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   37790篇
  免费   597篇
  国内免费   291篇
化学   16857篇
晶体学   383篇
力学   1547篇
综合类   12篇
数学   10005篇
物理学   9874篇
  2023年   70篇
  2022年   94篇
  2021年   147篇
  2020年   255篇
  2019年   230篇
  2018年   1283篇
  2017年   1555篇
  2016年   1021篇
  2015年   845篇
  2014年   811篇
  2013年   1067篇
  2012年   3644篇
  2011年   2928篇
  2010年   2153篇
  2009年   1849篇
  2008年   1022篇
  2007年   1040篇
  2006年   1010篇
  2005年   4750篇
  2004年   4229篇
  2003年   2570篇
  2002年   747篇
  2001年   455篇
  2000年   258篇
  1999年   295篇
  1998年   217篇
  1997年   192篇
  1996年   168篇
  1995年   163篇
  1994年   174篇
  1993年   125篇
  1992年   266篇
  1991年   242篇
  1990年   213篇
  1989年   202篇
  1988年   183篇
  1987年   134篇
  1986年   107篇
  1985年   88篇
  1984年   68篇
  1983年   80篇
  1981年   91篇
  1980年   72篇
  1979年   96篇
  1978年   99篇
  1977年   75篇
  1976年   131篇
  1975年   70篇
  1974年   74篇
  1973年   85篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
In this paper we present a method to solve numerically elliptic problems with multi-scale data using multiple levels of not necessarily nested grids. The method consists in calculating successive corrections to the solution in patches whose discretizations are not necessarily conforming. It resembles the FAC method (see Math. Comp. 46 (174) (1986) 439–456) and its convergence is obtained by a domain decomposition technique (see Math. Comp. 57 (195) (1991) 1–21). However it is of much more flexible use in comparison to the latter. To cite this article: R. Glowinski et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003).  相似文献   
23.
24.
Could simple intraannular-arm macrocyclic systems exist in enantiopure stable forms? The effective synthesis of two representative compounds of such a class, their resolution into enantiomers, and experiments justifying their stability toward racemization are presented.  相似文献   
25.
26.
Comparison of the anion binding properties of a series of uncharged macrocyclic tetraamides reveal significant effects of the receptor's size on the strength of its anion complexes. This study allowed for estimation of the optimal size of a macroring for complexation of common anions.  相似文献   
27.
The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis.  相似文献   
28.
The electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols on graphite electrodes was studied using cyclic voltammetry, chronoamperometry, constant-potential coulometry and preparative constant-potential electrolysis techniques. The data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro disc Pt-electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The compounds were subjected to constant-potential preparative electrolysis and the electrolysis products were purified and identified by spectroscopic methods. Based on these findings, a mechanism for the electro-reduction process is proposed.  相似文献   
29.
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA.  相似文献   
30.
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