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991.
992.
低速稳定传播火焰产生弱冲击波后的流场是自相似的,相平面守恒方程的奇异点Z=0、F=1对应冲击波马赫数为1.本文用自适应步长的四阶Runge-Kutta法对相平面的控制方程积分,求得弱冲击波后流场参数分布,与声波方法得到的结果相比,在低速稳定传播火焰的条件下,两者结果完全吻合,克服了前人在该条件下所得结果的不相容性. 相似文献
993.
S. B. Dorofeev V. P. Sidorov M. S. Kuznetsov A. E. Dvoinishnikov V. I. Alekseev A. A. Efimenko 《Shock Waves》1996,6(1):21-28
Large scale experiments were carried out to study the effect of fuel concentration on air blast parameters and heat radiation
from gaseous detonations. Hemispheric plastic envelope (4 meters in radius) was used with propane-air mixtures containing
from 4 to 7 vol. % of fuel. The expressions for overpressures and impulses were determined in Sachs variables. The effect
of fuel concentration on blast parameters is shown to be insignificant for the same amount of oxygen in the mixture volume.
Thus the blast wave parameters can be described as for stoichiometric mixtures using additional scaling for the explosion
energy according to oxygen content (cloud volume). The results of large scale experiments with fuel spray clouds containing
0.16–100 tons of fuel with mean concentration from stoichiometric () up to are reconsidered. These results confirm the proposed scaling of air blast parameters for a wide range of fuel types, cloud
volumes and fuel concentrations. Detonations of fuel rich gaseous mixtures result in a strong heat radiation. Heat radiation
energy, time and size of the fireball formed are studied as a function of fuel concentration.
Received March 10, 1995 / Accepted March 12, 1995 相似文献
994.
A.V. Clark 《Ultrasonics》1985,23(1):21-30
To assess the integrity of a structure containing a (known) flaw, it is necessary to know the stresses acting on the flaw. Many common structural elements (e.g. beams and plates) are subjected to either true plane stress or generalized plane stress. For either of these cases, there are three in-plane stresses (one shear stress and two normal stresses) to be determined in general.In this paper, we consider the application of the acoustic birefringence method to generalized plane stress states, where the thickness-averaged values of the shear and normal stresses are sought. It is shown that the times-of-flight are thickness-averaged effects, whereas the polarization directions depend upon local values of stress. Consequently, when the symmetric (axial) component of the stresses dominates the antisymmetric (bending) component, the acoustic birefringence method can be used to determine all three stresses, if the boundary conditions are known. For unknown boundary conditions, the normal stresses can be determined to within arbitrary functions.Problems arise in using the normal incidence technique when either the shear stress vanishes, or the symmetric (membrane) components of generalized plane stress do not dominate the bending components. In the former case, the thickness-averaged difference in normal stresses can be obtained, provided that the birefringence in the unstressed state is known. In the latter case, the (averaged) difference in normal stresses can be obtained by measuring time-of-flight differences of off-axis SH-waves propagating in the planes of material symmetry of the plate. 相似文献
995.
《科学通报(英文版)》1988,33(14):1219-1219
996.
Radio pulses from extensive air showers (EAS) at 30, 44, and 60 MHz frequencies have been studied, using wide band broad-side
arrays of half-wave dipole antenna systems. The experimental results support the theoretical prediction that the field strength
of radio emission depends on the shower size. An asymmetry has been noticed in the pulse height distributions of radio pulses
detected by North-South and East-West directed arrays. These observations are in agreement with the theory that the charge
separation mechanism is predominant in generating radio pulses from EAS and radio emission is polarised in the East-West direction.
Experimental data are compared with those of earlier workers. 相似文献
997.
P. Rapagnani 《Il Nuovo Cimento C》1982,5(4):385-408
Summary The characteristics of a new capacitive resonant transducer developed and tested on a small (M=11.2 kg) cryogenic gravitational-wave antenna at the liquid helium temperature are presented. The resonator frequency can
be tuned within 0.1 Hz of the antenna frequency. The system has a mechanical merit factorQ≃5·105 and a ratio between the electrical energy in the transducer and the energy in the antenna β=3·10−3 atT=4.2 K. With these parameters, the transducer allows one to reach an effective noise temperatureT
eff≃60 mK using a cooled FET preamplifier, and, if coupled to a r.f.-SQUID, allows one to reachT
eff≃10 mK for the 5000 kg cryogenic gravitational-wave antenna of the Roma group at CERN (Geneva).
Riassunto Si presentano le caratteristiche di un nuovo trasduttore risonante di tipo capacitivo. Il trasduttore è stato provato su una piccola antenna di 11.2 kg di massa, raffreddata alla temperature dell'elio liquido. La frequenza del risuonatore è stata accordata entro 0.1 Hz della frequenza dell'antenna. A 4.2 K, il sistema ha un fattore di merito meccanicoQ≃5·105 ed il rapporto tra l'energia elettrica nel trasduttore e l'energia nell'antenna è β=3·10−3. Con i valori dei parametri ottenuti, il trasduttore permette di raggiungere una temperatura efficace di rumoreT eff≃60 mK usando un amplificatore a FET raffreddato e, se accoppiato ad un r.f.-SQUID, consente di avereT eff≃10 mK per l'antenna gravitazionale criogenica di 5000 kg del gruppo di Roma, in funzione presso il CERN (Ginevra).相似文献
998.
The general high-frequency, rough-surface reflection process is treated by the method of stationary phase. In particular, the principle of stationary phase is applied to each of the local reflection events, which appear to depend on surface curvature as well as slope. However, we show that the number of reflecting highlights also depends on curvature and cancels the curvature dependence. These results agree fully with those obtained by Beckmann and Spizzichino for the special case of the Gaussian process. 相似文献
999.
V. P. Karassiov 《Theoretical and Mathematical Physics》2005,145(3):1666-1677
We present theoretical foundations for the quantum tomography of polarization states of light fields as a method for measuring
their polarization density operator
, which characterizes only the polarization degrees of freedom of the radiation. We mainly attend to the method in which the
tomographic observables (the
“measurement instruments”) are polarizable in nature. We show that the quantum nature of this method can be adequately expressed
using the quasispectral tomographic decompositions of
in special operator bases, which are finite sums of partially orthogonal projection operators determining the probability
distributions of tomographic observables as the decomposition coefficients. We obtain the matrix versions of such “tomographic”
representations of
, in particular, by projecting them on semiclassical operator bases determining the polarization quasiprobability functions.
We briefly discuss the information aspects of the schemes considered in the paper.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 145, No. 3, pp. 344–357, December, 2005. 相似文献
1000.
The emission of radiation from relativistic positrons moving in the 〈110〉 axial channels of an f.c.c. (diamond) crystal has
been studied. An expression for the radiation intensity has been obtained for the general case of positron motion. This expression
has been simplified for the particular case of well-collimated incident beam. Enhancement of the radiation over (ordinary)
bremsstrahlung has been discussed. 相似文献