全文获取类型
收费全文 | 1275篇 |
免费 | 84篇 |
国内免费 | 196篇 |
专业分类
化学 | 392篇 |
晶体学 | 3篇 |
力学 | 295篇 |
综合类 | 14篇 |
数学 | 540篇 |
物理学 | 311篇 |
出版年
2024年 | 5篇 |
2023年 | 24篇 |
2022年 | 47篇 |
2021年 | 57篇 |
2020年 | 44篇 |
2019年 | 37篇 |
2018年 | 35篇 |
2017年 | 33篇 |
2016年 | 38篇 |
2015年 | 30篇 |
2014年 | 58篇 |
2013年 | 93篇 |
2012年 | 31篇 |
2011年 | 60篇 |
2010年 | 49篇 |
2009年 | 63篇 |
2008年 | 77篇 |
2007年 | 71篇 |
2006年 | 75篇 |
2005年 | 63篇 |
2004年 | 70篇 |
2003年 | 75篇 |
2002年 | 64篇 |
2001年 | 45篇 |
2000年 | 57篇 |
1999年 | 41篇 |
1998年 | 40篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 15篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1555条查询结果,搜索用时 15 毫秒
31.
Manfred Einsiedler Douglas Lind 《Transactions of the American Mathematical Society》2004,356(5):1799-1831
We investigate algebraic -actions of entropy rank one, namely those for which each element has finite entropy. Such actions can be completely described in terms of diagonal actions on products of local fields using standard adelic machinery. This leads to numerous alternative characterizations of entropy rank one, both geometric and algebraic. We then compute the measure entropy of a class of skew products, where the fiber maps are elements from an algebraic -action of entropy rank one. This leads, via the relative variational principle, to a formula for the topological entropy of continuous skew products as the maximum of a finite number of topological pressures. We use this to settle a conjecture concerning the relational entropy of commuting toral automorphisms.
32.
针对柱状装药的周向预制破片战斗部,结合无量纲分析方法和爆炸驱动理论,确定了影响破片和冲击波相遇位置的关键参数,给出了由缩比战斗部推广预测原型战斗部爆炸产生的破片冲击波作用时序的方法。采用ANSYS/LS-DYNA有限元软件进行数值模拟,对比验证了理论分析和数值试验结果,分析了战斗部缩比比例对冲击波和破片作用时序的影响。结果表明:缩比模型与原型战斗部爆炸产生的破片和冲击波的相遇位置之比和相遇时间之比主要取决于两模型的质量比,在不考虑破片速度衰减时,两模型中载荷相遇位置之比和相遇时间之比等于其质量比的0.33次方。受破片速度衰减影响,该方法仅适用于质量缩比不小于0.2的模型。 相似文献
33.
《Journal of Pure and Applied Algebra》2022,226(12):107134
The notion of a group action can be extended to the case of gyrogroups. In this article, we examine a digraph and graph associated with a gyrogroup action on a finite nonempty set, called a Schreier digraph and graph. We show that algebraic properties of gyrogroups and gyrogroup actions such as being gyrocommutative, being transitive, and being fixed-point-free are reflected in their Schreier digraphs and graphs. We also prove graph-theoretic versions of the three fundamental theorems involving actions: the Cauchy–Frobenius lemma (also known as the Burnside lemma), the orbit-stabilizer theorem, and the orbit decomposition theorem. Finally, we make a connection between gyrogroup actions and actions of symmetric groups by evaluation via Schreier digraphs and graphs. 相似文献
34.
N. Pongali Sathya Prabu 《Phase Transitions》2013,86(7):592-607
In this study, complexes belonging to supramolecular hydrogen-bonded liquid crystal homologous series are synthesized and characterized. Hydrogen bond is formed between p-n-alkyloxy benzoic acids (nBAO, where n?=?5–11) and chlorobenzoic acid (ClBAO), respectively. The isolated homologues are characterized by various techniques such as polarizing optical microscopic (POM) studies, differential scanning calorimetry (DSC), and Fourier transform–infrared spectroscopy. Based on the POM and DSC studies, the phase diagram has been constructed and discussed. A new smectic ordering, labeled as smectic R, has been characterized, which exhibits a ribbon-like texture. This phase is observed in the complexes pertaining to the higher homologous series. Tilt angle in this phase has been experimentally deduced and the results are fitted to the power law which concurs with the mean-field theory predicted value. Optical shuttering action in the homologue has been detected in the nematic phase and the results are also discussed. 相似文献
35.
Martin Lorenz 《Algebras and Representation Theory》2001,4(3):293-304
Let G be a finite group acting by automorphism on a lattice A, and hence on the group algebra S=k[A]. The algebra of G-invariants in S is called an algebra of multiplicative invariants. We present an explicit version of a result of Farkas stating that multiplicative invariants of finite reflection groups are semigroup algebras. 相似文献
36.
This is a survey of some recent results on spherical tropical geometry. 相似文献
37.
Xin ZHANG 《Frontiers of Mathematics in China》2018,13(5):1189-1214
We introduce two Hopf algebroids associated to a proper and holomorphic Lie group action on a complex manifold. We prove that the cyclic cohomology of each Hopf algebroid is equal to the Dolbeault cohomology of invariant differential forms. When the action is cocompact, we develop a generalized complex Hodge theory for the Dolbeault cohomology of invariant differential forms. We prove that every cyclic cohomology class of these two Hopf algebroids can be represented by a generalized harmonic form. This implies that the space of cyclic cohomology of each Hopf algebroid is finite dimensional. As an application of the techniques developed in this paper, we generalize the Serre duality and prove a Kodaira type vanishing theorem. 相似文献
38.
Balasubramanian Sury 《Rendiconti del Circolo Matematico di Palermo》2009,58(1):99-108
We apply group actions to some natural situations like the natural ‘linear’ action of GL
r
(Z
n
) and some of its subgroups to derive number-theoretic identities like
.
相似文献
39.
An analysis of seismic attenuation in random porous media 总被引:1,自引:0,他引:1
LIU Jiong BA Jing MA JianWei & YANG HuiZhu Institute of Seismic Exploration School of Aerospace Tsinghua University Beijing China Research Institute of Petroleum Exploration & Development PetroChina Beijing 《中国科学:物理学 力学 天文学(英文版)》2010,(4)
The attenuation of seismic wave in rocks has been one of the interesting research topics, but till now no poroelasticity models can thoroughly explain the strong attenuation of wave in rocks. In this paper, a random porous medium model is designed to study the law of wave propagation in complex rocks based on the theory of Biot poroelasticity and the general theory of stochastic process. This model sets the density of grain, porosity, permeability and modulus of frame as random parameters in space, and only one fluid infiltrates in rocks for the sake of better simulation effect in line with real rocks in earth strata. Numerical simulations are implemented. Two different inverse quality factors of fast P-wave are obtained by different methods to assess attenuation through records of virtual detectors in wave field (One is amplitude decay method in time domain and the other is spectral ratio method in frequency domain). Comparing the attenuation results of random porous medium with those of homogeneous porous medium, we conclude that the attenuation of seismic wave of homogeneous porous medium is far weaker than that of random porous medium. In random porous media, the higher heterogeneous level is, the stronger the attenuation becomes, and when heterogeneity σ = 0.15 in simulation, the attenuation result is consistent with that by actual observation. Since the central frequency (50 Hz) of source in numerical simulation is in earthquake band, the numerical results prove that heterogeneous porous structure is one of the important factors causing strong attenuation in real stratum at intermediate and low frequency. 相似文献
40.
The purpose of this article is to characterize symplectic and Hamiltonian circle actions on symplectic manifolds in terms of symplectic embeddings of Riemann surfaces.More precisely, it is shown that(1) if(M, ω) admits a Hamiltonian S~1-action, then there exists a two-sphere S in M with positive symplectic area satisfying c1(M, ω), [S] 0,and(2) if the action is non-Hamiltonian, then there exists an S~1-invariant symplectic2-torus T in(M, ω) such that c1(M, ω), [T] = 0. As applications, the authors give a very simple proof of the following well-known theorem which was proved by Atiyah-Bott,Lupton-Oprea, and Ono: Suppose that(M, ω) is a smooth closed symplectic manifold satisfying c1(M, ω) = λ· [ω] for some λ∈ R and G is a compact connected Lie group acting effectively on M preserving ω. Then(1) if λ 0, then G must be trivial,(2) if λ = 0, then the G-action is non-Hamiltonian, and(3) if λ 0, then the G-action is Hamiltonian. 相似文献