全文获取类型
收费全文 | 349149篇 |
免费 | 3785篇 |
国内免费 | 1162篇 |
专业分类
化学 | 190734篇 |
晶体学 | 5681篇 |
力学 | 14710篇 |
综合类 | 18篇 |
数学 | 35632篇 |
物理学 | 107321篇 |
出版年
2021年 | 2322篇 |
2020年 | 2686篇 |
2019年 | 2939篇 |
2018年 | 3245篇 |
2017年 | 3348篇 |
2016年 | 5551篇 |
2015年 | 3874篇 |
2014年 | 5710篇 |
2013年 | 15779篇 |
2012年 | 11947篇 |
2011年 | 14848篇 |
2010年 | 9852篇 |
2009年 | 10048篇 |
2008年 | 13436篇 |
2007年 | 13331篇 |
2006年 | 12681篇 |
2005年 | 11591篇 |
2004年 | 10528篇 |
2003年 | 9369篇 |
2002年 | 9057篇 |
2001年 | 11031篇 |
2000年 | 8409篇 |
1999年 | 6417篇 |
1998年 | 4974篇 |
1997年 | 4947篇 |
1996年 | 4792篇 |
1995年 | 4380篇 |
1994年 | 4181篇 |
1993年 | 3921篇 |
1992年 | 4805篇 |
1991年 | 4699篇 |
1990年 | 4401篇 |
1989年 | 4400篇 |
1988年 | 4428篇 |
1987年 | 4387篇 |
1986年 | 4170篇 |
1985年 | 5710篇 |
1984年 | 5708篇 |
1983年 | 4527篇 |
1982年 | 4767篇 |
1981年 | 4727篇 |
1980年 | 4483篇 |
1979年 | 4732篇 |
1978年 | 4827篇 |
1977年 | 4883篇 |
1976年 | 4689篇 |
1975年 | 4412篇 |
1974年 | 4304篇 |
1973年 | 4317篇 |
1972年 | 2777篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
The formation of singularities in the three-dimensional Euler equation is investigated. This is done by restricting the number of Fourier modes to a set which allows only for local interactions in wave number space. Starting from an initial large-scale energy distribution, the energy rushes towards smaller scales, forming a universal front independent of initial conditions. The front results in a singularity of the vorticity in finite time, and has scaling form as function of the time difference from the singularity. Using a simplified model, we compute the values of the exponents and the shape of the front analytically. The results are in good agreement with numerical simulations. 相似文献
12.
C. Waldtmann H.-U. Everts B. Bernu C. Lhuillier P. Sindzingre P. Lecheminant L. Pierre 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):501-507
We study the exact low energy spectra of the spin 1/2 Heisenberg antiferromagnet on small samples of the kagomé lattice of up to N=36 sites. In agreement with the conclusions of previous authors, we find that these low energy spectra contradict the hypothesis
of Néel type long range order. Certainly, the ground state of this system is a spin liquid, but its properties are rather
unusual. The magnetic () excitations are separated from the ground state by a gap. However, this gap is filled with nonmagnetic () excitations. In the thermodynamic limit the spectrum of these nonmagnetic excitations will presumably develop into a gapless
continuum adjacent to the ground state. Surprisingly, the eigenstates of samples with an odd number of sites, i.e. samples with an unsaturated spin, exhibit symmetries which could support long range chiral order. We do not know if these
states will be true thermodynamic states or only metastable ones. In any case, the low energy properties of the spin 1/2 Heisenberg
antiferromagnet on the kagomé lattice clearly distinguish this system from either a short range RVB spin liquid or a standard chiral spin liquid. Presumably
they are facets of a generically new state of frustrated two-dimensional quantum antiferromagnets.
Received: 27 November 1997 / Accepted: 29 January 1998 相似文献
13.
E. Jackiewicz M. Lukasiak M. Kopcewicz K. Szpila N. Bakun-Czubarow 《Hyperfine Interactions》1992,70(1-4):993-996
Terrestrial basalt rocks considered to be a good analogues of the Martian regolith were studied by using the Mössbauer spectroscopy and X-ray diffraction. The weathering of basalts was followed by the changes of the Fe2+/Fe3+ ratio. The basalt rock undergoes alteration from primary mineral composition (olivine+pyroxene+plagioclase) through smectite to kaolinite clay with oxides and hydroxides with the increase of the Fe2+/Fe3+ ratio. 相似文献
14.
C. Fallnich B. Ruffing Th. Herrmann A. Nebel R. Beigang R. Wallenstein 《Applied physics. B, Lasers and optics》1995,60(5):427-436
We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency. 相似文献
15.
16.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields. 相似文献
17.
A. K. Lopatin 《Ukrainian Mathematical Journal》1997,49(1):51-74
We consider the method of normal forms, the Bogolyubov averaging method, and the method of asymptotic decomposition proposed by Yu. A. Mitropol’skii and the author of this paper. Under certain assumptions about group-theoretic properties of a system of zero approximation, the results obtained by the method of asymptotic decomposition coincide with the results obtained by the method of normal forms or the Bogolyubov averaging method. We develop a new algorithm of asymptotic decomposition by a part of the variables and its partial case — the algorithm of averaging on a compact Lie group. For the first time, it became possible to consider asymptotic expansions of solutions of differential equations on noncommutative compact groups. 相似文献
18.
19.
20.