全文获取类型
收费全文 | 6396篇 |
免费 | 159篇 |
国内免费 | 158篇 |
专业分类
化学 | 747篇 |
晶体学 | 86篇 |
力学 | 56篇 |
综合类 | 26篇 |
数学 | 4654篇 |
物理学 | 1144篇 |
出版年
2023年 | 18篇 |
2022年 | 52篇 |
2021年 | 83篇 |
2020年 | 46篇 |
2019年 | 153篇 |
2018年 | 145篇 |
2017年 | 99篇 |
2016年 | 54篇 |
2015年 | 62篇 |
2014年 | 140篇 |
2013年 | 316篇 |
2012年 | 229篇 |
2011年 | 340篇 |
2010年 | 285篇 |
2009年 | 413篇 |
2008年 | 451篇 |
2007年 | 458篇 |
2006年 | 446篇 |
2005年 | 348篇 |
2004年 | 287篇 |
2003年 | 196篇 |
2002年 | 205篇 |
2001年 | 170篇 |
2000年 | 162篇 |
1999年 | 160篇 |
1998年 | 126篇 |
1997年 | 122篇 |
1996年 | 161篇 |
1995年 | 138篇 |
1994年 | 133篇 |
1993年 | 76篇 |
1992年 | 68篇 |
1991年 | 58篇 |
1990年 | 33篇 |
1989年 | 50篇 |
1988年 | 33篇 |
1987年 | 44篇 |
1986年 | 30篇 |
1985年 | 57篇 |
1984年 | 39篇 |
1983年 | 30篇 |
1982年 | 34篇 |
1981年 | 27篇 |
1980年 | 31篇 |
1979年 | 19篇 |
1978年 | 22篇 |
1977年 | 15篇 |
1976年 | 19篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有6713条查询结果,搜索用时 31 毫秒
71.
Fe–Al alloys around the concentration of 30 at. % Al present re-entrant spin-glass behaviour at low temperatures. This behaviour is not completely understood and Mössbauer spectroscopy, combined with other experimental techniques, is useful to describe and explain this behaviour. Results show that the Mössbauer spectra coincide with the magnetic behaviour showed in literature and they can be explained as a magnetic cluster system whose magnetic clusters are getting smaller when the temperature is decreasing. When the temperature is reaching to the spin-glass transition at 92 K the spins in the paramagnetic matrix are moving slower and below this transition the spins are completely frozen. 相似文献
72.
A. Veiga N. Martínez P. Mendoza Zélis G. A. Pasquevich F. H. Sánchez 《Hyperfine Interactions》2006,167(1-3):905-909
A prototype of a programmable constant-velocity scaler is presented. This instrument allows the acquisition of partial Mössbauer spectra in selected energy regions using standard drivers and transducers. It can be fully operated by a remote application, thus data acquisition can be automated. The instrument consists of a programmable counter and a constant-velocity reference. The reference waveform generator is amplitude modulated with 13-bit resolution, and is programmable in a wide range of frequencies and waveforms in order to optimize the performance of the transducer. The counter is compatible with most standard SCA, and is configured as a rate-meter that provides counts per selectable time slice at the programmed velocity. As a demonstration of the instrument applications, a partial Mössbauer spectrum of a natural iron foil was taken. Only positive energies were studied in 512 channels, accumulating 20 s per channel. A line width of 0.20 mm/s was achieved, performing with an efficiency of 80%. 相似文献
73.
E. K. Sadykov V. V. Arinin G. I. Petrov A. V. Pyataev F. G. Vagizov O. A. Kocharovskaya 《Hyperfine Interactions》2006,167(1-3):893-896
The role of quantum interference (QI) in spectra of the resonant Mössbauer scattering is investigated. As a mechanism ensuring the QI conditions, the radio-frequency (RF) mixing of the spin sublevels of the excited nuclear state is considered. It is shown that QI leads to a significant intensity redistribution of the elastic and Raman scattering. 相似文献
74.
Hubert de Fraysseix 《Discrete Applied Mathematics》2007,155(9):1079-1095
Using a general resolution of barycentric systems we give a generalization of Tutte's theorem on convex drawing of planar graphs. We deduce a characterization of the edge coverings into pairwise non-crossing paths which are stretchable: such a system is stretchable if and only if each subsystem of at least two paths has at least three free vertices (vertices of the outer face of the induced subgraph which are internal to none of the paths of the subsystem). We also deduce that a contact system of pseudo-segments is stretchable if and only if it is extendible. 相似文献
75.
The 57Fe Mössbauer technique has been used to investigate the effect of zinc oxide substitution in (25???x)MnO–xZnO–15Fe2O3–60B2O3 glass system (x?=?0, 5, 10, 15 and 20 mol% of ZnO ). Mössbauer absorption spectra for all the samples recorded at room temperature suggest the existence of the two paramagnetic quadrupole doublets. The observed variations in hyperfine parameters have been explained on the basis of cations distribution and exchange interaction at the lattice sites and it is concluded that B–B interaction increases while the metal–metal interaction decreases due to replacement of manganese oxide by zinc oxide. These results suggest that the present glass system exhibits a paramagnetic behaviour that changes towards the weak paramagnetic when manganese oxide was replaced with zinc oxide. 相似文献
76.
This article deals with Leibniz's reception of Descartes' “geometry.” Leibnizian mathematics was based on five fundamental notions: calculus, characteristic, art of invention, method, and freedom. On the basis of methodological considerations Leibniz criticized Descartes' restriction of geometry to objects that could be given in terms of algebraic (i.e., finite) equations: “Descartes's mind was the limit of science.” The failure of algebra to solve equations of higher degree led Leibniz to develop linear algebra, and the failure of algebra to deal with transcendental problems led him to conceive of a science of the infinite. Hence Leibniz reconstructed the mathematical corpus, created new (transcendental) notions, and redefined known notions (equality, exactness, construction), thus establishing “a veritable complement of algebra for the transcendentals”: infinite equations, i.e., infinite series, became inestimable tools of mathematical research. 相似文献
77.
A survey of the contributions of Aldo Cossu in finite geometry is given.
Dedicated to the memory of Professor Aldo Cossu 相似文献
78.
部分相干光束通过硬边光阑的推广光束传输M2因子 总被引:2,自引:2,他引:0
给出部分相干光通过硬边光阑后的强度二阶矩的计算公式,由此可得到部分相干光通过硬边光阑后的推广光束传输M^2因子。以部分相干高斯-谢尔模型光束为例,推导出相应的M^2因子,并作了数值计算和分析讨论。 相似文献
79.
80.
Summary. The perfectly matched layer (PML) is an efficient tool to simulate propagation phenomena in free space on unbounded domain.
In this paper we consider a new type of absorbing layer for Maxwell's equations and the linearized Euler equations which is
also valid for several classes of first order hyperbolic systems. The definition of this layer appears as a slight modification
of the PML technique. We show that the associated Cauchy problem is well-posed in suitable spaces. This theory is finally
illustrated by some numerical results. It must be underlined that the discretization of this layer leads to a new discretization
of the classical PML formulation.
Received May 5, 2000 / Published online November 15, 2001 相似文献