全文获取类型
收费全文 | 84篇 |
免费 | 5篇 |
专业分类
89篇 |
出版年
2019年 | 1篇 |
2018年 | 2篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 4篇 |
2012年 | 5篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2009年 | 1篇 |
2008年 | 3篇 |
2007年 | 6篇 |
2006年 | 1篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有89条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
15.
Evolution of eutherian cytochrome c oxidase subunit II: heterogeneous rates of protein evolution and altered interaction with cytochrome c 总被引:3,自引:1,他引:2
Cytochrome c oxidase subunit II (COII), encoded by the mitochondrial
genome, exhibits one of the most heterogeneous rates of amino acid
replacement among placental mammals. Moreover, it has been demonstrated
that cytochrome c oxidase has undergone a structural change in higher
primates which has altered its physical interaction with cytochrome c. We
collected a large data set of COII sequences from several orders of mammals
with emphasis on primates, rodents, and artiodactyls. Using phylogenetic
hypotheses based on data independent of the COII gene, we demonstrated that
an increased number of amino acid replacements are concentrated among
higher primates. Incorporating approximate divergence dates derived from
the fossil record, we find that most of the change occurred independently
along the New World monkey lineage and in a rapid burst before apes and Old
World monkeys diverged. There is some evidence that Old World monkeys have
undergone a faster rate of nonsynonymous substitution than have apes. Rates
of substitution at four-fold degenerate sites in primates are relatively
homogeneous, indicating that the rate heterogeneity is restricted to
nondegenerate sites. Excluding the rate acceleration mentioned above,
primates, rodents, and artiodactyls have remarkably similar nonsynonymous
replacement rates. A different pattern is observed for transversions at
four-fold degenerate sites, for which rodents exhibit a higher rate of
replacement than do primates and artiodactyls. Finally, we hypothesize
specific amino acid replacements which may account for much of the
structural difference in cytochrome c oxidase between higher primates and
other mammals.
相似文献
16.
The Eb beta gene may have acted as the donor gene in a gene conversion-like event generating the Abm 12 beta mutant 总被引:6,自引:0,他引:6 下载免费PDF全文
At least two different class II histocompatibility antigens, I-A and I-E, are encoded by the murine major histocompatibility complex. Both types of class II antigens are composed of polypeptide chains called alpha and beta. Class II antigens display extensive genetic polymorphism, the main part of which resides in the NH2-terminal domains of the A alpha, A beta and E beta chains. Recently it was shown that the mutant gene Abm 12 beta differed from the wild-type gene Ab beta by three nucleotide substitutions, which all occur within a stretch of 14 nucleotides. Multiple substitutions of the type found in the Abm 12 beta gene suggest that the mutant arose by a gene conversion-like event. To examine whether the Eb beta gene may have served as the donor gene in the generation of the Abm 12 beta gene, we have isolated and sequenced a cDNA clone corresponding to the Eb beta gene. Comparisons of the Eb beta, the Ab beta and the Abm 12 beta nucleotide sequences revealed that the Eb beta sequence is identical to that of Abm 12 beta in the positions where the latter differs from the Ab beta sequence. This observation is consistent with the notion that the Abm 12 beta mutant gene arose by a gene conversion-like event involving the Eb beta gene. 相似文献
17.
Michail M. Yakimov Laura Giuliano Simone Cappello Renata Denaro Peter N. Golyshin 《Origins of life and evolution of the biosphere》2007,37(2):177-188
The composition of a metabolically active prokaryotic community thriving in hydrothermal mud fluids of the deep-sea hypersaline
anoxic Western Urania Basin was characterized using rRNA-based phylogenetic analysis of a clone library. The physiologically
active prokaryotic assemblage in this extreme environment showed a great genetic diversity. Most members of the microbial
community appeared to be affiliated to yet uncultured organisms from similar ecosystems, i.e., deep-sea hypersaline basins
and hydrothermal vents. The bacterial clone library was dominated by phylotypes affiliated with the epsilon-Proteobacteria subdivision recognized as an ecologically significant group of bacteria inhabiting deep-sea hydrothermal environments. Almost
18% of all bacterial clones were related to delta-Proteobacteria, suggesting that sulfate reduction is one of the dominant metabolic processes occurring in warm mud fluids. The remaining
bacterial phylotypes were related to alpha- and beta-Proteobacteria, Actinobacteria, Bacteroides, Deinococcus-Thermus, KB1 and OP-11 candidate divisions. Moreover, a novel monophyletic clade, deeply branched with unaffiliated 16S rDNA clones
was also retrieved from deep-sea sediments and halocline of Urania Basin. Archaeal diversity was much lower and detected phylotypes
included organisms affiliated exclusively with the Euryarchaeota. More than 96% of the archaeal clones belonged to the MSBL-1 candidate order recently found in hypersaline anoxic environments,
such as endoevaporitic microbial mats, Mediterranean deep-sea mud volcanoes and anoxic basins. Two phylotypes, represented
by single clones were related to uncultured groups DHVE-1 and ANME-1. Thus, the hydrothermal mud of hypersaline Urania Basin
seems to contain new microbial diversity. The prokaryotic community was significantly different from that occurring in the
upper layers of the Urania Basin since 60% of all bacterial and 40% of all archaeal phylotypes were obtained only from mud
fluids. The uniqueness of the composition of the active prokaryotic community could be explained by the complex environmental
conditions at the site. The interaction of oxygenated warm mud fluids with the cold hypersaline brine of the Urania Basin
seems to simultaneously select for various metabolic processes, such as aerobic and anaerobic heterotrophy, sulfide- and methane-dependent
chemotrophy along with anaerobic oxidation of methane, sulfate- and metal-reduction. 相似文献
18.
Molecular evolution of cytochrome c oxidase: rate variation among subunit VIa isoforms 总被引:2,自引:1,他引:2
Schmidt TR; Jaradat SA; Goodman M; Lomax MI; Grossman LI 《Molecular biology and evolution》1997,14(6):595-601
Cytochrome c oxidase (COX) consists of 13 subunits, 3 encoded in the
mitochondrial genome and 10 in the nucleus. Little is known of the role of
the nuclear-encoded subunits, some of which exhibit tissue-specific
isoforms. Subunit VIa is unique in having tissue-specific isoforms in all
mammalian species examined. We examined relative evolutionary rates for the
COX6A heart (H) and liver (L) isoform genes along the length of the
molecule, specifically in relation to the tissue-specific function(s) of
the two isoforms. Nonsynonymous (amino acid replacement) substitutions in
the COX6AH gene occurred more frequently than in the ubiquitously expressed
COX6AL gene. Maximum-parsimony analysis and sequence divergences from
reconstructed ancestral sequences revealed that after the ancestral COX6A
gene duplicated to yield the genes for the H and L isoforms, the sequences
encoding the mitochondrial matrix region of the COX VIa protein experienced
an elevated rate of nonsynonymous substitutions relative to synonymous
substitutions. This is expected for relaxed selective constraints after
gene duplication followed by purifying selection to preserve the
replacements with tissue-specific functions.
相似文献
19.
Sherin Antony Peeyush Kumar T Jobin Mathew TR Anju CS Paulose 《Journal of biomedical science》2010,17(1):7
Glucose homeostasis in humans is an important factor for the functioning of nervous system. Hypoglycemia and hyperglycemia is found to be associated with central and peripheral nerve system dysfunction. Changes in acetylcholine receptors have been implicated in the pathophysiology of many major diseases of the central nervous system (CNS). In the present study we showed the effects of insulin induced hypoglycemia and streptozotocin induced diabetes on the cerebellar cholinergic receptors, GLUT3 and muscle cholinergic activity. Results showed enhanced binding parameters and gene expression of Muscarinic M1, M3 receptor subtypes in cerebellum of diabetic (D) and hypoglycemic group (D + IIH and C + IIH). α7nAchR gene expression showed a significant upregulation in diabetic group and showed further upregulated expression in both D + IIH and C + IIH group. AchE expression significantly upregulated in hypoglycemic and diabetic group. ChAT showed downregulation and GLUT3 expression showed a significant upregulation in D + IIH and C + IIH and diabetic group. AchE activity enhanced in the muscle of hypoglycemic and diabetic rats. Our studies demonstrated a functional disturbance in the neuronal glucose transporter GLUT3 in the cerebellum during insulin induced hypoglycemia in diabetic rats. Altered expression of muscarinic M1, M3 and α7nAchR and increased muscle AchE activity in hypoglycemic rats in cerebellum is suggested to cause cognitive and motor dysfunction. Hypoglycemia induced changes in ChAT and AchE gene expression is suggested to cause impaired acetycholine metabolism in the cerebellum. Cerebellar dysfunction is associated with seizure generation, motor deficits and memory impairment. The results shows that cerebellar cholinergic neurotransmission is impaired during hyperglycemia and hypoglycemia and the hypoglycemia is causing more prominent imbalance in cholinergic neurotransmission which is suggested to be a cause of cerebellar dysfunction associated with hypoglycemia. 相似文献
20.
Mesocosm experiments were performed to study the changes on bacterial community composition following oil spill in marine environment. The analysis of 16S crDNA revealed a shift in the structure of initial bacterial population that was drastically different from that one measured after 15 days. The results showed that, after 15 days, bacteria closely related to the genus Alcanivorax became the dominant group of bacterial community in petroleum-contaminated sea water nitrogen and phosphorus amended. This suggested that these bacteria played the most important role in the process of bioremediation of oil-contaminated marine environments. 相似文献