全文获取类型
收费全文 | 467篇 |
免费 | 53篇 |
出版年
2021年 | 7篇 |
2020年 | 5篇 |
2018年 | 4篇 |
2016年 | 9篇 |
2015年 | 22篇 |
2014年 | 26篇 |
2013年 | 23篇 |
2012年 | 19篇 |
2011年 | 27篇 |
2010年 | 22篇 |
2009年 | 11篇 |
2008年 | 18篇 |
2007年 | 21篇 |
2006年 | 21篇 |
2005年 | 20篇 |
2004年 | 14篇 |
2003年 | 19篇 |
2002年 | 18篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1984年 | 4篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1968年 | 4篇 |
1965年 | 4篇 |
1962年 | 3篇 |
1956年 | 4篇 |
1947年 | 3篇 |
排序方式: 共有520条查询结果,搜索用时 15 毫秒
11.
Population genetics and phylogenetics of DNA sequence variation at multiple loci within the Drosophila melanogaster species complex 总被引:14,自引:1,他引:13
Two regions of the genome, a 1-kbp portion of the zeste locus and a 1.1-
kbp portion of the yolk protein 2 locus, were sequenced in six individuals
from each of four species: Drosophila melanogaster, D. simulans, D.
mauritiana, and D. sechellia. The species and strains were the same as
those of a previous study of a 1.9-kbp region of the period locus. No
evidence was found for recent balancing or directional selection or for the
accumulation of selected differences between species. Yolk protein 2 has a
high level of amino acid replacement variation and a low level of
synonymous variation, while zeste has the opposite pattern. This contrast
is consistent with information on gene function and patterns of codon bias.
Polymorphism levels are consistent with a ranking of effective population
sizes, from low to high, in the following order: D. sechellia, D.
melanogaster, D.mauritiana, and D. simulans. The apparent species
relationships are very similar to those suggested by the period locus
study. In particular, D. simulans appears to be a large population that is
still segregating variation that arose before the separation of D.
mauritiana and D. sechellia. It is estimated that the separation of
ancestral D. melanogaster from the other species occurred 2.5-3.4 Mya. The
separations of D. sechellia and D. mauritiana from ancestral D. simulans
appear to have occurred 0.58- 0.86 Mya, with D. mauritiana having diverged
from ancestral D. simulans 0.1 Myr more recently than D. sechellia.
相似文献
12.
The validity of the methylene blue colorimetric microassay for determining the response of monolayers of human ovarian tumour cell lines to different growth factors was investigated. Linearity of the relationship between cell density and optical density was confirmed for each cell line (r=0.989–0.999,p<0.001), and when initial cell density was optimised to give exponential growth over the assay period, differences in response to medium supplements were obvious. The response of target cells to growth factors, obtained using the methylene blue assay, were compared with, and found to parallel, previously documented responses obtained non-colorimetrically. Thus Mink lung epithelial cells (MLEC) were inhibited by TG (Holleyet al., 1983), EGF had an inhibitory effect on A431 cells (Gill & Lazar, 1981; Barnes, 1982), and the mesothelial cell line showed a proliferative response to EGF and hydrocortisone (Connell and Rheinwald, 1983).The methylene blue colorimetric microssay was found to be a simple, reliable, sensitive method with low variability, for determining the response of cultured cells to growth factors. 相似文献
13.
14.
15.
A rapid radiometric assay for measuring oxygen insensitive methyl red azoreductase has been developed. [14C]Methyl red was synthesized from [U-14C]aniline; the final product had a radiochemical purity of ≥98%. [14C]Methyl red was then used as the substrate to assay azoreductase activity using a modification of a previously published procedure. Results obtained by the radiometric assay were comparable to those obtained using the fluorescent procedure. The radiometric assay is quick, simple, and reliable. Methyl red azoreductase has been shown to be identical with DT-diaphorase [EC 1.6.99.2]. The assay described can therefore be used to assay DT-diaphorase activity and does not suffer from the limitations, such as lack of specificity and low sensitivity, usually associated with DT-diaphorase assays. 相似文献
16.
17.
18.
19.
20.
Bridgett M. vonHoldt John P. Pollinger Dent A. Earl Heidi G. Parker Elaine A. Ostrander Robert K. Wayne 《Mammalian genome》2013,24(1-2):80-88
The ability to detect recent hybridization between dogs and wolves is important for conservation and legal actions, which often require accurate and rapid resolution of ancestry. The availability of a genetic test for dog–wolf hybrids would greatly support federal and legal enforcement efforts, particularly when the individual in question lacks prior ancestry information. We have developed a panel of 100 unlinked ancestry-informative SNP markers that can detect mixed ancestry within up to four generations of dog–wolf hybridization based on simulations of seven genealogical classes constructed following the rules of Mendelian inheritance. We establish 95 % confidence regions around the spatial clustering of each genealogical class using a tertiary plot of allele dosage and heterozygosity. The first- and second-backcrossed-generation hybrids were the most distinct from parental populations, with >90 % correctly assigned to genealogical class. In this article we provide a tool kit with population-level statistical quantification that can detect recent dog–wolf hybridization using a panel of dog–wolf ancestry-informative SNPs with divergent allele frequency distributions. 相似文献