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   1657篇
  免费   63篇
  国内免费   8篇
化学   1307篇
晶体学   31篇
力学   23篇
数学   171篇
物理学   196篇
  2023年   9篇
  2021年   14篇
  2020年   23篇
  2019年   31篇
  2018年   17篇
  2017年   21篇
  2016年   39篇
  2015年   36篇
  2014年   40篇
  2013年   97篇
  2012年   112篇
  2011年   115篇
  2010年   55篇
  2009年   68篇
  2008年   116篇
  2007年   108篇
  2006年   100篇
  2005年   94篇
  2004年   94篇
  2003年   80篇
  2002年   65篇
  2001年   12篇
  2000年   29篇
  1999年   12篇
  1998年   24篇
  1997年   20篇
  1996年   14篇
  1995年   14篇
  1994年   7篇
  1993年   10篇
  1992年   14篇
  1991年   11篇
  1990年   10篇
  1989年   10篇
  1988年   7篇
  1987年   15篇
  1986年   6篇
  1985年   14篇
  1984年   14篇
  1983年   16篇
  1982年   20篇
  1981年   11篇
  1980年   24篇
  1979年   15篇
  1978年   14篇
  1977年   5篇
  1976年   11篇
  1975年   8篇
  1974年   5篇
  1973年   7篇
排序方式: 共有1728条查询结果,搜索用时 564 毫秒
91.
92.
93.
We consider the q-hypergeometric equation with q N = 1 and , , . We solve this equation on the space of functions given by a power series multiplied by a power of the logarithmic function. We prove that the subspace of solutions is two-dimensional over the field of quasi-constants. We get a basis for this space explicitly. In terms of this basis, we represent the q-hypergeometric function of the Barnes type constructed by Nishizawa and Ueno. Then we see that this function has logarithmic singularity at the origin. This is a difference between the q-hypergeometric functions with 0 < |q| < 1 and at |q| = 1.  相似文献   
94.
Intermolecular coupling reactions of 1,3-dienes and aldehydes via transmetalation of nickelacycle intermediate with (i)Bu(2)Al-acac were investigated. In the reactions, a linear adduct or a branched adduct was produced, depending upon the nature of 1,3-dienes and aldehydes, via two nickelacycles that were relatively stable among the four possible nickelacycles because of the equilibrium with pi-allynickel forms.  相似文献   
95.
We have demonstrated that prenylation of p-halophenols was dependent on the solvent effect and succeeded in o,o'-diprenylation of p-halophenols in water. Following the Mizoroki-Heck coupling of the diprenyl-p-iodophenol 3c with methyl acrylate and then hydrolysis, we first synthesized artepillin C [3-(4-hydroxy-3,5-di(3-methyl-2-butenyl)phenyl)-2(E)-propenoic acid] (1), which is a biologically active constituent of propolis. These reactions may be applicable to the synthesis of various useful natural products such as 2,4,6-trisubstituted phenol derivatives.  相似文献   
96.
Sorption and diffusion of water vapor are investigated gravimetrically for polyimide films. The activity dependence of the solubility and diffusion coefficients, S and D, respectively, is classified under four types: (1) constant S and D type, (2) dual-mode sorption and transport type, (3) dual-mode type followed by a deviation due to a plasticization effect at high vapor activity, and (4) constant S and D type followed by a deviation due to water cluster formation at high activity. For the dual-mode type, the Henry's law component is much larger than the Langmuir component except at low activity, and therefore deviation in behavior from the first type is small. S is larger for polyimides with higher content of polar groups such as carbonyl, carboxyl, and sulfonyl. D is larger for polyimides with a higher fraction of free space, with some exceptions. The polyimide from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and dimethyl-3,7-diaminodibenzothiophene-5, 5-dioxide belongs to the third type and displays both large S and large D. The polyimide from 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 4,4′-oxydianiline belongs to the fourth type, and has the largest D but rather small S because of the hydrophobic C(CF3)2 groups. © 1992 John Wiley & Sons, Inc.  相似文献   
97.
The structure of isometries on a Hilbert space are well studied. In this paper we study contractions which are one-dimensional perturbations of isometries, in particular, perturbations of the shift operator onH 2.  相似文献   
98.
99.
100.
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