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   710787篇
  免费   7152篇
  国内免费   2518篇
化学   355227篇
晶体学   10017篇
力学   36351篇
综合类   78篇
数学   102664篇
物理学   216120篇
  2021年   5818篇
  2020年   6463篇
  2019年   7179篇
  2018年   13665篇
  2017年   14028篇
  2016年   15591篇
  2015年   8029篇
  2014年   12513篇
  2013年   29185篇
  2012年   25232篇
  2011年   33991篇
  2010年   24007篇
  2009年   23861篇
  2008年   31335篇
  2007年   33166篇
  2006年   23931篇
  2005年   24285篇
  2004年   21124篇
  2003年   19391篇
  2002年   18290篇
  2001年   18672篇
  2000年   14590篇
  1999年   11059篇
  1998年   9510篇
  1997年   9338篇
  1996年   8969篇
  1995年   8013篇
  1994年   8064篇
  1993年   7727篇
  1992年   8265篇
  1991年   8670篇
  1990年   8232篇
  1989年   8126篇
  1988年   7916篇
  1987年   7623篇
  1986年   7390篇
  1985年   9574篇
  1984年   9943篇
  1983年   8360篇
  1982年   8776篇
  1981年   8203篇
  1980年   7782篇
  1979年   8332篇
  1978年   8707篇
  1977年   8541篇
  1976年   8564篇
  1975年   8112篇
  1974年   8026篇
  1973年   8386篇
  1972年   6190篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
Journal of Experimental and Theoretical Physics - We suggest that the principle of holographic duality be extended beyond conformal invariance and AdS isometry. Such an extension is based on a...  相似文献   
163.
164.
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   
165.
166.
167.
168.
169.
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   
170.
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   
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