全文获取类型
收费全文 | 1789篇 |
免费 | 45篇 |
国内免费 | 11篇 |
专业分类
化学 | 1177篇 |
晶体学 | 6篇 |
力学 | 81篇 |
数学 | 324篇 |
物理学 | 257篇 |
出版年
2022年 | 14篇 |
2021年 | 28篇 |
2020年 | 23篇 |
2019年 | 36篇 |
2018年 | 28篇 |
2017年 | 15篇 |
2016年 | 53篇 |
2015年 | 27篇 |
2014年 | 36篇 |
2013年 | 74篇 |
2012年 | 80篇 |
2011年 | 97篇 |
2010年 | 55篇 |
2009年 | 65篇 |
2008年 | 85篇 |
2007年 | 98篇 |
2006年 | 89篇 |
2005年 | 100篇 |
2004年 | 81篇 |
2003年 | 70篇 |
2002年 | 46篇 |
2001年 | 22篇 |
2000年 | 28篇 |
1999年 | 34篇 |
1998年 | 19篇 |
1997年 | 26篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 13篇 |
1992年 | 24篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1930年 | 6篇 |
1888年 | 8篇 |
排序方式: 共有1845条查询结果,搜索用时 15 毫秒
981.
982.
Coupled-mode systems are used in physical literature to simplify the nonlinear Maxwell and Gross–Pitaevskii equations with a small periodic potential and to approximate localized solutions called gap solitons by analytical expressions involving hyperbolic functions. We justify the use of the 1D stationary coupled-mode system for a relevant elliptic problem by employing the method of Lyapunov–Schmidt reductions in Fourier space. In particular, existence of periodic/anti-periodic and decaying solutions is proved and the error terms are controlled in suitable norms. The use of multi-dimensional stationary coupled-mode systems is justified for analysis of bifurcations of periodic/anti-periodic solutions in a small multi-dimensional periodic potential. 相似文献
983.
Guido Schneider Dominik Zimmermann 《Mathematical Methods in the Applied Sciences》2013,36(9):1003-1013
The Ginzburg–Landau equation appears as a universal amplitude equation for spatially extended pattern forming systems close to the first instability. It can be derived via multiple scaling analysis for the Marangoni convection problem that is driven by temperature‐dependent surface tension and is the subject of our interest. In this paper, we prove estimates between this formal approximation and true solutions of a scalar pattern forming model problem showing the same spectral picture as the Marangoni convection problem in case of a thin fluid. The new difficulties come from neutral modes touching the imaginary axis for the wave number k = 0 and from identical group velocities at the critical wave number k = kc and the wave number k = 0. The problem is solved by using the reflection symmetry of the system and by using the fact that the modes concentrate at integer multiples of the critical wave number k = kc. The paper presents a method that is applicable whenever this kind of instability occurs. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
984.
985.
Vapour–liquid equilibria of the Lennard–Jones potential, truncated and shifted at 2.5σ, are studied using molecular dynamics simulations, an attractive option for studying inhomogeneous systems. Comprehensive simulation data are reported for three cases: no interface, a planar interface, and a spherical interface between the coexisting phases, covering a wide range of temperatures. Spherical droplets are also studied for a range of radii between 5 and 16σ. The size dependence of the surface tension, based on the Irving–Kirkwood pressure tensor, and other properties is quantified for spherical interfaces. All simulation results are correlated with a consistent set of empirical equations. A comparison with the results of other authors as well as with experimental data for noble gases and methane is also presented. 相似文献
986.
Expressions for intermolecular forces and torques, derived from pair potentials between rigid non-spherical units, are presented. The aim is to give compact and clear expressions, which are easily generalized, and which minimize the risk of error in writing molecular dynamics simulation programs. It is anticipated that these expressions will be useful in the simulation of liquid crystalline systems, and in coarse-grained modelling of macromolecules. 相似文献
987.
The formation of a charge transfer complex between pyridine and halogens or mixed halogens(1,2) brings about perturbations in the infrared spectra of the pyridine molecule and many halogen complexes show two bands in the low frequency range, which can be attributed to the v X-X and v N…Y stretching vibrations. (3–5). However, by comparison, very little has been reported on the Raman spectra of such complexes. Klaboe(6) studied the v Br-Br Raman frequency of some bromine complexes and more recently the Raman spectra of pyridine complexed with Ni (CN)4 (7) and TiCl4 (8) have been reported. In this work, the Raman spectrum of the 3-Br pyridine-bromine charge transfer complex is investigated. 相似文献
988.
Molecular dynamics simulations in the isobaric–isothermal ensemble are used to investigate the structure and dynamics of an ionic liquid confined at ambient temperature and pressure in hydroxylated amorphous silica nanopores. The use of the isobaric–isothermal ensemble allows estimating the effect of confinement and surface chemistry on the density of the confined ionic liquid. The structure of the confined ionic liquid is investigated using density profiles and structural order parameters while its dynamics is assessed by determining the mobility and ionic conductivity of the confined phase. Despite the important screening of the electrostatic interactions (owing to the small Debye length in ionic liquids), the local structure of the confined ionic liquid is found to be mostly driven by electrostatic interactions. We show that both the structure and dynamics of the confined ionic liquid can be described as the sum of a surface contribution arising from the ions in contact with the surface and a bulk-like contribution arising from the ions located in the pore centre; as a result, most properties of the confined ionic liquid are a simple function of the surface-to-volume ratio of the host porous material. In contrast, the ionic conductivity of the confined ionic liquid, which is a collective dynamical property, is found to be similar to the bulk. This study sheds light on the complex behaviour of hybrid materials made up of ionic liquid confined in inorganic porous materials. 相似文献
989.
Elisabeth Schültke Ralf Menk Bernd Pinzer Alberto Astolfo Marco Stampanoni Fulvia Arfelli Laura‐Adela Harsan Guido Nikkhah 《Journal of synchrotron radiation》2014,21(1):242-250
Gold nanoparticles are excellent intracellular markers in X‐ray imaging. Having shown previously the suitability of gold nanoparticles to detect small groups of cells with the synchrotron‐based computed tomography (CT) technique both ex vivo and in vivo, it is now demonstrated that even single‐cell resolution can be obtained in the brain at least ex vivo. Working in a small animal model of malignant brain tumour, the image quality obtained with different imaging modalities was compared. To generate the brain tumour, 1 × 105 C6 glioma cells were loaded with gold nanoparticles and implanted in the right cerebral hemisphere of an adult rat. Raw data were acquired with absorption X‐ray CT followed by a local tomography technique based on synchrotron X‐ray absorption yielding single‐cell resolution. The reconstructed synchrotron X‐ray images were compared with images obtained by small animal magnetic resonance imaging. The presence of gold nanoparticles in the tumour tissue was verified in histological sections. 相似文献
990.
In has been shown in [5] that the NLS approximation makes wrong predictions for the water wave problem in case of small surface tension. We explain that the ideas used in [5] allow to show a similar result for the FWI approximation, too. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献