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In the past year, several new developments concerning the structure of intermediate filament proteins and their assembly into intact intermediate filaments have been made: the coiled-coil structure of a rod domain has been elucidated; the basis of the chain interaction and its role in intermediate filament assembly has been specified; the organization of nearest-neighbour molecules in keratin intermediate filaments has been determined; and the glycine loop structures of the terminal domains of epidermal keratin chains have been defined. In addition, mutations in intermediate filament chains that promote pathology have been reported for the first time. 相似文献
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P Paindavoine F Zampetti-Bosseler E Pays J Schweizer M Guyaux L Jenni M Steinert 《The EMBO journal》1986,5(13):3631-3636
Genetic exchange may occur between two particular Trypanosoma brucei clones simultaneously transmitted by the same tsetse fly. We report here that this exchange takes place in the fly, through nuclear fusion. The resulting hybrids appear to be sub-tetraploid, some particular DNA sequences from one of the parental stocks being lost before enough cloned hybrid trypanosomes could be harvested for DNA analysis. A further reduction of the DNA content of these hybrids occurs gradually upon growth and yields near diploid value in a major part of the population. This mode of hybrid generation is different from the fusion of haploid gametes, which is thought to occur normally upon inoculation of metacyclic trypanosomes in their mammalian host. In this respect, the sub-tetraploid hybrids appear to undergo meiosis in the fly, generating sub-diploid metacyclic forms, then fusion in the mammalian blood. 相似文献
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Kidney glomerular explants in serum-free media. Sequential morphologic and quantitative analysis of cell outgrowths 总被引:3,自引:0,他引:3
T D Oberley B W Steinert A H Yang P J Anderson 《Virchows Archiv. B, Cell pathology including molecular pathology》1986,50(3):209-235
Guinea pig glomeruli were grown in vitro for 22 days in a serum-free medium composed of Waymouth's MB 752/1 supplemented with sodium pyruvate, nonessential amino acids, antibiotics, insulin, transferrin, selenium, triiodothyronine, and fibronectin (FN), and sequential morphologic and quantitative studies of cell outgrowth were performed. Glomeruli grown in serum-free medium showed preservation of glomerular visceral epithelial cells but extensive necrosis of endocapillary cells (endothelial and mesangial cells). Morphologic analysis demonstrated progressive morphologic changes in cultured glomerular cells; however, most cell types observed in culture appeared to grow from the epithelial side of the glomerular basement membrane. Mitosis was a prominent component of glomerular cell outgrowth in vitro, and total DNA increased slightly during glomerular culture. FN was required for glomerular cell outgrowth, and studies using FN fragments demonstrated that the carboxy-terminal portion of FN was required for whole glomerular attachment. These results are used to develop a model for glomerular cell outgrowth in vitro. 相似文献
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Differential size variations between transcriptionally active and inactive telomeres of Trypanosoma brucei 总被引:19,自引:6,他引:13 下载免费PDF全文
We have studied the genes coding for the variant-specific surface antigen (VSA) in a series of seven trypanosome clones derived from AnTat 1.1: 1.1 leads to 1.3 leads to 1.6 leads to 1.16 leads to 1.1C leads to 1.3B leads to 1.18 These genes are all telomeric (1-5), and their surrounding, although sometimes similar, differs in each case. The length between these antigen genes and the corresponding DNA end appears to increase at each antigenic switch, with however occasional sharp size reductions, often linked to the involvement of the telomere in gene expression. This increase is due to a constant "growth" of the telomeres, at a rate of about 28 bp per day in at least four cases and probably linked to chromosome duplication. The telomere harbouring the transcribed VSA gene is growing slightly faster (about 36 bp per day), and it is the only one whose size reduction is progressive, leading to a terminal length heterogeneity within a clone. As a result, the active VSA gene is found in a population of telomeres which, as the trypanosomes divide, becomes increasingly heterogeneous, with however a preferred discrete size class about 1.4 kb smaller. The fact that the "active" telomere is the only one in a chromatin conformation highly sensitive to DNAaseI (1-4, 6), suggests that chromatin structure influences the rate and extent of both size increase and shortening of telomeres. 相似文献
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Expression of murine epidermal differentiation markers is tightly regulated by restricted extracellular calcium concentrations in vitro 总被引:22,自引:3,他引:19 下载免费PDF全文
Epidermal differentiation is characterized by a series of coordinated morphological and biochemical changes which result in a highly specialized, highly organized, stratified squamous epithelium. Among the specific markers expressed in differentiating epidermis are (a) two early spinous cell proteins, keratins 1 and 10 (K1 and K10); and (b) two later granular cell proteins, filaggrin and a cornified envelope precursor (CE). In vitro, epidermal basal cells are selectively cultured in 0.05 mM Ca2+ medium, and terminal differentiation is induced when the Ca2+ concentration is increased to 1 mM. However, only a small fraction of the cells express the markers K1, K10, CE, or filaggrin in the higher Ca2+ medium. To explore the factors required for marker expression, cultured epidermal cells were exposed to intermediate Ca2+ concentrations and extracts were analyzed using specific antibody and nucleic acid probes for the four markers of interest. These studies revealed that marker expression was enhanced at a restricted concentration of Ca2+ in the medium of 0.10-0.16 mM. At this Ca2+ concentration, both protein and mRNA levels for each marker were substantially increased, whereas at higher or lower Ca2+ concentrations they were diminished or undetected. The percentage of cells expressing each marker was increased two- to threefold in the permissive Ca2+ medium as determined by immunofluorescence analysis. This optimal level of Ca2+ was required both to initiate and sustain marker expression. At the permissive Ca2+ concentration, expression of the markers was sequential and similar to the order of appearance in vivo. K1 was expressed within 8-12 h and K10 was expressed in the ensuing 12-24-h period. CE and filaggrin were expressed in the subsequent 24 h. Inhibition of K1 expression by cycloheximide suggested that an inducible protein was involved. Other investigators have determined that a shallow Ca2+ gradient exists in epidermis, where the basal cells and spinous cells are in a Ca2+ environment substantially below serum Ca2+ levels. These in vitro results suggest that the Ca2+ environment is a fundamental regulator of expression of epidermal differentiation markers and provide an explanation for the existence of the Ca2+ gradient in vivo. 相似文献
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Michael Steinert Manfred Ott P. Christian Lück Egbert Tannich Jörg Hacker 《FEMS microbiology ecology》1994,15(3-4):299-308
Abstract Legionella pneumophila strains isolated from different sources were tested for their host range in the protists Acanthamoeba castellanii, Hartmannella vermiformis and Entamoeba histolytica . It has been shown that A. castellanii and H. vermiformis but not E. histolytica support the intracellular replication of L. pneumophila . Furthermore it could be demonstrated that in vivo virulence in the guinea pig and the intracellular growth in U937 cells coincides with the capability to replicate intracellularly in A. castellanii at 37°C. The infectivity of L. pneumophila that had sustained a 48 hours nutrient deprivation was not significantly different from that of legionellae grown to log-phase on BCYE plates. In contrast the nutrient limitation on A. castellanii increased the amount of intracellular legionellae at the beginning of infection. An initial opsonin independent attachement stage of legionellae to U937 cells was demonstrated by scanning electron microscopy. In contrast, L. pneumophila's capability of stable or long term attachmennt to A. castellanii was shown to be inefficient. 相似文献