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   255篇
  免费   30篇
化学   216篇
晶体学   1篇
力学   4篇
数学   42篇
物理学   22篇
  2021年   3篇
  2020年   4篇
  2019年   12篇
  2018年   1篇
  2017年   3篇
  2016年   15篇
  2015年   13篇
  2014年   13篇
  2013年   17篇
  2012年   20篇
  2011年   18篇
  2010年   14篇
  2009年   16篇
  2008年   19篇
  2007年   12篇
  2006年   14篇
  2005年   10篇
  2004年   13篇
  2003年   7篇
  2002年   9篇
  2001年   6篇
  2000年   4篇
  1999年   2篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1993年   3篇
  1989年   2篇
  1987年   3篇
  1986年   1篇
  1985年   3篇
  1984年   1篇
  1983年   1篇
  1982年   5篇
  1980年   3篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1975年   2篇
  1974年   1篇
  1973年   1篇
  1971年   1篇
  1969年   1篇
  1966年   1篇
  1961年   1篇
  1960年   1篇
排序方式: 共有285条查询结果,搜索用时 15 毫秒
11.
The insertion reaction of CS2 with Mg(NR2)2 (R= Et, iPr), MgR′2 (R′= Et, Ph) and R″MgBr (R″= iPr, Ph) respectively lead solid products, Mg(S2CNR2)2(THF)n ( 1 : R= Et, n=2; 2 : R= iPr, n=1), Mg(S2C′R)2(THF)2 ( 3 : ′R= Et, 4 : ′R= Ph), BrMg(S2C″R) (THF)3 ( 5 : ″R= iPr, 6 : ″R= Ph) in which the inserted carbon disulfides act as terminal chelating ligands. These compounds were characterized with 1H, 13C NMR, IR spectroscopy, mass spectrometry, elemental analyses, and X‐ray crystallography.  相似文献   
12.
13.
Sulfur‐substituted 4‐quinolizidinones, previously prepared by aza‐Diels‐Alder reactions and ring‐closing metathesis, are now subjected to further synthetic transformations. Formal synthesis of cermizine C and 5‐epi‐cermizine C, and some other useful reactions have been achieved.  相似文献   
14.
A new method for the synthesis of highly substituted naphthyridine‐based polyheteroaromatic compounds in high yields proceeds through rhodium(III)‐catalyzed multiple C H bond cleavage and C C and C N bond formation in a one‐pot process. Such highly substituted polyheteroaromatic compounds have attracted much attention because of their unique π‐conjugation, which make them suitable materials for organic semiconductors and luminescent materials. Furthermore, a possible mechanism, which involves multiple chelation‐assisted ortho C H activation, alkyne insertion, and reductive elimination, is proposed for this transformation.  相似文献   
15.
16.
Hsiang WW  Lin CY  Tien MF  Lai Y 《Optics letters》2005,30(18):2493-2495
By employing the technique of asynchronous mode locking, we have successfully demonstrated direct generation of stable 10 GHz 816 fs pulse trains with a supermode-suppression ratio >70 dB from a hybrid mode-locked Er-fiber laser. When the modulation frequency deviates from the cavity harmonic frequency by 15-40 kHz, stable femtosecond soliton pulses are formed. Our results demonstrate that asynchronous mode locking can act as an effective mechanism for achieving a shorter pulse width and for stabilizing high-repetition-rate pulse trains in soliton fiber lasers.  相似文献   
17.
A simple capillary zone electrophoresis method was developed for the quantitative enantiomeric analysis of piperazine antihistamines with teratogenic suspicion in animals. Enantioseparation of chlorcyclizine, hydroxyzine, and meclizine was performed in glycine buffer (0.6 mol L-1; pH 3.00) with sulfated -cyclodextrin (5 mg mL-1) as a chiral selector; and the separated drugs were monitored by ultra-violet detector. The lower quantitation of the individual enantiomer is attainable at 10 µmol L-1, using an achiral piperazine drug (cyclizine) as internal standard. The method is simple and rapid with a short run time (<5 min) for the analysis of chlorcyclizine, hydroxyzine or meclizine enantiomers.  相似文献   
18.
In this study, an improved process for the synthesis of etorphine and dihydroetorphine from codeine with an overall yield of 2.7% and 1.5% respectively is described. The structure of 19‐propylthevinol 7 was verfied by X‐ray structure analysis. This result is promising for synthesizing various morphine‐based drugs.  相似文献   
19.
JavaStatSoft, implemented using Java, is an open-source software for performing statistics. The current features of JavaStatSoft are described. Several well-known patterns the software used are introduced. In addition, based on these patterns and the experience in developing the software, a new framework, referred to as Data Analysis Module, is proposed to help programmers develop a user-friendly software for data analysis.  相似文献   
20.
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