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   605115篇
  免费   5057篇
  国内免费   1414篇
化学   294776篇
晶体学   8711篇
力学   31901篇
综合类   19篇
数学   87550篇
物理学   188629篇
  2021年   5209篇
  2020年   5626篇
  2019年   6388篇
  2018年   13144篇
  2017年   13539篇
  2016年   14227篇
  2015年   6834篇
  2014年   10943篇
  2013年   24609篇
  2012年   21728篇
  2011年   30041篇
  2010年   21326篇
  2009年   21309篇
  2008年   27541篇
  2007年   29538篇
  2006年   19645篇
  2005年   20727篇
  2004年   17847篇
  2003年   16638篇
  2002年   15358篇
  2001年   15715篇
  2000年   12228篇
  1999年   9365篇
  1998年   8034篇
  1997年   7882篇
  1996年   7462篇
  1995年   6665篇
  1994年   6648篇
  1993年   6341篇
  1992年   6752篇
  1991年   7230篇
  1990年   6929篇
  1989年   6799篇
  1988年   6673篇
  1987年   6475篇
  1986年   6163篇
  1985年   7788篇
  1984年   8180篇
  1983年   6816篇
  1982年   7126篇
  1981年   6631篇
  1980年   6259篇
  1979年   6828篇
  1978年   7064篇
  1977年   6894篇
  1976年   6874篇
  1975年   6546篇
  1974年   6350篇
  1973年   6677篇
  1972年   4892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.
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...  相似文献   
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