全文获取类型
收费全文 | 2344篇 |
免费 | 266篇 |
国内免费 | 261篇 |
专业分类
化学 | 117篇 |
晶体学 | 3篇 |
力学 | 183篇 |
综合类 | 67篇 |
数学 | 1719篇 |
物理学 | 782篇 |
出版年
2024年 | 4篇 |
2023年 | 36篇 |
2022年 | 21篇 |
2021年 | 53篇 |
2020年 | 77篇 |
2019年 | 58篇 |
2018年 | 49篇 |
2017年 | 52篇 |
2016年 | 70篇 |
2015年 | 63篇 |
2014年 | 129篇 |
2013年 | 157篇 |
2012年 | 85篇 |
2011年 | 88篇 |
2010年 | 124篇 |
2009年 | 130篇 |
2008年 | 164篇 |
2007年 | 193篇 |
2006年 | 144篇 |
2005年 | 131篇 |
2004年 | 138篇 |
2003年 | 132篇 |
2002年 | 134篇 |
2001年 | 89篇 |
2000年 | 87篇 |
1999年 | 93篇 |
1998年 | 72篇 |
1997年 | 73篇 |
1996年 | 49篇 |
1995年 | 33篇 |
1994年 | 35篇 |
1993年 | 19篇 |
1992年 | 12篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2871条查询结果,搜索用时 31 毫秒
141.
Shiffman proved his famous first theorem, that if A R3 is a compact minimal annulus bounded by two convex Jordan curves in parallel (say horizontal) planes, then A is foliated by strictly convex horizontal Jordan curves. In this article we use Perron's method to construct minimal annuli which have a planar end and are bounded by two convex Jordan curves in horizontal planes, but the horizontal level sets of the surfaces are not all convex Jordan curves or straight lines. These surfaces show that unlike his second and third theorems, Shiffman's first theorem is not generalizable without further qualification. 相似文献
142.
FANG FUQUAN 《数学年刊B辑(英文版)》2000,(4)
1. IntroductionBy [111, a hypersurface in a symmetric space is called equifocal if every normal geodesicperpendiculajr to it is closed of constant length, say l, and contains Zg focal points for somepositive integer g. This is a natural generalization of isoparametric hypersurfaces in sphereswhere the illteger g is the number of distinct principal curvatures. In this note we considerequifocal hypersurfaces in simply connected rank one symmetric spaces, i.e. the complexprojective space CP", th… 相似文献
143.
Large volume growth and finite topological type 总被引:5,自引:0,他引:5
D. Ordway B. Stephens D. G. Yang 《Proceedings of the American Mathematical Society》2000,128(4):1191-1196
It is shown in this paper that a complete noncompact -dimensional Riemannian manifold with nonnegative Ricci curvature, sectional curvature bounded from below, and large volume growth is of finite topological type provided that the volume growth rate of the complement of the cone of rays from a fixed base point is less than .
144.
Matthieu Fradelizi 《Proceedings of the American Mathematical Society》2000,128(9):2735-2744
We define the sectional bodies associated to a convex body in and two related measures of symmetry. These definitions extend those of Grünbaum (1963). As Grünbaum conjectured, we prove that the simplices are the most dissymmetrical convex bodies with respect to these measures. In the case when the convex body has a sufficiently smooth boundary, we investigate some limit behaviours of the volume of the sectional bodies.
145.
近年国外出现一种直接检测弯曲的低成本光纤曲率传感器,采用弯曲增敏技术提高光纤对弯曲的灵敏度。这种传感器的线性范围宽,能区分正向弯曲和负向弯曲,在测量较大弯曲变形的场合更具优势;并且适合埋入结构内部检测,通过转换还可测量轴向应变。然而其传感机理方面的研究仍处于探索阶段。通过分析光辐射度余弦定律理论、回音壁光线理论、沟槽角度理论等国内外对该传感器机理的研究成果,并基于平面波导的光散射损耗理论,提出了光纤曲率传感器的机理。指出弯曲引起光纤敏感区表面散射损耗的改变是导致光传输损耗改变的原因;推导出损耗与光纤弯曲半径、表面特性、光纤结构参量关系的数学模型,并通过实验验证了模型的有效性。 相似文献
146.
Nils M. Bezares-Roder Hemwati Nandan Heinz Dehnen 《International Journal of Theoretical Physics》2007,46(10):2429-2436
The exact static and spherically symmetric solutions of the vacuum field equations for a Higgs Scalar-Tensor theory (HSTT)
are derived in Schwarzschild coordinates. It is shown that in general there exists no Schwarzschild horizon and that the fields
are only singular (as naked singularity) at the center (i.e. for the case of a point-particle). However, the Schwarzschild
solution as in usual general relativity (GR) is obtained for the vanishing limit of Higgs field excitations. 相似文献
147.
Optical model, scalar or vectorial one, describing behaviour of an optical field within a diode-laser cavity, is one of the
most important parts of modelling of a diode-laser operation. As compared to more accurate vectorial optical approaches, scalar
ones are known to be less exact but simultaneously they need much less computation time. Besides, they have been sometimes
found to be surprisingly exact even beyond their confirmed range of validity. Therefore, in this paper, real validity limits
of their application have been determined by comparing their simplified results with more exact results obtained with the
aid of vectorial models. The analysis comprises a comparison of an application of the most popular scalar approach to optical
properties of diode lasers, i.e., the effective index method, and the vectorial method of lines for the standard 1.3-μm GaAs-based
stripe-geometry diode laser. The scalar model has been found to be quite exact in the case of a determination of the effective
refractive index, i.e., the wavelength of emitted radiation, whereas its exactness in the lasing threshold analysis is much
worse, especially in the case of higher-order modes. Our analysis is concluded with a determination of the regions where both
models give satisfactorily close results. 相似文献
148.
We present a systematic way to compute the scaling exponents of the structure functions of the Kraichnan model of turbulent
advection in a series of powers of ξ, adimensional coupling constant measuring the degree of roughness of the advecting velocity
field. We also investigate the relation between standard and renormalization group improved perturbation theory. The aim is
to shed light on the relation between renormalization group methods and the statistical conservation laws of the Kraichnan
model, also known as zero modes. 相似文献
149.
We investigated the propagation and transformation of laser beams and the formation of caustics in particular directions,
including optical axes of crystals. We found a direct connection between the particular directions and the curvature of wave
surfaces that is determined by the symmetry and optical properties of the crystals. We demonstrated that caustics in particular
directions are characterized by a degree of the curvature degeneracy and are described by particular solutions of the corresponding
nonlinear equations.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 491–498, July–August, 2007. 相似文献
150.
Following recent fit of supernovae data to Brans‐Dicke theory which favours the model with o = ‐ 3/2 [1] we discuss the status of this special case of Brans‐Dicke cosmology in both isotropic and anisotropic framework. It emerges that the limit o = ‐3/2 is consistent only with the vacuum field equations and it makes such a Brans‐Dicke theory conformally invariant. Then it is an example of the conformal relativity theory which allows the invariance with respect to conformal transformations of the metric. Besides, Brans‐Dicke theory with o = ‐3/2 gives a border between a standard scalar field model and a ghost/phantom model. In this paper we show that in o = ‐3/2 Brans‐Dicke theory, i.e., in the conformal relativity there are no isotropic Friedmann solutions of non‐zero spatial curvature except for k=‐1 case. Further we show that this k=‐1 case, after the conformal transformation into the Einstein frame, is just the Milne universe and, as such, it is equivalent to Minkowski spacetime. It generally means that only flat models are fully consistent with the field equations. On the other hand, it is shown explicitly that the anisotropic non‐zero spatial curvature models of Kantowski‐Sachs type are admissible in o = ‐3/2 Brans‐Dicke theory. It then seems that an additional scale factor which appears in anisotropic models gives an extra deegre of freedom and makes it less restrictive than in an isotropic Friedmann case. 相似文献