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排序方式: 共有90条查询结果,搜索用时 15 毫秒
1.
Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12
Background
Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis. 相似文献2.
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4.
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
5.
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
6.
To investigate the mechanism(s) of hepatocyte radioresistance (D0 2.7 Gy), the radiosensitivities of respiring (37 degrees C) and nonrespiring (0 degrees C) hepatocytes were determined as a function of oxygen concentration. Fischer 344 female rat hepatocytes were isolated by liver perfusion, equilibrated in Leibowitz-15 media with different oxygen tensions, and exposed to 60Co radiation at either 37 or 0 degrees C. Cell survival and DNA single-strand breaks were used as the biological end points of radiosensitivity. The K value for respiring hepatocytes (37 degrees C) was 14.3 +/- 0.5 mm Hg O2 (18.8 +/- 0.7 mumol O2/liter), demonstrating that the K value for freshly isolated parenchymal hepatocytes is significantly greater than those previously obtained for cultured cells. In contrast, the K value for nonrespiring hepatocytes (0 degree C) is 1.4 +/- 0.4 mm Hg O2 (3.7 +/- 1.0 mumol O2/liter) indicating that hepatocyte respiration results in a plasma membrane-to-nucleus oxygen gradient of approximately 12.9 +/- 0.6 mm Hg (15.1 +/- 1.2 microns O2/liter). The hypothesis that the hepatic nucleus typically resides in a hypoxic condition, although the liver is uniformly perfused with well-oxygenated blood, is supported by (1) the nonradom perinuclear distribution of the mitochondria, (2) the high cellular respiration rate, and (3) the large intracellular oxygen diffusion distance in hepatocytes (25 microns diameter). 相似文献
7.
Phylogenetic utility of the nuclear gene arginine decarboxylase: an example from Brassicaceae 总被引:10,自引:2,他引:8
Arginine decarboxylase (ADC) is an important enzyme in the production of
putrescine and polyamines in plants. It is encoded by a single or low-copy
nuclear gene that lacks introns in sequences studied to date. The rate of
Adc amino acid sequence evolution is similar to that of ndhF for the
angiosperm family studied. Highly conserved regions provide several target
sites for PCR priming and sequencing and aid in nucleotide and amino acid
sequence alignment across a range of taxonomic levels, while a variable
region provides an increased number of potentially informative characters
relative to ndhF for the taxa surveyed. The utility of the Adc gene in
plant molecular systematic studies is demonstrated by analysis of its
partial nucleotide sequences obtained from 13 representatives of
Brassicaceae and 3 outgroup taxa, 2 from the mustard oil clade (order
Capparales) and 1 from the related order Malvales. Two copies of the Adc
gene, Adc1 and Adc2, are found in all members of the Brassicaceae studied
to data except the basal genus Aethionema. The resulting Adc gene tree
provides robust phylogenetic data regarding relationships within the
complex mustard family, as well as independent support for proposed tribal
realignments based on other molecular data sets such as those from
chloroplast DNA.
相似文献
8.
9.
R. Gebhardt R. Jirtle A. F. M. Moorman W. H. Lamers G. Michalopoulos 《Histochemistry and cell biology》1989,92(4):337-342
Summary Isolated rat hepatocytes were transplanted into the interscapular and both anterior lateral fat pads of hepatectomized syngeneic rats. At various time points following transplantation, the fat pads were removed, fixed and embedded in paraffin. Serial sections were stained for glutamine synthetase (GS) and carbamoylphosphate synthetase (CPS) using specific antisera and the PAP technique. The initially low fraction of GS+-heptatocytes remained low up to the fourth day, then increased strikingly up to almost 100% and declined gradually after the 14th day. In contrast, the number of CPS+-cells declined continuously to about 30% after 28 days. If the animals were exposed to CCl4 prior to the isolation of the hepatocytes in order to reduce the number of GS+-cells in the initial cell suspension similar results were obtained and no difference in the probability of the colony formation was noted between this and the normal hepatocyte suspensions indicating that the appearance of the GS+-phenotype was not due to a selective survival of these cells. Analysis of the staining intensity of the transplanted hepatocytes revealed the appearance of two populations of GS+-hepatocytes, one with a strong and one with a weak staining, during the course of formation of larger nodules, while only a single weakly stained population could be discerned with respect to the staining for CPS. These results demonstrate that all hepatocytes or at least their descendents can be induced to express GS by the environmental conditions of the fat pads, and that GS and CPS can be co-expressed with an apparently reciprocal relationship. 相似文献
10.