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91.
92.
On mammalian sperm dimensions 总被引:10,自引:0,他引:10
Data on linear sperm dimensions in mammals are presented. There is information on a total of 284 species, representing 6.2% of all species; 17.2% of all genera and 49.2% of all families have some representation, with quantitative information missing only from the orders Dermoptera, Pholidota, Sirenia and Tubulidentata. In general, sperm size is inverse to body mass (except for the Chiroptera), so that the smallest known spermatozoa are amongst those of artiodactyls and the largest are amongst those of marsupials. Most variations are due to differences in the lengths of midpiece and principal piece, with head lengths relatively uniform throughout the mammals. 相似文献
93.
The elasticity of synthetic phospholipid vesicles obtained by photon correlation spectroscopy 总被引:3,自引:0,他引:3
Osmotic-swelling experiments were conducted on a variety of preparations of "uniform" unilamellar vesicle systems. The synthetic lipid preparations included both vesicles produced by extrusion through polycarbonate ultrafiltration membranes and vesicles produced by the pH-adjustment method. The vesicles were monitored by photon correlation spectroscopy during swelling as the osmolarity of the external solution was decreased. Contrary to our previously reported results [Aurora, T. S., Li, W., Cummins, H. Z., & Haines, T. H. (1985) Biochim. Biophys. Acta 820, 250-258; Li, W., & Haines, T. H. (1986) Biochemistry 25, 7477-7483; Li, W., Aurora, T. S., Haines, T. H., & Cummins, H. Z. (1986) Biochemistry 25, 8220-8229; Haines, T. H., Li, W., Green, M., & Cummins, H. Z. (1987) Biochemistry 26, 5439-5447] large unilamellar vesicles produced from acidic lipids by the pH-adjustment technique were highly polydisperse and did not swell in a manner that permitted the computation of a Young's modulus, presumably due to the polydispersity. Also contrary to our previous reports, membranes derived from bovine submitochondrial particles did not produce evidence of swelling when subjected to similar protocols. Analysis of osmotic swelling of extruded unilamellar vesicles has allowed us to assign Young's moduli for bilayers of dioleoylphosphatidylcholine and dioleoylphosphatidylglycerol, in the range (5-8) x 10(8) and (3-6) x 10(8) dyn/cm2, respectively. The diameters and polydispersites obtained with electron microscopy and photon correlation spectroscopy were compared directly and with computer-modeling techniques. While excellent agreement was obtained for distributions with low polydispersity (approximately greater than 0.1), serious disagreement was found when the polydispersity exceeded approximately 0.2. 相似文献
94.
Hyperkalemic periodic paralysis (HyperPP) is a disorder in which current through Na+ channels causes a prolonged depolarization of skeletal muscle fibers, resulting in membrane inexcitability and muscle paralysis. Although HyperPP mutations can enhance persistent sodium currents, unaltered slow inactivation would effectively eliminate any sustained currents through the mutant channels. We now report that rat skeletal muscle channels containing the mutation T698M, which corresponds to the human T704M HyperPP mutation, recover very quickly from prolonged depolarizations. Even after holding at -20 mV for 20 min, approximately 25% of the maximal sodium current is available subsequent to a 10-ms hyperpolarization (-100 mV). Under the same conditions, recovery is less than 3% in wild-type channels and in the F1304Q mutant, which has impaired fast inactivation. This effect of the T698M mutation on slow inactivation, in combination with its effects on activation, is expected to result in persistent currents such as that seen in HyperPP muscle. 相似文献
95.
Thermal Acclimation of Photosynthetic Electron Transport Activity by Thylakoids of Saxifraga cernua 总被引:2,自引:1,他引:1 下载免费PDF全文
Thermal acclimation by Saxifraga cernua to low temperatures results in a change in the optimum temperature for gross photosynthetic activity and may directly involve the photosynthetic apparatus. In order to test this hypothesis photosynthetic electron transport activity of S. cernua thylakoids acclimated to growth temperatures of 20°C and 10°C was measured in vitro. Both populations exhibited optimum temperatures for whole chain and PSII electron transport activity at temperatures close to those at which the plants were grown. Chlorophyll a fluorescence transients from 10°C-acclimated leaves showed higher rates in the rise and subsequent quenching of variable fluorescence at low measuring temperatures; 20°C-acclimated leaves showed higher rates of fluorescence rise at higher measuring temperatures. At these higher temperatures, fluorescence quenching rates were similar in both populations. The kinetics of State 1-State 2 transitions in 20°C- and 10°C-acclimated leaf discs were measured as changes in the magnitude of the fluorescence emission maxima measured at 77K. Leaves acclimated at 10°C showed a larger F730/F695 ratio at low temperatures, while at higher temperatures, 20°C-acclimated leaves showed a higher F730/F695 ratio after the establishment of State 2. High incubation temperatures also resulted in a decrease in the F695/F685 ratio for 10°C-acclimated leaves, suggesting a reduction in the excitation transfer from the light-harvesting complex of photosystem II to photosystem II reaction centers. The relative amounts of chlorophyll-protein complexes and thylakoid polypeptides separated electro-phoretically were similar for both 20°C- and 10°C-acclimated leaves. Thus, photosynthetic acclimation to low temperatures by S. cernua is correlated with an increase in photosynthetic electron transport activity but does not appear to be accompanied by major structural changes or different relative amounts in thylakoid protein composition. 相似文献
96.
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98.
Glycogen metabolism was studied in primary and Herpesvirus-transformed cultures of neonatal rat brain astrocytes. A small fraction of the glucose consumed was conserved in glycogen in both the primary and the transformed astrocytic cell cultures. After addition of culture medium containing 5.5 mM glucose, glycogen increased to maximal levels within 2.5 h, the approximate time at which half of the medium glucose was consumed, and rapidly declined thereafter in both the primary and transformed astrocytic cultures. Maximum levels of glycogen were apparently related to the cell density of the Herpesvirus-transformed cultures, but primary cultures did not show this behavior. At any given cell density, maximal levels of glycogen were dependent on the concentration of extracellular glucose. Administration of glucose caused a transient activation of glycogen synthase alpha and a rapid inactivation of glycogen phosphorylase alpha. 相似文献
99.
Frameshift Suppression in SACCHAROMYCES CEREVISIAE. III. Isolation and Genetic Properties of Group III Suppressors 总被引:11,自引:3,他引:8 下载免费PDF全文
Claudia M. Cummins Richard F. Gaber Michael R. Culbertson Richard Mann Gerald R. Fink 《Genetics》1980,95(4):855-875
Suppressors of ICR-induced mutations that exhibit behavior similar to bacterial frameshift suppressors have been identified in the yeast Saccharomyces cerevisiae. The yeast suppressors have been divided into two groups. Previous evidence indicated that suppressors of one group (Group II: SUF1, SUF3, SUF4, SUF5 and SUF6) represent mutations in the structural genes for glycyl-tRNA's. Suppressors of the other group (Group III: SUF2 and SUF7) were less well characterized. Although they suppressed some ICR-revertible mutations, they failed to suppress Group II frameshift mutations. This communication provides a more thorough characterization of the Group III suppressors and describes the isolation and properties of four new suppressors in that group (SUF8, SUF9, SUF10 and suf11).——In our original study, Group III suppressors were isolated as revertants of the Group III mutations his4–712 and his4–713. All suppressors obtained as ICR-induced revertants of these mutations mapped at the SUF2 locus near the centromere of chromosome III. Suppressors mapping at other loci were obtained in this study by analyzing spontaneous and UV-induced revertants of the Group III mutations. SUF2 and SUF10 suppress both Group III his4 mutations, whereas SUF7, SUF8, SUF9 and suf11 suppress his4–713, but not his4–712. All of the suppressors except suf11 are dominant in diploids homozygous for his4-713. The suppressors fail to suppress representative UAA, UAG and UGA nonsense mutations.——SUF9 is linked to the centromere of chromosome VI, and SUF10 is linked to the centromere of chromosome XIV. A triploid mapping procedure was used to determine the chromosome locations of SUF7 and SUF8. Subsequent standard crosses revealed linkage of SUF7 to cdc5 on chromosome XIII and linkage of SUF8 to cdc12 and pet3 on chromosome VIII. 相似文献
100.
Henry W. Vaillant G. T. M. Cummins Ralph M. Richart Bruce A. Barron 《BMJ (Clinical research ed.)》1968,3(5619):671-673
Follow-up studies of 7 to 19 months of two groups of 500 women each in Barbados, in one of which a Lippes loop had been inserted by a doctor and in the other by a nurse-midwife, showed a slightly higher incidence of pregnancy and expulsion of the loop in the second group, though the difference was not statistically significant. The insertion of loops by paramedical personnel when this is an economic necessity is thought not to be contraindicated, but adequate training is essential. 相似文献