全文获取类型
收费全文 | 2291篇 |
免费 | 108篇 |
国内免费 | 13篇 |
专业分类
化学 | 1649篇 |
晶体学 | 21篇 |
力学 | 69篇 |
数学 | 323篇 |
物理学 | 350篇 |
出版年
2024年 | 6篇 |
2023年 | 17篇 |
2022年 | 39篇 |
2021年 | 41篇 |
2020年 | 34篇 |
2019年 | 46篇 |
2018年 | 32篇 |
2017年 | 43篇 |
2016年 | 92篇 |
2015年 | 57篇 |
2014年 | 113篇 |
2013年 | 137篇 |
2012年 | 177篇 |
2011年 | 195篇 |
2010年 | 115篇 |
2009年 | 115篇 |
2008年 | 161篇 |
2007年 | 143篇 |
2006年 | 138篇 |
2005年 | 121篇 |
2004年 | 119篇 |
2003年 | 89篇 |
2002年 | 75篇 |
2001年 | 40篇 |
2000年 | 35篇 |
1999年 | 25篇 |
1998年 | 23篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 13篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 17篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1971年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有2412条查询结果,搜索用时 0 毫秒
31.
Sebastiaan van Dijken Xavier Fain Steven M. Watts Kentaro Nakajima J. M. D. Coey 《Journal of magnetism and magnetic materials》2004,280(2-3):322-326
A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe3O4 electrodes is presented. Fe3O4/Au/Fe3O4 spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe3O4 layers. By contrast, a negative GMR effect is measured on Fe3O4/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe3O4/Au interface or an induced spin scattering asymmetry in the Au interfacial layers. 相似文献
32.
It is known that under resonance conditions, a group of strongly interacting bosonic atoms, trapped in a double-well potential, mimics a single particle, performing Rabi oscillations between the wells. By implication, all atoms need to tunnel at roughly the same time, even though the Bose–Hubbard Hamiltonian accounts only for one-atom-at-a-time transfers. The mechanism of this collective behavior is analyzed, the Rabi frequencies in the process are evaluated, and the limitation of this simple picture is discussed. In particular, it is shown that the small rapid oscillations superimposed on the slow Rabi cycle result from splitting the transferred cluster at the sudden onset of tunnelling, and disappear if tunnelling is turned on gradually. 相似文献
33.
Xavier Buff Arnaud Ché ritat 《Proceedings of the American Mathematical Society》2007,135(4):1073-1080
In the family of quadratic polynomials with an irrationally indifferent fixed point, we show the existence of Siegel disks with a fine control on the degree of regularity of the linearizing map on their boundary. A general theorem is stated and proved. As a particular case, we show that in the quadratic family, there are Siegel disks whose boundaries are but not Jordan curves.
34.
S. A. Leonel A. C. R. Mendes W. Oliveira G. L. Silva L. M. V. Xavier 《Brazilian Journal of Physics》2014,44(1):108-118
We discuss the two-dimensional isotropic antiferromagnet in the framework of gauge invariance. Gauge invariance is one of the most subtle useful concepts in theoretical physics, since it allows one to describe the time evolution of complex physical system in arbitrary sequences of reference frames. All theories of the fundamental interactions rely on gauge invariance. In Dirac’s approach, the two-dimensional isotropic antiferromagnet is subject to second-class constraints, which are independent of the Hamiltonian symmetries and can be used to eliminate certain canonical variables from the theory. We have used the symplectic embedding formalism developed by a few of us to make the system under study gauge invariant. After carrying out the embedding and Dirac analysis, we systematically show how second-class constraints can generate hidden symmetries. We obtain the invariant second-order Lagrangian and the gauge-invariant model Hamiltonian. Finally, for a particular choice of factor ordering, we derive the functional Schröodinger equations for the original Hamiltonian and for the first-class Hamiltonian and show them to be identical, which justifies our choice of factor ordering. 相似文献
35.
Double-quantum filtered MAS NMR spectra of an isolated homonuclear spin-1/2 pair are considered, at and away from rotational resonance conditions. The pulse sequence used is the solid-state NMR equivalent of double-quantum filtered COSY, known from solution-state NMR. The 119Sn spin pair in [(chex3Sn)2S] is characterized by a difference in isotropic chemical shielding smaller than the two chemical shielding anisotropies and by direct dipolar and isotropic J-coupling constants of similar magnitudes. At rotational resonance, one-dimensional double-quantum filtered 119Sn lineshapes yield the relative orientation of the two 119Sn chemical shielding tensors. Good double-quantum filtration efficiencies are found at and away from rotational resonance conditions, despite the presence of large chemical shielding anisotropies. Numerical simulations illustrate the interplay of the direct dipolar and J-coupling pathways and identify the latter as the main pathway even at rotational resonance conditions. 相似文献
36.
F. Strieder L. Gialanella U. Greife C. Rolfs S. Schmidt W. H. Schulte H. P. Trautvetter D. Zahnow F. Terrasi L. Campajola A. D’Onofrio V. Roca M. Romano M. Romoli 《Zeitschrift für Physik A Hadrons and Nuclei》1996,355(1):209-218
The absolute cross sectionσ of thed(7Li,p)8Li reaction near theE cm=0.61 MeV resonance has been measured using a7Li ion beam and a windowless gas target system filled with D2 gas. The proton yield of the reaction and theβ-delayedα-activity of the residual nuclides8Li were observed both concurrently with the elastic scattering yield, relatingσ to the Rutherford scattering cross sectionσ R. The resulting values,σ (fromp)=143.6±8.9 mb andσ (from8Li)=151±20 mb, lead to a weighted mean value ofσ=153±6 mb (x 2=2.26) including all available values andσ=146±5 mb (x 2=0.05) removing some values from the data set. The consequences for the expected flux of high-energy solar neutrinos are discussed. 相似文献
37.
We consider the standard random geometric graph process in which n vertices are placed at random on the unit square and edges are sequentially added in increasing order of edge‐length. For fixed k?1, weprove that the first edge in the process that creates a k‐connected graph coincides a.a.s. with the first edge that causes the graph to contain k/2 pairwise edge‐disjoint Hamilton cycles (for even k), or (k?1)/2 Hamilton cycles plus one perfect matching, all of them pairwise edge‐disjoint (for odd k). This proves and extends a conjecture of Krivelevich and M ler. In the special case when k = 2, our result says that the first edge that makes the random geometric graph Hamiltonian is a.a.s. exactly the same one that gives 2‐connectivity, which answers a question of Penrose. (This result appeared in three independent preprints, one of which was a precursor to this article.) We prove our results with lengths measured using the ?p norm for any p>1, and we also extend our result to higher dimensions. © 2011 Wiley Periodicals, Inc. J Graph Theory 68:299‐322, 2011 相似文献
38.
Xavier Guyon 《Probability Theory and Related Fields》1987,75(2):179-193
Summary Let
be a stationary Gaussian random field, with covariance R. For d=1 and d=2, families of variations are described. The convergence in mean square of these variations and a subsequent identification of a model for X are studied. Under suitable glocal conditions for R, the behaviour of these variations depends on the local behaviour of R near the origin. The differences between the case d=1 and d=2 are particularly emphasised: for d=1, there exists only one variation; for d=2, several families of variations are available which provided a useful tool for identifying different models: for example, Orstein-Uhlenbeck processes can be identified in mean square on
, but not on
.
Variations de champs gaussiens stationnaires: application a l'identification相似文献
39.
Maxime Noël Sergey Ananev Mattias Mases Xavier Devaux Juhan Lee Ivan Evdokimov Manuel Dossot Edward McRae Alexander V. Soldatov 《固体物理学:研究快报》2014,8(11):935-938
We report on a first study of single walled carbon nanotubes (SWCNTs) after application of dynamic (shock) compression. The experiments were conducted at 19 GPa and 36 GPa in a recovery assembly. For comparison, an experiment at a static pressure of 36 GPa was performed on the material from the same batch in a diamond anvil cell (DAC). After the high pressure treatment the samples were characterized by Raman spectroscopy and transmission electron microscopy (TEM). After exposure to 19 GPa of shock compression the CNT material exhibited substantial structural damage such as CNT wall disruption, opening of the tube along its axis (“unzipping”) and tube shortening (“cutting”). Dynamic compression to 36 GPa resulted in essentially complete CNT destruction whereas at least a fraction of the nanotubes was recovered after 36 GPa of static compression though severely damaged. The results of these shock wave experiments underline the prospect of using SWCNTs as reinforcing units in material WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
40.