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51.
Activity, control and primer requirements of starch phosphorylase in developing barley endosperm were investigated. Phosphorylase was detected in endosperm extracts from 3 days after anthesis. Unprimed activity was predominant between 2 and 10 days after anthesis, when it constituted 70–80% of total activity, but this proportion declined rapidly as the grain developed. The existence of at least 2 isoenzymes was indicated by studies of pH dependence and phosphate inhibition, and was further supported by acrylamide gel electrophoresis and column chromatography using DEAE-cellulose. The two isoenzymes which ere possibly both glyco proteins, appear in barley endosperm soon after anthesis. One appears capable of unprimed activity, and may be associated with the initiation of a-1,2 glucans, which then serve as primers for starch synthetase. This disappears by 13–15 days after anthesis. The other isoenzyme is capable of some unprimed activity but undergoes modification between 15 and 20 days after anthesis, resulting in the loss of unprimed activity. The relevance of the results to initiation of starch synthesis and to starch synthetase in amyloplasts is discussed. 相似文献
52.
14,15-Leukotriene A4 is a pivotal biosynthetic intermediate in 15-lipoxygenase initiated leukotriene biosynthesis. This compound hydrolyzes instantaneously in phosphate buffer at pH 7.4. However, addition of human or bovine albumin to otherwise identical buffer solutions increases its stability. Intact 14,15-leukotriene A4 then decomposes by first-order kinetics with rate constants inversely proportional to the albumin concentration. Stabilization of 14,15-leukotriene A4 under certain conditions may influence its proportionate transformation by enzymatic vs non-enzymatic processes. 相似文献
53.
The contents of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in plasma and intestinal mucose were increased by dietary calcium and by dietary phosphorus restriction. The concentration of intestinal occupied receptors for 1,25(OH)2D3 was higher in calcium-restricted birds. The affinity (association constant) of intestinal receptors for 1,25(OH)2D3 was lower in phosphorus-restricted chicks, as compared to control or calcium-restricted chicks. The number of binding sites were not influenced by dietary calcium or phosphorus restriction. 相似文献
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A natural Diels—Alder type adduct, named kuwanon W, was isolated from ethyl acetate extracts of the root bark of cultivated mulberry tree, and its structure was determined on the basis of spectral and chemical evidence. Kuwanon W is regarded biogenetically as a Diels—Alder adduct of a chalcone derivative and dehydroprenyl-flavone. 相似文献
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The ability of photoautotrophic picoplankton Synechococcus to degrade urea was examined in the euphotic zone of Lake Biwa. Samples were divided into pico (0.2–2.0 μm) and larger (>2.0
μm) size fractions by filtration. The rates of urea degradation (the sum of the rates of incorporation of carbon into phytoplankton
cells and of liberation of CO2 into water) measured by radiocarbon urea were 8 and 17 μmol urea m−3 day−1 in June and July, respectively, for the picophytoplankton in the surface water, and 196 and 96 μmol urea m−3 day−1, respectively for the larger phytoplankton. The rates decreased with depth, somewhat similar to the vertical profiles of
the photosynthetic rate. The urea degradation rates were obviously high under light conditions. In daylight, urea was degraded
into two phases, carbon incorporation and CO2 liberation, whereas in the dark it was degraded only into the CO2 liberation phase. The contribution of picophytoplankton to total phytoplankton in urea degradation was high in the subsurface
to lower euphotic layer. Urea degradation activity was higher in the picophytoplankton fraction than in the larger phytoplankton
fraction. Shorter residence times of urea were obtained in the upper euphotic zone. The contribution of picophytoplankton
to urea cycling was 4% to 35%. The present results suggest that the picophytoplankton Synechococcus is able to degrade urea and effectively makes use of regenerated urea as a nitrogen source in the euphotic layer, and that
picophytoplankton play an important role in the biogeochemical nitrogen cycle in Lake Biwa.
Received: June 25, 1998 / Accepted: February 10, 1999 相似文献
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蓝舌病毒HbC株与不同种系细胞相互作用及群特异性抗原特征 总被引:5,自引:0,他引:5
BTV-HbC株和蓝舌病毒标准株BTV-10分别接种在不同种系细胞如猴肾传代细胞(Vero)、人宫颈癌细胞(Hela)和小鼠神经胶质瘤细胞(C6)等细胞株上,比较研究了BTV-HbC在不同种系细胞上的增殖特征,BTV-HbC与BTV-10在相同细胞上的复制增殖特征,病毒与细胞相互作用的显微和超微结构特征.用免疫交叉反应研究了BTV-HbC株与BTV-10型标准株之间的血清学关系.本研究结合本室对BTV-HbC株基因组图谱分析和蓝舌病毒群特异性抗原编码基因S7的RT-PCR分析,进一步证实了BTV-HbC株可能是一个新的血清型蓝舌病毒. 相似文献