全文获取类型
收费全文 | 2563篇 |
免费 | 53篇 |
国内免费 | 18篇 |
专业分类
化学 | 1480篇 |
晶体学 | 24篇 |
力学 | 61篇 |
数学 | 354篇 |
物理学 | 715篇 |
出版年
2021年 | 18篇 |
2020年 | 21篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 35篇 |
2015年 | 30篇 |
2014年 | 38篇 |
2013年 | 123篇 |
2012年 | 128篇 |
2011年 | 145篇 |
2010年 | 62篇 |
2009年 | 45篇 |
2008年 | 131篇 |
2007年 | 121篇 |
2006年 | 98篇 |
2005年 | 100篇 |
2004年 | 94篇 |
2003年 | 78篇 |
2002年 | 70篇 |
2001年 | 46篇 |
2000年 | 51篇 |
1999年 | 32篇 |
1998年 | 21篇 |
1997年 | 28篇 |
1996年 | 45篇 |
1995年 | 37篇 |
1994年 | 36篇 |
1993年 | 39篇 |
1992年 | 43篇 |
1991年 | 25篇 |
1990年 | 35篇 |
1989年 | 34篇 |
1988年 | 40篇 |
1987年 | 28篇 |
1986年 | 19篇 |
1985年 | 46篇 |
1984年 | 43篇 |
1983年 | 28篇 |
1982年 | 43篇 |
1981年 | 35篇 |
1980年 | 43篇 |
1979年 | 40篇 |
1978年 | 43篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 22篇 |
1974年 | 31篇 |
1973年 | 36篇 |
1972年 | 16篇 |
排序方式: 共有2634条查询结果,搜索用时 15 毫秒
1.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
2.
3.
Allen C. HirshfeldPeter Henselder 《Annals of Physics》2002,302(1):59-77
Deformation quantization, which achieves the passage from classical mechanics to quantum mechanics by the replacement of the pointwise multiplication of functions on phase space by the star product, is a powerful tool for treating systems involving bosonic degrees of freedom, both in quantum mechanics and in quantum field theory. In the present paper we show how these methods may be naturally extended to systems involving fermions. In particular we show how supersymmetric quantum mechanics can be formulated in this approach and consider examples involving both non-relativistic and relativistic systems. 相似文献
4.
We describe a new algorithm which uses the trajectories of a discrete dynamical system to sample the domain of an unconstrained objective function in search of global minima. The algorithm is unusually adept at avoiding nonoptimal local minima and successfully converging to a global minimum. Trajectories generated by the algorithm for objective functions with many local minima exhibit chaotic behavior, in the sense that they are extremely sensitive to changes in initial conditions and system parameters. In this context, chaos seems to have a beneficial effect: failure to converge to a global minimum from a given initial point can often be rectified by making arbitrarily small changes in the system parameters. 相似文献
5.
V. V. Popov T. V. Teperik O. V. Polischuk X. G. Peralta S. J. Allen N. J. M. Horing M. C. Wanke 《Physics of the Solid State》2004,46(1):153-156
The terahertz absorption spectra of plasmon modes in a grid-gated double-quantum-well field-effect transistor structure is analyzed theoretically and numerically using the scattering matrix approach and is shown to faithfully reproduce strong resonant features of recent experimental observations of terahertz photo-conductivity in such a structure. 相似文献
6.
Myron B. Allen Mark C. Curran 《Numerical Methods for Partial Differential Equations》1989,5(2):121-132
An adaptive grid refinement procedure allows accurate solutions to advection-dominated, time-dependent flows using finite-element collocation. The technique relies on a data structure that is readily amenable to parallel computing. The paper discusses computational aspects of the method. 相似文献
7.
This paper proposes a new method that extends the efficient global optimization to address stochastic black-box systems. The
method is based on a kriging meta-model that provides a global prediction of the objective values and a measure of prediction
uncertainty at every point. The criterion for the infill sample selection is an augmented expected improvement function with
desirable properties for stochastic responses. The method is empirically compared with the revised simplex search, the simultaneous
perturbation stochastic approximation, and the DIRECT methods using six test problems from the literature. An application
case study on an inventory system is also documented. The results suggest that the proposed method has excellent consistency
and efficiency in finding global optimal solutions, and is particularly useful for expensive systems. 相似文献
8.
Tony Donnelly 《Applied Surface Science》2006,252(13):4445-4448
Ultra-thin (0.5-5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a 26 ns KrF excimer laser at 1 J cm−2. The deposition was controlled using a Langmuir ion probe and a quartz crystal thickness monitor. Transmission electron microscopy showed that the films are not continuous, but are structured on nanometer size scales. Optical absorption spectra showed the expected surface plasmon resonance feature, which shifted to longer wavelength and increased in strength as the equivalent film thickness was increased. It is shown that Maxwell Garnett effective medium theory can be used to calculate the main features of optical absorption spectra. 相似文献
9.
Deformation quantization is a powerful tool for quantizing theories with bosonic and fermionic degrees of freedom. The star products involved generate the mathematical structures which have recently been used in attempts to analyze the algebraic properties of quantum field theory. In the context of quantum mechanics they provide a quantization procedure for systems with either bosonic or fermionic degrees of freedom. We illustrate this procedure for a number of physical examples, including bosonic, fermionic, and supersymmetric oscillators. We show how non-relativistic and relativistic particles with spin can be naturally described in this framework. 相似文献
10.
A hybrid finite-element method, combining ideas from a modified method of characteristics and the streamline diffusion method, delivers accurate solutions to the advection–diffusion equation. An error analysis for the case of tensorial diffusion shows that the lowest-order version of the scheme, which allows one to use a symmetric linear solvers at each time step, possesses first-order accuracy in time and space. Numerical experiments demonstrate the scheme's ability to model advection-dominated transport of solute plumes without distorting sharp fronts. © 1995 John Wiley & Sons, Inc. 相似文献