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111.
Results are given on simulation of the phase transition solid-liquid in copper by the molecular dynamics technique (MDT), pressure and volume being constant. A direct evidence for the possibility of vacancy mechanism of melting predicted by Frenkel is obtained. In the presence of the free surface (p = const) when the temperature of the medium approaches the melting point vacancies are formed at the surface monolayer (≈ 800 K). At higher temperatures an intense diffusion of defects takes place. The appearance of vacancies is associated with “premelting”. Real melting starts (Tm) with an inward diffusion of the “surface” vacancies, simultaneously the whole volume being characterised by generation of Frenkel pairs (≈ 1050 K). For V = const Tm increases appreciably (≈ 1710 K) due to thermal pressure. Mechanism in this case is similar to that for p = const. There is an instability of the lattice along the 〈100〉 direction that results in generation of Frenkel pairs at the melting point. The mechanism is associated with simultaneous perpendicular movement of the two neighbour atoms along the above directions. The lifetime of an unstable pair is about ≈ 10−13 s. Then it annihilates or falls into stable defects. An intense diffusion by a vacancy and interstitial mechanism is observed (≈ 5 × 10−5 cm2/s). 相似文献
112.
Radiation-induced creep (RIC) of the f.c.c. and b.c.c. metals is investigated in terms of the dislocation-diffusion approach in a wide range of temperatures considering the changes in the nature of radiation-induced defects. The possibility of simultaneous nucleation of vacancies, interstitials, dislocation loops of both types, and voids as well as absorption of point defects by neutral sinks are taken into account. A more real scheme of dislocation multiplication suggested by Weertman is introduced into the diffusion-dislocation creep model. The behaviour of RIC and radiation swelling upon stress, temperature, and the internal structure of the materials is analysed. Good qualitative agreement is obtained by a comparison with the known experimental data. 相似文献
113.
V. G. Chudinov V. P. Gogolin B. N. Goshchitskii V. I. Protasov 《physica status solidi (a)》1981,67(1):61-67
The collision cascade in Nb3Sn compounds is simulated by means of molecular dynamics technique. It is estimated, that focusing collisions propagate along the 〈120〉, 〈100〉, 〈111〉 directions and along the atomic chains of Nb. Formation of “antistructural” defects directly in the collision cascade seems to be hardly probable. The crystal structure of the cascade region is strongly disturbed after relaxation, which is likely to lead to distortion of the translational symmetry under irradiation by sufficiently large fluences. The comparison with the experimental data shows, that the calculated structures are observed at irradiation of Nb3Sn by light charged particles, during which cascade regions of small dimensions (≈ 15 Å) are formed. The results for Nb3Sn, irradiated by fast neutrons can be understood only in terms of evolution of a cascade region (≈ 70 Å) at the following stage of thermal spike. In this case, as distinct from the above mentioned, there may be local melting with subsequent superfast crystallization. Since the surrounding matrix keeps an ideal structure, in the cascade region the same structure should be observed; but atoms of Nb and Sn will not have enough time to occupy their right positions. 相似文献
114.
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119.
V. Ya. Kostyuchenko L. Yu. Protasov A. V. Voitsekhovskii 《Russian Physics Journal》2011,54(7):785-790
The influence of a graded-band near-boundary region with a linear change in the energy gap and potential step on the effective surface recombination rate is considered for heterostructures based on p-cadmiummercury-tellurium. It is shown that for decreasing the surface recombination rate it is necessary, in the initial stage, that the energy-gap width increased more slowly as compared with its increase according to the linear law. 相似文献
120.
E. Yu. Loktionov A. V. Ovchinnikov Yu. Yu. Protasov D. S. Sitnikov 《Bulletin of the Lebedev Physics Institute》2010,37(3):82-84
Optical gas-dynamic processes occurring in polymeric targets ((CH2O)
n
, (C2F4)
n
) exposed to ultrashort laser pulses (τ
0.5 ∼ 45 − 70 fs; λ
I,II,III
= 266, 400, 800 nm; and E/S ∼ 0.1 − 40 J/cm2 at r
0 ∼ 20 μm) were studied under normal conditions and in vacuum (p ∼ 10−2 Pa). The dynamics of the mass flow from the target surface (m′ ∼ 10−5 − 10−4 g/J) was studied and the spectral-energy thresholds of laser ablation, the electron density distribution (n
e
∼ 1014 − 1018 cm−3), the mass-averaged velocity of the material flow from the target surface (∼ 103 m/s), and the chemical composition and average temperature in the near-surface plasma formation (T ∼ 5000 K) were determined using interference microscopy, emission spectroscopy, and shadowgraphy. 相似文献