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   620193篇
  免费   5941篇
  国内免费   1654篇
化学   320012篇
晶体学   9185篇
力学   29926篇
综合类   22篇
数学   78360篇
物理学   190283篇
  2021年   5384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 15 毫秒
141.
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   
142.
143.
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   
144.
145.
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   
146.
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   
147.
148.
149.
150.
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