收费全文 | 9634篇 |
免费 | 449篇 |
国内免费 | 43篇 |
化学 | 6707篇 |
晶体学 | 40篇 |
力学 | 219篇 |
数学 | 1523篇 |
物理学 | 1637篇 |
2023年 | 77篇 |
2022年 | 71篇 |
2021年 | 140篇 |
2020年 | 200篇 |
2019年 | 200篇 |
2018年 | 131篇 |
2017年 | 132篇 |
2016年 | 383篇 |
2015年 | 325篇 |
2014年 | 315篇 |
2013年 | 561篇 |
2012年 | 593篇 |
2011年 | 704篇 |
2010年 | 410篇 |
2009年 | 353篇 |
2008年 | 558篇 |
2007年 | 511篇 |
2006年 | 490篇 |
2005年 | 473篇 |
2004年 | 395篇 |
2003年 | 362篇 |
2002年 | 324篇 |
2001年 | 208篇 |
2000年 | 160篇 |
1999年 | 144篇 |
1998年 | 106篇 |
1997年 | 124篇 |
1996年 | 124篇 |
1995年 | 100篇 |
1994年 | 79篇 |
1993年 | 96篇 |
1992年 | 63篇 |
1991年 | 58篇 |
1990年 | 54篇 |
1989年 | 54篇 |
1988年 | 53篇 |
1987年 | 52篇 |
1986年 | 53篇 |
1985年 | 51篇 |
1984年 | 50篇 |
1983年 | 37篇 |
1982年 | 57篇 |
1981年 | 38篇 |
1980年 | 53篇 |
1979年 | 30篇 |
1978年 | 36篇 |
1977年 | 42篇 |
1976年 | 30篇 |
1975年 | 31篇 |
1974年 | 41篇 |
The diffusive behavior of nanoparticles inside porous materials is attracting a lot of interest in the context of understanding, modeling, and optimization of many technical processes. A very powerful technique for characterizing the diffusive behavior of particles in free media is dynamic light scattering (DLS). The applicability of the method in porous media is considered, however, to be rather difficult due to the presence of multiple sources of scattering. In contrast to most of the previous approaches, the DLS method was applied without ensuring matching refractive indices of solvent and porous matrix in the present study. To test the capabilities of the method, the diffusion of spherical gold nanoparticles within the interconnected, periodic nanopores of inverse opals was analyzed. Despite the complexity of this system, which involves many interfaces and different refractive indices, a clear signal related to the motion of particles inside the porous media was obtained. As expected, the diffusive process inside the porous sample slowed down compared to the particle diffusion in free media. The obtained effective diffusion coefficients were found to be wave vector-dependent. They increased linearly with increasing spatial extension of the probed particle concentration fluctuations. On average, the slowing-down factor measured in this work agrees within combined uncertainties with literature data.
相似文献The combinatorial integral approximation decomposition splits the optimization of a discrete-valued control into two steps: solving a continuous relaxation of the discrete control problem, and computing a discrete-valued approximation of the relaxed control. Different algorithms exist for the second step to construct piecewise constant discrete-valued approximants that are defined on given decompositions of the domain. It is known that the resulting discrete controls can be constructed such that they converge to a relaxed control in the \(\hbox {weak}^*\) topology of \(L^\infty \) if the grid constant of this decomposition is driven to zero. We exploit this insight to formulate a general approximation result for optimization problems, which feature discrete and distributed optimization variables, and which are governed by a compact control-to-state operator. We analyze the topology induced by the grid refinements and prove convergence rates of the control vectors for two problem classes. We use a reconstruction problem from signal processing to demonstrate both the applicability of the method outside the scope of differential equations, the predominant case in the literature, and the effectiveness of the approach.
相似文献