全文获取类型
收费全文 | 172650篇 |
免费 | 2105篇 |
国内免费 | 650篇 |
专业分类
化学 | 89256篇 |
晶体学 | 3048篇 |
力学 | 7240篇 |
综合类 | 31篇 |
数学 | 19729篇 |
物理学 | 56101篇 |
出版年
2020年 | 1458篇 |
2019年 | 1617篇 |
2018年 | 2033篇 |
2017年 | 2101篇 |
2016年 | 3252篇 |
2015年 | 1953篇 |
2014年 | 3191篇 |
2013年 | 7764篇 |
2012年 | 5873篇 |
2011年 | 7019篇 |
2010年 | 5101篇 |
2009年 | 5091篇 |
2008年 | 6614篇 |
2007年 | 6517篇 |
2006年 | 6167篇 |
2005年 | 5580篇 |
2004年 | 5167篇 |
2003年 | 4641篇 |
2002年 | 4497篇 |
2001年 | 5243篇 |
2000年 | 3888篇 |
1999年 | 3007篇 |
1998年 | 2516篇 |
1997年 | 2410篇 |
1996年 | 2274篇 |
1995年 | 2142篇 |
1994年 | 2117篇 |
1993年 | 2022篇 |
1992年 | 2327篇 |
1991年 | 2267篇 |
1990年 | 2212篇 |
1989年 | 2146篇 |
1988年 | 2140篇 |
1987年 | 2134篇 |
1986年 | 2027篇 |
1985年 | 2637篇 |
1984年 | 2685篇 |
1983年 | 2384篇 |
1982年 | 2493篇 |
1981年 | 2309篇 |
1980年 | 2288篇 |
1979年 | 2430篇 |
1978年 | 2464篇 |
1977年 | 2389篇 |
1976年 | 2439篇 |
1975年 | 2360篇 |
1974年 | 2328篇 |
1973年 | 2508篇 |
1972年 | 1623篇 |
1971年 | 1337篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
M. A. Elkin B. S. Ishkhanov I. M. Kapitonov E. I. Lileeva E. V. Shirokov 《Physics of Atomic Nuclei》2004,67(4):653-661
An isotopic effect in the widths of giant dipole resonances is established on the basis of an analysis of the latest systematics of photoabsorption cross sections for nuclei containing 12 to 65 nucleons. This effect arises owing to isospin splitting of a giant resonance and is enhanced by its configuration splitting. 相似文献
992.
An experimental Dalitz plot distribution for the decay η → π
+
π
−
π
0 is fitted by the theoretical one obtained in chiral perturbation theory with unitarity corrections taken into account. The
fit shows that the difference of light-quark masses is larger than is expected from electromagnetic mass differences of neutral
and charged kaons.
From Yadernaya Fizika, Vol. 67, No. 2, 2004, pp. 443–445.
Original English Text Copyright ? 2004 by Martemyanov, Sopov.
This article was submitted by the authors in English. 相似文献
993.
B. A. Belyaev N. A. Drokin V. F. Shabanov V. A. Baranova 《Physics of the Solid State》2004,46(3):574-578
This paper reports on the results of investigations into the influence of variations in the chemical composition of the aromatic core of cyano-containing molecules of liquid crystals on their dielectric properties in the frequency range 1–2000 MHz. It is shown that the dispersion of the longitudinal permittivity is adequately described by the sum of two Debye processes with different weighting factors and relaxation times. The frequency dependence of the transverse permittivity is well approximated by the Debye process with a continuous distribution of relaxation times in a specified range. It is established that the replacement of one benzene ring in the biphenyl core of the 5CB liquid-crystal molecule by a cyclohexane (or bicyclooctane) fragment leads to a considerable decrease in both relaxation times for the longitudinal permittivity, a change in the low-frequency limit of the relaxation time range for the transverse permittivity, and the evolution of the frequency dependence of the dielectric anisotropy. 相似文献
994.
B. K. Kardashev Yu. A. Burenkov B. I. Smirnov A. R. de Arellano-Lopez J. Martinez-Fernandez F. M. Varela-Feria 《Physics of the Solid State》2004,46(10):1873-1877
The effect of the vibration strain amplitude on the Young modulus and ultrasonic absorption (internal friction) in biomorphic SiC ceramics is investigated in the temperature range 116–296 K. The biomorphic SiC ceramics is prepared through pyrolysis of eucalyptus with subsequent infiltration of silicon. It is demonstrated that the vibration loading of samples in air and under vacuum is accompanied by a number of unexpected effects. The behavior of the studied ceramics is governed by at least two mechanisms, which, to a large extent, are responsible for the elastic and inelastic properties of the material. One mechanism is associated with the adsorption-desorption of environmental molecules (hypothetically, owing to the presence of pores and residual carbon), and the other mechanism involves microplastic deformation due to the motion of dislocations or other (similar) structural units. 相似文献
995.
G. E. Malashkevich V. N. Sigaev G. I. Semkova B. Champagnon 《Physics of the Solid State》2004,46(3):552-556
The spectral-luminescent properties of silica gel glasses coactivated by Ce4+ and Eu3+ ions are investigated. The structure of the glasses is studied using x-ray powder diffraction and small-angle neutron scattering. The inference is drawn that Ce4+-Eu3+ centers with high-symmetry Eu(III) oxo complexes, which are formed in the glasses, have nanocrystalline nature. These centers are characterized by a weak vibronic interaction of Eu3+ ions with the matrix. The size of nanocrystallites formed under the synthesis conditions and at coactivator concentrations used is approximately equal to 10 nm. 相似文献
996.
R. M. Vlasova N. V. Drichko B. V. Petrov V. N. Semkin E. I. Zhilyaeva R. N. Lyubovskaya I. Olejniczak A. Kobayashi H. Kobayashi 《Physics of the Solid State》2004,46(11):1985-1993
Polarized reflectance and optical conductivity spectra of single crystals of two new isostructural organic conductors based
on the BEDT-TSeF molecule, namely, the κ-(BETS)4Hg2.84Br8 superconductor (T
c
=2 K) and the κ-(BETS)4Hg3Cl8 metal, which undergoes a smooth transition to the dielectric state near 35 K, have been obtained in the spectral region 700–6500
cm−1 at temperatures of 300–15 K. At 300 K, the spectra of both compounds are nearly identical and differ from the Drude spectrum
characteristic of metals. The nature of the observed difference is discussed, and the spectra are described in terms of a
cluster approach with inclusion of electron-electron correlations in the Hubbard approximation combined with the Drude model.
The parameters of the theory were determined, including the electron transfer integrals between molecules in a cluster. The
spectra in the conducting plane of the crystals were found to be essentially anisotropic, which should be assigned to specific
features of in-plane interaction between molecules. The spectra of the superconductor and the metal become increasingly different
as the temperature is lowered. The spectra of the metal obtained for T<150 K exhibit splitting of the broad electronic maximum in the mid-IR region into two bands, which is accompanied by a splitting
of a vibronic feature deriving from electron interaction with intramolecular BETS vibrations of ν3(A
g
) symmetry. No such splitting is observed in the superconductor spectra with decreasing temperature.
__________
Translated from Fizika Tverdogo Tela, Vol. 46, No. 11, 2004, pp. 1921–1929.
Original Russian Text Copyright ? 2004 by Vlasova, Drichko, Petrov, Semkin, Zhilyaeva, Lyubovskaya, Olejniczak, A. Kobayashi,
H. Kobayashi. 相似文献
997.
The phenomenon of spatial deterministic chaos is described. A transition from an ordinary differential equation to a discrete map is justified for modeling of the chaos. Methods of studying the chaos dynamics in this model are suggested. It is established how the physical properties of a nonlinear ring interferometer influence the structure of charts of the Lyapunov exponents. The approaches developed in the present study allow an optical cryptosystem to be optimized.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 65–71, December, 2004. 相似文献
998.
E. V. Podivilov B. I. Sturman M. V. Gorkunov 《Journal of Experimental and Theoretical Physics》2004,98(5):896-907
Certain feedback loops can be used in photorefractive optical schemes to implement periodic states and create spatial gratings characterized by extremely high or low diffraction efficiencies. This highly nonlinear phenomenon is studied both experimentally and numerically. An analytical method is developed for analyzing periodic states with the use of symmetries of time-dependent diffraction equations and fast feedback response. The method is applied to describe the properties of periodic states, including their spatial structure, diffraction-efficiency oscillation period and amplitude, and characteristics of feedback-controlled strong phase modulation. 相似文献
999.
An exact method based on Green's equation is used to find the diffusion-controlled faradaic current for certain electrode geometries that incorporate edges and vertices. Thereby the magnitudes of the time-independent current density associated with angled electrode/electrode and electrode/insulator junctions are calculated. As well, the square-root-of-time-dependent currents associated with vertices, receive attention. These terms extend to longer times, the Cottrell formulation appropriate for short times. Though most of the problems solved here have been tackled previously, the novel Green function approach is shown to be straightforward and intuitive. 相似文献
1000.
The optical nonlinearities of Cu(mpo)2 [formula = C10H8N2CuO2S2] complex have firstly been investigated by using the Z-scan technique with a nanosecond-pulsed Nd:YAG laser at its second harmonic (532 nm) radiation. The nonlinear optical absorption and refraction coefficients of Cu(mpo)2 have been measured with the different on-axial peak irradiances I
0 at the waist ranging from 0.48 to 5.66 GW/cm2. The nonlinear transmittance characteristics exhibit the near resonant two-photon absorption (TPA) at 532 nm and are explained by a population redistribution model. The nonlinear absorption originates from the near resonant TPA while the mechanism of the nonlinear refraction is the near resonant TPA transition enhancement. The linear increasing dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant TPA. 相似文献