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991.
Darwin P. R. Kint Antxon Martínez De Ilarduya Sebastin Muoz‐Guerra 《Journal of Polymer Science.Polymer Physics》2001,39(13):1553-1564
The microstructure and crystallization behavior of a set of poly(ethylene terephthalate‐co‐5‐nitroisophthalate) copolymers (PETNI) containing 5‐nitroisophthalic units in the 10–50 mol % range were examined and compared to those of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate‐co‐isophthalate) (PETI) copolymers. A 13C NMR analysis of PETNI copolymers in a trifluoroacetic acid solution indicates that they are random copolymers with average sequence lengths in accordance with ideal polycondensation statistics. Differential scanning calorimetry (DSC) studies show that PETNI containing 5‐nitroisophthalic units up to 20 mol % are able to crystallize and that crystallization takes place in these copolymers at much slower rates than in PET. Wide‐angle X‐ray diffraction from powder and fibers reveals that crystallizable PETNI adopts the same triclinic crystal structure as PET, with the nitroisophthalate units being excluded from crystallites. Fourier transform infrared in combination with cross‐polarization/magic‐angle spinning 13C NMR spectroscopy demonstrates the occurrence of a gauche–trans conversion encompassing the crystallization process. A correlation between DSC and spectroscopic data leads us to conclude that the content of trans conformer in the noncrystallized phase of PETNI is higher than in both PET and PETI copolymers and suggests that secondary crystallization in the homopolymer must proceed by a mechanism different than that in copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1553–1564, 2001 相似文献
992.
993.
G. Spavieri V. Guerra R. De Abreu G. T. Gillies 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(3):457-463
Propagation of Aharonov-Bohm matter waves and light waves in moving media is
characterized by the interaction electromagnetic momentum. Thus, recent
models of light propagation in moving rarefied media justify and call for an optical experiment of the Mascart-Jamin type,
capable of testing the
modern interpretations of ether drift experiments. 相似文献
994.
H. E. Roman A. Celi G. De Filippi 《The European physical journal. Special topics》2008,161(1):195-205
We study long-term behaviour of air temperature, wave heights and wind speed time
series recorded for the period 1993–1997 at a meteo-marine station located in the
Adriatic Sea. The scaling analysis shows that fluctuations of air temperature
display long-range autocorrelations, while those for wave heights show a more complex
behaviour, crossing over from a persistent regime at intermediate time scales (up
to about 20 days) to an anti-persistence behaviour at longer times. Furthermore,
the crosscorrelations of their records are found to be large, with a covariance
of about -0.3 (indicating anti-crosscorrelations) within the full 5-years period,
giving a quantitative measure of the actual coupling between the two data sets. Wind
speed fluctuations are found to be strongly crosscorrelated (about 0.6) with those
of wave heights, indicating as expected that wind is the main driving force for wave
height fluctuations. 相似文献
995.
Francesca De Mori 《Czechoslovak Journal of Physics》2002,52(5):735-735
Table of Contents
Contents of the Supplement B to Vol. 52 (2002) 相似文献996.
S. S. De 《International Journal of Theoretical Physics》2002,41(7):1291-1305
From a consideration of extended hadron structure in the microlocal anisotropic space-time, the mesonic and baryonic states with their internal quantum numbers such as strangeness, hypercharge, baryon number are constructed. The SU
3 baryonic multiplets of baryons with spin (j +
) are generated from the SU
3 mesonic multiplets of mesons with spin j. The meson–baryon mass differences are also derived here. The composite particle field of hadrons for the macroscopic space-time are obtained. In particular, the meson field and one particle meson state are considered here. These one particle hadron states of the macroscopic space-time also possess the quantum numbers (strangeness, hypercharge, etc.) which are regarded as the manifestations of the anisotropic nature of the microlocal space-time. The composite fields constructed here are usable in the reduction formulae of the S-matrix approach for strong interaction. 相似文献
997.
Oxidizing species in the mechanism of cytochrome P450 总被引:2,自引:0,他引:2
This review discusses the mechanisms of oxygen activation by cytochrome P450 enzymes, the possible catalytic roles of the various iron--oxygen species formed in the catalytic cycle, and progress in understanding the mechanisms of hydrocarbon hydroxylation, heteroatom oxidation, and olefin epoxidation. The focus of the review is on recent results, but earlier work is discussed as appropriate. The literature through to February 2002 is surveyed, and 175 referenced are cited. 相似文献
998.
G. J. Goetz-Grandmont J. P. Brunette A. De Cian N. Kyritsakas 《Structural chemistry》2002,13(5-6):459-470
From IR, UV, 31P, 1H, and 13C NMR spectroscopic data, it is shown that the three 3-phenyl-4-acyl-isoxazol-5-ones, HPXI (HPBI, HPTI, and HPtbBI with acyl-, benzoyl-, toluoyl-, and para-(tert-butyl)benzoyl-, respectively), promising extractants of actinides, appear under the same major tautomeric forms, both in the solid and in solutions in various solvents: the diketo-enamine form in methanol, a -ketoenolic form in the solid, and in chloroform, benzene, and toluene. The radiocrystallographic structures of HPTI and HPtbBI have been determined. They appear as 3-phenyl-4-(-hydroxybenzylidene)isoxazol-5-ones, forming intramolecular chelates through H-bonds. -Aryl interactions might influence the relative positions of the -ketoenolic oxygen atoms and, hence, the bite angle and the cone angle of these ligands. Spectroscopic data give evidence of strong TOPO–HPXI interactions (TOPO: tri-n-octylphosphine oxide) in toluene, of the same order of magnitude for the three acylisoxazolones, in the order: HPBI > HPTI > HPtbBI. 相似文献
999.
Syvitski RT Li Y Auclair K Ortiz De Montellano PR La Mar GN 《Journal of the American Chemical Society》2002,124(48):14296-14297
Solution 1H NMR is used to probe the environments of the donor protons of eight strong hydrogen bonds on the distal side of the heme substrate in the cyanide-inhibited, substrate-bound complex of human heme oxygenase, hHO. It is demonstrated that significant magnetization transfer from the bulk water signal to the eight labile protons does not result from chemical exchange, but from direct nuclear Overhauser effect due to the dipolar interaction of these labile protons with "ordered" water molecules. The enzyme labile proton to water proton distances are estimated at approximately 3 A. It is proposed that the role of the strong hydrogen-bonding network is to immobilize numerous water molecules which both stabilize the activated hydroperoxy species and funnel protons to the active site. 相似文献
1000.
Tinnefeld P Weston KD Vosch T Cotlet M Weil T Hofkens J Müllen K De Schryver FC Sauer M 《Journal of the American Chemical Society》2002,124(48):14310-14311
The photophysics of a dendrimer containing four chromophores are investigated at the single-molecule level. First, the multichromophoric character of single dendrimers' absorption is probed by modulating the linear polarization of the excitation beam. Subsequently, using circular polarization, the same dendrimers are excited, and their fluorescence transients are recorded. Using pulsed excitation in combination with the classical Hanbury-Brown and Twiss coincidence setup the presented data demonstrate that efficient singlet-singlet annihilation ensures that always only one photon is emitted even when several excitations are generated in an individual multichromophoric molecule. 相似文献