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   4747篇
  免费   714篇
  国内免费   545篇
化学   3536篇
晶体学   52篇
力学   260篇
综合类   36篇
数学   500篇
物理学   1622篇
  2024年   20篇
  2023年   75篇
  2022年   135篇
  2021年   177篇
  2020年   163篇
  2019年   179篇
  2018年   160篇
  2017年   136篇
  2016年   228篇
  2015年   195篇
  2014年   239篇
  2013年   341篇
  2012年   346篇
  2011年   391篇
  2010年   275篇
  2009年   273篇
  2008年   301篇
  2007年   266篇
  2006年   282篇
  2005年   196篇
  2004年   177篇
  2003年   157篇
  2002年   176篇
  2001年   135篇
  2000年   104篇
  1999年   113篇
  1998年   97篇
  1997年   86篇
  1996年   54篇
  1995年   76篇
  1994年   68篇
  1993年   51篇
  1992年   51篇
  1991年   32篇
  1990年   36篇
  1989年   16篇
  1988年   19篇
  1987年   12篇
  1986年   26篇
  1985年   24篇
  1984年   17篇
  1983年   15篇
  1982年   12篇
  1981年   12篇
  1980年   6篇
  1979年   11篇
  1977年   4篇
  1974年   7篇
  1973年   7篇
  1969年   4篇
排序方式: 共有6006条查询结果,搜索用时 0 毫秒
81.
In the product of carbon made from tar oil by plasma pyrogenation, some nanowires, whose diameter is 9~20 nm and whose length is 300 nm were found. The result of X-ray Energy Dispersed Spectrum (EDS) indicated that it is a new compound K2Ti8O15, which has never been reported before. Compared with the corresponding stoichiometry compound K2Ti8O15, it is a non-stoichiometry compound in which two oxygen atoms are absent. It is due to the fact that the intensive deoxidization occured in the experimental process and the valence of titalium is alterable. Its microstructure in detail by high revolution electromicroscopy (HREM) and X-ray diffraction were studied.  相似文献   
82.
83.
Abstract

Blends of poly(pyridinium ethyl methacrylate perchloride) and poly[oligo(oxyethylene) methacrylate-co-acrylamide] were prepared, and the ionic conductivity and mobility of the blends were investigated. Results indicate that both the transference of perchlorate anion and the dissociation of the polymeric salt in the comblike polyether obey the thermoactivation mechanism, and that the perchlorate anion in the blends is free.  相似文献   
84.
Four novel stilbene-twelve alkyl quaternary ammonium salts 5a–d were synthesized. All synthesized compounds were characterized by FT-IR, 1H-NMR and elemental analysis. Compounds 5ad showed efficient whitening effect on cotton fiber and high fastness. Furthermore, compound 5c showed better stability to light than C186 in aqueous solution. The preliminary biological experiment demonstrated compounds 5ad possessed significant antibacterial activities. Among them, compound 5d turned out to be the most active compound against Candida albicans with MIC50 4 μg/mL as well as E. coli with MIC50 16 μg/mL.  相似文献   
85.
The title compound undergoes a novel excited state intramolecular redox reaction in which the 'distal' side chain benzylic alcohol is oxidized to the aldehyde and the carbonyl moieties of anthraquinone reduced, with evidence suggesting that the primary photochemical process is a deprotonation of the benzylic C-H proton (by water) mediated by the solvent.  相似文献   
86.
A theoretical study on the adsorption and decomposition of molybdenum carbonyl on the copper (001) surface is reported. The adsorption structures and energies of Mo(CO)n molecules (n = 1 … 6) are computed systematically using density functional theory with Van der Waals corrections. By analyzing the energies of the various conformations, the main factors that determine the stable adsorption geometry are identified. Insight into the thermodynamics of decomposition is gained by calculating the reaction energy for dissociation of Mo(CO)n into Mo(CO)n?1 and CO. In the gas phase, this reaction is highly endothermic for all n. On the Cu surface, however, removal of the first CO group (n = 6) becomes strongly exothermic. The subsequent dissociation steps (n < 6), are endothermic even on the surface, but the reaction energies are much reduced. Dissociation is found energetically more favorable than desorption in all cases. The results clearly show that molybdenum carbonyl decomposition is strongly facilitated by the presence of the Cu surface. © 2014 Wiley Periodicals, Inc.  相似文献   
87.
Electrochemical impedance spectroscopy (EIS) was first used for the characterization of polyfuran (PFu) films thathad been formed electrochemically on an Au electrode. The polyfuran was measured in high oxidation state, intermediateoxidation state and reduction state, respectively. As the oxidation level is increased, the ionic conductivity of PFu/BF_4~-increases. And impedance studies on PFu show that the anion BF_4~- appears to be mobile with a high diffusion coefficient ofapproximately 10~(-8)cm~2· s~(-1).  相似文献   
88.
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