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   263519篇
  免费   4131篇
  国内免费   829篇
电工技术   5172篇
综合类   329篇
化学工业   37761篇
金属工艺   10492篇
机械仪表   8800篇
建筑科学   6129篇
矿业工程   1077篇
能源动力   6655篇
轻工业   23064篇
水利工程   2564篇
石油天然气   3911篇
武器工业   68篇
无线电   35574篇
一般工业技术   51191篇
冶金工业   46684篇
原子能技术   5523篇
自动化技术   23485篇
  2021年   2196篇
  2019年   2179篇
  2018年   3663篇
  2017年   3720篇
  2016年   3961篇
  2015年   2510篇
  2014年   4310篇
  2013年   11616篇
  2012年   6961篇
  2011年   9378篇
  2010年   7274篇
  2009年   8131篇
  2008年   8963篇
  2007年   8807篇
  2006年   7994篇
  2005年   7286篇
  2004年   7027篇
  2003年   6856篇
  2002年   6497篇
  2001年   6571篇
  2000年   6262篇
  1999年   6346篇
  1998年   14309篇
  1997年   10322篇
  1996年   8167篇
  1995年   6451篇
  1994年   5729篇
  1993年   5610篇
  1992年   4569篇
  1991年   4221篇
  1990年   4057篇
  1989年   3795篇
  1988年   3592篇
  1987年   3144篇
  1986年   3043篇
  1985年   3578篇
  1984年   3356篇
  1983年   2986篇
  1982年   2817篇
  1981年   2916篇
  1980年   2737篇
  1979年   2627篇
  1978年   2478篇
  1977年   2916篇
  1976年   3527篇
  1975年   2300篇
  1974年   2298篇
  1973年   2287篇
  1972年   1841篇
  1971年   1720篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Application of brown titanium dioxide (TiO2-x) and its modified composite forms in the photocatalytic decomposition of organic pollutants in the environment is a promising way to provide solutions for environmental redemption. Herein, we report the synthesis of effective and stable TiO2-x nanoparticles with g-C3N4, RGO, and multiwalled carbon nanotubes (CNTs) using a simple hydrothermal method. Among all the as-synthesized samples, excellent photocatalytic degradation activity was observed for RGO-TiO2-x nanocomposite with high rate constants of 0.075 min?1, 0.083 min?1 and 0.093 min?1 for methylene blue, rhodamine-B, and rosebengal dyes under UV–Visible light irradiation, respectively. The altered bandgap (1.8 eV) and the large surface area of RGO-TiO2-x nanocomposite impacts on both absorption of visible light and efficiency of photogenerated charge electron (e?)/hole (h+) pair separation. This resulted in enhanced photocatalytic property of carbon-based TiO2-x nanocomposites. A systematic study on the influence of different carbon nanostructures on the photocatalytic activity of brown TiO2-x is carried out.  相似文献   
83.
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   
84.
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   
85.
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   
86.
Environmental concerns continue to pose the challenge to replace petroleum-based products with renewable ones completely or at least partially while maintaining comparable properties. Herein, rigid polyurethane (PU) foams were prepared using soy-based polyol for structural and thermal insulation applications. Cell size, density, thermal resistivity, and compression force deflection (CFD) values were evaluated and compared with that of petroleum-based PU foam Baydur 683. The roles of different additives, that is, catalyst, blowing agent, surfactants, and different functionalities of polyol on the properties of fabricated foam were also investigated. For this study, dibutyltin dilaurate was employed as catalyst and water as environment friendly blowing agent. Their competitive effect on density and cell size of the PU foams were evaluated. Five different silicone-based surfactants were employed to study the effect of surface tension on cell size of foam. It was also found that 5 g of surfactant per 100 g of polyol produced a foam with minimum surface tension and highest thermal resistivity (R value: 26.11 m2·K/W). However, CFD values were compromised for higher surfactant loading. Additionally, blending of 5 g of higher functionality soy-based polyol improved the CFD values to 328.19 kPa, which was comparable to that of petroleum-based foam Baydur 683.  相似文献   
87.
The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included.  相似文献   
88.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for...  相似文献   
89.
90.
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