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101.
Egbert Hahn Johanna Fruwert und Heinz Böhlig 《Monatshefte für Chemie / Chemical Monthly》1984,115(8-9):935-942
Comparable force fields for HCOO–, HFCO, HClCO and HDCO have been calculated on the basis of internal coordinates. Linear relations between (i) the carbonyl bond order and the carbonyl stretching force constant, (ii) the sum of the three in-plane bending force constants and the hydrogen out-of-plane force constantf
, (iii) a combination of orbital electronegativities andf
, have been obtained. The observed in-plane vibrational frequencies have been calculated with an average error of 6.3 cm–1 or 0.4%. 相似文献
102.
103.
104.
Mg2TiO4:Cr3+ annealed at 560°C shows luminescence properties which differ considerably from those of the unannealed phosphor used so far. In both cases the regular Cr3+ ions only absorb the irradiated energy transferring it radiationless to the real luminescence centres, but the annealed phosphor reveals a new spectrum consisting of a few sharp lines. The radiance of the single lines can be influenced by powdering, which in connection with the annealing effect shows that the centres of both types of phosphors consist of clusters of lattice defects and octahedrally coordinated Cr3+ ions. These clusters or associates form themselves by thermal diffusion during the annealing process. Furthermore criteria have been found showing that the R lines do not come from only one but from two Cr3+ ions situated in non-equivalent lattice sites. 相似文献
105.
Synchrotron radiation with its intense continuum and its excellent time structure has been exploited for time resolved luminescence spectroscopy in the solid state. By selective excitation of n = 1, n′ = 2 exciton states of Xe, Kr and Ar atoms in a neon matrix we were able to identify the emitting states involved. Lifetimes within the cascade of radiative and radiationless relaxation between excited states as well as the radiative lifetimes for transitions to the ground state have been derived from the decay curves. Energy positions and radiative lifetimes of the emitting states correspond quite well with those of the free atoms. Radiative and radiationless relaxation processes take place within the manifold of excited states of the guest atoms. The rate constants for radiationless decay confirm an energy gap law. The order of the radiationless processes reaches in some cases extremely high values. Selection rules for spin and angular momentum are essential to understand the observed radiationless transition rates. 相似文献
106.
An outbreak of anthrax in a single homogeneous geographical region is modelled. The spread of the disease to neigbouring regions is also simulated and the model is compared with data from the 1970 epizoötic in the Kruger National Park.Two possible driving mechanisms for the epizoötic are proposed and examined, viz. environmental contamination or direct contact between vulnerable animals and fresh carcases. In the latter case, it is shown that the model exhibits a threshold effect, in that an epizoötic will only arise if the vulnerable population exceeds a threshold value which is determined in terms of one of the parameters of the model. 相似文献
107.
It is shown that no computer manageable sample cluster is large enough to eliminate size effects in the calculations of the density of states (DOS) for tetrahedrally bonded amorphous semiconductors. A method which correctly reduces such effects is described. Special attention is given to the anisotropy of the bulk structure, and to the surface bonds. The size sensitive energy regions are identified and further corrections are made. With this method, we can confidently compare the details of the DOS for different existing model structures. 相似文献
108.
The high-pressure absolute rate constants for the decomposition of nitrosobenzene and pentafluoronitrosobenzene were determined using the very-low-pressure pyrolysis (VLPP) technique. Bond dissociation energies of DH0(C6H5? NO) = 51.5 ± 1 kcal/mole and DH0 (C6F5? NO) = 50.5 ± 1 kcal/mole could be deduced if the radical combination rate constant is set at log kr(M?1·sec?1) = 10.0 ± 0.5 for both systems and the activation energy for combination is taken as 0 kcal/mole at 298°K. δHf0(C6H5NO), δHf0(C6F5NO), and δHf0(C6F5) could be estimated from our kinetic data and group additivity. The values are 48.1 ± 1, –160 ± 2, and – 130.9 ± 2 kcal/mole, respectively. C–X bond dissociation energies of several perfluorinated phenyl compounds, DH0(C6F5–X), were obtained from the reported values of δHf0(C6F5X) and our estimated δHf0(C6F5) [X = H, CH3, NO, Cl, F, CF3, I, and OH]. 相似文献
109.
The extrema of the position dependent spontaneous magnetization in a periodically layered two-dimensional Ising model are calculated exactly. Theor asymptotic behaviour for large width of a homogeneous sublayer is given, the magnetization increase far from a free surface discussed. 相似文献
110.