全文获取类型
收费全文 | 503篇 |
免费 | 16篇 |
国内免费 | 5篇 |
专业分类
化学 | 333篇 |
晶体学 | 2篇 |
力学 | 15篇 |
数学 | 61篇 |
物理学 | 113篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 16篇 |
2012年 | 27篇 |
2011年 | 26篇 |
2010年 | 11篇 |
2009年 | 11篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 25篇 |
2005年 | 30篇 |
2004年 | 22篇 |
2003年 | 23篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 9篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 4篇 |
1969年 | 2篇 |
1968年 | 3篇 |
排序方式: 共有524条查询结果,搜索用时 968 毫秒
41.
Henri Edouard Audier Arielle Milliet Georges Sozzi Steen Hammerum 《Journal of mass spectrometry : JMS》1990,25(1):44-48
The key intermediates to the fragmentation of metastable methyl and ethyl benzoate radical cations are α- and β-distonic isomers of the molecular ions. The α-distocic isomers are also formed by fragmentation of longer chain alkyl benzoates, but may not be long-lived, stable species. Rearrangement of the α-distonic ions prior to fragmentation can take place, but (re)formation of the benzoate molecular ions does not occur. 相似文献
42.
Per Helvig Christensen Steen Mørup Henrik Topsøe Bjerne Steffen Clausen 《Hyperfine Interactions》1986,28(1-4):945-948
Bimetallic Fe-Co alloy catalysts supported on silica have been studied by use of combined Mössbauer absorption and emisson spectroscopy. Effects of carburization on samples with different particle size are discussed. 相似文献
43.
44.
Steen Markvorsen 《Geometriae Dedicata》2008,133(1):7-34
For a given combinatorial graph G a geometrization (G, g) of the graph is obtained by considering each edge of the graph as a 1-dimensional manifold with an associated metric g. In this paper we are concerned with minimal isometric immersions of geometrized graphs (G, g) into Riemannian manifolds (N
n
, h). Such immersions we call minimal webs. They admit a natural ‘geometric’ extension of the intrinsic combinatorial discrete Laplacian. The geometric Laplacian on
minimal webs enjoys standard properties such as the maximum principle and the divergence theorems, which are of instrumental
importance for the applications. We apply these properties to show that minimal webs in ambient Riemannian spaces share several
analytic and geometric properties with their smooth (minimal submanifold) counterparts in such spaces. In particular we use
appropriate versions of the divergence theorems together with the comparison techniques for distance functions in Riemannian
geometry and obtain bounds for the first Dirichlet eigenvalues, the exit times and the capacities as well as isoperimetric
type inequalities for so-called extrinsic R-webs of minimal webs in ambient Riemannian manifolds with bounded curvature.
相似文献
45.
46.
Jens Martin Knudsen Steen Mørup Jolanta Galazka-Friedman 《Hyperfine Interactions》1990,57(1-4):2231-2235
Both the USSR and US have plans of performing rover missions and sample return missions to the planet Mars in the coming decade. There may be possibilities of performingin situ Mössbauer spectroscopy on Mars or on fresh samples returned to a space station. 相似文献
47.
Dr. Xin-Ming Hu Magnus H. Rønne Prof. Dr. Steen U. Pedersen Prof. Dr. Troels Skrydstrup Prof. Dr. Kim Daasbjerg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(23):6568-6572
In a comparative study of the electrocatalytic CO2 reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO2 becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO2. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone. 相似文献
48.
H. J. J. Hardy C. H. Massen C. van der Steen J. A. Poulis 《Applied Scientific Research》1973,27(1):129-132
In the preceeding paper on this subject a method was described which enabled the measurement of magnetic susceptibilities in constant magnetic fields. In the present paper it is demonstrated that the application of an alternating magnetic field instead of a constant field is advantageous.Many environmental disturbances are eliminated, the measurement time is highly reduced and the amplitude of the magnetizing field can be brought back to 60 Oersted at which fields the sensitivity is still a few percent for diamagnetic substances. 相似文献
49.
Resonant vibration control of rotating beams 总被引:3,自引:0,他引:3
Martin Nymann Svendsen Steen Krenk Jan Høgsberg 《Journal of sound and vibration》2011,330(9):1877-1256
Rotating structures, like e.g. wind turbine blades, may be prone to vibrations associated with particular modes of vibration. It is demonstrated, how this type of vibrations can be reduced by using a collocated sensor-actuator system, governed by a resonant controller. The theory is here demonstrated by an active strut, connecting two cross-sections of a rotating beam. The structure is modeled by beam elements in a rotating frame of reference following the beam. The geometric stiffness is derived in a compact form from an initial stress formulation in terms of section forces and moments. The stiffness, and thereby the natural frequencies, of the beam depend on the rotation speed and the controller is tuned to current rotation speed to match the resonance frequency of the selected mode. It is demonstrated that resonant control leads to introduction of the intended level of damping in the selected mode and, with good modal connectivity, only very limited modal spill-over is generated. The controller acts by resonance and therefore has only a moderate energy consumption, and successfully reduces modal vibrations at the resonance frequency. 相似文献
50.
It is shown that the conductance relaxations observed in electrical field effect measurements on granular Al films are the sum of two contributions. One is sensitive to gate voltage changes and gives the already reported anomalous electrical field effect. The other one is independent of the gate voltage history and starts when the films are cooled down to low temperature. Their relative amplitude is strongly thickness-dependent which demonstrates the existence of a finite screening length in our insulating films and allows its quantitative estimate (about 10 nm at 4 K). This metalliclike screening should be taken into account in the electron glass models of disordered insulators. 相似文献