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   834490篇
  免费   8745篇
  国内免费   2254篇
化学   422262篇
晶体学   11772篇
力学   41945篇
综合类   26篇
数学   118930篇
物理学   250554篇
  2021年   7033篇
  2020年   7686篇
  2019年   8593篇
  2018年   14537篇
  2017年   14704篇
  2016年   17995篇
  2015年   9876篇
  2014年   15377篇
  2013年   35914篇
  2012年   29457篇
  2011年   38601篇
  2010年   27334篇
  2009年   27194篇
  2008年   35722篇
  2007年   37000篇
  2006年   28785篇
  2005年   28070篇
  2004年   25017篇
  2003年   22754篇
  2002年   21689篇
  2001年   22766篇
  2000年   17714篇
  1999年   13718篇
  1998年   11621篇
  1997年   11311篇
  1996年   10940篇
  1995年   9867篇
  1994年   9777篇
  1993年   9442篇
  1992年   10190篇
  1991年   10553篇
  1990年   10218篇
  1989年   9875篇
  1988年   9757篇
  1987年   9592篇
  1986年   9118篇
  1985年   11773篇
  1984年   12179篇
  1983年   10002篇
  1982年   10384篇
  1981年   9968篇
  1980年   9385篇
  1979年   10090篇
  1978年   10390篇
  1977年   10213篇
  1976年   10131篇
  1975年   9604篇
  1974年   9476篇
  1973年   9675篇
  1972年   6952篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
Temperature dependences of the relative reactivity of potassium aryloxides XC6H4O?K+ toward 2,4‐dinitrophenyl benzoate in 50 mol% dimethylformamide (DMF)–50 mol% H2O mixture have been studied using the competitive reactions technique. Correlation analyses of the relative rate constants kX/kH and differences in the activation parameters (ΔΔН and ΔΔS) of the competitive reactions have revealed the existence of two isokinetic series of the reactions of 2,4‐dinitrophenyl benzoate with potassium aryloxides with electron‐donating substituent (EDS) and electron‐withdrawing substituent (EWS), respectively. We have investigated the effect of the substituent X on the activation parameters for each isokinetic series and concluded that the mechanism of the reactions of 2,4‐dinitrophenyl benzoate with potassium aryloxides XC6H4O?K+ in 50 mol% DMF–50 mol% H2O mixture is the same as in DMF. Analysis of the obtained data with using the method of two‐dimensional reaction coordinate diagram leads to the conclusion that the variation of the solvent from DMF to 50 mol% DMF–50 mol% H2O mixture affects the reaction pathway. The rate constant kX for the reaction of 3‐nitrophenyl benzoate with potassium 4‐methoxyphenoxide and the relative rate constants kX/kH for the reaction of 3‐nitrophenyl benzoate with potassium aryloxides XC6H4O?K+ with EDS were measured in 50 mol% DMF–50 mol% H2O mixtures at 25°C, and it has been shown that the addition of water to DMF does not change the mechanism but slows down these reactions.  相似文献   
183.
184.
185.
186.
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237  相似文献   
187.
Physics of Atomic Nuclei - We have studied the mechanisms influencing production of cumulative pions and protons in the fragmentation of the incident deuterons into cumulative pions and protons...  相似文献   
188.
189.
Journal of Solid State Electrochemistry - The “shuttle effect” of polysulfides is a serious issue, resulting in a decrease in the life-cycle of lithium-sulfur (Li-S) batteries. To...  相似文献   
190.
Russian Journal of Organic Chemistry - A green protocol has been developed for the preparation of 2,2′-(arylmethylene)bis(3-hydroxy-5,5-dimethylcyclohex-2-en-1-ones) following the...  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