全文获取类型
收费全文 | 21527篇 |
免费 | 546篇 |
国内免费 | 491篇 |
专业分类
化学 | 4263篇 |
晶体学 | 939篇 |
力学 | 704篇 |
综合类 | 51篇 |
数学 | 12440篇 |
物理学 | 4167篇 |
出版年
2023年 | 63篇 |
2022年 | 108篇 |
2021年 | 168篇 |
2020年 | 176篇 |
2019年 | 440篇 |
2018年 | 455篇 |
2017年 | 314篇 |
2016年 | 381篇 |
2015年 | 383篇 |
2014年 | 660篇 |
2013年 | 1447篇 |
2012年 | 555篇 |
2011年 | 1630篇 |
2010年 | 1445篇 |
2009年 | 1378篇 |
2008年 | 1484篇 |
2007年 | 1428篇 |
2006年 | 1131篇 |
2005年 | 1002篇 |
2004年 | 901篇 |
2003年 | 701篇 |
2002年 | 724篇 |
2001年 | 439篇 |
2000年 | 421篇 |
1999年 | 397篇 |
1998年 | 407篇 |
1997年 | 309篇 |
1996年 | 343篇 |
1995年 | 345篇 |
1994年 | 321篇 |
1993年 | 251篇 |
1992年 | 250篇 |
1991年 | 174篇 |
1990年 | 185篇 |
1989年 | 176篇 |
1988年 | 109篇 |
1987年 | 125篇 |
1986年 | 95篇 |
1985年 | 167篇 |
1984年 | 122篇 |
1983年 | 70篇 |
1982年 | 94篇 |
1981年 | 135篇 |
1980年 | 122篇 |
1979年 | 67篇 |
1978年 | 117篇 |
1977年 | 100篇 |
1976年 | 97篇 |
1975年 | 48篇 |
1974年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
We synthesized a new intercalation compound, 1,5-diaminonaphathalene(DAN)-saponite where intercalated DAN molecules were shown to have a formal charge of +0.67 The measurement of optical diffuse reflectance spectra revealed the formation of electronic bands with a gap of ca. 1 eV suggesting semiconducting behaviour of this system. From ESR measurements, the radical formation in DAN-saponite was confirmed and the spin concentration was determined to be 1 spin per 200 and 300 DAN-molecules at 290 and 7.9 K, respectively. This temperature dependence of the spin density also implies the semiconductive nature of DAN-saponite. 相似文献
132.
Ewa Stró?yna 《Journal of Differential Equations》2003,193(1):239-259
We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence. 相似文献
133.
Yong-Gao Chen 《Journal of Number Theory》2003,98(2):310-319
In this paper we prove that if (r,12)?3, then the set of positive odd integers k such that kr−2n has at least two distinct prime factors for all positive integers n contains an infinite arithmetic progression. The same result corresponding to kr2n+1 is also true. 相似文献
134.
We studied the low speed fracture regime (10−4-10−9 m s−1) in different glassy materials (soda-lime glass, glass ceramics) with variable but controlled length scale of heterogeneity. The chosen mechanical system enabled us to work in pure mode I (tensile) and at a fixed load on double cleavage drilled compression specimen. The internal residual stresses of studied samples were carefully relaxed by appropriate thermal treatment. By means of optical and atomic force microscopy techniques fracture surfaces have been examined. We have shown for the first time that the crack front line underwent an out-of-plane oscillating behavior as a result of a reproducible sequence of instabilities. The wavelength of such a phenomenon is in the micrometer range and its amplitude in the nanometer range. These features were observed for different glassy materials providing that a typical length scale characterizing internal heterogeneities was lower than a threshold limit estimated to few nanometers. This effect is the first clear experimental evidence of crack path instabilities in the low speed regime in a uniaxial loading experiment. This phenomenon has been interpreted by referring to the stability criterion for a straight crack propagation as presented by Adda-Bedia et al. [Phys. Rev. Lett. 76 (1996) 1497]. 相似文献
135.
We study a generalized Crank–Nicolson scheme for the time discretization of a fractional wave equation, in combination with
a space discretization by linear finite elements. The scheme uses a non-uniform grid in time to compensate for the singular
behaviour of the exact solution at t = 0. With appropriate assumptions on the data and assuming that the spatial domain is convex or smooth, we show that the
error is of order k
2 + h
2, where k and h are the parameters for the time and space meshes, respectively. 相似文献
136.
We deal with the q-numerical radius of weighted unilateral and bilateral shift operators. In particular, the q-numerical radius of weighted shift operators with periodic weights is discussed and computed. 相似文献
137.
Gunhild U. von Oertzen 《Journal of Physics and Chemistry of Solids》2007,68(3):324-330
Ab initio density functional calculations (plane wave GGA, CASTEP) were performed to determine the effect of O deficiency on the electronic structure of rutile, TiO2. O deficiency was introduced through either the removal of O or the insertion of interstitial Ti atoms. At physically realistic concentrations of O vacancies in the rutile lattice (i.e. 25% and less) O deficiency results in the population of the bottom of the conduction band, the location of the Ti 3d orbitals in the pure structure, increasingly with increasing vacancy concentration. We propose that this could be confused with the formation and population of gap states especially where O vacancies occur in isolated positions in the lattice. In contrast, Ti interstitials introduce a defect state into the energy gap, without an overall reduction in the size of the energy gap. O vacancies result in a spin polarized solution, whereas Ti interstitials do not. 相似文献
138.
In this paper, by using fixed point theorems in cones, we study the existence of at least one, two and three positive solutions of a nonlinear second-order three-point boundary value problem for dynamic equations on time scales. As an application, we also give some examples to demonstrate our results. 相似文献
139.
The steady-state two-phase flow non-linear equation is considered in the case when one of phases has low effective permeability in some periodic set, while on the complementary set it is high; the second phase has no contrast of permeabilities in different zones. A homogenization procedure gives the homogenized model with macroscopic effective permeability of the second phase depending on the gradient and on the second order derivatives of the macroscopic pressure of the first phase. This effect cannot be obtained by classical (one small parameter) homogenization. To cite this article: G.P. Panasenko, G. Virnovsky, C. R. Mecanique 331 (2003). 相似文献
140.
For a conformal manifold we introduce the notion of an ambient connection, an affine connection on an ambient manifold of
the conformal manifold, possibly with torsion, and with conditions relating it to the conformal structure. The purpose of
this construction is to realise the normal conformal Tractor holonomy as affine holonomy of such a connection. We give an
example of an ambient connection for which this is the case, and which is torsion free if we start the construction with a
C-space, and in addition Ricci-flat if we start with an Einstein manifold. Thus, for a C-space this example leads to an ambient metric in the weaker sense of Čap and Gover, and for an Einstein space to a Ricci-flat
ambient metric in the sense of Fefferman and Graham.
Current address for first author: Erwin Schr?dinger International Institute for Mathematical Physics (ESI), Boltzmanngasse
9, 1090 Vienna, Austria
Current address for second author: Department of Mathematics, University of Hamburg, Bundesstra?e 55, 20146 Hamburg, Germany 相似文献