首页 | 官方网站   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   18731篇
  免费   1146篇
  国内免费   418篇
工业技术   20295篇
  2024年   29篇
  2023年   312篇
  2022年   409篇
  2021年   593篇
  2020年   573篇
  2019年   543篇
  2018年   583篇
  2017年   659篇
  2016年   621篇
  2015年   724篇
  2014年   1038篇
  2013年   1172篇
  2012年   954篇
  2011年   1765篇
  2010年   1330篇
  2009年   1310篇
  2008年   1214篇
  2007年   1078篇
  2006年   1191篇
  2005年   922篇
  2004年   720篇
  2003年   624篇
  2002年   498篇
  2001年   229篇
  2000年   195篇
  1999年   214篇
  1998年   170篇
  1997年   136篇
  1996年   105篇
  1995年   111篇
  1994年   64篇
  1993年   36篇
  1992年   28篇
  1991年   36篇
  1990年   28篇
  1989年   9篇
  1988年   11篇
  1987年   11篇
  1986年   15篇
  1985年   14篇
  1984年   11篇
  1983年   4篇
  1982年   1篇
  1979年   1篇
  1951年   4篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
81.
Only two water works in the UK apply ozone at present as part of their treatment, onefor taste and odor control and theother forcolor removal. Forthetwo applicationus ozone was the most economical option at thetime theplants were installed andozone has been successful for the purpose for which it was designed.  相似文献   
82.
In this study, ferromagnetic microstructures in highly oriented pyrolytic graphite and superparamagnetic spots in polyimide foils were created by 2.25 MeV proton microbeam irradiation and characterized using atomic and magnetic force microscopy. For this purpose, graphite samples were irradiated with cross-like patterns of 15 μm × 15 μm size using ion fluences in the range of (0.003–2.5) × 1018 cm−2. The irradiated crosses showed strong magnetic signals and a complex domain structure in the magnetic images depending on the geometrical dimensions of the crosses. Furthermore, polyimide foils were irradiated with microspots and fluences in the range of (0.016–3.1) × 1019 cm−2. Magnetic force microscopy shows very strong phase shifts in these irradiated areas.  相似文献   
83.
The results of investigation of initial stage of the tantalum borating as well as the effect of oxygen and hydrogen on it are presented. The scheme of the initial stage of tantalum boron saturation is proposed.  相似文献   
84.
85.
86.
单壁碳纳米管的制备及生长特性研究   总被引:1,自引:0,他引:1  
采用Fe/MgO作为催化剂 ,催化裂解CH4制备了较纯的单壁碳纳米管 ,用TEM和Raman对碳纳米管进行了表征 ,对不同生长温度下制备的碳纳米管Raman径向呼吸振动峰 (RBM)进行了分析 ,研究了生长温度对单壁碳纳米管生长特性和结构特性的影响  相似文献   
87.
88.
The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H2S and SO2 in humid air at 25 °C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 °C or with ammonia/steam at 800 °C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption-regeneration cycles showed important differences between oxidative retention of H2S and SO2 and the subsequent catalyst/support regeneration process.  相似文献   
89.
90.
Alumina-supported vanadium oxide, VOx/Al2O3, and binary vanadium–antimony oxides, VSbOx/Al2O3, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by SBET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO2 pulse methods. VSbOx/Al2O3 exhibited enhanced catalytic activity and especially on-stream stability compared to VOx/Al2O3 catalyst. Incorporation of antimony into VOx/Al2O3 increased dispersion of active VOx species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V0.43Sb0.57Ox/Al2O3 system.  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-23

京公网安备 11010802026262号