全文获取类型
收费全文 | 196篇 |
免费 | 15篇 |
出版年
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 10篇 |
2014年 | 8篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2009年 | 6篇 |
2008年 | 3篇 |
2007年 | 5篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有211条查询结果,搜索用时 312 毫秒
1.
2.
Pertussis toxin as a probe of neutrophil activation 总被引:11,自引:0,他引:11
E L Becker J C Kermode P H Naccache R Yassin J J Munoz M L Marsh C K Huang R I Sha'afi 《Federation proceedings》1986,45(7):2151-2155
In reviewing our own and other work, it is clear that pertussis toxin treatment of neutrophils causes a time- and concentration-dependent inhibition of granule enzyme secretion induced by formylmethionylleucylphenylalanine (fMet-Leu-Phe), C5a, leukotriene (LT) B4 and platelet-activating factor (PAF). Chemotaxis, O2- generation, aggregation, and arachidonic acid production induced by fMet-Leu-Phe are also inhibited by pertussis toxin. Granule enzyme release caused by A23187 or phorbol 12-myristate 13-acetate is not inhibited. The inhibition of neutrophil function correlates closely with the NAD-ribosylation of a 41,000-dalton protein in the neutrophil plasma membrane, presumably the GTP-binding regulatory protein Ni. Pertussis toxin treatment prevents or obtunds the increased influx of Ca2+ induced by fMet-Leu-phe and LTB4, but not that caused by stimulation of neutrophils with PAF. Pertussis toxin prevents the receptor-induced breakdown of polyphosphoinositides in intact neutrophils and isolated membrane and prevents or decreases the production of inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol. The hypothesis advanced by us and others is that pertussis toxin interacts with a GTP-binding regulatory protein identical or similar to Ni, which couples receptor-chemotactic factor interaction to phospholipase C activation. Inhibition of the activation prevents the production of IP3 and the resulting release of Ca2+ from intracellular stores and of 1,2-diacylglycerol and thus, the activation of protein kinase C. The lack of these two mediators is the immediate cause of the depression of neutrophil activation resulting from pertussis toxin. Some of the limitations and uncertainties of our present knowledge with respect to this hypothesis are discussed. 相似文献
3.
The inhibition of neutrophil granule enzyme secretion and chemotaxis by pertussis toxin 总被引:21,自引:2,他引:19
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
E L Becker J C Kermode P H Naccache R Yassin M L Marsh J J Munoz R I Sha'afi 《The Journal of cell biology》1985,100(5):1641-1646
Pertussis toxin treatment of rabbit peritoneal neutrophils causes a concentration-dependent inhibition of granule enzyme secretion induced by formylmethionyl-leucyl-phenylalanine, C5a, and leukotriene B4. It also inhibits chemotaxis induced by formylmethionyl-leucyl-phenylalanine. The same toxin treatment, however, has no effect on granule enzyme secretion induced by the calcium ionophore A23187 or phorbol 12-myristate 13-acetate. Moreover, pertussis toxin treatment does not affect either the number or affinity of the formylpeptide receptors on the neutrophil nor does it have any effect on the unstimulated levels of cyclic AMP (cAMP) or the transient rise in cAMP induced by chemotactic factor stimulation in these cells. We hypothesize that pertussis toxin, as in other cells, interacts with a GTP binding regulatory protein identical with or analogous to either Ni or transducin which mediates the receptor-induced inhibition or activation of a target protein or proteins required in neutrophil activation. The nature of the target protein is unknown, but it is not the catalytic unit of adenylate cyclase. The target protein acts after binding of chemotactic factor to its receptor in the sequence that leads to the receptor-induced rise in intracellular Ca2+. It does not affect the responses elicited by the direct introduction of calcium into the cells or the activity of protein kinase C. 相似文献
4.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
5.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
6.
Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves 总被引:4,自引:0,他引:4
A puzzling population-genetic phenomenon widely reported in allozyme
surveys of marine bivalves is the occurrence of heterozygote deficits
relative to Hardy-Weinberg expectations. Possible explanations for this
pattern are categorized with respect to whether the effects should be
confined to protein-level assays or are genomically pervasive and expected
to be registered in both protein- and DNA-level assays. Anonymous nuclear
DNA markers from the American oyster were employed to reexamine the
phenomenon. In assays based on the polymerase chain reaction (PCR), two
DNA-level processes were encountered that can lead to artifactual genotypic
scorings: (a) differential amplification of alleles at a target locus and
(b) amplification from multiple paralogous loci. We describe symptoms of
these complications and prescribe methods that should generally help to
ameliorate them. When artifactual scorings at two anonymous DNA loci in the
American oyster were corrected, Hardy-Weinberg deviations registered in
preliminary population assays decreased to nonsignificant values.
Implications of these findings for the heterozygote-deficit phenomenon in
marine bivalves, and for the general development and use of PCR-based
assays, are discussed.
相似文献
7.
8.
9.
The 5[prime] Flanking Regions of Vicilin and Napin Storage Protein Genes Are Down-Regulated by Desiccation in Transgenic Tobacco 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Drying of seeds, when imposed prematurely, elicits a switch in metabolism; events unique to development, such as synthesis of storage protein, are terminated, whereas syntheses associated with germination and growth are initiated. To determine the role of desiccation in down-regulating the expression of genes for storage proteins, the desiccation responsiveness of the 5[prime] and 3[prime] regulatory regions of the genes encoding the pea storage protein vicilin and the Brassica napus storage protein napin was tested in transgenic tobacco seed. Chimeric genes were introduced into tobacco; these genes consisted of the coding region of the reporter gene for [beta]-glucuronidase (GUS) and 5[prime] and/or 3[prime] regions from the vicilin or napin genes or, as controls, the same regions derived from constitutively expressed genes, presumed to be desiccation insensitive. In transgenic seed expressing the gene constructs containing the vicilin or napin promoters, GUS activities declined during late seed development, and more dramatically, after imbibition of mature dry seed or prematurely dried seed. In contrast, GUS activities increased after seed rehydration when the constitutive viral promoter replaced the storage-protein gene 5[prime] region. Transient expression assays support the hypothesis that premature drying down-regulates the expression of the storage-protein gene promoter. Following desiccation, this region may become insensitive to positive controlling factors; alternatively, changes to trans-acting factors may occur. 相似文献
10.
A highly conserved nuclear gene for low-level phylogenetics: elongation factor-1 alpha recovers morphology-based tree for heliothine moths 总被引:8,自引:2,他引:6
Cho S; Mitchell A; Regier JC; Mitter C; Poole RW; Friedlander TP; Zhao S 《Molecular biology and evolution》1995,12(4):650-656
Molecular systematists need increased access to nuclear genes. Highly
conserved, low copy number protein-encoding nuclear genes have attractive
features for phylogenetic inference but have heretofore been applied mostly
to very ancient divergences. By virtue of their synonymous substitutions,
such genes should contain a wealth of information about lower-level
taxonomic relationships as well, with the advantage that amino acid
conservatism makes both alignment and primer definition straightforward. We
tested this postulate for the elongation factor-1 alpha (EF-1 alpha) gene
in the noctuid moth subfamily Heliothinae, which has probably diversified
since the middle Tertiary. We sequenced 1,240 bp in 18 taxa representing
heliothine groupings strongly supported by previous morphological and
allozyme studies. The single most parsimonious gene tree and the
neighbor-joining tree for all nucleotides show almost complete concordance
with the morphological tree. Homoplasy and pairwise divergence levels are
low, transition/transversion ratios are high, and phylogenetic information
is spread evenly across gene regions. The EF-1 alpha gene and presumably
other highly conserved genes hold much promise for phylogenetics of
Tertiary age eukaryote groups.
相似文献