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31.
Structure and coordination of CuB in the Acidianus ambivalens aa
3 quinol oxidase heme–copper center
Tiago M. Bandeiras Manuel M. Pereira Miguel Teixeira Pierre Moenne-Loccoz Ninian J. Blackburn 《Journal of biological inorganic chemistry》2005,10(6):625-635
The coordination environment of the CuB center of the quinol oxidase from Acidianus ambivalens, a type B heme–copper oxygen reductase, was investigated by Fourier transform (FT) IR and extended X-ray absorption fine
structure (EXAFS) spectroscopy. The comparative structural chemistry of dinuclear Fe–Cu sites of the different types of oxygen
reductases is of great interest. Fully reduced A. ambivalens quinol oxidase binds CO at the heme a
3 center, with ν(CO)=1,973 cm−1. On photolysis, the CO migrated to the CuB center, forming a CuBI–CO complex with ν(CO)=2,047 cm−1. Raising the temperature of the samples to 25°C did not result in a total loss of signal in the FTIR difference spectrum
although the intensity of these signals was reduced sevenfold. This observation is consistent with a large energy barrier
against the geminate rebinding of CO to the heme iron from CuB, a restricted limited access at the active-site pocket for a second binding, and a kinetically stable CuB–CO complex in A. ambivalens aa
3. The CuB center was probed in a number of different states using EXAFS spectroscopy. The oxidized state was best simulated by three
histidines and a solvent O scatterer. On reduction, the site became three-coordinate, but in contrast to the bo
3 enzyme, there was no evidence for heterogeneity of binding of the coordinated histidines. The CuB centers in both the oxidized and the reduced enzymes also appeared to contain substoichiometric amounts (0.2 mol equiv) of
nonlabile chloride ion. EXAFS data of the reduced carbonylated enzyme showed no difference between dark and photolyzed forms.
The spectra could be well fit by 2.5 imidazoles, 0.5 Cl− and 0.5 CO ligands. This arrangement of scatterers would be consistent with about half the sites remaining as unligated Cu(his)3 and half being converted to Cu(his)2Cl−CO, a 50/50 ratio of Cu(his)2Cl− and Cu(his)3CO, or some combination of these formulations.
Electronic Supplementary Material Supplementary material is available for this article at . 相似文献
32.
Telomeres protect chromosome ends from fusing to double-stranded breaks (DSBs). Using a quantitative real-time PCR assay, we show that nonhomologous end joining between a telomere and an inducible DSB was undetectable in wild-type cells, but occurred within a few hours of DSB induction in approximately 1/2000 genomes in telomerase-deficient cells and in >1/1000 genomes in telomerase-deficient cells also lacking the ATM homolog Tel1p. The fused telomeres contained very little telomeric DNA, suggesting that catastrophic telomere shortening preceded fusion. Lengthening of telomeres did not prevent such catastrophic telomere shortening and fusion events. Telomere-DSB fusion also occurred in cells containing a catalytically inactive telomerase and in tel1 mec1 cells where telomerase cannot elongate telomeres. Thus, telomerase and Tel1p function in telomere protection as well as in telomere elongation. 相似文献
33.
A. V. Golovin I. V. Smirnov A. V. Stepanova A. O. Zalevskiy A. S. Zlobin N. A. Ponomarenko A. A. Belogurov V. D. Knorre E. N. Hurs S. D. Chatziefthimiou M. Wilmanns G. M. Blackburn R. M. Khomutov A. G. Gabibov 《Doklady. Biochemistry and biophysics》2017,475(1):245-249
It is proposed to perform quantum mechanical/molecular dynamics calculations of chemical reactions that are planned to be catalyzed by antibodies and then conduct a virtual screening of the library of potential antibody mutants to select an optimal biocatalyst. We tested the effectiveness of this approach by the example of hydrolysis of organophosphorus toxicant paraoxon using kinetic approaches and X-ray analysis of the antibody biocatalyst designed de novo. 相似文献
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Using a modified single telomere length analysis protocol (STELA) to clone and examine the sequence composition of individual human XpYp telomeres, we discovered a distinct class of extremely short telomeres in human cancer cells with active telomerase. We name them "t-stumps," to distinguish them from the well-regulated longer bulk telomeres. T-stumps contained arrangements of telomeric repeat variants and a minimal run of seven canonical telomeric TTAGGG repeats, but all could bind at least one TRF1 or TRF2 in vitro. The abundance of t-stumps was unaffected by ATM alteration but could be changed by manipulating telomerase catalytic subunit (hTERT) levels in cancer cells. We propose that in the setting of active telomerase and compromised checkpoints characteristic of human cancer cells, t-stumps define the minimal telomeric unit that can still be protected by a TRF1/TRF2-capping complex and, further, that hTERT (or telomerase) may have a role in protecting t-stumps. 相似文献
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