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1.
Pancreatic islet homogenates contain a Mg2+-requiring phospholipid methyltransferase activity, the activity of which was doubled by calcium (K0.5 less than 5 microM). Other divalent metal ions stimulated the activity from 11 to 35%, but zinc and strontium were inhibitory. Cyclic AMP had no effect on the enzyme activity and cyclic GMP inhibited it slightly. Calcium increased the Vmax of the enzyme without affecting its Km with respect to S-adenosylmethionine (6 microM). Chlorpromazine, trifluoperazine, and dibucaine inhibited the calcium-stimulatable activity without affecting the activity in the absence of calcium. Phosphatidylserine stimulated, and arachidonic acid and palmitic acid inhibited, the basal enzyme activity. The methylated products were found to be primarily mono- and dimethylphosphatidylethanolamine (30%) and phosphatidylcholine (43%) and an, as yet unidentified, nonpolar lipid fraction (27%), as judged by thin-layer chromatography. In the presence of calcium, incorporation of methyl groups into phosphatidylcholine, mono- and dimethylphosphatidylethanolamine, and nonpolar lipids was increased by 131, 60, and 46%, respectively. Based on the localization of the enzyme activity in the insulin secretory granule fraction, it is proposed that phospholipid methylation plays a role in coupling the stimulus to the initial events in insulin secretion, leading to the exocytosis of insulin. 相似文献
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V Savelli R Rizzoli E Rizzi A Galanzi A Buffa R Rana G Lattanzi B Baratta 《Bollettino della Società italiana di biologia sperimentale》1991,67(12):1081-1088
In order to investigate the kinetics of vocal fold epithelium a bromodeoxyuridine-anti bromodeoxyuridine method has been applied in vivo at both light and electron microscopy level. This method is able to define the length of both epithelium turnover and cell-cycle in basal elements, as well as the existence of a higher proliferation rate during night time in comparison with day time. Moreover distinct labeling patterns observed in incorporating cells allow us to define the precise localization in S-phase of cycling elements. 相似文献
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Methyl mercury uptake in free cells and different immobilizates of the cyanobacteriumNostoc calcicola has been examined. The general growth of the immobilized cyanobacterial cells could be negatively correlated with methyl mercury uptake. Alginate spheres proved most efficient in terms of uptake rate (0.48 nmol mg protein–1 min–1, 10 min) and total bioaccumulation (10.71 nmol mg protein–1, 1 h) with a bioconcentration factor of 3.3×103. Alginate biofilms showed a faster methyl mercury accumulation rate (0.83 nmol mg protein–1 min–1, 10 min) with a saturation of 10.28 nmol mg protein–1 reached within only 30 min (bioconcentration factor, 3.1×103). Foam preparations with a slow initial uptake approximated biofilms but were characterized by a lower bioconcentration factor (2.8×103). Free cells, in comparison, maintained the initial slow rate of uptake (0.62 nmol mg protein–1 min–1, 10 min), saturating at 30 min (8.81 nmol mg protein–1), and the resultant lowest bioconcentration factor (2.7×103). Cell ageing (30 days) brought a drastic reduction (3-fold) in organomercury uptake by free cells while alginate spheres maintained the same potential. Foam preparations of the same age showed a significant improvement in methyl mercury uptake followed by only a marginal decline in alginate biofilms. Data are discussed in the light of the physiological efficiency and longevity of immobilized cells. 相似文献
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Y L Lai M W Rana 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1986,181(3):371-381
Retinas of 4-, 10-, and 20-year-old monkeys were studied by light microscopy, electron microscopy, and scanning electron microscopy. Sections from the midperipheral region of every retina were selected for comparison. Although no significant differences were found between 4- and 10-year-old retinas, four major changes were found in 20-year-old monkey retinas: (i) increased number of displaced photoreceptor cells (DPC), (ii) increased number of macrophages of different morphology in subretinal space, (iii) increase in pigment granules in retinal pigment epithelium (RPE) cells, and (iv) altered morphology of Muller cells. DPC included both rods and cones. Their location and morphology depended on the stage of their displacement. These cells were usually oval or rounded in shape and were found either among the outer segments of other photoreceptor cells, having stalks extending into the outer nuclear layer, or were located in the subretinal space and had no stalk. A narrow space around the DPC stalks, indicating a change in the intercellular connection between photoreceptor cells and Muller cells, was observed. Furthermore, the Muller cells related to DPC had shortened and markedly reduced microvilli. Two types of macrophages were found in the subretinal space of aged monkey retinas. One type was similar in morphology to RPE cells. Some of these cells were noticed detaching from RPE. Other types of macrophages were nonpigmented. The modifications in RPE were closely related to the changes in the associated neuroretina. The RPE cells in aged retina were devoid of microvilli or had a few thin microvilli. The pleomorphic pigment granules were dispersed throughout the cytoplasm. These cells varied in their size, shape, and surface features. These changes could significantly alter the retinal metabolic equilibrium and may be indicative of age related degenerative processes. 相似文献
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Quantitative cytochemical studies of cortical parenchyma cells of roots of Pisum sativum in which the central vascular bundle is severed, showed esterase activity to be an early marker of the determination of cells to form a vascular bridge. Explantation, onto a basal culture medium, of wound segments taken from roots at different times after severing the stele showed the irreversibility of the esterase activity on removal from the inducing environment, so confirming this as a marker of cell determination. A general determination for the stele was shown to occur by 8–10 h after wounding, but information relating to tracheid secondary-cell-wall formation was not apparently available until 18–20 h after wounding. Determination appeared to occur well before mitosis. The timings of the differentiation steps indicate a simple diffusion model to explain the mechanism of arrival of the initiating molecules. 相似文献