全文获取类型
收费全文 | 232331篇 |
免费 | 3324篇 |
国内免费 | 506篇 |
专业分类
化学 | 128072篇 |
晶体学 | 3782篇 |
力学 | 8684篇 |
综合类 | 11篇 |
数学 | 24590篇 |
物理学 | 71022篇 |
出版年
2020年 | 2152篇 |
2019年 | 2206篇 |
2018年 | 2617篇 |
2017年 | 2701篇 |
2016年 | 4343篇 |
2015年 | 2894篇 |
2014年 | 4342篇 |
2013年 | 10825篇 |
2012年 | 7831篇 |
2011年 | 9605篇 |
2010年 | 6544篇 |
2009年 | 6342篇 |
2008年 | 8702篇 |
2007年 | 8560篇 |
2006年 | 8006篇 |
2005年 | 7182篇 |
2004年 | 6437篇 |
2003年 | 5842篇 |
2002年 | 5579篇 |
2001年 | 6690篇 |
2000年 | 5141篇 |
1999年 | 3861篇 |
1998年 | 3060篇 |
1997年 | 3000篇 |
1996年 | 2990篇 |
1995年 | 2796篇 |
1994年 | 2696篇 |
1993年 | 2617篇 |
1992年 | 3191篇 |
1991年 | 3006篇 |
1990年 | 2959篇 |
1989年 | 2931篇 |
1988年 | 2972篇 |
1987年 | 2965篇 |
1986年 | 2813篇 |
1985年 | 3669篇 |
1984年 | 3656篇 |
1983年 | 2917篇 |
1982年 | 3037篇 |
1981年 | 3111篇 |
1980年 | 2845篇 |
1979年 | 3142篇 |
1978年 | 3161篇 |
1977年 | 3271篇 |
1976年 | 3068篇 |
1975年 | 2802篇 |
1974年 | 2733篇 |
1973年 | 2698篇 |
1972年 | 1808篇 |
1968年 | 1831篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
I.L. Lyubchanskii N.N. Dadoenkova M.I. Lyubchanskii E.A. Shapovalov A.E. Zabolotin K.Y. Guslienko T. Rasing 《Applied physics. B, Lasers and optics》2002,74(7-8):711-714
Nonlinear (at the second-harmonic frequency of the incident light) optical reflection by two-dimensional magnetic superstructures
is theoretically studied. A square lattice of magnetic dots and a hexagonal lattice of magnetic bubbles (cylindrical magnetic
domains) are considered. Because the periods of these structures are comparable with the wavelengths of the fundamental and
the second-harmonic radiation, it would be possible to observe diffraction at the second-harmonic frequency. A polarization
analysis of nonlinearly diffracted radiation is performed and the numbers of observable diffraction orders for the above structures
are estimated.
Received: 10 January 2002 / Published online: 11 June 2002 相似文献
992.
Hadroprduction ofJ/ψ in π? nucleus collisions is studied in the context of the colour singlet model using nuclear structure functions from three different models of the EMC effect. We conclude that it is possible to understand the data on the large transverse momentum (p T ) and small Feynmanx (x F ) of theJ/ψ in terms of the nuclear dependence of structure functions alone. We further show that these data can be used to distinguish between different models of the EMC effect, and that a study of distributions in various kinematic variables in photoproduction ofJ/ψ should be able to very effectively supplement the information obtained from hadroproduction experiments. 相似文献
993.
A cluster mechanism is considered for the detachment of particles when the surface of a high-temperature superconducting target
absorbs laser pulses. By proposing a fractal nature for the surface, one can model it as an assembly of a large number of
nonlinear oscillators (clusters). Utilizing the method of sudden perturbations, a calculation was made of the probability
of dissociation of these oscillators, i.e., of the detachment of clusters from the surface. The calculated probability decreases
rapidly as the power density of the laser radiation is reduced to some limiting value. This is in agreement with experiments.
State Institute of Sensory Microelectronics. Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya
Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 73–77, June, 1997. 相似文献
994.
We construct polynomial orthonormal bases in various function spaces. Our bases have linear order of growth of degrees of
polynomials. We show that this order is optimal. 相似文献
995.
Exact cylindrically symmetric solutions are obtained for a class of interacting scalar and vector fields in a rotating Godel Universe. We select those with the properties of solitons with smooth decrease of the fields to asymptotics and those with sharp boundaries (droplets). It is shown that only some of the droplets are stable with respect to perturbations that preserve cylindrical symmetry.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 24–27, May, 1991. 相似文献
996.
Magnetization measurements in the (Dy
x
Y1−x
)Fe2 intermetallic compounds show evidence of blocking of domain wall motion. This effect is a function of concentrationx. The direction of magnetization is also dependent on the Dy concentration. We have used the Mossbauer spectroscopy of57Fe to verify the direction of magnetization in the series as a function ofx and temperature. The results show that this change in easy direction occurs at higher temperatures than those where the blocking
is detected through DC magnetization measurements.
supported by RHAE/SCT. 相似文献
997.
V. G. Artjuschenko K. I. Kalaidjian M. M. Mirakian 《International Journal of Infrared and Millimeter Waves》1991,12(10):1175-1185
The results of the efficiency of low-mode excitation of a parallel-plate hollow metallic waveguides (HMW) as a function of beam and waveguide parameters are represented. Coupling of two waveguides is also discussed. 相似文献
998.
999.
The asymptotic null distribution of the likelihood ratio test for two cases of ordered hypotheses in a particular genetic model is considered. A simple iterative process is proposed in order to get the restricted estimates. It is shown that both tests have asymptotically a chi-bar squared distribution and the same size. A simulation study is also conducted in order to compare the usual unrestricted test with the corresponding one of ordered hypotheses. Finally, the results are extended to some special cases. 相似文献
1000.
Deuterium NMR investigations are presented on members of two new mesogenic series derived from the naturally occurring stereoisomers myo- and scW/o-inositol. Tetraethers of these two series exhibit thermotropic columnar phases in which the columns are apparently formed by stacked hydrogen bonded dimers of these molecules which chemically are vicinal diols. Deuterium NMR measurements were performed on the tetraoctyl homologues 2e (a cis diol) and 3e (a trans diol) of these series. We have investigated mixtures of these diols with small amounts of benzene-d6 as probe molecules as well as samples of the neat diol compounds deuteriated at their hydroxyl groups. The results obtained show that the mesophases of both compounds are uniaxial and align partially in a magnetic field upon slow cooling from their isotropic liquids. The alignment is with the director parallel to the field direction indicating that the anisotropic magnetic susceptibility of this mesophase is positive. The deuterium quadrupole splitting of the benzene-d6 probe in both systems is temperature dependent and in the trans diol 3e it even changes sign. This is interpreted in terms of a model in which the benzene-d6 probe equilibrates rapidly between two (or more) solvation sites with quadrupole splittings of opposite signs The deuterium spectra of the neat deuterium labelled cis diol 2e exhibit two different signals due to the two deuterons which are located at the axial and equatorial hydroxyl groups. This indicates that there is no fast intra- or intermolecular exchange of the hydroxyl hydrogens. The overall quadrupole splittings of the hydroxyl deuterons in this compound are highly reduced compared to their static values and this is interpreted in terms of motional modes involving both reorientation of the hydroxyl deuterons about their C-O axis and overall reorientation of the molecules (or pairs of molecules) around the columnar axes. The corresponding spectra of the neat deuteriated trans diol 3e exhibit a single spectrum indicating that both hydroxyl deuterons in this compound are equivalent, or very nearly so. Within the mesophase region the spectrum undergoes gradual changes due to the increase in the molecular mobility, but the overall motional narrowing is less than in the cis isomer 2e. Apparently due to stronger hydrogen bonding in the trans isomer 3e the precession of the hydroxyl groups is hindered and a fast molecular reorientation is only possible at high temperatures. 相似文献