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991.
Patrícia M. Paes de Sousa Sofia R. Pauleta M. Lurdes Simões Gonçalves Graham W. Pettigrew Isabel Moura José J. G. Moura Margarida M. Correia dos Santos 《Journal of biological inorganic chemistry》2011,16(2):209-215
In this work it is demonstrated that the characterization of c-type haem containing proteins by electrochemical techniques needs to be cautiously performed when using pyrolytic graphite
electrodes. An altered form of the cytochromes, which has a redox potential 300 mV lower than that of the native state and
displays peroxidatic activity, can be induced by interaction with the pyrolytic graphite electrode. Proper control experiments
need to be performed, as altered conformations of the enzymes containing c-type haems can show activity towards the enzyme substrate. The work was focused on the study of the activation mechanism
and catalytic activity of cytochrome c peroxidase from Paracoccus
pantotrophus. The results could only be interpreted with the assignment of the observed non-turnover and catalytic signals to a non-native
conformation state of the electron-transferring haem. The same phenomenon was detected for Met–His monohaem cytochromes (mitochondrial
cytochrome c and Desulfovibrio
vulgaris cytochrome c-553), as well as for the bis-His multihaem cytochrome c
3 from Desulfovibrio
gigas, showing that this effect is independent of the axial coordination of the c-type haem protein. Thus, the interpretation of electrochemical signals of c-type (multi)haem proteins at pyrolytic graphite electrodes must be carefully performed, to avoid misassignment of the signals
and incorrect interpretation of catalytic intermediates. 相似文献
992.
Cristiano S. Mota Maria G. Rivas Carlos D. Brondino Isabel Moura José J. G. Moura Pablo J. González Nuno M. F. S. A. Cerqueira 《Journal of biological inorganic chemistry》2011,16(8):1255-1268
Metal-dependent formate dehydrogenases (Fdh) from prokaryotic organisms are members of the dimethyl sulfoxide reductase family
of mononuclear molybdenum-containing and tungsten-containing enzymes. Fdhs catalyze the oxidation of the formate anion to
carbon dioxide in a redox reaction that involves the transfer of two electrons from the substrate to the active site. The
active site in the oxidized state comprises a hexacoordinated molybdenum or tungsten ion in a distorted trigonal prismatic
geometry. Using this structural model, we calculated the catalytic mechanism of Fdh through density functional theory tools.
The simulated mechanism was correlated with the experimental kinetic properties of three different Fdhs isolated from three
different Desulfovibrio species. Our studies indicate that the C–H bond break is an event involved in the rate-limiting step of the catalytic cycle.
The role in catalysis of conserved amino acid residues involved in metal coordination and near the metal active site is discussed
on the basis of experimental and theoretical results. 相似文献
993.
André T. Fernandes Manuela M. Pereira Catarina S. Silva Peter F. Lindley Isabel Bento Eduardo Pinho Melo Lígia O. Martins 《Journal of biological inorganic chemistry》2011,16(4):641-651
The contribution of the disulfide bridge in CotA-laccase from Bacillus subtilis is assessed with respect to the enzyme’s functional and structural properties. The removal of the disulfide bond by site-directed
mutagenesis, creating the C322A mutant, does not affect the spectroscopic or catalytic properties and, surprisingly, neither
the long-term nor the thermodynamic stability parameters of the enzyme. Furthermore, the crystal structure of the C322A mutant
indicates that the overall structure is essentially the same as that of the wild type, with only slight alterations evident
in the immediate proximity of the mutation. In the mutant enzyme, the loop containing the C322 residue becomes less ordered,
suggesting perturbations to the substrate binding pocket. Despite the wild type and the C322A mutant showing similar thermodynamic
stability in equilibrium, the holo or apo forms of the mutant unfold at faster rates than the wild-type enzyme. The picosecond
to nanosecond time range dynamics of the mutant enzyme was not affected as shown by acrylamide collisional fluorescence quenching
analysis. Interestingly, copper uptake or copper release as measured by the stopped-flow technique also occurs more rapidly
in the C322A mutant than in the wild-type enzyme. Overall the structural and kinetic data presented here suggest that the
disulfide bridge in CotA-laccase contributes to the conformational dynamics of the protein on the microsecond to millisecond
timescale, with implications for the rates of copper incorporation into and release from the catalytic centres. 相似文献
994.
995.
Sebesten fruits (Cordia myxa L.) in Gallia Narbonensis (Southern France): a trade item from the Eastern Mediterranean? 总被引:1,自引:0,他引:1
Laurent Bouby Anne Bouchette Isabel Figueiral 《Vegetation History and Archaeobotany》2011,20(5):397-404
Archaeobotanical studies carried out by rescue archaeology at N?mes and Marseille (Southern France) provided evidence of Cordia myxa during the 2nd and 3rd centuries a.d. The fruit stones were found both waterlogged in domestic contexts and charred in a cremation grave (plant offering). Data
from these finds and a survey of historical documents and archaeobotanical literature are combined here to discuss the origins
and uses of these fruits in the western world. 相似文献
996.
997.
B. Rodríguez-Porrata G. Lopez-Martinez M. Redón M. Sancho A. Mas N. Rozès R. Cordero-Otero 《World journal of microbiology & biotechnology》2011,27(1):75-83
In the present study, we analysed metabolite features during the dehydration-rehydration process for different yeast species
genetically closely related to S. cerevisiae, in order to determine whether metabolites might play a role in cell viability. We ranked the species S. cerevisiae, S. paradoxus, S. kudriavzevii, L. kluyveri, N. castellii, S. mikatae, S. bayanus, and S. servazzii according to their viability rate after the dehydration-rehydration process, and showed that desiccation tolerance across
the species did not correlate with the intracellular content of trehalose or glycogen. Cell lipid composition was also investigated
during this process, to see whether the content of triacylglycerols and phosphatidylcholine showed significant variations
across the species. The increase of phosphatidylcholine level increase in both S. paradoxus and S. bayanus cells grown in supplemented media enhanced both their cell viability after stress imposition and lipid storage. 相似文献
998.
999.
Enayatizamir N Tabandeh F Rodríguez-Couto S Yakhchali B Alikhani HA Mohammadi L 《Bioresource technology》2011,102(22):10359-10362
The in vivo biodegradation of the diazo dye Reactive Black 5 (RB5) by Phanerochaete chrysosporium immobilised on cubes of nylon sponge and on sunflower-seed shells (SS) in laboratory-scale bioreactors was investigated. The SS cultivation led to the best results with a decolouration percentage of 90.3% in 72 h for an initial RB5 concentration of 100 mg/L. It was found that the addition of 0.4 mM veratryl alcohol (VA) into the medium considerably increased the decolouration rate in SS cultivation. However, the addition of VA had no effect in the nylon cultivation. Thin layer chromatography (TLC) revealed that RB5 was transformed into one metabolite after 24 h. UV-vis spectroscopy and Fourier Transform Infrared (FT-IR) also confirmed the biodegradation of RB5. Toxicity of RB5 solutions before and after fungal treatment was assayed using Sinorhizobium meliloti as a sensitive soil microorganism. P. chrysosporium transformed the toxic dye RB5 into a non-toxic product. 相似文献
1000.
Catalán V Gómez-Ambrosi J Rodríguez A Ramírez B Silva C Rotellar F Hernández-Lizoain JL Baixauli J Valentí V Pardo F Salvador J Frühbeck G 《The Journal of nutritional biochemistry》2011,22(7):634-641