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91.
In this work relativistic corrections to the magnetic shielding constant (σM), which arise from scalar field-dependent operators (both linear and bilinear), are calculated and decomposed into contributions from molecular orbitals (MOs). Numerical results for the magnetic shielding constant of the heavy nucleus X in closed shell atomic ions X? and HX compounds (X = F, Cl, Br, I) are presented. The relative importance of inner-shell and valence electrons in the definition of each one of these terms is thus assessed and its relation with their sensitivity to changes in a chemical environment is discussed. 相似文献
92.
We simulate adaptive feedback control to coherently shape a femtosecond infrared laser pulse by means of a 4f-spatial light modulator in order to selectively excite the rovibrational modes of a polyatomic molecule. We preferentially populate an arbitrarily chosen upper rovibrational level by only employing these tailored temporally shaped pulses. A second laser would then allow for mode selective chemistry to interact selectively with the excited population. Alternatively the excited molecules enhanced reactivity could be exploited for selective chemistry. 相似文献
93.
Based on the general analysis of the grand canonical partition function in the S-matrix framework, a method is presented to calculate the equation of state of dilute warm nuclear matter. The result is a model-independent virial series for the pressure and density that systematically includes contributions from all the ground and excited states of all the stable nuclear species and their scattering channels. The multiplicity distribution of these species to keep the matter in statistical equilibrium is found out and then the pressure, incompressibility and the symmetry energy of the system are evaluated. The calculated symmetry energy coefficients are found to be in fair agreement with the recent experimental data. 相似文献
94.
The nature of equation of state for the neutron star matter is crucially governed by the density dependence of the nuclear symmetry energy. We attempt to probe the behaviour of the nuclear symmetry energy around the saturation density by exploiting the empirical values for volume and surface symmetry energy coefficients extracted from the precise data on the nuclear masses. 相似文献
95.
SOMNATH DE 《Pramana》2014,82(6):1039-1047
We have studied the production of single isolated prompt photons in high-energy proton–proton collisions at the RHIC ( \(\sqrt {s}\) = 200 GeV) and the LHC ( \(\sqrt {s}\) = 7 TeV) energies within the framework of perturbative QCD upto next-to leading order of strong coupling (α s). We have used five different parametrizations of parton distribution function (PDF) starting from the old CTEQ4M to the new CT10 distributions and compared our results with the recent single-prompt photon data from the PHENIX and the CMS Collaborations. The prompt photon cross-section is found to be described equally well by all the PDFs within the experimental errors at the RHIC and the LHC energies. The deviation in the single-prompt photon yield for different PDF sets is within ±20% when compared to CTEQ4M, indicating the upper bound of uncertainty in determining the gluon density. The diphoton measurement could be a potential candidate to constrain the gluon distribution inside the proton. 相似文献
96.
JUAN E. PERALTA VERÓNICA BARONE MARTÍN C. RUIZ DE AZÚA RUBÉN H. CONTRERAS 《Molecular physics》2013,111(8):655-661
In this work an implementation of the FPT-DFT approach for calculating the spin-dipolar contribution to NMR spin-spin coupling constants is presented. This method was tested in a set of small molecules, giving results in excellent agreement when comparing them with values taken from the literature, which were obtained with state-of-the-art calculations. To obtain an insight into the relative importance of the spin-dipolar contribution in unsaturated compounds, calculations of J(F,C), J(F,F) and J(F,H) couplings in 1,2-, 1,3-, and 1,4-difluorobenzenes were performed. An important spin-dipolar contribution to 3 J(F, F) and 5 J(F,F) was found, suggesting that this term might be important in some cases. When performing DFT calculations the non-singlet instabilities usually found in unsaturated compounds are overcome. 相似文献
97.
L. D. CARLOS C. DE MELLO DONEGÁ R. Q. ALBUQUERQUE S. ALVES JR J. F. S. MENEZES O. L. MALTA 《Molecular physics》2013,111(7):1037-1045
The synthesis, luminescence properties, experimental determination and theoretical calculation of the emission quantum yield of Eu(NTA)3.2L complexes, where NTA is naphtoiltri-fluroacetone and L denotes H2O or DMSO (dimethyl sulphoxide), were reported. The compounds were characterized by elemental analysis (carbon, hydrogen and europium), thermal analysis, UV-visible absorption and photoluminescence spectroscopies. The experimental quantum yields were determined based on a method previously proposed by Bril and collaborators. The Eu(NTA)3.2DMSO compound shows a high value for the Ω2 intensity parameter (35.8 × 10?20 cm2), reflecting the hypersensitive nature of the 5D0 → 7F2 transition and indicating that the lanthanide ion is in a highly polarizable chemical environment. The experimental quantum yield measured for that compound, 0.75, is one of the highest so far reported for solid-state europium complexes. The theoretical calculations of the quantum yield were carried out by solving an appropriate set of rate equations and by using empirical spectroscopic parameters and energy transfer rates. The theoretical results agree well with the experimental data for both complexes. The photostability of Eu(NTA)3.2DMSO at 358K was evaluated in order to verify whether this complex can be applied as a phosphor for blue light emitting devices. 相似文献
98.
ENRIQUE DE MIGUEL 《Molecular physics》2013,111(15):2449-2459
This work reexamines and updates earlier investigations on the phase behaviour of the Gay-Berne liquid crystal model, concentrating on the effect of varying temperature. Constant volume and constant pressure Monte Carlo simulations are combined for systems consisting of N = 500 molecules along different isotherms over the reduced temperature range 0.60 ≤ T ≤ 1.25. As in previous simulation studies of the model, the study identifies nematic and smectic B phases on compressing the isotropic fluid, the particular phase sequence depending on temperature. The nematic phase is found to be stable with respect to the isotropic phase for reduced temperatures T ≥ 0.75. In the temperature range 0.75 ≤ T ≤ 1.25, the phase boundaries of the isotropic-nematic transition are obtained by computing the Helmholtz free energy of both phases from thermodynamic integration. From the simulation data, the relative volume change at the isotropic-nematic transition is about 2%, and this value appears to be rather insensitive to changes in temperature. On compressing the nematic phase, the Gay-Berne fluid undergoes a strong first-order transition to the smectic B phase. This transition is studied by using constant pressure simulation, and the coexistence properties are estimated from the limits of mechanical stability of the nematic phase. Larger relative volume changes are found at the transition than those suggested by previous studies, with typical values increasing up to 10.5% as the temperature is decreased. The results are consistent with the existence of strong coupling between nematic and smectic order parameters. For temperatures T ≤ 0.70 the nematic phase is no longer stable, and the phase sequence isotropic-smectic B is observed. Therefore, the Gay-Berne model exhibits an isotropic-nematic-smectic B triple point. Extrapolating the present simulation data, this triple point is located approximately at reduced temperature TINB ? 0.70 and reduced pressure PINB ? 1.825. 相似文献
99.
M. S. DE GROOT I. A. M. HESSELMANN J. SCHMIDT J. H. VAN DER WAALS 《Molecular physics》2013,111(1):31-43
Experiments have been performed to determine the path of entry into and exit from the phosphorescent triplet state T0 of quinoxaline in a durene host. First of all the decay of phosphorescence after flash excitation was followed at 4.2 and 1.34 °K. It was found that for both perdeutero- and perhydroquinoxaline the lifetime is shortened by a factor of about three when the temperature is lowered from 4.2 to 1.34 °K. At 1.34 °K relaxation between the spin components (i.e. re-orientation of the triplet spin angular momentum) is slow relative to the decay, and the observed reduction in lifetime indicates that entry into and exit from T0, are through the same spin component. Similar decay experiments were then carried out at 1.34 °K in a 10 kG magnetic field or in a somewhat weaker field so chosen that the effect of microwave saturation of one of the E.S.R. transitions between the components could be observed. From the results it follows that on intersystem crossing the molecules enter the manifold T0 through the top zero-field component and thus initially have their spins aligned. Decay departs almost exclusively from the same component, even in the case of perhydroquinoxaline, where at least 45 per cent of it must be radiationless. The decay route agrees with out-of-plane polarization of phosphorescence for the free molecule. Finally, spin alignment on intersystem crossing is discussed from the theoretical point of view. It appears that the phenomenon is clear-cut only in molecules such as those of the aza-aromatics, where strong spin-orbit coupling of the atomic type occurs betwen ππ? and nπ? states. 相似文献
100.