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   34650篇
  免费   1167篇
  国内免费   1074篇
化学   14380篇
晶体学   301篇
力学   1822篇
综合类   54篇
数学   9718篇
物理学   10616篇
  2023年   138篇
  2022年   209篇
  2021年   207篇
  2020年   241篇
  2019年   260篇
  2018年   1362篇
  2017年   1624篇
  2016年   967篇
  2015年   844篇
  2014年   758篇
  2013年   989篇
  2012年   3642篇
  2011年   2869篇
  2010年   2179篇
  2009年   1837篇
  2008年   955篇
  2007年   956篇
  2006年   931篇
  2005年   4732篇
  2004年   4166篇
  2003年   2470篇
  2002年   639篇
  2001年   426篇
  2000年   197篇
  1999年   328篇
  1998年   225篇
  1997年   191篇
  1996年   172篇
  1995年   161篇
  1994年   129篇
  1993年   97篇
  1992年   229篇
  1991年   220篇
  1990年   203篇
  1989年   162篇
  1988年   141篇
  1987年   84篇
  1986年   75篇
  1985年   63篇
  1984年   42篇
  1983年   37篇
  1976年   81篇
  1975年   37篇
  1974年   41篇
  1973年   48篇
  1972年   39篇
  1970年   34篇
  1969年   37篇
  1968年   35篇
  1966年   37篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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   
22.
The microstructure of CosoNi22Ga28 ribbon with the L10 structure is examined. The band-like morphology is observed. These bands with the width in a range of 40-200 nm appear along the transverse direction of the ribbon. The giant magnetoimpedance (GMI) effect in this alloy is measured. The results show that Co5oNi22Ga28 exhibits a sharp peak of the GAI effect. The maximum GAH ratio up to 360% is detected. The GMI effect measured versus temperature shows large jumps of the magnetoimpedance amplitude at the reversal martensitic transformation temperature 240℃ and Curie temperature 375℃C respectively. The jump ratios of the magnetoimpedance amplitude examined at these temperatures are about 5 and 10, respectively.  相似文献   
23.
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   
24.
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   
25.
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA.  相似文献   
26.
27.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents.  相似文献   
28.
29.
30.
关于实Hilbert环   总被引:2,自引:2,他引:0  
曾广兴  戴执中 《数学学报》1997,40(2):175-184
通过引进“强实Hilbert环”这一概念,本文证明了,一个环A是强实Hilbert环,当且仅当多项式环A[X]是实Hilbert环,当且仅当A[X]的每个实极大理想在A上的局限是实极大的,从而文献[1]中两个主要结果被否定.此外,本文还研究了所谓的“严格的实Hilbert环”,这类环对于半代数零点定理等方面的探讨更具应用意义.  相似文献   
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