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Ian R. Record Jennifer K. McInerney Ivor E. Dreosti 《Biological trace element research》1996,53(1-3):27-43
Previous studies have shown that tea consumption can impair trace element metabolism, particularly iron status, and increase
the risk of anemia in humans and animals. More recently, however, evidence has been accumulating to show that, in animals,
consumption of green tea or its polyphenols is associated with a reduction of the incidence and severity of a variety of experimentally
induced cancers. In this study we have monitored the growth, trace element status, including hematological parameters of weanling
rats given either (1) water, (2) 1% black tea, (3) 1% green, tea, or (4) 0.2% crude green tea extract as their sole drinking
fluid while consuming diets containing either adequate or low amounts of iron. With the exception of manaanese, none of the
trace elements studied (iron, copper, zinc, and manganese) or the hematological indices measured were affected by the type
of beverage supplied, even though the polyphenol extract was shown to chelate metals in vitro and all the animals fed the
low iron diet were shown to be anemic. There appeared to be an effect of black and green teas on manganese balance in, both
the first and last weeks of the study. A lower level of brain managanese was associated with green tea consumption, and a
higher level of this element in the kidneys of animals fed black tea. The results demonstrate that both black and green teas
and a green tea polyphenol extract do not represent a risk to animals consuming the beverages as their sole fluid intake with
respect to iron availability, although the interactions with manganese deserve further study. 相似文献
7.
The influence of sampling method on the classification of wetland macroinvertebrate communities 总被引:1,自引:1,他引:0
Macroinvertebrate communities sampled by a corer, plankton net and sweep net from five wetlands on the Swan Coastal Plain
were compared. The composition of the fauna collected in sweeps and tows was generally similar and differed from that collected
in the cores. Cores caught fewer species than tows and sweeps at all wetlands and did not capture fast swimming hemipterans
or less abundant taxa. The highest species richness was recorded in sweep samples in four out of the five wetlands. Classification
(TWIN-SPAN) and ordination (SSH) of the samples collected in sweeps and tows gave good separation of the wetlands, whereas
classification of core samples did not. Coring appeared to be the least suitable sampling method for describing the major
components of the macroinvertebrate communities of these wetlands. Plankton tows were useful if the time available for sorting
was limited as these samples were free of sediments and generally gave similar results to those obtained with sweeps. Sweeps
appeared to be the most useful method for a large classification study as they collected more species and resulted in the
best discrimination amongst wetlands. 相似文献
8.
Eduardo A. Nillni Theodore C. Friedman Roberta B. Todd †Nigel P. Birch Y. Peng Loh Ivor M. D. Jackson 《Journal of neurochemistry》1995,65(6):2462-2472
Abstract: Pro-thyrotropin-releasing hormone (proTRH) is the precursor to thyrotropin-releasing hormone (TRH; pGlu-His-Pro-NH2), the hypothalamic releasing factor that stimulates synthesis and release of thyrotropin from the pituitary gland. Five copies of the TRH progenitor sequence (Gln-His-Pro-Gly) and seven cryptic peptides are formed following posttranslational proteolytic cleavage of the 26-kDa rat proTRH precursor. The endopeptidase(s) responsible for the physiological conversion of proTRH to the TRH progenitor form is currently unknown. We examined the in vitro processing of [3H]leucine-labeled or unlabeled proTRH by partially purified recombinant PC1. Recombinant PC1 processed the 26-kDa TRH precursor by initially cleaving the prohormone after the basic amino acid at either position 153 or 159. Based on the use of our well-established antibodies, we propose that the initial cleavage gave rise to the formation of a 15-kDa N-terminal peptide (preproTRH25–152 or preproTRH25–158) and a 10-kDa C-terminal peptide (preproTRH154–255 or preproTRH160–255). Some initial cleavage occurred after amino acid 108 to generate a 16.5-kDa C-terminal peptide. The 15-kDa N-terminal intermediate was further processed to a 6-kDa peptide (preproTRH25–76 or preproTRH25–82) and a 3.8-kDa peptide (preproTRH83–108), whereas the 10-kDa C-terminal intermediate was processed to a 5.4-kDa peptide (preproTRH206–255). The optimal pH for these cleavages was 5.5. ZnCl2, EDTA, EGTA, and the omission of Ca2+ inhibited the formation of pYE27 (preproTRH25–50), one of the proTRH N-terminal products, by 48, 82, 72, and 45%, respectively. This study provides evidence, for the first time, that recombinant PC 1 enzyme can process proTRH to its predicted peptide intermediates. 相似文献
9.
The incorporation of3H-thymidine into DNA in the brains of the 17-day and 20-day old rat fetuses was significantly reduced by maternal zinc restriction
during pregnancy. The activity of the enzyme thymidine kinase (EC 2.7.1.21) was similarly reduced in the zine-deprived fetal
brains on days 14 and 20 of gestation, but not on day 17. Fetal brain alkaline phosphatase (EC 3.1.3.1) was significantly
depressed by maternal zinc deprivation on days 17 and 20 of pregnancy.
The data suggest an association between thymidine kinase and the reduced incorporation of3H-thymidine into DNA in the brains of 20-day old fetuses but not in animals on day 17. Alkaline phosphatase was however depressed
at this stage.
The suggestion is made that because of the complexity of brain development, future biochemical studies in this area should
concern specific structures in the brain at particular critical stages during neurogenesis. 相似文献
10.
Summary A new method is described for the histochemical localization of acid phosphatase. Naphthol AS BI, enzymatically released from naphthyl AS BI phosphoric acid, is coupled with diazotized 2,5-dibromoaniline to produce a fine insoluble red azo dye. The histochemical and cytochemical localization of this final reaction product in rat liver is described. In the electron microscope, sites of the azo dye can be detected by X-ray microanalysis of ultrathin cryosections of reactive tissue.This research was supported by Scientific Research Council Grant No. B/RG/67527 相似文献