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排序方式: 共有621条查询结果,搜索用时 15 毫秒
1.
W. Arklay Steel 《BMJ (Clinical research ed.)》1935,1(3883):1165-1167
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Radiation damage repair capacity of a human germ-cell tumour cell line: inhibition by 3-aminobenzamide 总被引:1,自引:0,他引:1
L R Kelland L Burgess G G Steel 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1987,51(2):227-241
The capacity of a human germ-cell tumour line to repair radiation damage has been investigated by means of a clonogenic assay. Dose-rate dependence studies, split-dose experiments and experiments designed to measure repair of potentially lethal damage have been performed. The cells showed some ability to repair radiation-induced damage in all three types of experiment. An attempt has been made to understand the possible cellular mechanisms of these repair processes by the use of 3-aminobenzamide (3-AB), an agent thought to act by inhibition of ADP-ribosylation. 3-AB added 2 h prior to and removed 18 h after irradiation at a non-toxic dose to unirradiated cells caused a small but consistent increase in cell kill with acute (150 cGy min-1) irradiation, largely involving a reduction in the shoulder region of the survival curve, but had a greater effect in increasing cell kill at a dose rate of 7.6 cGy min-1 and an even greater effect at a dose rate of 1.6 cGy min-1. When 3-Ab was present 2 h prior to the first dose and between two equal doses in a split-dose experiment, inhibition of split-dose recovery was observed. In addition, some inhibition of potentially lethal damage recovery was observed with 3-AB. A possible role for poly(ADP-ribosylation) is thus implicated in the repair of radiation-induced damage of this human tumour cell line during continuous low dose rate or fractionated radiation schedules, although other effects of 3-AB on respiratory metabolism and/or purine synthesis cannot be eliminated as the cause of the observed inhibitory effects. 相似文献
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Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
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Arachidonic acid and linoleic acid supplementation increase prostanoid production in rats fed a butter-enriched diet 总被引:2,自引:0,他引:2
M. S. Steel J. M. Naughton G. W. Hopkins A. J. Sinclair K. O''Dea 《Prostaglandins, leukotrienes, and essential fatty acids》1990,40(4):249-253
Male Sprague Dawley rats were fed a butter-enriched diet (50% fat) for 2 weeks and then supplemented orally with either 90 mg of ethyl arachidonate or ethyl linoleate daily for 2 weeks. For comparative reasons, one group of animals was fed standard laboratory rat chow for 4 weeks. Aortic prostacyclin (PGI2) production, platelet aggregation and thromboxane A2 (TXA2) production and plasma and aortic phospholipid (PL) fatty acids were measured. When compared to butter-fed rats, aortic PGI2 production, collagen-induced platelet aggregation and TXA2 production were significantly increased in rats supplemented with ethyl arachidonate to levels similar to those seen in chow-fed rats. Ethyl linoleate supplementation also tended to increase aortic PGI2 production, collagen-induced platelet aggregation and TXA2, but not to the same extent. These changes were accompanied by increases in the level of arachidonic acid and linoleic acid in aortic and plasma PL and a decrease in the level of eicosapentaenoic acid (EPA) and docsahexaenoic acid (DHA). These data indicate that supplementation with small doses of preformed arachidonic acid was more effective than supplementation with its precursor, linoleic acid, in reversing the effects on prostanoid production and phospholipid fatty acid composition in rats fed diets enriched with butter. 相似文献
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Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells 总被引:4,自引:2,他引:2
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Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction. 相似文献
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The survival of mice after whole-body exposure to a modified fission neutron-gamma field (n: gamma = 1:1) was used to examine radiation protection by WR-2721, 16,16-dimethyl PGE2(DiPGE2), and the combination of both agents. Administration of WR-2721 (453 mg/kg) increased the LD50/30 from 5.24 to 7.17 Gy (DMF = 1.37), whereas pretreatment with DiPGE2 (1.6 mg/kg) increased the LD50/30 to 5.77 Gy (dose modification factor (DMF) = 1.10). The combination of 453 mg/kg WR-2721 and 0.4 mg/kg DiPGE2 resulted in an LD50/30 of 7.33 Gy, yielding a DMF of 1.39. However, no significant difference in protection was obtained with the combination of the two agents compared to that seen with WR-2721 alone. 相似文献
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