首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   66篇
  免费   7篇
  2023年   1篇
  2020年   1篇
  2017年   1篇
  2016年   2篇
  2015年   3篇
  2014年   4篇
  2013年   1篇
  2012年   5篇
  2011年   2篇
  2010年   3篇
  2009年   4篇
  2008年   1篇
  2007年   6篇
  2005年   3篇
  2004年   1篇
  2003年   5篇
  2002年   1篇
  2001年   3篇
  1999年   1篇
  1998年   3篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1991年   1篇
  1990年   2篇
  1989年   3篇
  1986年   1篇
  1985年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1980年   2篇
  1966年   1篇
  1962年   1篇
  1952年   1篇
  1948年   1篇
  1946年   1篇
排序方式: 共有73条查询结果,搜索用时 15 毫秒
1.
Developmental changes in keratin patterns during epidermal maturation   总被引:10,自引:0,他引:10  
The biochemical maturation of the epidermis of Xenopus laevis was examined through an identification of the keratins expressed at selected stages of development. The keratin patterns obtained were compared to those observed in the adult epidermis and two Xenopus non-epidermal, epithelial cell lines. The keratins expressed during development can be grouped into three classes: (1) keratins which are restricted to the embryonic epidermis (58 and 59 kDa); (2) keratins which are prominent during development, but become minor components of the adult epidermis (47, 48, and 60 kDa); and (3) keratins which accumulate during development to become the major keratins of the adult epidermis (49, 53, 56, and 63 kDa). The embryo-specific keratins are present at all developmental stages prior to metamorphosis which we have investigated, but disappear when the epidermis keratinizes during metamorphosis. Both class 1 and 2 keratins, while undetectable or minor components of the adult skin, are present in the two non-epidermal cell lines. In contrast, the class 3 keratins show little overlap with the keratins of these cell lines. All of the class 3 keratins appear after hatching with the exception of the 53-kDa keratin which is present at the earliest developmental stage which we have examined. All of the major keratins of the adult epidermis accumulate as metamorphosis proceeds, while the embryo-restricted keratins are gradually lost.  相似文献   
2.
Summary The oxygen binding of whole blood from humans and two arctic mammals, reindeer and muskox, has been studied as a function of carbon dioxide and temperature. All bloods display a marked Bohr effect with Bohr coefficients in the range –0.44––0.73. The Bohr effect is more pronounced at 20°C. The temperature sensitivity of reindeer and muskox blood expressed by the apparent heat of oxygenation, H, is almost three times lower than that of human HbA under the same experimental conditions. This thermodynamic difference gives special benefits to arctic mammals with large heterothermy by safeguarding oxygen unloading at very low ambient temperatures.  相似文献   
3.
4.
Under copper limiting growth conditions the methanotrophic bacterium Methylococcus capsulatus (Bath) secrets essentially only one protein, MopE*, to the medium. MopE* is a copper-binding protein whose structure has been determined by X-ray crystallography. The structure of MopE* revealed a unique high affinity copper binding site consisting of two histidine imidazoles and one kynurenine, the latter an oxidation product of Trp130. In this study, we demonstrate that the copper ion coordinated by this strong binding site is in the Cu(I) state when MopE* is isolated from the growth medium of M. capsulatus. The conclusion is based on X-ray Near Edge Absorption spectroscopy (XANES), and Electron Paramagnetic Resonance (EPR) studies. EPR analyses demonstrated that MopE*, in addition to the strong copper-binding site, also binds Cu(II) at two weaker binding sites. Both Cu(II) binding sites have properties typical of non-blue type II Cu (II) centres, and the strongest of the two Cu(II) sites is characterised by a relative high hyperfine coupling of copper (A|| = 20 mT). Immobilized metal affinity chromatography binding studies suggests that residues in the N-terminal part of MopE* are involved in forming binding site(s) for Cu(II) ions. Our results support the hypothesis that MopE plays an important role in copper uptake, possibly making use of both its high (Cu(I) and low Cu(II) affinity properties.  相似文献   
5.
6.
Double-stranded RNA-binding proteins function in regulating the stability, translation, and localization of specific mRNAs. In this study, we have demonstrated that the neuron-specific, calcium-binding protein, visinin-like protein (VILIP) contains one double-stranded RNA-binding domain, a protein motif conserved among many double-stranded RNA-binding proteins. We showed that VILIP can specifically bind double-stranded RNA, and this interaction specifically requires the presence of calcium. Mobility shift studies indicated that VILIP binds double-stranded RNA as a single protein-RNA complex with an apparent equilibrium dissociation constant of 9.0 x 10(-6) M. To our knowledge, VILIP is the first double-stranded RNA-binding protein shown to be calcium-dependent. Furthermore, VILIP specifically binds the 3'-untranslated region of the neurotrophin receptor, trkB, an mRNA localized to hippocampal dendrites in an activity-dependent manner. Given that VILIP is also expressed in the hippocampus, these data suggest that VILIP may employ a novel, calcium-dependent mechanism to regulate its binding to important localized mRNAs in the central nervous system.  相似文献   
7.
A variety of organic compounds have been documented to bind to the oestrogen receptor and induce oestrogenic effects in different vertebrates. The presence of these environmental oestrogens or oestrogen mimics in the aquatic environment has been suspected of disrupting the normal endocrinology of wild populations of fish. In this study, induction of vitellogenin synthesis in primary hepatocytes from Atlantic salmon (Salmo salar) was optimized and validated as an oestrogenic in vitro bioassay using a sensitive capture vitellogenin enzyme-linked immunosorbent assay. After proper optimization (cell media supplements, cell density, temperature and exposure time), this assay gave a sensitive and reproducible response to both endogenous steroids (relative potency: 17beta-oestradiol>oestriol>oestrone>17alpha-oestradiol) and a range of common oestrogen mimics (relative potency: ethynyloestradiol and diethylstilboestrol>genistein and zearalenone>bisphenol A and 4-t-octylphenol>4-n-nonylphenol and 2'-chloro,4-chloro-diphenyltrichloroethane (o,p'-DDT). However, the androgen testosterone and the putative oestrogen mimics dieldrin and toxaphene were not shown to be oestrogenic using this hepatocyte bioassay. Oestrogen-induced vitellogenin synthesis was efficiently inhibited by the anti-oestrogen ZM 189.154, suggesting that this bioassay may be used for testing both the oestrogenic and the anti-oestrogenic properties of chemicals.  相似文献   
8.
The natural reservoir of Francisella tularensis , the causative agent of tularaemia, is yet to be identified. We investigated the possibility that Francisella persists in natural aquatic ecosystems between outbreaks. It was hypothesized that nutrient-rich environments, with strong protozoan predation, favour the occurrence of the tularaemia bacterium. To investigate the differences in adaptation to aquatic environments of the species and subspecies of Francisella , we screened 23 strains for their ability to survive grazing by the ciliate Tetrahymena pyriformis . All the Francisella strains tested were consumed at a low rate, although significant differences between subspecies were found. The survival and virulence of gfp -labelled F. tularensis ssp. holarctica were then studied in a microcosm experiment using natural lake water, with varying food web complexities and nutrient availabilities. High nutrient conditions in combination with high abundances of nanoflagellates were found to favour F. tularensis ssp. holarctica . The bacterium was observed both free-living and within the cells of a nanoflagellate. Francisella tularensis entered a viable but nonculturable state during the microcosm experiment. When studied over a longer period of time, F. tularensis ssp. holarctica survived in the lake water, but loss of virulence was not prevented by either high nutrient availability or the presence of predators.  相似文献   
9.

Background

Protein translocation across the membrane of the Endoplasmic Reticulum (ER) is the first step in the biogenesis of secretory and membrane proteins. Proteins enter the ER by the Sec61 translocon, a proteinaceous channel composed of three subunits, α, β and γ. While it is known that Sec61α forms the actual channel, the function of the other two subunits remains to be characterized.

Results

In the present study we have investigated the function of Sec61β in Drosophila melanogaster. We describe its role in the plasma membrane traffic of Gurken, the ligand for the Epidermal Growth Factor (EGF) receptor in the oocyte. Germline clones of the mutant allele of Sec61β show normal translocation of Gurken into the ER and transport to the Golgi complex, but further traffic to the plasma membrane is impeded. The defect in plasma membrane traffic due to absence of Sec61β is specific for Gurken and is not due to a general trafficking defect.

Conclusion

Based on our study we conclude that Sec61β, which is part of the ER protein translocation channel affects a post-ER step during Gurken trafficking to the plasma membrane. We propose an additional role of Sec61β beyond protein translocation into the ER.  相似文献   
10.
Supplementary feeding of wild large herbivores is a widespread practice in North America and Europe. The presence of feeding stations may have ecological consequences through changes to animal distributions, patterns of herbivory and a net nutrient input into the ecosystem. In Fennoscandia, supplementary feeding of moose in winter (Alces alces) is increasing. Although it has been shown to affect bird communities, its effects on small mammal communities were unknown. Here, we studied the effects of moose supplementary feeding stations on plants and on abundance, reproduction, and biomass of small mammals in years with low and high vole abundance. We sampled small mammals with snap traps and conducted surveys of the field layer vegetation, at varying distances from moose supplemental feeding stations. Due to the vegetation changes induced by feeding stations, abundance of common shrews (Sorex araneus) and Microtus voles were positively affected by long-term moose winter feeding, while bank voles (Myodes glareolus) were not affected. Moose feeding stations did not affect reproduction, individual body mass, or the total biomass of small mammals. Moose winter-feeding stations have impacts on nontarget species, providing islands of preferred grass and forb habitat for Microtus spp. and common shrews, allowing them to penetrate into a matrix of less preferred forest habitat.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号