全文获取类型
收费全文 | 439篇 |
免费 | 32篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 24篇 |
2014年 | 18篇 |
2013年 | 30篇 |
2012年 | 23篇 |
2011年 | 25篇 |
2010年 | 33篇 |
2009年 | 32篇 |
2008年 | 18篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 20篇 |
2004年 | 15篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 17篇 |
1981年 | 6篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1969年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有471条查询结果,搜索用时 390 毫秒
1.
We have determined the canine and feline N-, K-, and H-ras gene sequences from position +23 to +270 covering exons I and II which contain the mutational hot spot codons 12, 13, and
61. The results were used to assess the degree of similarity between ras gene DNA regions containing the critical domains affected in neoplastic disorders in different mammalian species. The comparative
analyses performed included human, canine, feline, murine, rattine, and, whenever possible, bovine, leporine (rabbit), porcelline
(guinea pig), and mesocricetine (hamster) ras gene sequences within the region of interest. Comparison of feline and canine nucleotide sequences with the corresponding
regions in human DNA revealed a sequence similarity greater than 85% to the human sequence. Contemporaneous analysis of previously
published ras DNA sequences from other mammalian species showed a similar degree of homology to human DNA. Most nucleotide differences
observed represented synonymous changes without effect on the amino acid sequence of the respective proteins. For assessment
of the phylogenetic evolution of ras gene family, a maximum parsimony dendrogram based on multiple sequence alignment of the common region of exons I and II in
the N-, K-, and H-ras genes was constructed. Interestingly, a higher substitution rate among the H-ras genes became apparent, indicating accelerated sequence evolution within this particular clade. The most parsimonious tree
clearly shows that the duplications giving rise to the three ras genes must have occurred before the mammalian radiation.
Received: 23 July 1997 / Accepted: 30 October 1997 相似文献
2.
3.
4.
5.
The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
6.
本实验合并应用枸杞有效成份和大蒜有效成份,作用于U_14腹水型宫颈癌小鼠,腹腔注射第四天,发现一般状况改善,取腹水观察,癌细胞破损,DNA、RNA荧光染色强度减弱,有大量白细胞和巨噬细胞围绕;流式细胞分析G_1期细胞堆积,超微结构显示胞质中线粒体肿胀,嵴破坏甚至中空,粗面内质网扩大、脱颗粒,肯定了其作用的效果。此因枸杞有效成分活化巨噬细胞与肿瘤细胞紧密结合而起到溶瘤作用,与大蒜有效成分直接杀伤而作用维持短暂结合起来,可大大提高抗癌作用。 相似文献
7.
8.
9.
10.