全文获取类型
收费全文 | 402篇 |
免费 | 59篇 |
出版年
2021年 | 8篇 |
2018年 | 10篇 |
2016年 | 6篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 20篇 |
2012年 | 14篇 |
2011年 | 11篇 |
2010年 | 8篇 |
2009年 | 16篇 |
2008年 | 13篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 14篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1980年 | 4篇 |
1979年 | 16篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 5篇 |
1972年 | 10篇 |
1971年 | 7篇 |
1970年 | 3篇 |
1969年 | 9篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1961年 | 3篇 |
排序方式: 共有461条查询结果,搜索用时 234 毫秒
11.
The use of phosphorothioate-modified DNA in restriction enzyme reactions to prepare nicked DNA 总被引:55,自引:18,他引:37
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The RF IV form of M13 DNA was synthesized enzymatically in vitro, using the viral (+)strand as template, to contain phosphorothioate-modified internucleotidic linkages of the Rp configuration on the 5' side of every base of a particular type in the newly-synthesized (-)strand. Twenty nine restriction enzymes were then tested for their reactions with the appropriate modified DNA types having a phosphorothioate linkage placed exactly at the cleavage site(s) of these enzymes in the (-)strand. Eleven of the seventeen restriction enzymes tested that had recognition sequences of five bases or more could be used to convert the phosphorothioate DNA entirely into the nicked form, either by simply allowing the reaction to go to completion with excess enzyme (Ava I, Ava II, Ban II, Hind II, Nci I, Pst I or Pvu I) or by stopping the reaction at the appropriate time before the nicked DNA is linearized (Bam HI, Bgl I, Eco RI or Hind III). Only modification of the exact cleavage site in the (-)strand could block linearization by the first class of enzymes. The results presented imply that the restriction enzyme-directed nicking of phosphorothioate M13 DNA occurs exclusively in the (+)strand. 相似文献
12.
Inhibition of restriction endonuclease Nci I cleavage by phosphorothioate groups and its application to oligonucleotide-directed mutagenesis. 总被引:109,自引:13,他引:96
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M13 RF IV DNA where phosphorothioate groups are incorporated at restriction endonuclease Nci I recognition sites in the (-)strand is efficiently nicked by the action of this enzyme. Incubation of such nicked DNA with exonuclease III produces gapped DNA. The gap can be filled by reaction with deoxynucleoside triphosphates and DNA polymerase I. When this sequence of reactions is performed with DNA containing a mismatch oligonucleotide primer in the (-)-strand mutational frequencies of 70-90% can be obtained upon transformation. The general nature of this methodology has been further shown to be applicable to other restriction enzymes such as Hind II, Pst I and Fsp I. The mutational frequency obtained using these enzymes is between 40-80% mainly because of less efficient nicking and gapping. Studies on inhibition of Nci I cleavage show that in addition to a phosphorothioate group at the position of cleavage an additional group in the 5'-neighbouring position is necessary for complete inhibition. 相似文献
13.
Stereochemical course of DNA hydrolysis by nuclease S1 总被引:9,自引:0,他引:9
Nuclease S1 hydrolyzes the Sp-diastereomer of 5'-O-(2'-deoxyadenosyl)-3'-O-thymidyl phosphorothioate in H2(18)O to [18O]deoxyadenosine 5'-O-phosphorothioate which can be phosphorylated enzymatically to the Sp-diastereomer of [alpha-18O]deoxyadenosine 5'-O-(1-thiotriphosphate). 31P nmr spectroscopy shows the oxygen-18 in this compound to be in a nonbridging position at the alpha-phosphorus, indicating that the hydrolysis reaction catalyzed by nuclease S1 proceeds with inversion of configuration at phosphorus. This result is compatible with a direct nucleophilic attack of H2O at phosphorus without the involvement of a covalent enzyme intermediate. 相似文献
14.
15.
This investigation was undertaken to study heat stress and dehydration effects on 1) plasma lactic acid (LA) concentration and 2) plasma LA effect on plasma volume conservation during thermal dehydration. Experiments were performed on conscious nonacclimated and heat-acclimated laboratory rats subjected to various levels of heat stress and/or dehydration (37-42 degrees C with and without drinking water). During the exposures, rectal temperature (Tre), plasma LA pyruvic acids, and hematocrit were measured. From these data, excess LA, indicative of anaerobic metabolism, was calculated. In separate experiments, transvascular protein efflux (half time of Evans blue-labeled albumin) was measured before and after plasma LA elevation, either by LA infusion or thermal dehydration. The results show that elevation of plasma LA was associated with a rise in Tre, with accelerated elevation within a Tre range of 41-42 degrees C. LA concentrations were similar for the same Tre in all experimental groups. In nonacclimated rats, this rise was accompanied by a significant rise in excess LA. In acclimated rats, only a minor rise in excess LA was observed. A positive correlation was found between plasma LA elevation and the increase in plasma protein efflux. It is concluded that there is a temperature threshold for the rise in plasma LA. In nonacclimated rats, local hypoxia may contribute to this rise. The data also suggest that, in nonacclimated rats, lactacidemia accelerates plasma protein and fluid loss, leading to circulatory failure during acute thermal dehydration. 相似文献
16.
17.
alpha 1-Proteinase inhibitor (alpha 1-PI), a member of the serine
proteinase inhibitor superfamily, has a primary role in controlling
neutrophil elastase activity within the mammalian circulation. Several
studies have indicated that the reactive center region of alpha 1-PI, the
amino acid sequence of which is critical to recognition of and binding to
target proteinases, is highly divergent within and among species. This
appears to be a consequence of accelerated rates of evolution that may have
been driven by positive Darwinian selection. In order to examine this and
other features of alpha 1-PI evolution in more detail, we have isolated and
sequenced cDNAs representing alpha 1- PI mRNAs of the mouse species Mus
saxicola and Mus minutoides and have compared these with a number of other
mammalian alpha 1-PI mRNAs. Relative to other mammalian mRNAs, the extent
of nonsynonymous substitution is generally high throughout the alpha 1-PI
mRNA molecule, indicating greater overall rates of amino acid substitution.
Within and among mouse species, the 5'-half of the mRNA, but not the
3'-half, has been homogenized by concerted evolution. Finally, the reactive
center is under diversifying or positive Darwinian selection in murid
rodents (rats, mice) and guinea pigs yet is under purifying selection in
primates and artiodactyls. The significance of these findings to alpha 1-PI
function and the possible selective forces driving evolution of serpins in
general are discussed.
相似文献
18.
Mitochondrial DNA polymorphisms in subterranean mole-rats of the Spalax ehrenbergi superspecies in Israel, and its peripheral isolates 总被引:1,自引:0,他引:1
Nevo E; Honeycutt RL; Yonekawa H; Nelson K; Hanzawa N 《Molecular biology and evolution》1993,10(3):590-604
Patterns of mitochondrial DNA (mtDNA) variation were examined in 133
mole-rats constituting all four chromosomal species (2n = 52, 2n = 54, 2n =
58, and 2n = 60) of the Spalax ehrenbergi superspecies in Israel, as well
as the peripheral isolates of 2n = 60. In the main range of the complex, a
total of 28 mtDNA haplotypes were found in 64 mole-rats, with most
haplotypes being unique to either a single chromosomal species or
population. mtDNA divergence increased from low to high diploid number in a
north-to-south direction in Israel. Overall levels of mtDNA diversity were
unexpectedly the highest in the 2n = 60, the youngest species of the
complex. The mtDNA haplotypes can be separated into two major groups, 2n =
52-54 and 2n = 58-60, and a phylogenetic analysis for each group revealed
evidence of a few haplotypes not sorted by diploid number. The overall
patterns of mtDNA divergence seen within and among the four chromosomal
species are consistent with the parapatric mode of speciation as suggested
from previous studies of allozyme and DNA hybridization. In a separate data
set the patterns of mtDNA variation were examined across the main
geographic range and across peripheral semi-isolates and isolates of the 2n
= 60 chromosomal species. Fifteen haplotypes were found in 69 mole-rats.
High levels of mtDNA diversity characterized the main range, semi-isolated,
and even some desert isolated populations. The peripheral isolates contain
much mtDNA diversity, including novel haplotypes.
相似文献
19.
20.