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   620429篇
  免费   5940篇
  国内免费   1654篇
化学   320222篇
晶体学   9185篇
力学   29931篇
综合类   22篇
数学   78360篇
物理学   190303篇
  2021年   5392篇
  2020年   5962篇
  2019年   6661篇
  2018年   8862篇
  2017年   8956篇
  2016年   12537篇
  2015年   6909篇
  2014年   11428篇
  2013年   27152篇
  2012年   20812篇
  2011年   24964篇
  2010年   18472篇
  2009年   18160篇
  2008年   23471篇
  2007年   23321篇
  2006年   21464篇
  2005年   19432篇
  2004年   17938篇
  2003年   16174篇
  2002年   16014篇
  2001年   17099篇
  2000年   13276篇
  1999年   10275篇
  1998年   8963篇
  1997年   8842篇
  1996年   8260篇
  1995年   7577篇
  1994年   7431篇
  1993年   7154篇
  1992年   7680篇
  1991年   8140篇
  1990年   7794篇
  1989年   7728篇
  1988年   7594篇
  1987年   7390篇
  1986年   7041篇
  1985年   9064篇
  1984年   9500篇
  1983年   7996篇
  1982年   8505篇
  1981年   7898篇
  1980年   7622篇
  1979年   8087篇
  1978年   8482篇
  1977年   8303篇
  1976年   8263篇
  1975年   7887篇
  1974年   7625篇
  1973年   8099篇
  1972年   5741篇
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
891.
892.
893.
Literatur     
Ohne Zusammenfassung  相似文献   
894.
    
Ohne Zusammenfassung  相似文献   
895.
The principal types of electronic transitions in absorption spectra of deoxyvasicinone and its 6-amino- and 6-nitro-derivatives were determined by analyzing the electron-density distributions in excited states calculated using ZINDO/S.  相似文献   
896.
A model describing the roles of bound and unbound vacancies is proposed in order to predict defect decay and short-range-order kinetics of quenched binary alloys during linear heating experiments. This is an alternative treatment of a previous approach. The model has been applied to the differential scanning calorimetry (DSC) curves of Cu-5 at.% Zn quenched from different temperatures. An expression to calculate the activation energy for migration of solute-vacancy complexes was also developed which make use of DSC trace data. A value of 89.12±0.32 kJ mol-1 was obtained for the above alloy. The relative contribution of bound and unbound vacancies to partition of effective activation energy corresponding to the ordering process as influenced by quenching temperature was also assessed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
897.
Various antimonate compounds are well known as important inorganic ion exchangers, since they resist radiation and chemical degradation and also exhibit selectivities towards different cations. Ceric, silicon, titanium and ferric antimonates were prepared as inorganic ion exchangers. Characterization of these materials has been described using different techniques, including thermal analysis, surface area measurements, X-ray diffraction and IR-spectroscopy. In batch distribution experiments the influence of HNO3 molarity and Mo concentration for Mo sorption on different matrices is described in terms of their retention capacities and distribution coefficients.The selectivities of these exchangers towards molybdenum are in the order: CeSb > SiSb > FeSb > TiSb.  相似文献   
898.
Results of two urgent and practically important directions of research on the indirect oxidation of organic compounds by highly reactive intermediates generated electrochemically from oxygen (HO2 , HO2 ·, HO·) are considered and orderly arranged. The studies in question are the indirect synthesis and mineralization of organic toxicants in waste water.  相似文献   
899.
The thermal conductivity of crystalline chrysotile asbestos made up of hollow tubular Mg3Si2O5(OH)4 filaments is measured in the range 5–300 K. The paper discusses the possibility of using this material in studies of the thermal conductivity of thin filaments of metals and semiconductors incorporated into the channels of crystalline chrysotile asbestos tubes.  相似文献   
900.
Times of longitudinal T 1b and transverse T 2b magnetic relaxation of hexane and decane molecules in micropores of ZSM-5 silicalite were measured as functions of the content of these liquid n-alkanes in zeolite and of temperature. The stepwise changes in the T 1b and T 2b times were revealed in the region of 8% content of hydrocarbons. The observed changes in the concentration and temperature dependences of T 1b and T 2b times are explained by the rearrangement of silicalite crystal lattice under the action of adsorbed molecules.  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