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Axial ligands of chloroplast cytochrome b-559: identification and requirement for a heme-cross-linked polypeptide structure 总被引:5,自引:0,他引:5
Optical, resonance Raman, and electron paramagnetic resonance spectroscopies have been used to characterize the ligands and spin state of the chloroplast cytochrome b-559. The protein was isolated from both maize and spinach in a low-potential form. The spectroscopic data indicate that the heme iron in both ferric and ferrous cytochrome b-559 is in its low-spin state and ligated in its fifth and sixth coordination positions by histidine nitrogens. Electron paramagnetic resonance data for the purified spinach cytochrome are in good agreement with those determined by Bergstr?m and V?nng?rd [Bergstr?m, J., & V?nng?rd, T. (1982) Biochim. Biophys. Acta 682, 452-456] for a low-potential membrane-bound form of cytochrome b-559. The g values of high-potential cytochrome b-559 are shifted from those of its low-potential forms; this shift is interpreted as arising from a deviation of the planes of the two axial histidine imidazole rings from a parallel orientation. The model is consistent with the physical data and may also account for the facility with which cytochrome b-559 can be converted between low- and high-potential forms. Recent biochemical and molecular biological data [Widger, W. R., Cramer, W. A., Hermodson, M., Meyer, D., & Gullifor, M. (1984) J. Biol. Chem. 259, 3870-3876; Herrmann, R. G., Alt, J., Schiller, D., Cramer, W. A., & Widger, W. R. (1984) FEBS Lett. 179, 239-244] have shown that two polypeptides, one with 83 residues and a second with 39 residues, most likely constitute the protein of the cytochrome.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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Hepatic glycogen patterns in fasted and fed rats 总被引:5,自引:0,他引:5
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Examination and characterization of distribution system biofilms 总被引:14,自引:0,他引:14
Investigations concerning the role of distribution system biofilms on water quality were conducted at a drinking water utility in New Jersey. The utility experienced long-term bacteriological problems in the distribution system, while treatment plant effluents were uniformly negative for coliform bacteria. Results of a monitoring program showed increased coliform levels as the water moved from the treatment plant through the distribution system. Increased coliform densities could not be accounted for by growth of the cells in the water column alone. Identification of coliform bacteria showed that species diversity increased as water flowed through the study area. All materials in the distribution system had high densities of heterotrophic plate count bacteria, while high levels of coliforms were detected only in iron tubercles. Coliform bacteria with the same biochemical profile were found both in distribution system biofilms and in the water column. Assimilable organic carbon determinations showed that carbon levels declined as water flowed through the study area. Maintenance of a 1.0-mg/liter free chlorine residual was insufficient to control coliform occurrences. Flushing and pigging the study area was not an effective control for coliform occurrences in that section. Because coliform bacteria growing in distribution system biofilms may mask the presence of indicator organisms resulting from a true breakdown of treatment barriers, the report recommends that efforts continue to find methods to control growth of coliform bacteria in pipeline biofilms. 相似文献
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Intracellular polyamine biosynthesis is required for interleukin 2 responsiveness during lymphocyte mitogenesis 总被引:2,自引:0,他引:2
The objective of the present investigation was to define a more precise role for intracellular polyamine biosynthesis with respect to specific inducible events which regulate lymphocyte mitogenesis. In this regard, we have examined the effect of polyamine depletion on interleukin 2 (IL-2) production, receptor expression, and responsiveness in Con A stimulated mononuclear leukocytes (MNL). Polyamine depletion was achieved utilizing the specific irreversible inhibitor of ornithine decarboxylase (ODC), DL-alpha-difluoromethylornithine (DFMO). Polyamine depletion of MNL augmented detectable levels of Con A-induced IL-2 activity. In contrast, the ability of polyamine depleted MNL to respond to saturating levels of IL-2 (100 U/ml) following 72 or 96 hr of Con A stimulation was reduced 100 and 81%, respectively. Nonetheless, polyamine depletion did not impair the induction of IL-2 receptor expression. High-affinity IL-2 receptor density in the polyamine depleted population was greater than control cells late in culture (96 hr). The expression of high-affinity IL-2 receptors did not correlate with an ability to respond to IL-2 in the polyamine depleted population. The results of this study demonstrate for the first time that intracellular polyamine biosynthesis is required for IL-2 responsiveness during a primary mitogenic lymphocyte response. 相似文献
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Curtis W. Hoganson Demetrios F. Ghanotakis Gerald T. Babcock Charles F. Yocum 《Photosynthesis research》1989,22(3):285-293
Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn2+. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Yz
+, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Yz
+ reduction by benzidine was a linear function of benzidine concentration. The rate of Yz
+ reduction by Mn2+ at pH 6 increased linearly at low Mn2+ concentrations and reached a maximum at the Mn2+ concentrations equal to several times the reaction center concentration. The rate was inhibited by K+, Ca2+ and Mg2+. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Yz
+ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn2+ near Yz
+ at a site that may be one of the native manganese binding sites.Abbreviations PS II
Photosystem II
- YD
tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum
- Yz
tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation
- ESR
electron spin resonance
- DPC
diphenylcarbazide
- DCIP
dichlorophenolindophenol 相似文献
10.
Water oxidation in photosystem II: from radical chemistry to multielectron chemistry 总被引:8,自引:0,他引:8
G T Babcock B A Barry R J Debus C W Hoganson M Atamian L McIntosh I Sithole C F Yocum 《Biochemistry》1989,28(25):9557-9565