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281.
Protection from UV-B-induced DNA damage by flavonoids 总被引:11,自引:0,他引:11
Arend Kootstra 《Plant molecular biology》1994,26(2):771-774
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Proton NMR studies are presented on the interaction of nonaminoacylated yeast tRNAPhe and elongation factor Tu X GTP from Bacillus stearothermophilis. From experiments in which transfer of magnetization is observed between proton spins of tRNA and the protein, it is concluded that complex formation takes place. Amino acid residues of the protein come into close contact with the base pair A5U68 and/or U52A62 of the acceptor T psi C limb of the tRNA molecule. From the line broadening of tRNA resonances, associated with complex formation, an association constant of 10(3)-10(4) M-1 is estimated. The NMR experiments do not monitor a significant conformational change of the tRNA molecule upon interaction with the protein. However, at times long after the onset of complex formation, spectral changes indicate that the upper part of the acceptor helix becomes distorted. 相似文献
285.
Karl J. A. McCullagh Carsten Juel Moira O'Brien Arend Bonen 《Molecular and cellular biochemistry》1996,156(1):51-57
The aim of this study was to examine the effects of chronic low frequency stimulation on the lactate transport across the plasma membrane of the tibialis anterior (TA) muscle of the rat. Stimulating electrodes were implanted on either side of the peroneal nerve in one hindlimb. Chronic stimulation (10 Hz, 50 psec bursts, 24 h/day) commenced 7 days after surgery, and were continued for 7 days. Animals were then left for 24 h, and thereafter muscles were obtained. Cytochrome C-oxidase activity was increased 1.9-fold in the stimulated TA compared to the control TA (p < 0.05). Lactate transport (zero-trans) was measured in giant sarcolemmal vesicles obtained from the chronically stimulated TA and the control TA. At each of the concentrations used in these studies a significant increase in lactate transport was observed: 2.8-fold increase at 1 mM lactate p < 0.05); 2-fold increases at both 30 mM and 50 mM lactate p < 0.05). These studies have shown that lactate transport capacity is markedly increased in response to chronic muscle contraction. 相似文献
286.
Anila S Mathai Arend Bonen Carley R Benton D L Robinson Terry E Graham 《Journal of applied physiology》2008,105(4):1098-1105
The mRNA of the nuclear coactivator peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) increases during prolonged exercise and is influenced by carbohydrate availability. It is unknown if the increases in mRNA reflect the PGC-1alpha protein or if glycogen stores are an important regulator. Seven male subjects [23 +/- 1.3 yr old, maximum oxygen uptake (Vo(2 max)) 48.4 +/- 0.8 ml.kg(-1).min(-1)] exercised to exhaustion ( approximately 2 h) at 65% Vo(2 max) followed by ingestion of either a high-carbohydrate (HC) or low-carbohydrate (LC) diet (7 or 2.9 g.kg(-1).day(-1), respectively) for 52 h of recovery. Glycogen remained depressed in LC (P < 0.05) while returning to resting levels by 24 h in HC. PGC-1alpha mRNA increased both at exhaustion (3-fold) and 2 h later (6.2-fold) (P < 0.05) but returned to rest levels by 24 h. PGC-1alpha protein increased (P < 0.05) 23% at exhaustion and remained elevated for at least 24 h (P < 0.05). While there was no direct treatment effect (HC vs. LC) for PGC-1alpha mRNA or protein, there was a linear relationship between the changes in glycogen and those in PGC-1alpha protein during exercise and recovery (r = -0.68, P < 0.05). In contrast, PGC-1beta did not increase with exercise but rather decreased (P < 0.05) below rest level at 24 and 52 h, and the decrease was greater (P < 0.05) in LC. PGC-1alpha protein content increased in prolonged exercise and remained upregulated for 24 h, but this could not have been predicted by the changes in mRNA. The beta-isoform declined rather than increasing, and this was greater when glycogen was not resynthesized to rest levels. 相似文献
287.
Prolonged papain digestion of rat IgG2a has recently been shown to yield two species of Fc fragments, termed Fc(I) AND Fc(II). The results of structural studies indicated that Fc(II) fragment was 15 to 20% smaller than Fc(I), probably secondary to loss of a carboxy-terminal peptide. The effects of these structural laterations on the catabolism and biologic properties of the Fc fragments were determined. The results of catabolic experiments indicated that after injection into normal rats Fc(I) fragments were retained in the circulation and slowly catabolized whereas Fc(II) fragments rapidly underwent filtration in the kidneys. In nephrectomized rats, however, both Fc(I) and Fc(II) fragments possessed identical slow rates of catabolism, as determined by serum disappearance and whole body catabolic experiments. Fragment pFc, corresponding to Cgamma3 domain, was different from either of the Fc fragments in exhibiting rapid rates of catabolism in both normal and nephrectomized rats. Fc(I) was more active in complement fixation and in adherence to the Fc receptor on monocytes in comparison with Fc(II). These results support the conclusion that catabolism of Fc and maintenance in circulation are separate processes influenced by different structures in the Fc fragment. The catabolism of Fc is controlled by structures in the Cgamma2 domain. This process probably is not related either to complement fixation or to adherence to the Fc receptor on monocytes. Some correlations between the structure and biologic properties of these Fc fragments are discussed. 相似文献
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