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Summary The idea has been tested here that the aberration in amino acid controlled regulation of RNA synthesis in a mutant strain ofE. coli might reflect a major breakdown in the specificity of transfer of amino acids to S-RNA. For this purpose, S-RNA and amino acid activating enzymes were extracted from bacteria carrying either the normalRC
st or the aberrantRC
rel allele of the RNA control gene. The purified S-RNA preparations were first charged enzymatically with one or more of the 20 standard amino acids, then oxidized with periodate, and finally reisolated and retested for their residual capacity to accept an amino acid that was absent from the preliminary charging mixture. If preliminary charging transferred an amino acid to a non-cognate S-RNA species belonging to an absent amino acid, then the acceptor capacity for the missing amino acid would survive periodate oxidation and reveal its presence on recharging with that amino acid after post-periodate reisolation of the S-RNA. The results presented here show that there does not appear to exist any such major breakdown of transfer specificity in eitherRC
st orRC
rel bacteria: preliminary charging of the S-RNA fromRC
rel bacteria with 19 of the 20 standard amino acids by use of the homologous amino acid activating enzymes does not afford protection against periodate oxidation for any appreciable fraction of the acceptor capacity for the absent 20th amino acid (when that amino acid is either methionine or arginine). It is unlikely, therefore, that thecatholic inducer, postulated to explain the continued RNA synthesis ofRC
rel amino acid auxotrophs in the absence of their growth requirement, is one of the 20 standard amino acids.This investigation was supported by Public Health Service Research Grant CA 02129, from the National Cancer Institute. 相似文献
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Direction of chain growth in enzymic RNA synthesis 总被引:19,自引:0,他引:19
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Subject Index
Subject index to volume 32 相似文献7.
An oscillatory intersegmental neuronal network drives the swimming rhythm of the leech. This network consists of interneurons joined via inhibitory connections to form a series of segmentally iterated, concatenated rings. Recurrent cyclic inhibition in these rings produces a multiphasic activity rhythm. By theoretical analysis of such concatenated interneuronal rings and construction of their electronic analogs it is shown that the interneural network identified in the central nervous system of the leech has properties appropriate for generating the observed motor output. 相似文献
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Movement of ribosomes over messenger RNA in polysomes of rel + and rel - Escherichia coli strains 总被引:2,自引:0,他引:2
The in vitro movement of ribosomes over messenger RNA was studied in both the presence and the absence of protein synthesis. For this purpose, labeled polysomes were extracted from rel+ and rel? strains of Escherichia coli grown in the presence of radioactive uracil and incubated in a cell-free system containing tRNA, amino acids, soluble enzymes and a source of energy. The gradual conversion of the labeled polysomes into monosomes and ribosomal subunits was followed by subjecting the reaction mixture to sucrose gradient sedimentation after various incubation times and measuring the radioactivity present in the three relevant ribosomal fractions.It was found that when the conditions of incubation allow protein synthesis to occur, polysomes extracted from rel+ and rel? cells are converted mainly into free monosomes, which can be made to dissociate into subunits by high-sodium or low-magnesium ion concentrations. Under conditions in which protein synthesis cannot occur because a mutant aminoacyl-tRNA synthetase has been rendered inactive, polysome conversion still occurs, though to a reduced extent. When the products of such residual run-off are examined, however, a difference is manifest between polysomes extracted from rel+ and from rel? strains: whereas the polysomes from the rel? strain are still converted into free monosomes even in the absence of protein synthesis, the polysomes from the rel+ strain are now converted mainly into subunits. It can be inferred, therefore, that ribosomes from rel? bacteria, but not those from rel+ bacteria, continue movement over messenger RNA in the absence of protein synthesis.Studies of mixed extracts from rel? and rel+ bacteria have shown that the character of the run-off process does not depend on the source of tRNA and soluble enzymes; the proportions of monosomes and subunits among the run-off products formed in the absence of protein synthesis depend only on the source of the polysomes. It is suggested that the mutation of the rel gene alters the functional architecture of ribosomes. 相似文献
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