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971.
Agnello M Belli G Bendiscioli G Bertin A Botta E Bressani T Bruschi M Bussa MP Busso L Calvo D Cereda B Cerello PG Cicalò C Corradini M Costa S De Castro S Donzella A Feliciello A Ferrero L Filippi A Filippini V Fontana A Galli D Garfagnini R Giacobbe B Gianotti P Grasso A Guaraldo C Iazzi F Lanaro A Lodi Rizzini E Lucherini V Marcello S Marconi U Masoni A Minetti B Montagna P Morando M Nichitiu F Panzieri D Pauli G Piccinini M Puddu G Rossetto E Rotondi A Rozhdestvensky AM Saino A Salvini P 《Physical review letters》1995,74(3):371-374
972.
973.
Noise in spontaneous respiratory neural activity of the neonatal rat isolated brainstem-spinal cord preparation stimulated with acetylcholine (ACh) exhibits positive correlation. Neural activity from the C4 (phrenic) ventral spinal rootlet, integrated and corrected for slowly changing trend, is interpreted as a fractal record in time by rescaled range, relative dispersional, and power spectral analyses. The Hurst exponent H measured from time series of 64 consecutive signal levels recorded at 2 s intervals during perfusion of the preparation with artificial cerebrospinal fluid containing ACh at concentrations 62.5 to 1000 &mgr;M increases to a maximum of 0.875+/-0.087 (SD) at 250 &mgr;M ACh and decreases with higher ACh concentration. Corrections for bias in measurement of H were made using two different kinds of simulated fractional Gaussian noise. Within limits of experimental procedure and short data series, we conclude that in the presence of added ACh of concentration 250 to 500 &mgr;M, noise which occurs in spontaneous respiratory-related neural activity in the isolated brainstem-spinal cord preparation observed at uniform time intervals exhibits positive correlation. (c) 1995 American Institute of Physics. 相似文献
974.
Summary We obtain trace ideal criteria for 0
A 2 () of a Bounded symmetric diomain in n. 相似文献
975.
Sterically hindered ligands generally form metal complexes with lower coordination numbers than less hindered ligands. In contrast to dogma, the solid state vanadium(V) complexes with ethylene glycol and pinacol contain four- and five-coordinate vanadium atoms, respectively. Ab initio and electrostatic potential distribution calculations were conducted on both experimental and optimized geometries of the four- and five-coordinate oxovanadium chloroalkoxides. Ab initio energy calculations favor the five-coordinate species for all ligands at all levels of theory examined. No significant differences in the electrostatic properties of the vanadium atoms in the two types of molecules were observed by using electrostatic potential distribution analysis. Methyl group substitutions on the ligand did not change the electronics of the vanadium atoms sufficiently to be a factor. Thus, we conclude that neither electronics nor sterics at the metal center explains the experimental geometries. In the absence of a significant observable electronic effect at the vanadium, we note that the experimental observations can be attributed to ligand geometric effects such as the Thorpe-Ingold and/or gem-dialkyl effects. 相似文献
976.
Bernard Laude Mohamed Soufiaoui Et Jean Arriau 《Journal of heterocyclic chemistry》1977,14(7):1183-1190
The reactivity of N-methylindole towards diarylnitrilimines has been studies. The cycloadducts are 8-methyl-3a,8a-dihydro-pyrazolo[3,4-b] indole derivatives. The structure reported was assigned on the bases of satisfactory analytical, spectroscopic and chemical data. An interpretation based on the second order perturbation method of frontier orbitals is in agreement with the observed regiospecificity. 相似文献
977.
Quantum mechanical calculations using the PCILO method have been performed on the tripeptide model CH3CO-X-Y-NHCH3. Competition between C5, C7, C10 rings and open structures has been investigated through mapping of the whole {φ, Ψ} conformational space and energy minimization.
From these results, it appears that the C10 ring simulating the folding named U-turn, involving a hydrogen bond between the i...i + 3 residues, is the most probable structure although not the most stable in energy. The results are used for predicting
the frequency of U-turns in proteins, α-chymotrypsin is given as an example. 相似文献
978.
D'Souza LJ Gigant B Knossow M Green BS 《Journal of the American Chemical Society》2002,124(10):2114-2115
The crystal structures of catalytic antibody D2.3 Fab with the two enantiomers, 7D and 7L, which represent transition state analogues for the hydrolysis of the corresponding esters, 6D and 6L, were determined to better understand remarkable reactivity differences: the L-ester displayed significantly tighter binding (K(M)) and increased catalytic activity (k(cat)) with D2.3, even though the chiral center is 7 bonds distant from the reaction center. Surprisingly, the electron densities of the liganded phosphonates, 7D and 7L, within the D2.3 binding/reaction site were essentially identical, highlighting the subtle influences of protein interactions on chemical behavior. 相似文献
979.
Because of their successful use in dye-sensitized solar cells, Ru(II) polypyridyl complex dyes adsorbed on nanocrystalline TiO2 films have been regarded as model systems for the experimental study of the ultrafast dynamics of interfacial light-induced electron transfer. Most studies have reported charge injection kinetics from Ru(dcbpyH2)2(NCS)2 (N3) to take place with a fast (sub-100 fs) phase, followed by a slower (0.7-100 ps) multiexponential component. This complex, multiphasic behavior observed for the electron injection process has prevented the development of a satisfying kinetic model and has led to often contradicting conclusions. Here, we show that the observed kinetic heterogeneity can result from the aggregation of sensitizer molecules on the surface. Carefully controlled deposition of Ru(II) complex dye molecules onto nanocrystalline titania consistently yields a monophasic injection dynamics with a time constant shorter than 20 fs. The latter figure suggests the process is beyond the scope of vibration-mediated electron transfer kinetic models and might be controlled by the electron dephasing in the solid. 相似文献
980.
Kuad P Borkovec M Desage-El Murr M Le Gall T Mioskowski C Spiess B 《Journal of the American Chemical Society》2005,127(4):1323-1333
The microscopic protonation mechanism, at an inframolecular level, of norbadione A, a pigment extracted from mushrooms and known to complex cesium cations, was determined by using 1H NMR titrations and the cluster expansion method. This study revealed a pH dependent Z to E isomer switch that occurs in both pulvinic moieties. As a consequence, norbadione A can exist in solution in four stereomeric forms (E-E, E-Z, Z-E, and Z-Z), which can be of interest in the development of molecular-level devices. In the presence of 0.15 M NaCl, the calculated microconstants showed an unusual apparent cooperativity between the enol groups, which results from the release of the sodium cations upon protonation of norbadione A. 相似文献