全文获取类型
收费全文 | 25451篇 |
免费 | 2195篇 |
国内免费 | 1741篇 |
专业分类
化学 | 11285篇 |
晶体学 | 252篇 |
力学 | 2065篇 |
综合类 | 285篇 |
数学 | 4127篇 |
物理学 | 11373篇 |
出版年
2023年 | 215篇 |
2022年 | 358篇 |
2021年 | 561篇 |
2020年 | 588篇 |
2019年 | 572篇 |
2018年 | 571篇 |
2017年 | 625篇 |
2016年 | 797篇 |
2015年 | 697篇 |
2014年 | 1015篇 |
2013年 | 1654篇 |
2012年 | 1611篇 |
2011年 | 1656篇 |
2010年 | 1316篇 |
2009年 | 1727篇 |
2008年 | 1584篇 |
2007年 | 1676篇 |
2006年 | 1367篇 |
2005年 | 1044篇 |
2004年 | 954篇 |
2003年 | 919篇 |
2002年 | 927篇 |
2001年 | 718篇 |
2000年 | 720篇 |
1999年 | 648篇 |
1998年 | 579篇 |
1997年 | 389篇 |
1996年 | 294篇 |
1995年 | 293篇 |
1994年 | 258篇 |
1993年 | 262篇 |
1992年 | 330篇 |
1991年 | 208篇 |
1990年 | 173篇 |
1989年 | 143篇 |
1988年 | 153篇 |
1987年 | 132篇 |
1986年 | 108篇 |
1985年 | 95篇 |
1984年 | 98篇 |
1983年 | 60篇 |
1982年 | 113篇 |
1981年 | 184篇 |
1980年 | 192篇 |
1979年 | 197篇 |
1978年 | 168篇 |
1977年 | 104篇 |
1976年 | 113篇 |
1973年 | 84篇 |
1972年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 355 毫秒
71.
A carousel is a dynamical system that describes the movement of an equilateral linkage in which the midpoint of each rod travels parallel to it. They are closely related to the floating body problem. We prove, using the work of Auerbach, that any figure that floats in equilibrium in every position is drawn by a carousel. Of special interest are such figures with rational perimetral density of the floating chords, which are then drawn by carousels. In particular, we prove that for some perimetral densities the only such figure is the circle, as the problem suggests. 相似文献
72.
M. A. Efendiev J. Fuhrmann S. V. Zelik 《Mathematical Methods in the Applied Sciences》2004,27(8):907-930
For the Boussinesq approximation of the equations of coupled heat and fluid flow in a porous medium we show that the corresponding system of partial differential equations possesses a global attractor. We give lower and upper bounds of the Hausdorff dimension of the attractor depending on a physical parameter of the system, namely the Rayleigh number of the flow. Numerical experiments confirm the theoretical findings and raise new questions on the structure of the solutions of the system. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
73.
Toshihiro Kobayashi 《Mathematical Methods in the Applied Sciences》2004,27(18):2171-2184
In this paper low‐gain adaptive stabilization of undamped semilinear second‐order hyperbolic systems is considered in the case where the input and output operators are collocated. The linearized systems have an infinite number of poles and zeros on the imaginary axis. The adaptive stabilizer is constructed by a low‐gain adaptive velocity feedback. The closed‐loop system is governed by a non‐linear evolution equation. First, the well‐posedness of the closed‐loop system is shown. Next, an energy‐like function and a multiplier function are introduced and the exponential stability of the closed‐loop system is analysed. Some examples are given to illustrate the theory. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
74.
胡迪鹤 《数学物理学报(B辑英文版)》2005,25(1):23-29
This paper is a continuation of [8]. In Section 1, three kinds of communication are introdnced for two states and the relations among them are investigated. In Section 2, two kinds of period of a state are introdnced and it is obtained that the period is a “class property” ,i.e. two states x and y belong to same class implies the period of x is equal to the period of y. 相似文献
75.
In this paper, we evaluate various analytic Feynman integrals of first variation, conditional first variation, Fourier-Feynman
transform and conditional Fourier-Feynman transform of cylinder type functions defined over Wiener paths in abstract Wiener
space. We also derive the analytic Feynman integral of the conditional Fourier-Feynman transform for the product of the cylinder
type functions which define the functions in a Banach algebra introduced by Yoo, with n linear factors. 相似文献
76.
GLOBAL ATTRACTOR OF A SPATIALLY DISCRETIZED REACTION-DIFFUSION SYSTEM WITH HAMILTONIAN STRUCTURE 总被引:1,自引:0,他引:1
1HamiltonianStructureinReaction-DifusionsystemConsiderasystemofreaction-difusionequationsut=uxx+f(u,v)vt=vxx+g(u,v){(1.1)wher... 相似文献
77.
B. Sadashive Gowda G.S.V.L. Narasimham M.V. Krishna Murthy 《International Journal of Heat and Fluid Flow》1997,18(6):613-624
In this paper, a mathematical model for forced-air precooling of spherical food products in bulk is developed. The foods are arranged in horizontal layers stacked one above the other to form a rectangular parallelepiped with a vertical gap in between the product layers. The foods are cooled by chilled air blown along the height of the package. The governing equations for the conduction heat transfer in the foods, simultaneous heat and mass transfer at the food-air interface and in the air stream are solved numerically using finite-difference methods. A comprehensive numerical study is performed by varying the process parameters over a wide range. Typical results showing the variation of moist air properties along the height of the package and the effect of each parameter on the process time are presented. The ranges of parameters for advantageous operation of the precooling system are identified. Correlations are obtained for the process time based on the product center and mass-averaged temperatures in terms of process parameters. 相似文献
78.
E. Hatta H. Hosoi H. Akiyama T. Ishii K. Mukasa 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):347-349
We have observed a remarkable two-armed spiral in the collapse process of a floating monolayer at the air-water interface
by phase contrast microscopy. This demonstrates that the floating monolayer as a form of soft condensed matter reorganizes
itself due to a certain kind of macroscopic or collective behavior of molecules as it collapses. This pattern formation is
caused by the breakdown of a critical dynamical balance between the deformation of solid domain and the applied surface pressure.
The fragility as well as the flexibility of the floating monolayer can be associated with the observed pattern growth. There
are also observed interesting, periodically arranged collections of molecules in numerous collapsed regions.
Received: 8 July 1997 / Accepted: 4 November 1997 相似文献
79.
An assignment of the near-infrared bands in the 600–800 nm spectral region observed in magnetic circular dichroism (MCD)
spectra of high-spin ferrous haemoproteins is presented. The assignment is based on a relative energy level scheme for iron
d-electrons, a comparison of predicted and measured temperature dependences of MCD intensity, a sign of MCD bands and a group
theoretical analysis of allowed transitions. The proposed assignment is consistent with the ∼15-nm red shift of the ∼760 nm
band on breakage of the Fe-His bond in deoxy-myoglobin at low pH, with low-temperature photolysis experiments available for
CO complexes of several haemoproteins. In accordance with the observations, the intensity of the MCD bands for proteins with
a sulphur anion of cysteine as proximal haemligand (cytochrome P450 and chloroperoxidase) is predicted to be diminished by
at least one order of magnitude compared to that for proteins with an imidazole of a histidine as a protein-derived haemligand
(i.e. myoglobin, haemoglobin and horseradish peroxidase).
Received: 4 February 1997 / Accepted: 1 May 1997 相似文献
80.
Alexander Afriat 《Foundations of Physics Letters》1995,8(5):467-480
We consider the question of factorizability in tensor product spaces, and argue that the correlations associated with entangled states are even more problematic in the general case involving any tensor product of Hilbert spaces, than in the Einstein, Podolsky, and Rosen case with only two [1]. 相似文献