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   655461篇
  免费   7299篇
  国内免费   1745篇
化学   326169篇
晶体学   8542篇
力学   33989篇
综合类   26篇
数学   107134篇
物理学   188645篇
  2021年   5792篇
  2020年   6374篇
  2019年   7077篇
  2018年   18919篇
  2017年   18657篇
  2016年   18913篇
  2015年   8615篇
  2014年   12443篇
  2013年   27224篇
  2012年   25576篇
  2011年   35008篇
  2010年   23794篇
  2009年   23695篇
  2008年   29843篇
  2007年   31488篇
  2006年   21895篇
  2005年   21035篇
  2004年   19856篇
  2003年   18030篇
  2002年   16576篇
  2001年   15873篇
  2000年   12461篇
  1999年   9507篇
  1998年   8210篇
  1997年   8018篇
  1996年   7745篇
  1995年   6835篇
  1994年   6850篇
  1993年   6660篇
  1992年   6980篇
  1991年   7363篇
  1990年   6998篇
  1989年   6889篇
  1988年   6676篇
  1987年   6474篇
  1986年   6223篇
  1985年   7924篇
  1984年   8220篇
  1983年   6867篇
  1982年   7231篇
  1981年   6738篇
  1980年   6382篇
  1979年   6834篇
  1978年   7097篇
  1977年   6894篇
  1976年   6902篇
  1975年   6573篇
  1974年   6420篇
  1973年   6705篇
  1972年   4838篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
961.
962.
Literatur     
Ohne Zusammenfassung  相似文献   
963.
    
Ohne Zusammenfassung  相似文献   
964.
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   
965.
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   
966.
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points.  相似文献   
967.
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   
968.
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   
969.
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   
970.
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