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Simian virus 40 gene A function and maintenance of transformation.   总被引:107,自引:70,他引:37       下载免费PDF全文
Transformants have been isolated after infection of rat embryo cells at 33 C with either wild-type simian virus 40 or with the temperature-sensitive gene A mutants, tsA7 and tsA28. Examination of properties usually associated with transformation such as growth in 1% serum, growth rate, saturation density, and morphology show that these properties are temperature dependent in the tsA transformants characterized, but are not temperature dependent in the wild-type transformants that have been examined. In the most thoroughly characterized tsA transformants the expression of T antigen also appears to be temperature dependent. These data suggest that an active A function is required for the maintenance of transformation in these cells. In the lytic cycle, the A function is involved in the initiation of DNA synthesis. Thus transformation by simian virus 40 may be the direct consequence of the introduction of the simian virus 40 replicon and the presence of its DNA initiator function, which causes the cell to express a transformed phenotype.  相似文献
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N Geisler  K Weber 《The EMBO journal》1982,1(12):1649-1656
The complete amino acid sequence of muscle desmin reported here is the first for an intermediate filament protein. Alignment with partial data available for vimentin, glial fibrillary acid protein, neurofilament 68 K, two wool alpha-keratins, and a recently described DNA clone covering 90% of an epidermal keratin shows that all seven proteins have extensive homologies and therefore form a complex multigene family, the intermediate filament proteins. The hard alpha-keratins of wool appear to be a special subset of epithelial keratins. The sequence information reveals, as the dominant structural principle, a rod-like middle domain arising from several alpha-helical segments able to form interchain coiled-coil elements. The proposed helices are separated by short spacers, which like the two terminal domains seem built from non-alpha-helical material. Attention is drawn to the sometimes very striking sequence homologies along the rod and the high sequence variability in the terminal domains. Finally, chemical cross-linking experiments performed on the isolated desmin rod show that intermediate filament structure seems not to be based on triple-stranded coiled-coils as currently thought, but rather reflects protofilament units built as a dimer of normal interchain double-stranded coiled-coils.  相似文献
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Complete amino acid sequences for four mammalian muscle actins are reported: bovine skeletal muscle actin, bovine cardiac actin, the major component of bovine aorta actin, and rabbit slow skeletal muscle actin. The number of different actins in a higher mammal for which full amino acid sequences are now available is therefore increased from two to five. Screening of different smooth muscle tissues revealed in addition to the aorta type actin a second smooth muscle actin, which appears very similar if not identical to chicken gizzard actin. Since the sequence of chicken gizzard actin is known, six different actins are presently characterized in a higher mammal. The two smooth muscle actins--bovine aorta actin and chicken gizzard actin--differ by only three amino acid substitutions, all located in the amino-terminal end. In the rest of their sequences both smooth muscle actins share the same four amino acid substitutions, which distinguish them from skeletal muscle actin. Cardiac muscle actin differs from skeletal muscle actin by only four amino acid exchanges. No amino acid substitutions were found when actins from rabbit fast and slow skeletal muscle were compared. In addition we summarize the amino acid substitution patterns of the six different mammalian actins and discuss their tissue specificity. The results show a very close relationship between the four muscle actins in comparison to the nonmuscle actins. The amino substitution patterns indicate that skeletal muscle actin is the highest differentiated actin form, whereas smooth muscle actins show a noticeably cloer relation to nonmuscle actins. By these criteria cardiac muscle actin lies between skeletal muscle actin and smooth muscle actins.  相似文献
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V Gerke  K Weber 《The EMBO journal》1984,3(1):227-233
Membrane vesicles derived from the apical side of procine intestinal epithelial cells retain, after demembranation in the presence of calcium, two major proteins (I, II) which are released by the addition of calcium chelators. We have purified and characterized these two calcium-binding proteins. Protein I has a mol. wt. of 85 000 and contains two copies of a 36-K subunit and an additional 10-K subunit. It binds in a calcium-dependent manner to F-actin as well as to non-erythroid spectrin. Immunofluorescence microscopy reveals protein I-related antigens in the terminal web of the intestinal cell and in a submembraneous cortical layer in various tissue culture cells. Biochemical and immunological results document that the 36-K subunit of protein I is identical with the cellular p36K recognized as a major substrate for tyrosine phosphorylation by the sarc gene kinase in Rous sarcoma virus-transformed cells. The biochemical properties of protein I agree with its location seen in immunofluorescence microscopy and cell fractionation and suggest that the actin-spectrin network in the cortical layer may be affected by virus transformation.  相似文献
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The display of microtubules in transformed cells.   总被引:48,自引:0,他引:48  
M Osborn  K Weber 《Cell》1977,12(3):561-571
Monospecific tubulin antibodies have been used in indirect immunofluorescence microscopy on a variety of well characterized, transformed cell lines grown in tissue culture. Networks of colcemid-sensitive fibers are seen in SV40-transformed 3T3 cells, SV40-transformed rat embryo cells, HeLa cells and other transformed cell lines. In each case, greater than 90% of the cells contain visible microtubular networks, and where individual microtubules can be distinguished, they run for long distances. Documentation of these metworks is more difficult in transformed than in normal cells, because transformed cells are in general more rounded and have less well spread cytoplasm. In addition, the microtubular networks can be readily visualized in "cytoskeletons" of both normal and transformed cells, obtained by treatment of cells with nonionic detergents in a buffer which stabilizes microtubules in vitro. Addition of calcium to this buffer results in in situ fragmentation and destruction of the microtubular network. In view of these results, we conclude that transformed cells contain significant numbers of microtubules, and that in transformed cells, as in normal cells, microtubules are arranged in networks.  相似文献
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