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   2605篇
  免费   71篇
  国内免费   8篇
化学   1935篇
晶体学   15篇
力学   25篇
综合类   1篇
数学   139篇
物理学   569篇
  2022年   20篇
  2021年   25篇
  2020年   35篇
  2019年   46篇
  2018年   32篇
  2017年   18篇
  2016年   57篇
  2015年   45篇
  2014年   54篇
  2013年   106篇
  2012年   145篇
  2011年   186篇
  2010年   83篇
  2009年   103篇
  2008年   158篇
  2007年   164篇
  2006年   128篇
  2005年   121篇
  2004年   122篇
  2003年   100篇
  2002年   86篇
  2001年   52篇
  2000年   34篇
  1999年   43篇
  1998年   28篇
  1997年   30篇
  1996年   36篇
  1995年   28篇
  1994年   25篇
  1993年   31篇
  1992年   33篇
  1991年   31篇
  1990年   29篇
  1989年   25篇
  1988年   37篇
  1987年   28篇
  1986年   15篇
  1985年   27篇
  1984年   35篇
  1983年   19篇
  1982年   17篇
  1981年   23篇
  1980年   25篇
  1979年   23篇
  1978年   24篇
  1977年   24篇
  1976年   13篇
  1975年   13篇
  1974年   16篇
  1969年   11篇
排序方式: 共有2684条查询结果,搜索用时 15 毫秒
31.
32.
33.
Triacetyl--cyclodextrin (TA--CyD), a hydrophobic cyclodextrin derivative, that is insoluble in water, was used to form a complex with flufenamic acid (FA). FA-TA--CyD complex formation was demonstrated by differential scanning calorimetry and powder X-ray diffractometry. The release rate of FA from the FA-TA--CyD complexes in phosphate buffer pH 6.8 was significantly retarded compared to that of FA from the FA and glucose mixture. When the FA-TA--CyD complexes were administered directly into the intraduodenal lumen, the plasma concentration of FA remained at a plateau level (10-18 g/ml) for 6–8 h. An increased mean residence time of FA following FA-TA--CyD complexes administration was observed. These results indicate that TA--CyD may serve as a hydrophobic carrier in prolonged-release preparations of FA.  相似文献   
34.
35.
36.
37.
In the course of a population study of alpha 1-antitrypsin polymorphism by separator isoelectric focusing, a variant phenotype having a somewhat narrower spacing than PI M1M3 was observed in a Japanese blood donor. Family studies by hybrid isoelectric focusing in a carrier ampholyte-supplemented immobilized pH gradient from 4.35-4.65 revealed that the products of the responsible gene, PI*Mtoyoura, were extremely close but slightly cathodal to those of PI*M1. The difference in isoelectric point between them corresponded to the resolving limit of isoelectric focusing. For this reason, although the propositus' father was deduced to have the genotype PI*M1/PI*Mtoyoura, the products of these two genes failed to form a double band pattern. Thus, the gene frequency for PI*Mtoyoura was unknown. These findings, however, indicate that a further microheterogeneity in the PI M subtype exists at least in the Japanese.  相似文献   
38.
A variety of aromatic compounds with both activating and deactivating substituents were brominated with sodium monobromoisocyanurate (SMBI) 1, diethyl ether, diethyl ether-methanesulfonic acid, trifluoroacetic acid, or sulfuric acid were employed as solvents. Thus nitrobenzene was conveniently brominated in sulfuric acid, benzene was readily monobrominated in diethyl ether-methanesulfonic acid, and phenol was selectively brominated at the ortho position under mild conditions in refluxing diethyl ether. With substituents that are easily protonated, trifluoroacetic acid may be employed as solvent in the reaction with 1, in contrast NBS was ineffective in trifluoroacetic acid. This renders 1 a superior reagent relative to NBS. In addition to aromatics, alkenes, ketones and esters were also brominated with 1. Diethyl malonate was brominated with 1 and then subjected to a Bingel reaction with NaH to afford the desired methanofullerene in reasonable yield.  相似文献   
39.
40.
The structures of enopeptins A and B, novel depsipeptide antibiotics with 1,3,5,7,9-decapentaene-1,10-dicarboxylic acid and 2-amino-3-hydroxycyclopent-2-enone in a side chain, were determined by chemical and spectroscopic means.  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