全文获取类型
收费全文 | 208篇 |
免费 | 21篇 |
专业分类
229篇 |
出版年
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 5篇 |
2012年 | 4篇 |
2011年 | 3篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1989年 | 2篇 |
1986年 | 2篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1960年 | 4篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1953年 | 3篇 |
1952年 | 2篇 |
1947年 | 2篇 |
1940年 | 2篇 |
1938年 | 4篇 |
1937年 | 2篇 |
1936年 | 9篇 |
1935年 | 5篇 |
1934年 | 2篇 |
1933年 | 8篇 |
1932年 | 9篇 |
1931年 | 9篇 |
1930年 | 2篇 |
1929年 | 7篇 |
1924年 | 2篇 |
1923年 | 3篇 |
1920年 | 2篇 |
1918年 | 3篇 |
1910年 | 2篇 |
1909年 | 1篇 |
1907年 | 1篇 |
排序方式: 共有229条查询结果,搜索用时 15 毫秒
171.
Balfourier F Roussel V Strelchenko P Exbrayat-Vinson F Sourdille P Boutet G Koenig J Ravel C Mitrofanova O Beckert M Charmet G 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2007,114(7):1265-1275
Bread wheat (Triticum aestivum), one of the world’s major crops, is genetically very diverse. In order to select a representative sample of the worldwide
wheat diversity, 3,942 accessions originating from 73 countries were analysed with a set of 38 genomic simple sequence repeat
(SSR) markers. The number of alleles at each locus ranged from 7 to 45 with an average of 23.9 alleles per locus. The 908
alleles detected were used together with passport data to select increasingly large sub-samples that maximised both the number
of observed alleles at SSR loci and the number of geographical origins. A final core of 372 accessions (372CC) was selected
with this M strategy. All the different geographical areas and more than 98% of the allelic diversity at the 38 polymorphic
loci were represented in this core. The method used to build the core was validated, by using a second set of independent
markers [44 expressed sequence tag (EST)-SSR markers] on a larger sample of 744 accessions: 96.74% of the alleles observed
at these loci had already been captured in the 372CC. So maximizing the diversity with a first set of markers also maximised
the diversity at a second independent set of locus. To relate the genetic structure of wheat germplasm to its geographical
origins, the two sets of markers were used to compute a dissimilarity matrix between geographical groups. Current worldwide
wheat diversity is clearly divided according to wheat’s European and Asian origins, whereas the diversity within each geographical
group might be the result of the combined effects of adaptation of an initial germplasm to different environmental conditions
and specific breeding practices. Seeds from each accession of the 372CC were multiplied and are now available to the scientific
community. The genomic DNA of the 372CC, which can be entirely contained in a 384-deep-well storage plate, will be a useful
tool for future studies of wheat genetic diversity.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
172.
Release of spectrin-free vesicles from human erythrocytes during ATP depletion: 1. characterization of spectrin-free vesicles 总被引:1,自引:0,他引:1 下载免费PDF全文
Human erythrocytes incubated without glucose at 37 degrees C (in vitro aging) release spectrin-free vesicles after 12 or more hours. The release of vesicles is dependent upon ATP depletion. If the endogenous level of ATP is maintained, vesicle release is completely inhibited up to 54 h. Vesicle release is independent of hemolysis because in vitro aged cells and cells that maintain their ATP levels lose identical amounts of hemoglobin up to 45 h. 93 percent of all membrane particles released constitute a uniform population of spheres with a diameter of 185 +/- 23nm. These vesicles are of slightly varying densities due to varying contents of hemoglobin. Vesicles contain half the amount of membrane protein that is found in intact membranes when referred to the content of phospholipids phosphorus. This is primarily due to the absence of spectrin. However, their content of protein component III, glycophorin, and cholesterol remains the same as in intact membranes. Thus, the major integral membrane proteins are present in vesicles in similar quantities were surface area as in cells except for the enzyme acetylcholinesterase that is enriched up to twofold. The phospholipids composition of these vesicles is representative of the intact membrane except that the amount of phosphatidic acid is 10-fold higher and the amount of phosphatidylethanolamine is slightly lower than in erythrocytes. These results suggest a selective release of membrane domains that lack peripheral membrane proteins and are enriched in acetylcholinesterase. This release of spectrin-free vesicles from cells aged in vitro could represent an acceleration of the physiological aging process. 相似文献
173.
Arabidopsis histone deacetylase HDA6 is required for maintenance of transcriptional gene silencing and determines nuclear organization of rDNA repeats 下载免费PDF全文
174.
Bill Pedrini Ching-Ju Tsai Guido Capitani Celestino Padeste Mark S. Hunter Nadia A. Zatsepin Anton Barty W. Henry Benner Sébastien Boutet Geoffrey K. Feld Stefan P. Hau-Riege Richard A. Kirian Christopher Kupitz Marc Messerschmitt John I. Ogren Tommaso Pardini Brent Segelke Garth J. Williams John C. H. Spence Rafael Abela Matthew Coleman James E. Evans Gebhard F. X. Schertler Matthias Frank Xiao-Dan Li 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2014,369(1647)
Membrane proteins arranged as two-dimensional crystals in the lipid environment provide close-to-physiological structural information, which is essential for understanding the molecular mechanisms of protein function. Previously, X-ray diffraction from individual two-dimensional crystals did not represent a suitable investigational tool because of radiation damage. The recent availability of ultrashort pulses from X-ray free-electron lasers (XFELs) has now provided a means to outrun the damage. Here, we report on measurements performed at the Linac Coherent Light Source XFEL on bacteriorhodopsin two-dimensional crystals mounted on a solid support and kept at room temperature. By merging data from about a dozen single crystal diffraction images, we unambiguously identified the diffraction peaks to a resolution of 7 Å, thus improving the observable resolution with respect to that achievable from a single pattern alone. This indicates that a larger dataset will allow for reliable quantification of peak intensities, and in turn a corresponding increase in the resolution. The presented results pave the way for further XFEL studies on two-dimensional crystals, which may include pump–probe experiments at subpicosecond time resolution. 相似文献
175.
176.
177.
Positive selection driving the evolution of a gene of male reproduction, Acp26Aa, of Drosophila: II. Divergence versus polymorphism 总被引:4,自引:1,他引:4
The evolution of the gene for a male ejaculatory protein, Acp26Aa, has been
shown to be driven by positive selection when nonsibling species in the
Drosophila melanogaster subgroup are compared. To know if selection has
been operating in the recent past and to understand the details of its
dynamics, we obtained DNA sequences of Acp26Aa and the nearby Acp26Ab gene
from 39 D. melanogaster chromosomes. Together with the 10 published
sequences, we analyzed 49 sequences from five populations in four
continents. The southern African population is somewhat differentiated from
all other populations, but its nucleotide diversity is lower at these two
loci. We find the following results for Acp26Aa: (1) The R: S (replacement
: silent changes) ratio is significantly higher in the between-species
comparisons than in the within-species data by the McDonald and Kreitman
test. Positive selection is probably responsible for the excess of amino
acid replacements between species. (2) However, within-species nucleotide
diversity is high. Neither the Tajima test nor the Fu and Li test indicates
a reduction in nucleotide diversity due to positive selection in the recent
past. (3) The newly derived nucleotides in D. melanogaster are at high
frequency significantly more often than predicted by the neutral
equilibrium. Since the nearby Acp26Ab gene does not show these patterns,
these observations cannot be attributed to the characteristics of this
chromosomal region. We suggest that positive selection is active, but may
be weak, for each amino acid change in the Acp26Aa gene.
相似文献
178.
179.
180.