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   823篇
  免费   106篇
  国内免费   1篇
  2020年   9篇
  2018年   12篇
  2017年   7篇
  2016年   12篇
  2015年   19篇
  2014年   16篇
  2013年   35篇
  2012年   30篇
  2011年   26篇
  2010年   26篇
  2009年   20篇
  2008年   25篇
  2007年   29篇
  2006年   24篇
  2005年   37篇
  2004年   46篇
  2003年   13篇
  2002年   34篇
  2001年   25篇
  2000年   26篇
  1999年   35篇
  1998年   9篇
  1997年   15篇
  1996年   11篇
  1995年   16篇
  1994年   16篇
  1993年   12篇
  1992年   19篇
  1991年   14篇
  1990年   20篇
  1989年   33篇
  1988年   15篇
  1987年   10篇
  1986年   13篇
  1985年   16篇
  1984年   17篇
  1983年   10篇
  1980年   14篇
  1978年   9篇
  1976年   13篇
  1975年   8篇
  1973年   6篇
  1972年   9篇
  1971年   8篇
  1970年   7篇
  1969年   9篇
  1968年   5篇
  1967年   5篇
  1966年   6篇
  1962年   5篇
排序方式: 共有930条查询结果,搜索用时 990 毫秒
1.
E Weir 《CMAJ》2000,162(13):1843-1848
Raves are all-night dance parties attended by large numbers of youth, sometimes in excess of 20,000. The rave scene, which is international in scope, is distinguished by clandestine venues, hypnotic electronic music and the liberal use of drugs such as ecstasy (3,4-methylenedioxymethamphetamine), GHB (gamma-hydroxybutyrate) and ketamine. Several rave-related deaths in Canada in 1999 alerted health authorities, parents and police to the health risks of rave attendance. Family physicians, emergency physicians and pediatricians should have some understanding of raves, the drugs and the health risks so they can effectively counsel and treat patients. The rave culture in Canada and the drugs commonly used at raves are reviewed, and strategies and initiatives for harm reduction are discussed.  相似文献   
2.
The complete sequence of recombinant human interleukin-2 expressed in Escherichia coli has been confirmed by thermospray liquid chromatography-mass spectrometry (TS-LC-MS) of a tryptic digest derived from 100 micrograms (7 nmol) of reduced carboxymethylated interleukin-2. The preparation was shown by this method to contain predominantly unprocessed N-terminal initiator Met, with some authentic N-terminal Ala; the rest of the protein was as predicted from the DNA sequence, though some deamidated material was noted. TS-LC-MS proved to be a rapid and efficient method for surveying the protein tryptic peptide products allowing all the data to be collected in one chromatographic run; all tryptic fragments were identified by their molecular ions including those for the larger peptides (Mr 1500-3500) which, due to the presence of doubly and triply charged molecular ions, were brought within the mass range of the instrument (1800 Da). It is proposed that TS-LC-MS is a good general method for analyzing recombinant protein digests with respect to sequence confirmation, processing, and post-translational modification, and since each chromatographic peak is identified allows for subsequent monitoring of the protein by LC using uv detection. The method suffers from the disadvantages that all the sample is consumed during the experiment and that no fragment (sequence) ions are generally observed.  相似文献   
3.
4.
5.
Summary

Polyunsaturated fatty acids (PUFAs) have been shown to modulate the activity of ionic channels by an unknown mechanism. Some channels are activated (i.e. certain delayed-rectifier, potassium channels) and others are inhibited (i.e. certain calcium, sodium and other potassium channels). We have previously demonstrated that PUFAs can act as electron carriers. It is known that ionic channels can be redox modulated. The ability of fatty acids to serve as electron shuttling agents is proportional to their unsaturation. These PUFAs cause reduction of disulfides through a superoxide radical-independent mechanism, probably related to enhanced electron delocalization. The present study shows that there is a strong correlation between the ability of a PUFA to transfer an electron to a disulfide and its reported ability to modulate ionic channels. This suggests that electron transfer could be the mechanism of PUFAs action on particular ionic channels.  相似文献   
6.
7.
Summary In immobilized cell preparations growth of cells outside the immobilization matrix as free cells is normally undesirable due to the appearance of cells in the product stream and clogging of such systems. Antibiotics could be used to arrest such free cell growth while allowing the synthesis and excretion of the product into the medium. Chloramphenicol (200 /ml) and/or novobiocin (10 /ml), when added during the growth of Bacillus subtilis allowed the production and excretion of lysine into the medium. Chloramphenicol at 200 /ml effectively arrested free cell growth and hence the lysine being produced was almost entirely due to immobilized cells. Novobiocin on the other hand at concentrations of 100 /ml, stopped free cell growth, but also prevented the production of l-lysine. Productivities and yields of lysine were adversely affected by chloramphenicol or novobiocin, probably due to a great decrease in cell viability.Offprint requests to: C. J. Israilides  相似文献   
8.
Our objective was to determine whether hydroxylamine is a possible intermediate in the oxidative conversion of L-arginine to nitric oxide. Vasorelaxation by hydroxylamine is known to be mediated by nitric oxide. The vasorelaxant properties of hydroxylamine were examined using rat aortic rings and an isolated rat lung perfusion model. Hydroxylamine and acetylcholine were equally effective in relaxing norepinephrine-contracted intact aortic rings, whereas only hydroxylamine relaxed aortic rings with endothelium removed. This endothelium-independent vasorelaxation by hydroxylamine indicated that the hydroxylamine-converting enzyme is not localized solely within endothelial cells. Catalase, an enzyme known to oxidize hydroxylamine to nitric oxide, was present in homogenates of intact and endothelium-denuded rings. Cyanamide, another catalase substrate and a known precursor of nitroxyl (HNO), was not a vasorelaxant of aortic rings or of isolated, hypoxia-constricted lungs. These results suggest that free nitroxyl is not an intermediate in the oxidation of hydroxylamine to nitric oxide. An overall pathway for the oxidative conversion of L-arginine through an hydroxylamine intermediate to nitric oxide is proposed.  相似文献   
9.
J P Weir  K R Steffy  M Sethna 《Gene》1990,89(2):271-274
A herpes simplex virus type 1 (HSV-1) insertion vector, pGal8, was designed for analysis of herpesvirus promoters during virus infection. This vector contains a multiple cloning site (MCS) positioned at the 5' end of the lacZ gene for the insertion of promoter sequences. The MCS and lacZ are flanked by sequences from the HSV-1 thymidine kinase encoding gene (tk) to direct homologous recombination into the tk locus of the viral genome. The utility of this vector is demonstrated by construction and comparison of recombinant viruses that express lacZ from the promoters of the genes encoding glycoprotein C, glycoprotein H and glycoprotein E.  相似文献   
10.
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