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Analysis of Rous sarcoma virus Gag protein by mass spectrometry indicates trimming by host exopeptidase. 总被引:3,自引:3,他引:0 下载免费PDF全文
We have used electrospray ionization-mass spectrometry to investigate Gag protein structure and processing in Rous sarcoma virus, the prototype of the avian sarcoma and leukemia viruses. Molecular masses determined for the mature virion proteins MA, CA, NC, and PR agree closely with those predicted by currently accepted models for their structures. However, the data for p10 imply that only about 10% of the product has the predicted mass while the remainder is missing the C-terminal methionine residue. Molecular masses also were obtained for products generated by PR cleavage in vitro of a Gag precursor polyprotein expressed in Escherichia coli. The data confirm the predicted Gag cleavage sites for PR. Thus, carboxypeptidase activity appears to be responsible for generating the des-Met form of p10. The same activity may account for the small amount of the mature des-Met CA, as previously reported. Analysis of cleavage products generated in vitro also serves to define the PR processing site separating the p2a and p2b peptides, Asn-164-Cys-165. In conjunction with published characterizations of these two peptides processed from the segment of Gag between MA and p10, these data suggest trimming of p2b by an aminopeptidase. Finally, the molecular masses determined for the MA-related species p19f, p23, and p35 now accurately define the structures of these proteins. 相似文献
34.
TheGNOM gene is required for pattern formation along the main body axis of the embryo in the flowering plantArabidopsis thaliana. Mutations in theGNOM gene alter the asymmetric division of the zygote and interfere with the formation of distinct apical-basal regions in the developing embryo. We have isolated theGNOM gene by positional cloning, characterised its structure and determined the molecular lesions in mutant alleles. Although the predicted 163 kDa GNOM protein has a conserved domain in common with the yeast secretory protein Sec7p, it is most closely related in size and overall similarity to the product of the yeastYEC2 gene, which is not essential for cell viability. Four fully complementinggnom alleles carry missense mutations in conserved regions, seven partially complementing alleles have premature stop codon mutations and two non-complementing alleles have splice-site lesions. Our results suggest that the GNOM protein acts as a complex of identical subunits and that partial complementation may involve low levels of full-length protein generated by inefficient translational read-through.Communicated by H. Saedler 相似文献
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Ochratoxin A (OTA) is a nephrotoxin which blocks plasma membrane anion conductance in Madin-Darby canine kidney (MDCK) cells. Added to the culture medium, OTA transforms MDCK cells in a manner similar to exposure to alkaline stress. By means of video-imaging and microelectrode techniques, we investigated whether OTA (1 mol/liter) affects intracellular pH (pH.), Cl– (Cl
i
–
) or cell volume of MDCK cells acutely exposed to normal (pHnorm=7.4) and alkaline (pHalk=7.7) conditions. At pHnorm, OTA increased Cl
i
–
by 2.6±0.4 mmol/liter (n=14, P<0.05) but had no effect on pH
i
. At pHalk, application of OTA increased Cl
i
–
by 8.6±2.6 mmol/liter (n=10, P< 0.05) and raised pH
i
by 0.11±0.03 (n= 8, P<0.05). The Cl–HCO
3
–
exchange inhibitor DNDS (4,4-dinitro-stilbene-2, 2-disulfonate; 10 mol/liter) eliminated the OTA-induced changes of pH
i
and Cl
i
–
. OTA did not affect cell volume under both pHnorm and pHalk conditions.We conclude that the OTA-induced blockade of plasma membrane anion conductance increases Cl
i
–
without changing cell volume. The driving force of plasma membrane Cl–/HCO
3
–
exchange dissipates, leading to a rise of pH
i
when cells are exposed to an acute alkaline load. Thus, OTA interferes with pH
i
and Cl
i
–
homeostasis leading to morphological and functional alterations in MDCK cells.The work was supported by the Deutsche Forschungsgemeinschaft (DFG, Si 170/7-1).We thank the Zeiss Company (Oberkochen, Germany) for providing the Attofluor video-imaging system for the intracellular Ca2+ measurements.This study was carried out with the technical assistance of Sigrid Mildenberger and Ruth Freudinger. 相似文献
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Summary Proteasomes, also known as multicatalytic proteinase complexes, were localized in suspension cells of potato (Solanum tuberosum) by direct immunofluorescence using polyclonal antibodies labelled with fluorescein isothiocyanate. The method used allows an estimate of relative amounts of proteasomal antigens in different cell components. Proteasomes are present in the nuclei and the cytoplasm. The nucleoplasm contains small areas of weak fluorescence. The peripheral cytoplasm and possibly elements of the cytoskeleton show higher fluorescence than other parts of the cytoplasm. This indicates a localization of proteasomes similar to that known from animal cells.Abbreviations DMSO
dimethylsulfoxide
- EGTA
ethyleneglycol-bis-(-aminoethylether)-N,N,N,N-tetra acetic acid
- FITC
fluorescein isothiocyanate
- PBS
phosphate buffered saline
- PIPES
piperazine-1,4-bis-(2-ethanesulfonic acid) 相似文献