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21.
Abstract. 1. The eggs of Euptychiine butterflies are laid singly, but their distributions tend to be contagious. However, these insects do not discriminate between egg-laden and egg-free plants.
2. Response to conspecific eggs is not part of the mechanism responsible for clumped egg distribution. 相似文献
2. Response to conspecific eggs is not part of the mechanism responsible for clumped egg distribution. 相似文献
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Inactivation of Calcitonin by Specific Organs 总被引:2,自引:0,他引:2
FREDERICK R. SINGER JOEL F. HABENER ELIZABETH GREENE PAUL GODIN JOHN T. POTTSJUN. 《Nature: New biology》1972,237(78):269-270
THE greater biological potency of salmon calcitonin (SCT) as compared with mammalian calcitonins may be due to the relative resistance of SCT to inactivation in vivo1,2. SCT infused into dogs disappears from the circulation more slowly than does porcine calcitonin (PCT) or human calcitonin (HCT)1–3. For example, the metabolic clearance rate (MCR) of PCT in the dog is approximately 10 times greater than that of SCT1,2. Neither renal excretion3,4 nor inactivation by plasma1,2 is sufficient to account for the rapid clearance of the calcitonins that we have observed in vivo and thus it seemed likely that inactivation of the hormones must occur during passage through one or more organs. Here we present data that suggest the kidney, the liver and muscle and/or bone as the sites of inactivation of the calcitonins in the dog. SCT is relatively resistant to inactivation in the latter two sites. 相似文献
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CLIFF E. SINGER GERALD R. SMITH RICCARDO CORTESE BRUCE N. AMES 《Nature: New biology》1972,238(81):72-74
TRANSFER RNA has been implicated in the regulation of a number of amino-acid biosynthetic operons1–4. Histidyl-tRNAHis has been shown to be involved in regulation of the histidine operon by analysis of six genes (hisO, hisR, hisS, hisT, hisU, hisW), mutation of which causes derepression of the enzymes of the histidine biosynthetic pathway in Salmonella typhimurium5–7. A class of derepressed mutants (hisR) has only about 55% as much tRNAHis as the wild type4 and in the one example sequenced, contains tRNAHIS with a structure identical to that of the wild type8. Studies of mutants of the gene for histidyl-tRNA synthetase (hisS) indicated that the derepressed phenotype was associated with defects in the charging of tRNAHISin vitro2. The amounts of charged and uncharged tRNAHis present in vivo during physiological derepression of the wild type and in the six classes of regulatory mutants, have been determined9. This work has shown that repression of the histidine operon is correlated directly with the concentration of charged histidyl-tRNAHisin vivo and not with the ratio of charged to uncharged or the absolute amount of uncharged tRNAHis. The derepression observed in mutants, of hisS (the gene for histidyl-tRNA synthetase), hisR (the presumed structural gene for the single species of tRNAHis) and hisU and hisW (genes presumably involved in tRNA modification) may be explained by the lower cellular concentration of charged tRNAHis which these mutants contain. 相似文献
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