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排序方式: 共有428条查询结果,搜索用时 109 毫秒
1.
Daniel A. Vardy Csaba Kari Gerald S. Lazarus Pamela J. Jensen Asher Zilberstein Gregory D. Plowman Ulrich Rodeck 《Journal of cellular physiology》1995,163(2):257-265
Autocrine activation of the epidermal growth factor (EGF) receptor on keratinocytes has been recognized as an important growth regulatory mechanism involved in epithelial homeostasis, and, possibly, hyperproliferative diseases. Insulin-like growth factor (IGF)-1 and insulin have been shown to be paracrine keratinocyte mitogens that bind to the type I IGF receptor which is expressed on actively proliferating keratinocytes in situ. In this report, we demonstrate that IGF-1/insulin induced production of keratinocyte-derived autocrine growth factors that bind to the EGF receptor. Increased steady-state mRNA levels for transforming growth factor alpha (TGF-α) and for amphiregulin (AR) were observed upon incubation of keratinocytes with mitogenic concentrations of IGF-1. IGF-1 also induced production and secretion of TGF-α and AR proteins as detected by immunoassays. An EGF receptor antagonistic monoclonal antibody abolished the mitogenic effect of IGF-1 on cultured keratinocytes. These results suggest that stimulation of keratinocyte growth by IGF-1 requires activation of an EGF receptor-mediated autocrine loop. © 1995 Wiley-Liss, Inc. 相似文献
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Isolation and characterization of a large,neurite-associated glycoconjugate from neuroblastoma cells
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A high molecular weight glycoconjugate has been isolated from neurite-producing neuronal tumor cells in culture and has been designated as I(0) based on its elution characteristics in gel filtration chromatography. This molecule cannot be found in a variety of nonneuronal cells. I(0) is found in the substratum-attached material or cell fraction of neurite-producing neuroblastoma cells, depending upon culture conditions. It is found in the substratum-bound fraction of B104 rat neuroblastoma cells during serum starvation and in the EGTA-detached cell fraction of B104 cells grown in chemically defined N2 medium. It occurs only in the cell fraction of the human neuroblastoma line Platt. Examination of behavioral variants of the B104 rat line further strengthens the association of I(0) with neurite production; the constitutive neurite-producing E(R)B9 variant contains I(0) while the non-neurite-producing E(R)A11 variant does not. I(0) is large, eluting in the void volume of sepharose-CL2B columns. Radioiodination of intact cells with lactoperoxidase shows I(0) to be a cell surface component. Metabolic radiolabeling studies show that it contains a high proportion of polysaccharide to protein, does not contain mannose, and is unsulfated. Alkaline borohydride reduction release two size classes of large polysaccharide chain. The alkaline reduction results, along with the mannose incorporation studies, show the presence of O-glycosidic linkages and few, if any, N-linkages. Resistance to nitrous acid deamination, insensitivity to glycosaminoglycan lyases, and the absence of sulfation, indicate that I(0) does not contain the glycosaminoglycans hyaluronic acid, chondroitin-, dermatan-, or heparin- sulfates. Affinity column chromatography reveals high binding affinity of I(0) to polyornithine and no binding to gelatin (collagen) or the glycosaminoglycans hyaluronate and heparin. These studies describe a unique high molecular weight glycoconjugate on the surface of neurite-producing neuroblastoma cell lines from two species. 相似文献
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Deep-level diagnostic value of the rDNA-ITS region 总被引:14,自引:0,他引:14
The similarity of certain reported angiosperm rDNA internal transcribed
spacer (ITS) region sequences to those of green algae prompted our analysis
of the deep-level phylogenetic signal in the highly conserved but short
5.8S and hypervariable ITS2 sequences. We found that 5.8S sequences yield
phylogenetic trees similar to but less well supported than those generated
by a ca. 10-fold longer alignment from rDNA-18S sequences, as well as
independent evidence. We attribute this result to our finding that,
compared to 18S, the 5.8S has a higher proportion of sites subject to vary
and greater among-site substitution rate homogeneity. We also determined
that our phylogenetic results are not likely affected by intramolecular
compensatory mutation to maintain RNA secondary structure nor by evident
systematic biases in base composition. Despite historical homology, there
appears to be no ITS2 primary sequence similarity shared sufficient
similarity to cluster correctly on the basis of alignability. Our results
indicate that groups, however, share sufficient similarity to cluster
correctly on the basis of alignability. Our results indicate that ITS
region sequences can diagnose organismal origins and phylogenetic
relationships at many phylogenetic levels and provide a useful paradigm for
molecular evolutionary study.
相似文献
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Production of Serine Proteases by the Oyster Pathogen Perkinsus marinus (Apicomplexa) In Vitro 总被引:1,自引:1,他引:0
JEROME F. LA PEYRE DORIS Y. SCHAFHAUSER ESAM H. RIZKALLA MOHAMED FAISAL 《The Journal of eukaryotic microbiology》1995,42(5):544-551
ABSTRACT. Analysis of the cell-free supernatants of Perkinsus marinus cultures by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining revealed the presence of as many as 17 bands ranging in molecular weight from 239 to 32 kDa. These bands were not present in un-inoculated medium. Moreover, P. marinus produces extracellular proteins that possess proteolytic activities; the cell-free supernatants of P. marinus cultures could digest a variety of proteins including gelatin, casein, fibronectin and laminin. Oyster plasma was also digested by cell-free culture supernatants. The proteolytic activity in cell-free culture supernatants was detected 24 h post-inoculation, while no proteolytic activity could be detected in cell lysates. The proteolytic activities were characterized using substrate-impregnated sodium dodecylsulfate-polyacrylamide gels and had approximate molecular weights ranging from 55 to 35 kDa. The proteolytic activity of cell-free culture supernatants was inhibited by the serine protease inhibitors phenylmethylsulphonyl fluoride, 3,4-dichloroisocoumarin and soybean trypsin inhibitor. In contrast, inhibitors (i.e. trans-epoxysuccinyll-leucylamido(4-guanidino)-butane, 1, 10-phenanthroline, captopril, ethylenediaminetetracetic acid, pepstatin A or diazoacetyl-DL-norleucine methyl ester) from the other three classes of proteases had no effect. It was concluded that the P. marinus proteases in cell-free culture supernatants are serine proteases. 相似文献
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Robert W. Puls Donald A. Clark Cynthia J. Paul Jim Vardy 《Soil & Sediment Contamination》1994,3(2):203-224
A detailed characterization of the underlying and adjacent soils of a chrome‐plating shop was performed to provide information on the extent of soil and aquifer contamination at the site and on the potential for off‐site migration and environmental impact. Intact, moist cores were obtained from more than 40 different locations, resulting in more than 200 discrete samples for total metal analysis, selective extraction tests, and adsorption‐reduction experiments, to assess the chemical speciation and distribution of chromium on the contaminated soils and its leaching potential. Surface analytical techniques were also used to determine chemical speciation and to further elucidate mineral fractions responsible for retention of the chromium on the soils and sediments. Adsorption and reduction capacities of the saturated aquifer sediments were variable and low, while the unsaturated soils’ reduction capacities were much greater and were correlated with depth (decreasing capacity with increasing depth). The soils’ adsorption and reduction capacities were eventually overwhelmed, however, and permitted the passage of Cr(VI) into the underlying ground water. Adsorption capacity differences were primarily related to clay content and pH, and less so to the presence of amorphous iron oxide coatings on matrix minerals as operationally defined by the selective extraction methods used in the study. Reduction of Cr(VI) to Cr(III) and subsequent precipitation as (Fe, Cr)(OH)3 is proposed as the primary attenuation mechanism in the unsaturated soils immediately beneath the shop, based on extraction and surface analyses results. 相似文献
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