全文获取类型
收费全文 | 2871篇 |
免费 | 45篇 |
国内免费 | 10篇 |
专业分类
化学 | 1729篇 |
晶体学 | 59篇 |
力学 | 96篇 |
数学 | 272篇 |
物理学 | 770篇 |
出版年
2023年 | 17篇 |
2022年 | 28篇 |
2020年 | 23篇 |
2019年 | 37篇 |
2018年 | 27篇 |
2017年 | 30篇 |
2016年 | 64篇 |
2015年 | 42篇 |
2014年 | 66篇 |
2013年 | 158篇 |
2012年 | 130篇 |
2011年 | 219篇 |
2010年 | 143篇 |
2009年 | 133篇 |
2008年 | 157篇 |
2007年 | 204篇 |
2006年 | 154篇 |
2005年 | 125篇 |
2004年 | 101篇 |
2003年 | 102篇 |
2002年 | 68篇 |
2001年 | 32篇 |
2000年 | 35篇 |
1999年 | 38篇 |
1998年 | 29篇 |
1997年 | 29篇 |
1996年 | 29篇 |
1995年 | 28篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 28篇 |
1991年 | 22篇 |
1990年 | 31篇 |
1989年 | 19篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 19篇 |
1982年 | 31篇 |
1981年 | 36篇 |
1980年 | 22篇 |
1979年 | 34篇 |
1978年 | 27篇 |
1976年 | 22篇 |
1975年 | 21篇 |
1974年 | 19篇 |
1973年 | 20篇 |
1972年 | 19篇 |
1971年 | 16篇 |
排序方式: 共有2926条查询结果,搜索用时 15 毫秒
51.
We obtain, by extensive direct numerical simulations, time-dependent and equal-time structure functions for the vorticity, in both quasi-Lagrangian and Eulerian frames, for the direct-cascade regime in two-dimensional fluid turbulence with air-drag-induced friction. We show that different ways of extracting time scales from these time-dependent structure functions lead to different dynamic-multiscaling exponents, which are related to equal-time multiscaling exponents by different classes of bridge relations; for a representative value of the friction we verify that, given our error bars, these bridge relations hold. 相似文献
52.
We demonstrate a 300?μm long silicon photonic crystal (PC) slot waveguide device for on-chip near-infrared absorption spectroscopy, based on the Beer-Lambert law for the detection of methane gas. The device combines slow light in a PC waveguide with high electric field intensity in a low-index 90?nm wide slot, which effectively increases the optical absorption path length. A methane concentration of 100?ppm (parts per million) in nitrogen was measured. 相似文献
53.
R.A. Hefferlin G.V. Zhuvikin K.E. Caviness P.J. Duerksen 《Journal of Quantitative Spectroscopy & Radiative Transfer》1984,32(4):257-268
The atoms have long been classified into a periodic system, which is now based on quantum mechanics and group theory. A classification of molecules containing any number (N) of atoms is proposed. It is an extension of the periodic system of the atoms. The approach in this paper is that of group theory, although the proposed system has been subjected to exhaustive comparison with experimental and ab initio computational results for diatomic molecules, and conforms to the commonly known behaviours of molecules with larger N. Orthonormal transformations are performed so that the molecules can be arranged according to their numbers of electrons and to the differences of atomic numbers of the constituent atoms. These arrangements parallel the physical reality of atomic bonding and permit partial three-dimensional models of the systems to be constructed for molecules with as many as four atoms. 相似文献
54.
K. Westerholt H. Bach S. Methfessel D.K. Ray S.K. Ghatak 《Solid State Communications》1983,45(2):137-140
The magnetic field dependence of the structural transition temperature Tm from the cubic to the tetragonal phase has been determined for single crystals of La3S4 and La3Se4. The observed field dependence of Tm can be accounted for by the band Jahn-Teller model of the coupling of an eg-band to the shear mode of the cubic lattice without invoking any coupling to acoustic or optical phonons. 相似文献
55.
56.
Susanto Chakraborty Pranab Krishna Chanda Dipankar Ray 《International Journal of Theoretical Physics》1995,34(11):2223-2244
Under some assumptions and transformations of variables, Yang's equations forR-gauge fields on Euclidean space lead to conformally invariant equations permitting one to obtain infinitely many other solutions from any solution of these conformally invariant equations. These conformally invariant equations closely resemble the mathematically interesting generalized Lund-Regge equations. Some exact solutions of these conformally in variant equations are obtained. Except for some singular situations, these solutions are self-dual. 相似文献
57.
Because of the long propagation distances, Computational Aeroacoustics schemes must propagate the waves at the correct wave speeds and lower the isotropy error as much as possible. The spatial differencing schemes are most frequently analyzed and optimized for one-dimensional test cases. Therefore, in multidimensional problems such optimized schemes may not have isotropic behavior. In this work, optimized finite difference schemes for multidimensional Computational Aeroacoustics are derived which are designed to have improved isotropy compared to existing schemes. The derivation is performed based on both Taylor series expansion and Fourier analysis. Various explicit centered finite difference schemes and the associated boundary stencils have been derived and analyzed. The isotropy corrector factor, a parameter of the schemes, can be determined by minimizing the integrated error between the phase or group velocities on different spatial directions. The order of accuracy of the optimized schemes is the same as that of the classical schemes, the advantage being in reducing the isotropy error. The present schemes are restricted to equally-spaced Cartesian grids, so the generalized curvilinear transformation method and Cartesian grid methods are good candidates. The optimized schemes are tested by solving various multidimensional problems of Aeroacoustics. 相似文献
58.
Monika Sinha Manjari Bagchi Jishnu Dey Mira Dey Subharthi Ray Siddhartha Bhowmick 《Physics letters. [Part B]》2004,590(3-4):120-125
Strange stars (ReSS) calculated from a realistic equation of state (EOS), that incorporate chiral symmetry restoration as well as deconfinement at high density [Phys. Lett. B 438 (1998) 123; Phys. Lett. B 447 (1999) 352, Addendum; Phys. Lett. B 467 (1999) 303, Erratum; Indian J. Phys. B 73 (1999) 377] show compact objects in the mass radius curve. We compare our calculations of incompressibility for this EOS with that of nuclear matter. One of the nuclear matter EOS has a continuous transition to ud-matter at about five times normal density. Another nuclear matter EOS incorporates density dependent coupling constants. From a look at the consequent velocity of sound, it is found that the transition to ud-matter seems necessary. 相似文献
59.
60.
We derive invariants for a nonlinear equation of motion containing arbitrary functions. The method employed is the recently discussed direct method of Sarlet and Bahar. The resulting invariants are a special case of Ermakov invariants. We compare these results to the results obtained by applying Noether's theorem to the same equation of motion. 相似文献