全文获取类型
收费全文 | 635篇 |
免费 | 5篇 |
国内免费 | 13篇 |
专业分类
化学 | 218篇 |
晶体学 | 12篇 |
力学 | 24篇 |
数学 | 198篇 |
物理学 | 201篇 |
出版年
2021年 | 13篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 44篇 |
2012年 | 27篇 |
2011年 | 31篇 |
2010年 | 23篇 |
2009年 | 35篇 |
2008年 | 43篇 |
2007年 | 40篇 |
2006年 | 38篇 |
2005年 | 26篇 |
2004年 | 21篇 |
2003年 | 17篇 |
2002年 | 12篇 |
2001年 | 21篇 |
2000年 | 15篇 |
1999年 | 16篇 |
1998年 | 6篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 8篇 |
1948年 | 2篇 |
1932年 | 2篇 |
1930年 | 2篇 |
排序方式: 共有653条查询结果,搜索用时 15 毫秒
131.
A consistent quantum theory of self-action and cross-interaction of coherent light pulses in a cubically nonlinear medium is developed by using the momentum operator of the field, which takes into account the inertial nonlinearity. Specific features of generation of the quadrature-squeezed states of light pulses are considered. The spectrum of fluctuations of a quadrature below the shot-noise level is analyzed as a function of the relaxation time of nonlinearity and the magnitude of nonlinear phase additions, related to the self-action and cross-interaction. 相似文献
132.
In this paper, we find new refinements to the Massey inequality, which relates the Shannon and guessing entropies, introducing a new concept: the Massey gap. By shrinking the Massey gap, we improve all previous work without introducing any new parameters, providing closed-form strict refinements, as well as a numerical procedure improving them even further. 相似文献
133.
This paper in concerned with the linear theory of materials with memory that possess a double porosity structure. First, the formulation of the initial-boundary-value problem is presented. Then, a uniqueness result is established. The semigroup theory of linear operators is used to prove existence and continuous dependence of solutions. A minimum principle for the dynamical theory is also derived. 相似文献
134.
Attempts to construct structural models of glassy CdGeAs2 are described. Microcrystal models with normal and appropriately distorted crystallites gave poor fits with the experiment. Relaxed random network models, in which force constants and equilibrium distances and angles obtained by an energy relaxation of the crystal were used to minimize their free energy, provided excellent agreement with experiment if only even-numbered rings and, therefore, no wrong bonds were allowed to form. 相似文献
135.
Cezarina Morosanu Larisa Popescu Liviu Sacarescu Dana Ortansa Dorohoi Lacramioara Anca Oprica 《Molecular Crystals and Liquid Crystals》2020,698(1):38-45
AbstractThe biomedical applications of magnetic nanoparticles require the surface modification with organic, hydrophilic molecules, able to ensure the stability of the resulted colloidal suspensions. We present the quantum mechanical approach of two molecules developing stable interfaces with magnetic Co0.5Fe2.5O4 nanoparticles. Sodium oleate, and citric acid, ensuring steric and respectively electrostatic stabilization are comparatively analyzed. The roles of dipole moment and frontier orbitals energies were emphasized to better understanding of some interface phenomena for the optimization of magnetic nanoparticle suspension preparation. Further, practical yielding of colloidal Co0.5Fe2.5O4 nanoparticles by coating with sodium oleate and respectively with citric acid is discussed. 相似文献
136.
V.A. Popescu 《Optics Communications》2005,250(4-6):274-279
The finite element and variational methods are used to determine the propagation constants in a titanium indiffused lithium niobate waveguide with the reconstructed refractive index profile (in depth) from the near field measurements. A subsequent second diffusion of magnesium affects the shape of the calculated electric field and we have defined an effective depth of the profile. 相似文献
137.
The goal of this paper is to study the anatomy of the shape Hessian for some classes of smooth shape functionals. A structure theorem gives a decomposition of the shape Hessian in three additive bilinear forms acting on the two fields: the first one acting on the normal components at the boundary, the second one being symmetrical and the third one involving a half of the Lie bracket of the pair of fields at which the shape Hessian is computed. Applications to the commutation of the mixed derivatives and the symmetry of the linear operator which appears in the structure theorem are given. 相似文献
138.
Summary LetA→A′ be a regular morphism between two noetherian rings. Then for everyA-algebra of finite typeB, everyA-morphism fromB toA′ can be factorised through aB-algebra of finite typeB′ which is standard (smooth) overA and which is ?as smooth as possible? overB (i.e. except above the singular locus ofB overA). This result is a positive answer to one conjecture due to M. Artin.
Riassunto SiaA→A′ un omomorfismo regolare di anelli noetheriani. Si dimostra che per ogniA-algebraB di tipo finito, ogniA-omomorfismoB→A′ si può fattorizzare mediante unaB-algebraB′ di tipo finito che è liscia suA ed è ?la più liscia posibile? suB (più precisamente liscia suB meno il luogo singolare diB suA). Questo risultato è una risposta affermativa a una congettura di M. Artin.相似文献
139.
A. Korichi N. Perrin C. Bourgeois D. Hojman D. G. Popescu H. Sergolle F. Hannachi M. G. Porquet 《Zeitschrift für Physik A Hadrons and Nuclei》1992,343(1):15-19
The population of the oblate and the prolate structures in187Au has been studied using the “Château de Cristal” set-up through the172Yb(19F, 4n) reaction at 90, 95 and 100 MeV beam energy. γ — γ, γ-Fold and γ -Sum energy coincidence measurements were performed, γ-ray intensity measurements showed that as the beam energy increases the prolate system is less populated than the oblate one. Fold and Sum-energy associated with oblate and prolate structures showed a different behaviour with increasing beam energy. Two mechanisms are suggested to explain these results. 相似文献
140.
I. Puica V. Popescu P. Mazzetti A. Stepanescu Gh. Ciobanu 《Physica C: Superconductivity and its Applications》1997,290(3-4):303-310
The 1/f voltage noise in bulk polycrystalline high-temperature superconductors (HTSC) under bias current and magnetic field has its origin in the noise current-dependence of the grain boundary junctions (GBJs), due in turn to the correlated effects of junction critical current and normal resistance fluctuations. The analogy between the results obtained by varying the bias current through the specimen and those performed with temperature as variable is evidenced. The noise maxima obtained in both sets of measurements turn out to be caused by the junction critical current fluctuations, which dominate when the currents flowing through the GBJs are close to the Josephson critical current. The anti-phase correlation between the normal resistance and the critical current fluctuations is responsible for the monotonical decrease of the noise at constant bias current, with the temperature exceeding the value corresponding to the noise maximum. In contrast, varying the bias current at fixed temperature, the voltage noise exhibits a local minimum followed by an increasing tendency after passing through the maximum. 相似文献