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   1304420篇
  免费   25722篇
  国内免费   7679篇
化学   645319篇
晶体学   20081篇
力学   73997篇
综合类   102篇
数学   238757篇
物理学   359565篇
  2021年   13471篇
  2020年   15897篇
  2019年   16019篇
  2016年   27303篇
  2015年   20568篇
  2014年   30271篇
  2013年   74135篇
  2012年   35933篇
  2011年   31411篇
  2010年   35723篇
  2009年   38397篇
  2008年   31230篇
  2007年   26398篇
  2006年   33913篇
  2005年   25695篇
  2004年   27700篇
  2003年   26447篇
  2002年   27868篇
  2001年   26219篇
  2000年   23460篇
  1999年   21866篇
  1998年   20768篇
  1997年   20773篇
  1996年   20979篇
  1995年   19068篇
  1994年   18501篇
  1993年   18034篇
  1992年   17764篇
  1991年   18105篇
  1990年   17324篇
  1989年   17392篇
  1988年   16953篇
  1987年   16965篇
  1986年   15852篇
  1985年   22314篇
  1984年   23619篇
  1983年   19871篇
  1982年   21581篇
  1981年   20813篇
  1980年   20150篇
  1979年   20260篇
  1978年   21615篇
  1977年   21186篇
  1976年   20870篇
  1975年   19557篇
  1974年   19182篇
  1973年   19663篇
  1972年   14185篇
  1968年   12059篇
  1967年   12411篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The characterization of the clusters formed on alkaline hydrolysis of [PdCl4]2– was performed using17O,23Na,35Cl,133Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)2] n ·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993.  相似文献   
142.
143.
144.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6.  相似文献   
145.
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity.  相似文献   
146.
New analytical formulas for the torsionL-tensor are reported, which are used in molecular normal mode analysis calculations for the nonlinear transformation of the force constants from internal coordinates to normal coordinates. The proposed formalism exhibits a relative simplicity as compared to previous reported results. Sample calculations for methanol and hydrazine are presented.  相似文献   
147.
We develop an approach to the solution of the spinless Bethe-Salpeter equation for the different-mass case. Although the calculations are developed for spinzero particles in any arbitratry spherically symmetric potential, the non-Coulombic effective power-law potential is used as a kernel to produce the spin-averaged bound states of the non-self-conjugate mesons. The analytical formulas are also applicable to the self-conjugate mesons in the equal-mass case. The flavor-independent case is investigated in this work. The calculations are carried out to the third-order correction of the energy series. Results are consistent with those obtained before.  相似文献   
148.
149.
The electrical conductivity of hydrosols of ultradispersed diamonds was studied. The electromembrane method for cleaning and concentrating of ultradispersed diamonds in hydrosols was considered. The influence exerted by the concentration of the dispersed phase on the electrical characteristics of the cleaning process was analyzed. A mathematical relation making it possible to evaluate the output characteristics of the process and to determine the geometrical characteristics of the apparatus was proposed.  相似文献   
150.
The microhardness and content of carbon in electroplated gold coatings were studied as influenced by the operation time of citrate and citrate-phosphate gold-plating electrolytes. Such physicomechanical properties as porosity, microhardness, internal stress, plasticity, and microstructure of electroless-plated and electroplated nickel coatings were studied and analyzed.  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