全文获取类型
收费全文 | 250篇 |
免费 | 39篇 |
国内免费 | 1篇 |
出版年
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 2篇 |
2015年 | 10篇 |
2014年 | 10篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 13篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1985年 | 2篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1977年 | 2篇 |
1972年 | 4篇 |
1970年 | 2篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1954年 | 1篇 |
1951年 | 1篇 |
1910年 | 1篇 |
1887年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有290条查询结果,搜索用时 31 毫秒
61.
Paleolithic and neolithic lineages in the European mitochondrial gene pool. 总被引:36,自引:13,他引:23
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M. Richards H. Crte-Real P. Forster V. Macaulay H. Wilkinson-Herbots A. Demaine S. Papiha R. Hedges H. J. Bandelt B. Sykes 《American journal of human genetics》1996,59(1):185-203
Phylogenetic and diversity analysis of the mtDNA control region sequence variation of 821 individuals from Europe and the Middle East distinguishes five major lineage groups with different internal diversities and divergence times. Consideration of the diversities and geographic distribution of these groups within Europe and the Middle East leads to the conclusion that ancestors of the great majority of modern, extant lineages entered Europe during the Upper Paleolithic. A further set of lineages arrived from the Middle East much later, and their age and geographic distribution within Europe correlates well with archaeological evidence for two culturally and geographically distinct Neolithic colonization events that are associated with the spread of agriculture. It follows from this interpretation that the major extant lineages throughout Europe predate the Neolithic expansion and that the spread of agriculture was a substantially indigenous development accompanied by only a relatively minor component of contemporary Middle Eastern agriculturalists. There is no evidence of any surviving Neanderthal lineages among modern Europeans. 相似文献
62.
63.
Direct comparison of levels of genetic variation among barley accessions detected by RFLPs, AFLPs, SSRs and RAPDs 总被引:38,自引:0,他引:38
J. R. Russell J. D. Fuller M. Macaulay B. G. Hatz A. Jahoor W. Powell R. Waugh 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,95(4):714-722
RFLPs, AFLPs, RAPDs and SSRs were used to determine the genetic relationships among 18 cultivated barley accessions and the
results compared to pedigree relationships where these were available. All of the approaches were able to uniquely fingerprint
each of the accessions. The four assays differed in the amount of polymorphism detected. For example, all 13 SSR primers were
polymorphic, with an average of 5.7 alleles per primer set, while nearly 54% of the fragments generated using AFLPs were monomorphic.
The highest diversity index was observed for AFLPs (0.937) and the lowest for RFLP (0.322). Principal co-ordinate analysis
(PCoA) clearly separated the spring types from the winter types using RFLP and AFLP data with the two-row winter types forming
an intermediate group. Only a small group of spring types clustered together using SSR data with the two-row and six-row winter
varieties more widely dispersed. Direct comparisons between genetic similarity (GS) estimates revealed by each of the assays
were measured by a number of approaches. Spearman rank correlation ranked over 70% of the pairwise comparisons between AFLPs
and RFLPs in the same order. SSRs had the lowest values when compared to the other three assays. These results are discussed
in terms of the choice of appropriate technology for different aspects of germplasm evaluation. 相似文献
64.
Nucleotide sequence analysis of the lemur beta-globin gene family: evidence for major rate fluctuations in globin polypeptide evolution 总被引:1,自引:0,他引:1
Lemur beta-related globin genes have been isolated and sequenced. Orthology
of prosimian and human epsilon-, gamma-, and beta-related globin genes was
established by dot-matrix analysis. All of these lemur globin genes
potentially encode functional beta-related globin polypeptides, though
precisely when the gamma-globin gene is expressed remains unknown. The
organization of the 18-kb brown lemur beta-globin gene cluster (5'
epsilon-gamma-[psi eta-delta]-beta 3') is consistent with its evolution by
contraction via unequal crossing-over from the putative ancestral mammalian
beta-globin gene cluster (5' epsilon-gamma- eta-delta-beta 3'). The dwarf
lemur nonadult globin genes are arranged as in the brown lemur. Similar
levels of synonymous (silent) nucleotide substitutions and noncoding DNA
sequence differences have accumulated between species in all of these
genes, suggesting a uniform rate of noncoding DNA divergence throughout
primate beta-globin gene clusters. These differences are comparable with
those observed in the nonfunctional psi eta pseudogene and have therefore
accumulated at the presumably maximal neutral rate. In contrast,
nonsynonymous (replacement) nucleotide substitutions show a significant
heterogeneity in distribution for both the same gene in different lineages
and different genes in the same lineage. These major fluctuations in
replacement but not silent substitution rates cannot be attributed to
changes in mutation rate, suggesting that changes in the rate of globin
polypeptide evolution in primates is not governed solely by variable
mutation rates.
相似文献
65.
Both adipocyte plasma membranes and microsomes possess insulin-sensitive low Km cyclic AMP phosphodiesterase activity. The activity of the enzyme from both sources was susceptible to activation by several anionic phospholipids. Activators of the plasma membrane enzyme were lysophosphatidylglycerol greater than lysophosphatidylcholine greater than lysophosphatidylserine greater than phosphatidylserine greater than phosphatidylglycerol. These same phospholipids activated the microsomal enzyme but the extent of activation by each phospholipid was reversed. Neutral phospholipids and other anionic phospholipids were without effect. The phospholipids had no effect on high Km cAMP phosphodiesterase in either membrane. The results suggest that the phospholipid headgroup was an important determinant for enzyme activation by phospholipid. The increased susceptibility of the plasma membrane enzyme to lysophospholipid may be attributed to a difference in the plasma membrane enzyme compared to the microsomal membrane enzyme or to differences in plasma membrane and microsomal membrane phospholipid composition and their ability to regulate low Km cAMP phosphodiesterase activity. 相似文献
66.
The ability of nine phospholipids to alter the activity of low-Km cyclic AMP phosphodiesterase was examined in microsomal fractions of rat adipocytes. The enzyme was activated by phosphatidylserine (21% at 300 microM) and phosphatidylglycerol (36% at 300 microM). The activation was concentration dependent over the range 1-1000 microM. Six other phospholipids were without effect. Phosphatidylinositol 4-phosphate inhibited the activity of the enzyme over the same range of concentrations (26% at 300 microM). Phosphatidylserine also activated a partially purified preparation of the enzyme, whereas phosphatidylinositol 4-phosphate was ineffective. The mechanism of the activation of the enzyme by phosphatidylserine and phosphatidylglycerol involved an increase in the apparent Vmax of the enzyme, while the inhibition by phosphatidylinositol 4-phosphate was associated with an increase in the Km of the enzyme for substrate. The phospholipid modulators of low-Km cyclic AMP phosphodiesterase activity did not alter the activity of high-Km cyclic AMP phosphodiesterase. The ability of phospholipids to alter the activity of low-Km cyclic AMP phosphodiesterase in native membranes suggests a possible role for phospholipids in metabolic regulation. 相似文献
67.
M J Seibel W Macaulay R Jelsma F Saed-Nejad A Ratcliffe 《Archives of biochemistry and biophysics》1992,296(2):410-418
The influence of (a) antigen structure, (b) type of monoclonal antibody, and (c) antibody bivalency on the immunochemical detection and quantification of keratan sulfate (KS) from aggrecan has been studied. Apparent KS epitope levels were determined by immunoglobulin G (IgG)-enzyme-linked immunosorbent assay (ELISA) in preparations of human aggrecan and in a defined series of lower molecular weight proteoglycan preparations generated by proteolytic and alkali treatment of aggrecan. Gel filtration chromatography showed KS epitope to be preferentially detected in the higher molecular weight fragments of the preparations. In single KS chains the epitope was detected in the chains of higher M(r). The ability of the proteoglycan to inhibit in the IgG-ELISA decreased with a reduction in proteoglycan fragment size, ranging between 6- and 260-fold, depending on the antibody used. This was considered to be a cooperative binding effect. With most antibodies, the sensitivity of the IgG-ELISA (represented by the steepness of the inhibition slope) was also reduced with smaller inhibitor sizes. The lowest limit of detectability (the amount of KS required to generate 20% inhibition) varied by up to 60-fold depending on the antibody used. The use of monovalent Fab fragments instead of the whole IgG anti-KS antibody in the ELISA showed that the bivalency of the antibody also affected the quantitation of the assay. In the Fab-ELISA the assay was found to have an increased detectability (by 9.5-fold with aggrecan as the inhibitor), and the proteoglycan fragments and aggrecan all generated parallel inhibition curves. Although the Fab-ELISA was somewhat influenced by the structural presentation of the KS, this was not apparent for small fragments and single chains. Thus the effects of cooperative binding and antibody valency could be overcome and quantitative data could be obtained for all samples, using papain-digested samples and the Fab-ELISA. Application of this assay to analysis of body fluids showed the KS-containing fragments in synovial fluid, serum, and urine were of different sizes and could be quantified. 相似文献
68.
69.
Stomata regulate gas exchange and their closure in response to pathogens may, in some cases, contribute to resistance. However, in the cereal mildew and rust systems, stomatal closure follows establishment of compatible infections. In incompatible systems, expression of major (R) gene controlled hypersensitive responses (HR), causes drastic, permanent stomatal dysfunction: stomata become locked open following powdery mildew attack and locked shut following rust attack. Thus, stomatal locking can be a hitherto unsuspected negative consequence of R gene resistance that carries a physiological cost affecting plant performance.Key Words: stomata, rust, mildew, hypersensitive response, stomatal lock-up 相似文献
70.
Salvador Casares Eiso AB Henk Eshuis Obdulio Lopez-Mayorga Nico AJ van Nuland Francisco Conejero-Lara 《BMC structural biology》2007,7(1):22