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   551731篇
  免费   4839篇
  国内免费   1545篇
化学   276977篇
晶体学   7431篇
力学   27252篇
综合类   29篇
数学   76409篇
物理学   170017篇
  2021年   5032篇
  2020年   5504篇
  2019年   6237篇
  2018年   9538篇
  2017年   9903篇
  2016年   12272篇
  2015年   6684篇
  2014年   10883篇
  2013年   24082篇
  2012年   21125篇
  2011年   23854篇
  2010年   17772篇
  2009年   17480篇
  2008年   21178篇
  2007年   21054篇
  2006年   19165篇
  2005年   20643篇
  2004年   19027篇
  2003年   16046篇
  2002年   14293篇
  2001年   14905篇
  2000年   11420篇
  1999年   8869篇
  1998年   7696篇
  1997年   7530篇
  1996年   6978篇
  1995年   6294篇
  1994年   6307篇
  1993年   6039篇
  1992年   6500篇
  1991年   6979篇
  1990年   6668篇
  1989年   6570篇
  1988年   6389篇
  1987年   6180篇
  1986年   5896篇
  1985年   7430篇
  1984年   7792篇
  1983年   6551篇
  1982年   6839篇
  1981年   6245篇
  1980年   5911篇
  1979年   6454篇
  1978年   6680篇
  1977年   6610篇
  1976年   6598篇
  1975年   6275篇
  1974年   6101篇
  1973年   6436篇
  1972年   4704篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Journal of Thermal Analysis and Calorimetry - This article considers viscoelastic effects on the enhancement of transportation of heat in thin-film flow when the relaxation time phenomenon is...  相似文献   
132.
Journal of Computer-Aided Molecular Design - Accurate predictions of acid dissociation constants are essential to rational molecular design in the pharmaceutical industry and elsewhere. There has...  相似文献   
133.
This mini-review highlights key structural features that should be taken into account when creating ambipolar redox-active closed-shell metal-free molecules. This type of compound is strongly required for the fabrication of all-organic ‘poleless’ batteries and semiconductors. The suggested strategies aimed at stabilization of both oxidized (cationic) and reduced (anionic) redox-states are based on the comprehensive analysis of the most successful structures taken from the recent publications.  相似文献   
134.
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   
135.
136.
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   
137.
138.
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   
139.
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   
140.
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