全文获取类型
收费全文 | 2243篇 |
免费 | 253篇 |
国内免费 | 180篇 |
专业分类
化学 | 786篇 |
晶体学 | 23篇 |
力学 | 254篇 |
综合类 | 20篇 |
数学 | 106篇 |
物理学 | 1487篇 |
出版年
2024年 | 3篇 |
2023年 | 20篇 |
2022年 | 55篇 |
2021年 | 60篇 |
2020年 | 48篇 |
2019年 | 52篇 |
2018年 | 52篇 |
2017年 | 65篇 |
2016年 | 87篇 |
2015年 | 83篇 |
2014年 | 90篇 |
2013年 | 146篇 |
2012年 | 114篇 |
2011年 | 153篇 |
2010年 | 133篇 |
2009年 | 119篇 |
2008年 | 121篇 |
2007年 | 128篇 |
2006年 | 128篇 |
2005年 | 121篇 |
2004年 | 114篇 |
2003年 | 118篇 |
2002年 | 111篇 |
2001年 | 74篇 |
2000年 | 67篇 |
1999年 | 49篇 |
1998年 | 55篇 |
1997年 | 31篇 |
1996年 | 33篇 |
1995年 | 36篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 16篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2676条查询结果,搜索用时 31 毫秒
21.
The frequency or dispersion relation for the least‐squares mixed formulation of the shallow‐water equations is analysed. We consider the use of different approximation spaces corresponding to co‐located and staggered meshes, respectively. The study includes the effect of Coriolis, and the dispersion properties are compared analytically and graphically with those of the mixed Galerkin formulation. Numerical solutions of a test problem to simulate slow Rossby modes illustrate the theoretical results. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
22.
针对重力输水管道设计中存在的问题,文章以管道造价最小为目标,应用动态规划,提出了一种新的重力输水管道优化设计方法,对输水管的当量管径、流量分配、连接管设置与可靠性校核计算等问题作了探讨。该方法可用于沿线有节点流量流出的并联输水管道优化设计,能明显节省投资,有良好的实用性 相似文献
23.
V.I. Anisimov I.A. Nekrasov D.E. Kondakov T.M. Rice M. Sigrist 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):191-201
The electronic structures of the metallic and insulating phases of the alloy series Ca2-xSrxRuO4 ( 0 ?
x
? 2) are calculated using LDA, LDA+U and Dynamical Mean-Field Approximation methods. In the end members the groundstate respectively
is an orbitally non-degenerate antiferromagnetic insulator (x
= 0) and a good metal (x
= 2). For x
> 0.5 the observed Curie-Weiss paramagnetic metallic state which possesses a local moment with the unexpected spin S
= 1/2, is explained by the coexistence of localized and itinerant Ru-4d-orbitals. For 0.2 <
x
< 0.5 we propose a state with partial orbital and spin ordering. An effective model for the localized orbital and spin degrees
of freedom is discussed. The metal-insulator transition at x
= 0.2 is attributed to a switch in the orbital occupation associated with a structural change of the crystal.
Received 27 July 2001 相似文献
24.
25.
Horst-Heino v. Borzeszkowski Hans-Jürgen Treder 《General Relativity and Gravitation》2002,34(11):1909-1918
The affine theory was conceived as a geometric model, wherein the connection field is the primary structure of the space-time. According to the program lying on the basis of this theory, metric and some sort of matter are somehow to be deduced from the connection field. In the present paper, we point out classical ways to a realization of this program. It is shown that, even in that case where the introduction of the metric seems to exclude the coupling of gravity to matter, the situation is not so hopeless as one may assume. In particular, for a symmetric Einstein tensor, it is answered the old question as to a self-consistent introduction of a metric and a metrical energy-momentum tensor controversially debated by Einstein, Eddington, and Weyl. 相似文献
26.
James B. Hartle 《International Journal of Theoretical Physics》2006,45(8):1390-1396
Familiar quantum mechanics assumes a fixed spacetime geometry. Quantummechanics must therefore be generalized for quantum gravity where spacetime geometry is not fixed but rather a quantum variable. This extended abstract sketches a fully fourdimensional generalized quantum mechnics of cosmological spacetime geometries that is one such generalization.This contribution to the proceedings of the Glafka Conference is an extended abstract of the author's talk there. More details can be found in the references cited at the end of the abstract expecially (Hartle, 1995). 相似文献
27.
M. N. Smolyakov 《General Relativity and Gravitation》2007,39(1):41-53
A model with one compact extra dimension and a scalar field of Brans–Dicke type in the bulk is discussed. It describes two branes with non-zero tension embedded into the space-time with flat background. This setup allows one to use a very simple method for stabilization of the size of extra dimension. It appears that the four-dimensional Planck mass is expressed only through parameters of the scalar field potentials on the branes. 相似文献
28.
A way of determining the flexibility of wood-pulp fibres is developed, which involves i) a precise measurement of the topology
of single-fibres by using a confocal laser scanning microscope and ii) the measurement of the elastic modulus of the fibres
by using a single-fibre fatigue cell. Reported in this paper are the initial results of tests carried out on black spruce
fibres, which have been subjected to three different levels of mechanical refining energy, namely ∼1100, 2300, and 3500 kWh/t.
It is found that the fibre flexibility rises significantly between the first and second energy levels, but it does not change
to the same degree between the second and third ones. The described procedure of measuring the flexibility of fibres may be
used to establish the appropriate refiner energy necessary for the production of a specific grade of paper.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 115–128, January–February, 2006. 相似文献
29.
Stochastic modeling of a billiard in a gravitational field: Power law behavior of Lyapunov exponents
We consider the motion of a point particle (billiard) in a uniform gravitational field constrained to move in a symmetric wedge-shaped region. The billiard is reflected at the wedge boundary. The phase space of the system naturally divides itself into two regions in which the tangent maps are respectively parabolic and hyperbolic. It is known that the system is integrable for two values of the wedge half-angle
1 and
2 and chaotic for
1<<
2. We study the system at three levels of approximation: first, where the deterministic dynamics is replaced by a random evolution; second, where, in addition, the tangent map in each region is, replaced by its average; and third, where the tangent map is replaced by a single global average. We show that at all three levels the Lyapunov exponent exhibits power law behavior near
1 and
2 with exponents 1/2 and 1, respectively. We indicate the origin of the exponent 1, which has not been observed in unaccelerated billiards. 相似文献
30.