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   1432499篇
  免费   29380篇
  国内免费   7851篇
化学   722650篇
晶体学   21099篇
力学   77177篇
综合类   131篇
数学   251031篇
物理学   397642篇
  2021年   13632篇
  2020年   16056篇
  2019年   16155篇
  2018年   16791篇
  2017年   15523篇
  2016年   29909篇
  2015年   21404篇
  2014年   30680篇
  2013年   74895篇
  2012年   43139篇
  2011年   44566篇
  2010年   41242篇
  2009年   42822篇
  2008年   42562篇
  2007年   39782篇
  2006年   40713篇
  2005年   36198篇
  2004年   35201篇
  2003年   32196篇
  2002年   32249篇
  2001年   31561篇
  2000年   26749篇
  1999年   23443篇
  1998年   21448篇
  1997年   21368篇
  1996年   21351篇
  1995年   19315篇
  1994年   18809篇
  1993年   18375篇
  1992年   18569篇
  1991年   18842篇
  1990年   17997篇
  1989年   18023篇
  1988年   17656篇
  1987年   17584篇
  1986年   16472篇
  1985年   22891篇
  1984年   24086篇
  1983年   20196篇
  1982年   21798篇
  1981年   21015篇
  1980年   20378篇
  1979年   20708篇
  1978年   21923篇
  1977年   21539篇
  1976年   21298篇
  1975年   20008篇
  1974年   19703篇
  1973年   20136篇
  1972年   14614篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
251.
ABSTRACT

A new density functional for the study of associating inhomogeneous fluids based on Wertheim's first-order thermodynamic perturbation theory is presented and compared to the most currently used associating density functionals. This functional is developed using the weighted density approximation in the range of association of hard spheres. We implement this functional within the framework of classical density functional theory together with modified fundamental measure theory to account for volume exclusion of hard spheres. This approach is tested against molecular simulations from literature of pure associating hard spheres and mixtures of non-associationg and associating hard spheres with different number of bonding sites close to a hard uniform wall. Furthermore, we compare and review our results with the performance of associating functionals from literature, one based on fundamental measure theory and the inhomogeneous version of Wertheim's perturbation theory. Results obtained with classical DFT and the three functionals show excellent agreement with molecular simulations in systems with one hard wall. For the cases of small pores where only one or two layers of fluid are allowed discrepancies between results with classical DFT and molecular simulations were found.  相似文献   
252.
253.
254.
255.
Journal of Structural Chemistry - Thermodynamic characteristics are calculated for aqueous alkanolamine solutions that are obtained by substituting alkyl radicals for the protons in the amino group...  相似文献   
256.
The first immobilized catalyst for Ir‐catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π‐allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments.  相似文献   
257.
The current work utilizes three separate techniques to study the physical aging process in amorphous poly(ethylene furanoate) (PEF), which is a recently introduced engineering thermoplastic with enhanced properties compared to petroleum‐sourced poly(ethylene terephthalate). Differential scanning calorimetry aging experiments were conducted at multiple aging temperatures and times, and the resultant enthalpic recovery values compared to the theoretical maximum enthalpy loss evaluated from calculations involving extrapolation of the equilibrium liquid line. Density measurements reveal densification of the matrix for the aged versus unaged samples, and provide an estimate for the reduction in free volume for the aged samples. Complementary oxygen permeation and pressure‐decay sorption experiments provide independent verification of the free volume reduction mechanism for physical aging in glassy polymers. The current work provides the first detailed aging study for PEF. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 389–399  相似文献   
258.
259.
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs).  相似文献   
260.
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