全文获取类型
收费全文 | 656267篇 |
免费 | 7641篇 |
国内免费 | 2118篇 |
专业分类
化学 | 354045篇 |
晶体学 | 9414篇 |
力学 | 28430篇 |
综合类 | 19篇 |
数学 | 79868篇 |
物理学 | 194250篇 |
出版年
2021年 | 5002篇 |
2020年 | 5623篇 |
2019年 | 5953篇 |
2018年 | 7263篇 |
2017年 | 7066篇 |
2016年 | 11565篇 |
2015年 | 7851篇 |
2014年 | 11590篇 |
2013年 | 30201篇 |
2012年 | 22972篇 |
2011年 | 28445篇 |
2010年 | 19229篇 |
2009年 | 18921篇 |
2008年 | 25846篇 |
2007年 | 26022篇 |
2006年 | 24445篇 |
2005年 | 22074篇 |
2004年 | 20277篇 |
2003年 | 17986篇 |
2002年 | 17588篇 |
2001年 | 19539篇 |
2000年 | 14907篇 |
1999年 | 11869篇 |
1998年 | 9786篇 |
1997年 | 9440篇 |
1996年 | 9366篇 |
1995年 | 8409篇 |
1994年 | 8187篇 |
1993年 | 7881篇 |
1992年 | 8864篇 |
1991年 | 8788篇 |
1990年 | 8361篇 |
1989年 | 8136篇 |
1988年 | 8253篇 |
1987年 | 7990篇 |
1986年 | 7657篇 |
1985年 | 10301篇 |
1984年 | 10503篇 |
1983年 | 8487篇 |
1982年 | 8880篇 |
1981年 | 8874篇 |
1980年 | 8379篇 |
1979年 | 8840篇 |
1978年 | 8974篇 |
1977年 | 8939篇 |
1976年 | 8790篇 |
1975年 | 8348篇 |
1974年 | 8194篇 |
1973年 | 8354篇 |
1972年 | 5539篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Abstract Under a suitable ellipticity condition, we show that classical SG-pseudodifferential operators of nonnegative order possess
complex powers. We show that the powers are again classical and derive an explicit formula for all homogeneous components.
Keywords: Complex power, Weighted symbols, Noncompact manifolds 相似文献
42.
The interferometric intensity patterns from a 2D shearing interferometer are shown and discussed. The intensity patterns can be obtained in two different approaches incorporating differential and extended wavefront controlled displacements. The reliable directional sensitivity of this interferometer allows the optimization of the measurement parameters to estimate the wavefront of the intensity patterns by regularization techniques. 相似文献
43.
J. C. Fabris S. V. B. Gonçalves P. E. de Souza 《General Relativity and Gravitation》2002,34(12):2111-2126
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate. 相似文献
44.
The Wheeler–DeWitt equation of arbitrary Hartle–Hawking factor ordering for several minisuperspace universe models, such as the pure gravity Friedmann–Robertson–Walker and Taub ones, is mapped onto the dynamics of corresponding classical oscillators. The latter ones are studied by the classical Ermakov invariant method, which is a natural approach in this context. For the more realistic case of a minimally coupled massive scalar field, one can study, within the same type of approach, the corresponding squeezing features as a possible means of describing cosmological evolution. Finally, we comment on the analogy with the accelerator physics. 相似文献
45.
A.-S. F. Obada M. Darwish H. H. Salah 《International Journal of Theoretical Physics》2002,41(9):1755-1768
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined. 相似文献
46.
A piecewise linearization method based on the linearization of nonlinear ordinary differential equations in small intervals, that provides piecewise analytical solutions in each interval and smooth solutions everywhere, is developed for the study of the limit cycles of smooth and non-smooth, conservative and non-conservative, nonlinear oscillators. It is shown that this method provides nonlinear maps for the displacement and velocity which depend on the previous values through the nonlinearity and its partial derivatives with respect to time, displacement and velocity, and yields non-standard finite difference formulae. It is also shown by means of five examples that the piecewise linearization method presented here is more robust and yields more accurate (in terms of displacement, energy and frequency) solutions than the harmonic balance procedure, the method of slowly varying amplitude and phase, and other non-standard finite difference equations. 相似文献
47.
Aidan Mooney John G. Keating Daniel M. Heffernan 《Chaos, solitons, and fractals》2006,30(5):1088-1097
A digital watermark is a visible, or preferably invisible, identification code that is permanently embedded in digital media, to prove owner authentication and provide protection for documents. Given the interest in watermark generation using chaotic functions a detailed study of one chaotic function for this purpose is performed. In this paper, we present an approach for the generation of watermarks using the logistic map. Using this function, in conjunction with seed management, it is possible to generate chaotic sequences that may be used to create highpass or lowpass digital watermarks. In this paper we provide a detailed study on the generation of optically detectable watermarks and we provide some guidelines on successful chaotic watermark generation using the logistic map, and show using a recently published scheme, how care must be taken in the selection of the function seed. 相似文献
48.
M. Brokate D. Rachinskii 《NoDEA : Nonlinear Differential Equations and Applications》2006,13(4):385-411
The paper is concerned with the study of plasticity models described by differential equations with stop and play operators.
We suggest sufficient conditions for the global stability of a unique periodic solution for the scalar models and for the
vector models with biaxial inputs of a particular form, namely the sum of a uniaxial function and a constant term. For another
class of simple biaxial inputs, we present an example of the existence of unstable periodic solutions.
The paper was written during the research stay of D. Rachinskii at the Technical University Munich supported by the research
fellowship from the Alexander von Humboldt Foundation. His work was partially supported by the Russian Science Support Foundation, Russian Foundation for Basic Research (Grant No. 01-01-00146, 03-01-00258), and the Grants of the President of Russia (Grant No. MD-87.2003.01, NS-1532.2003.1). The support is gratefully acknowledged. 相似文献
49.
I. J. Tchoupaeva 《Journal of Mathematical Sciences》2006,135(5):3409-3419
Some geometric theorems can be stated in coordinate-free form as polynomials in Grassman algebra and can be proven by the anticommutative Gröbner basis method. In this article, we analyze some properties of both sets of hypotheses and conclusions of the theorem. 相似文献
50.
R. J. Hinde 《Few-Body Systems》2006,38(2-4):187-191
We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2-H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set
for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster
theory and find that a fully iterative treatment of connected triples may be required to estimate the H2-H2 vibrational coupling accurately using coupled cluster theory. 相似文献