly contribute to improving the sphericity and size of the AP particles, respectively.  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