全文获取类型
收费全文 | 1671篇 |
免费 | 98篇 |
国内免费 | 12篇 |
专业分类
化学 | 1168篇 |
晶体学 | 1篇 |
力学 | 55篇 |
数学 | 224篇 |
物理学 | 333篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 36篇 |
2021年 | 57篇 |
2020年 | 66篇 |
2019年 | 60篇 |
2018年 | 40篇 |
2017年 | 33篇 |
2016年 | 85篇 |
2015年 | 68篇 |
2014年 | 71篇 |
2013年 | 102篇 |
2012年 | 111篇 |
2011年 | 142篇 |
2010年 | 67篇 |
2009年 | 92篇 |
2008年 | 117篇 |
2007年 | 112篇 |
2006年 | 102篇 |
2005年 | 92篇 |
2004年 | 63篇 |
2003年 | 41篇 |
2002年 | 53篇 |
2001年 | 12篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1944年 | 1篇 |
排序方式: 共有1781条查询结果,搜索用时 31 毫秒
131.
F. H. Sánchez C. Rodríguez Torres F. D. Saccone Alejandro Ayala 《Hyperfine Interactions》2001,133(1-4):33-40
In this work a practical method of fitting complex multiphase Mössbauer effect spectra is proposed. The task is simplified imposing specific restrictions to the analysing functions, which are appropriate for cases where the component phases spectra do not change substantially during the process under study. The ME spectra can be analysed using the phases subspectra, by defining only a reduced number of parameters. The constraints are equivalent to assume a Doppler velocity transformation v=(v–m)B
m0/B
m+m0 for each phase, where m and B
m are fitting parameters containing information on the phase mean isomer shift and hyperfine field and m0 and B
m0 their reference values. In this manner physically meaningful results are easy to obtain. The idea was applied to partially nitrogenated R2Fe17N
x
(R= Sm and Y) and partially hydrogen-decomposed Nd–Fe–B materials. 相似文献
132.
Stanisław Lewanowicz Eduardo Godoy Iván Area André Ronveaux Alejandro Zarzo 《Numerical Algorithms》2000,23(1):31-50
We propose an algorithm to construct recurrence relations for the coefficients of the Fourier series expansions with respect
to the q-classical orthogonal polynomials pk(x;q). Examples dealing with inversion problems, connection between any two sequences of q-classical polynomials, linearization
of ϑm(x) pn(x;q), where ϑm(x) is xmor (x;q)m, and the expansion of the Hahn-Exton q-Bessel function in the little q-Jacobi polynomials are discussed in detail.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
133.
The Einstein–Podolsky–Rosen–Bohm (EPRB) experiment performed with random variable and spatially separated analyzers is a milestone
test in the controversy between Objective Local Theories (OLT) and Quantum Mechanics (QM). Only a few OLT are still possible.
Some of the surviving OLT (specifically, the so called non-ergodic theories) would be undetectable in the averaged statistical
values, but they may leave their trace in the time dynamics. For, while QM predicts random processes, the OLT of this kind
predict the existence of regularities that may be revealed as a low dimensional object in the phase space. We perform a numerical
analysis of the time-resolved data recorded in that experiment to unveil any hypothetical low dimensional dynamics that may
be present. We find no consistent indication of such dynamics except for one data file, the longest of all in the real time.
The possible causes of these dynamics are discussed.
相似文献
134.
Rose Mary Michell Alejandro J. Müller Mariya Spasova Philippe Dubois Stefano Burattini Barnaby W. Greenland Ian W. Hamley Daniel Hermida‐Merino Nicolas Cheval Amir Fahmi 《Journal of Polymer Science.Polymer Physics》2011,49(19):1397-1409
The thermal properties, crystallization, and morphology of amphiphilic poly(D ‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PDLA‐b‐PDMAEMA) and poly (L ‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were studied and compared to those of the corresponding poly(lactide) homopolymers. Additionally, stereocomplexation of these copolymers was studied. The crystallization kinetics of the PLA blocks was retarded by the presence of the PDMAEMA block. The studied copolymers were found to be miscible in the melt and the glassy state. The Avrami theory was able to predict the entire crystallization range of the PLA isothermal overall crystallization. The melting points of PLDA/PLLA and PLA/PLA‐b‐PDMAEMA stereocomplexes were higher than those formed by copolymer mixtures. This indicates that the PDMAEMA block is influencing the stability of the stereocomplex structures. For the low molecular weight samples, the stereocomplexes particles exhibited a conventional disk‐shape structure and, for high molecular weight samples, the particles displayed unusual star‐like shape morphology. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1397–1409, 2011 相似文献
135.
Alejandro R. Diaz Noboru Klkuchl Panos Papalambros John E. Taylor 《基于设计的结构力学与机械力学》2013,41(2):215-230
ABSTRACT Finite element solutions of improved quality are obtained by optimizing the location of nodes of the finite element grid, while keeping the number of degrees of freedom fixed. The formulation of the grid optimization problem is based on the reduction of error associated with interpolation of the exact solution, using functions from the finite element space. Element sizes are selected as design variables: length in R1 and area in R2. Analytically derived optimality conditions are presented and an approximation to these conditions is introduced to obtain a set of operationally useful equations that can be used as guidelines for construction of improved grids. Example problems are given for illustration. 相似文献
136.
137.
138.
Ivn Brito Danitza Vargas Andrea Reyes Alejandro Crdenas Matías Lpez‐Rodríguez 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(4):o234-o236
The title compound, C27H19NO2S, contains chains of fused (19) rings formed by intermolecular C—H·O=C hydrogen bonds and running along the [011] and [01] directions. These chains are linked through short intermolecular C—H·π contacts, giving rise to sheets. The conformation of the title compound is dominated primarily by the nearly orthogonal lone‐pair orbitals on the N and S atoms. 相似文献
139.
Alejandro Cabo-Bizet 《Physics letters. A》2009,373(21):1865-1869
Special solutions of the Hartree-Fock (HF) problem for Coulomb interacting electrons described by a simple model of the Cu-O planes in La2CuO4 are presented. One of the mean field states obtained, is able to predict some of the most interesting properties of this material, such as its insulator character and the antiferromagnetic order. The natural appearance of pseudogaps in some states of this material is also indicated by another of the HF states obtained. These surprising results follow after eliminating spin and crystal symmetry restrictions usually imposed on the single particle HF orbitals, by employing the rotational invariant formulation of the HF scheme originally introduced by Dirac. Therefore, it is exemplified here, how up to know considered strong correlation effects, can be described by improving the HF solution of the considered system. In other words, it has been argued, that defining correlation effects as the ones shown by the system and not predicted by the HF best (lowest energy) solution, allows to explain important, up to know considered as strong correlation properties, as simple mean field ones. The discussion also helps to clarify the role of the antiferromagnetism and pseudogaps in the physical properties of the HTSC materials and indicates a promising way to start conciliating the Mott and Slater pictures in the physics of the transition metal oxides and other strongly correlated electron systems. 相似文献
140.
Raquel da Silva Cabral Andre L. L. Aquino Alejandro C. Frery Osvaldo A. Rosso Jaime A. Ramírez 《Central European Journal of Physics》2013,11(12):1645-1652
Wireless sensor networks are an important technology for making distributed autonomous measures in hostile or inaccessible environments. Among the challenges they pose, the way data travel among them is a relevant issue since their structure is quite dynamic. The operational topology of such devices can often be described by complex networks. In this work, we assess the variation of measures commonly employed in the complex networks literature applied to wireless sensor networks. Four data communication strategies were considered: geometric, random, small-world, and scale-free models, along with the shortest path length measure. The sensitivity of this measure was analyzed with respect to the following perturbations: insertion and removal of nodes in the geometric strategy; and insertion, removal and rewiring of links in the other models. The assessment was performed using the normalized Kullback-Leibler divergence and Hellinger distance quantifiers, both deriving from the Information Theory framework. The results reveal that the shortest path length is sensitive to perturbations. 相似文献