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901.
The guanyl radical or neutral guanine radical G(-H)• results from the loss of a hydrogen atom (H•) or an electron/proton (e–/H+) couple from the guanine structures (G). The guanyl radical exists in two tautomeric forms. As the modes of formation of the two tautomers, their relationship and reactivity at the nucleoside level are subjects of intense research and are discussed in a holistic manner, including time-resolved spectroscopies, product studies, and relevant theoretical calculations. Particular attention is given to the one-electron oxidation of the GC pair and the complex mechanism of the deprotonation vs. hydration step of GC•+ pair. The role of the two G(-H)• tautomers in single- and double-stranded oligonucleotides and the G-quadruplex, the supramolecular arrangement that attracts interest for its biological consequences, are considered. The importance of biomarkers of guanine DNA damage is also addressed. 相似文献
902.
Summary The specific heats of (R2O3)
x
(P2O5)1−x
glasses containing high concentrations of La3+ and Y3+ ions have been measured between 1.5K and 30K. It is shown that, in addition to the usual Debye contribution, there is an
excess specific heat arising from localized vibrational states which has been discussed in terms of two distinct models. The
first predicts a maximum in the temperature dependence of the excess specific heat associated with the crossover frequency
from phonon to fracton behaviour. The phonon-fracton density of states used to fit the excess specific heat gives rise to
model parameters having the same magnitudes as those found previously for other glasses including samarium phosphates. The
second model, formulated on the basis of soft vibrations in glasses, predicts a minimum in the excess specific heat, which
is also observed.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Capanello, Italy, July 4–8, 1994. 相似文献
903.
此文利用分子动力学计算机模拟方法,研究温度达到一千度,压力为几十万大气压下气体的振动弛豫速率与双原子分子的非谐性及温度的关系,发现振动弛豫速率随双原子分子的非谐性增大而迅速加快,却与温度几乎无关。 相似文献
904.
A. E. Ciolino O. I. Pieroni B. M. Vuano M. A. Villar E. M. Valls 《Journal of polymer science. Part A, Polymer chemistry》2004,42(12):2920-2930
We report preliminary results for the synthesis of polyethylene‐graft‐poly(dimethylsiloxane) copolymers obtained by catalytic hydrogenation of polybutadiene‐graft‐poly(dimethylsiloxane) copolymers (PB‐g‐PDMS). These last copolymers were synthesized by hydrosilylation reactions between commercial polybutadiene and ω‐silane poly(dimethylsiloxane). The reaction was carried in solution catalyzed by cis‐dichloro bis(diethylsufide) platinum(II) salt. The PB‐g‐PDMS copolymers were analyzed by 1H and 13C NMR spectroscopies, and the relative weight percentages of the grafted poly(dimethylsiloxane) macromonomer were determined from the integrated peak areas of the spectra. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2920–2930, 2004 相似文献
905.
U. Hohenester P. Kocevar N.E. Hecker R. Rodrigues-Herzog 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):143-152
We present a systematic study of the dependence of the energy relaxation of photo-excited minority electrons on the doping
concentration in highly p-doped GaAs. A nonmonotonic dependence is found in the region where the characteristics of the carrier-carrier interaction
changes from plasmon-mediated to quasistatically screened. Using a detailed Monte-Carlo study we are able to attribute this
observation to a general property of plasmas at high density.
Received: 1st April 1998 / Revised: 6 May 1998 /
Accepted: 18 May 1998 相似文献
906.
Crystals from the rich family of alkylammonium halogenoantimonates(III) and bismuthates(III) containing small bioctahedra as well as infinite two- or one-dimensional polyoctahedral units attract particular attention from the point of view of possible applications. Such crystals exhibit a wealth of phase transitions including those to ferroelectric and ferroelastic phases. The analysis of vibrational spectra performed in this paper with respect to modes assigned to alkylammonium group shows that their interactions with polyanionic sublattice is of medium strength. The absorption pattern and particularly the splitting of bands on cooling very well correlates with other anomalies of physical properties and particularly with the behaviour of second moment of PMR lines and T1 and T1ρ relaxation times as functions of temperature. The temperature behaviour of modes is well described in terms of pseudospin–phonon coupling model that we presented for different modes in various crystals. The role of anionic dynamics is not sufficiently recognised but in one case, namely for the low temperature transition in (MA)3Bi2Br9 crystal this role is predominant, according to vibrational and NQR spectra of methylammonium and isostructural caesium salt. 相似文献
907.
Usingab initio data of the potential surface for the ground state of NH3 a function is obtained to represent, with a very high precision, the potential along the inversion coordinate. The inversion spectra of NH3, ND3, NH2D and NHD2 are found by numerically solving the Schrödinger equation for this potential. Comparison is made of the calculated inversion frequencies and the experimental values, and the molecular constants of NH3 are also compared to those found in the literature. 相似文献
908.
通过振动光谱的频率参数,结合构象与键级的关系,观测了芳香酯液晶分子(一种高分子液晶模型化合物)在相态变化过程中的构象结构变化。认为这种液晶化合物在由晶态到液晶态的变化过程中是从酯基与苯环呈相互垂直状态到酯基与A环是共平面状态而与B环不共平面即垂直的状态。 相似文献
909.
Raman spectrum of allyl acetate molecule has been photographed in liquid phase using 4358 ? line of mercury arc as the exciting
line. Infrared absorption spectrum of the molecule has been recorded in liquid phase in the frequency range 200–4000 cm−1. Both the spectra have been analysed to identify the fundamental frequencies. AssumingC
s
symmetry, the observed fundamental frequencies have been assigned to various modes of vibration and compared with the frequencies
of allyl halides and acetic acid. On the basis of present assignments of fundamental vibrational frequencies and assumed approximate
structural parameters of the molecule, thermodynamic functions have been computed. 相似文献
910.
Richard J. Bettega 《Theoretical chemistry accounts》1984,64(4):277-291
A model consisting of a proton which is harmonically bound along a line and an electron bound to the proton is treated. Spectral features of the model system considered include energy level shifts, vibronic intensities, and interactions between members of degenerate manifolds not predicted by the application of the Born-Oppenheimer approximation to the model system. A time dependent process resulting in vibrationally induced preionization is also investigated. The results have special physical relevance in that they serve to facilitate understanding of vibrational effects on molecular Rydberg spectra. 相似文献