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991.
《Vibrational Spectroscopy》2007,43(2):333-340
Harmonic and anharmonic vibrations of free nicotinamide (NIA) and picolinamide (PIA) molecules together with their hydrogen bonded complexes H2O–NIA and H2O–PIA have been studied by means of density functional method. The calculation results of the vibrational spectra of free molecules have been investigated and are compared to the available experimental spectra. The vibrational wavenumbers of both molecules have also been calculated by polarizable continuum model (PCM) that represents the solvent as a polarizable continuum and places the solute in a cavity within the solvent (water is chosen as the solvent in this study). The results of PCM calculations and the H2O–NIA, H2O–PIA complexes, are used to investigate the H-bonding interactions of both molecules with the water molecule. The harmonic wavenumbers have been scaled by proper factors obtained by comparing the observed versus calculated wavenumbers and it is shown that anharmonic corrections on the vibrational spectra provided a better agreement between the observed and calculated wavenumbers compared to the results obtained by scaling factor method. 相似文献
992.
《Vibrational Spectroscopy》2007,43(2):284-287
Geometrically frustrated pyrochlore Y2Ru2O7, which shows a spin-glass-like transition at TG ∼ 80 K, were investigated by temperature-dependent Raman scattering. Three discernable phonons appear around 315, 410, and 510 cm−1 without any abrupt change in the number of Raman active modes within the temperature range of 10–300 K. Fitting each phonon with Lorentz oscillators, we analyzed the effects of temperature on the phonon frequencies and the linewidths. The temperature-dependence of the mode near 510 cm−1 shows abnormal behavior below TG, while the other two phonons follow the usual thermal effect of lattice vibration. This behavior can be understood in terms of spin–phonon coupling. Considering the atomic modulations of each phonon mode, it is conjectured that the 510 cm−1 phonon mode is isotropically coupled to the spin degree of freedom, while the other modes are not. 相似文献
993.
《Vibrational Spectroscopy》2007,43(2):184-187
Drop coating deposition Raman spectroscopy represents a new technique that enables nondestructive measurements of solutions with concentration of biomolecules down to 1 μM. It has been demonstrated that the solution structure is preserved even after drying and Raman spectra taken from the glass-like dried deposit and a solution are virtually identical. Here, we report for the first time measurements of the structure of a drop coating ring. Proteins deposited at the outer part of the ring perimeter are affected by desiccation and the spectra differ significantly from those taken in solution. Reproducible measurements of biomolecules by means of drop coating deposition Raman spectroscopy must therefore be obtained from central or slightly inward-located parts of the coating ring. The structure as well as mechanisms participating in the formation of the coating rings is explained on the basis of recently published physical theories of droplets desiccation. Formation of the final shape of the ring is analogous to processes that give rise to desiccated droplets, whereas the coating ring behaves as an “independent ring droplet” in final stages of desiccation of an ancestral droplet. Its structure is dominated by a dip or plateau in the upper part. Oscillation of the ancestral droplet contact line is probably responsible for complete desiccation of the proteins at the outer perimeter of the coating ring. It seems plausible the arrangement of a glassy “skin” at the coating ring surface caused by the accumulation of the biomolecules near this region plays an important role in preservation of “solution-like” spectral shape. 相似文献
994.
Yuelei Bai Xiaodong He Yue Sun Chuncheng Zhu Mingwei Li Liping Shi 《Solid State Sciences》2010,12(7):1220-1225
The chemical bonding and elastic properties as well as the effect of atomic radii for A element in the Ti3AC2 phases (A = Si, Ge, and Sn) were studied by ab initio total energy calculations using plane-wave pseudopotential method based on DFT. The atomic radii of A element has a weak effect on the electronic structure. However, the bond stiffness was quantitatively examined, which shows that the bond stiffness is affected by the atomic radii of A element. The calculated results including lattice constants, internal coordinate, elastic modulus, sound velocity, and Debye temperature agree with experimental values very well. With the increase of atomic radii of A element from Si, Ge to Sn, the cohesive energy and elastic moduli as well as Debye temperature decrease, but the elastic anisotropy increases. This is related to the change of bond stiffness. It can be predicted that the fracture toughness of Ti3SnC2 would be comparable with that of Ti3SiC2 and Ti3GeC2. 相似文献
995.
Yexia Fan Chao Xu Shixing Xia Chengxiang Guan Liangcai Cao Qingsheng He Guofan Jin 《Journal of Crystal Growth》2010,312(11):1875-1878
In this paper, Zr:Fe:LiNbO3 crystals with various Li/Nb ratios were grown by the Czochralski method from melts having compositions varying between 48.6 and 58 mol% Li2O. X-ray powder diffraction (XRD), inductively coupled plasma optical emission/mass spectrometry (ICP-OE/MS), ultraviolet–visible (UV–vis) absorption and the infrared (IR) spectrum were measured and are discussed in terms of the spectroscopic characterization. It was found that as the Li/Nb ratio increases in the melt, the Li/Nb ratio in the crystal also increases, the distribution coefficients of Fe and Zr ions decrease, the absorption edge shifts to a shorter wavelength, and the ZrO2 threshold concentration of the samples decreases. 相似文献
996.
Jimin Zhang Meng Fan Xiaoyuan Chang 《Nonlinear Analysis: Theory, Methods & Applications》2012,75(2):670-683
This paper focuses on nonlinear perturbations of flows in Banach spaces, corresponding to a nonautonomous dynamical system on measure chains admitting a nonuniform exponential dichotomy. We first define the nonuniform exponential dichotomy of linear nonuniformly hyperbolic systems on measure chains, then establish a new version of the Grobman-Hartman theorem for nonuniformly hyperbolic dynamics on measure chains with the help of nonuniform exponential dichotomies. Moreover, we also construct stable invariant manifolds for sufficiently small nonlinear perturbations of a nonuniform exponential dichotomy. In particular, it is shown that the stable invariant manifolds are Lipschitz in the initial values provided that the nonlinear perturbation is a sufficiently small Lipschitz perturbation. 相似文献
997.
Yunan Cui Henryk Hudzik Rajeev Kumar Romesh Kumar 《Applied Mathematics Letters》2012,25(11):1778-1783
In this work, we present necessary and sufficient conditions for compactness of the composition operator on Orlicz–Lorentz spaces and determine upper and lower estimates for the essential norm of the composition operator on these spaces. 相似文献
998.
A.V. Krysko J. Awrejcewicz I.V. Papkova V.A. Krysko 《Chaos, solitons, and fractals》2012,45(6):709-720
In second part of the paper both classical and novel scenarios of transition from regular to chaotic dynamics of dissipative continuous mechanical systems are studied. A detailed analysis allowed us to detect the already known classical scenarios of transition from periodic to chaotic dynamics, and in particular the Feigenbaum scenario. The Feigenbaum constant was computed for all continuous mechanical objects studied in the first part of the paper. In addition, we illustrate and discuss different and novel scenarios of transition of the analysed systems from regular to chaotic dynamics, and we show that the type of scenario depends essentially on excitation parameters. 相似文献
999.
1000.