全文获取类型
收费全文 | 3799篇 |
免费 | 326篇 |
国内免费 | 194篇 |
专业分类
化学 | 361篇 |
晶体学 | 6篇 |
力学 | 820篇 |
综合类 | 33篇 |
数学 | 1396篇 |
物理学 | 1703篇 |
出版年
2024年 | 4篇 |
2023年 | 35篇 |
2022年 | 53篇 |
2021年 | 75篇 |
2020年 | 84篇 |
2019年 | 87篇 |
2018年 | 80篇 |
2017年 | 84篇 |
2016年 | 105篇 |
2015年 | 127篇 |
2014年 | 171篇 |
2013年 | 285篇 |
2012年 | 150篇 |
2011年 | 167篇 |
2010年 | 136篇 |
2009年 | 194篇 |
2008年 | 228篇 |
2007年 | 260篇 |
2006年 | 207篇 |
2005年 | 166篇 |
2004年 | 161篇 |
2003年 | 166篇 |
2002年 | 135篇 |
2001年 | 134篇 |
2000年 | 177篇 |
1999年 | 132篇 |
1998年 | 110篇 |
1997年 | 97篇 |
1996年 | 63篇 |
1995年 | 57篇 |
1994年 | 48篇 |
1993年 | 55篇 |
1992年 | 40篇 |
1991年 | 40篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 24篇 |
1987年 | 26篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1977年 | 8篇 |
1973年 | 12篇 |
1972年 | 4篇 |
1969年 | 3篇 |
排序方式: 共有4319条查询结果,搜索用时 15 毫秒
131.
We investigate the small ball problem for d-dimensional fractional Brownian sheets by functional analytic methods. For this reason we show that integration operators of Riemann–Liouville and Weyl type are very close in the sense of their approximation properties, i.e., the Kolmogorov and entropy numbers of their difference tend to zero exponentially. This allows us to carry over properties of the Weyl operator to the Riemann–Liouville one, leading to sharp small ball estimates for some fractional Brownian sheets. In particular, we extend Talagrand's estimate for the 2-dimensional Brownian sheet to the fractional case. When passing from dimension 1 to dimension d2, we use a quite general estimate for the Kolmogorov numbers of the tensor products of linear operators. 相似文献
132.
Vahedi Tafreshi H. Piseri P. Barborini E. Benedek G. Milani P. 《Journal of nanoparticle research》2002,4(6):511-524
We describe a simulation of the nanoparticle trajectories in a pulsed cluster beam source. Clusters, formed by condensation of atomic vapor in a helium bath, and considered here as rigid spheres having a diameter of 1.5nm, were tracked during their travel inside the source cavity, an aerodynamic lens, and a cylindrical nozzle. Steady state supersonic laminar flow of helium is considered in an axi-symmetric geometry aiming to simulate, within some limitations, the conditions under which cluster formation takes place in a pulsed microplasma cluster source. In spite of the unsteady nature of the pulsed source, the time scale characterizing particle motion in the flow field is significantly smaller than the characteristic time constant for the evolution of gas pressure in the source. For this reason, a steady simulation can shed some light on the understanding of processes governing nanoparticle motion in a pulsed vaporization source. The extent to which the Brownian diffusion can affect the particle extraction from the source is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the source internal walls. However, it does not hinder the aerodynamic focalization produced by the lens even in nano-size cluster regime. This result is qualitatively confirmed by experiment. 相似文献
133.
Geocenter motion (GCM) is one important topic for constructing and maintaining the terrestrial reference frame and its applications.
GCM is studied from CHAMP with the multi-step approach in this paper. Geometric orbits of CHAMP in 2001–2006 are precisely
determined with the kinematic method only from the satellite-borne GPS zero-difference data. Then a GCM time series is estimated
from the precise kinematic orbits based on the theory of satellite dynamics to fit the CHAMP’s real geometric orbits. We compare
the series with the geocenter series used in ITRF2005. Then the GCM series are analyzed with Fourier transform and wavelet
transformation. The mean motions within 6 years in TX, TY and TZ directions are respectively 0.8 mm, 2.2 mm, and 7.9 mm. The trends of GCM in the three directions are 0.495 mm/a, −0.004
mm/a, and 1.309 mm/a, respectively. The long-term movement (2001–2006) indicates that the crustal figure is changing. The
seasonal variations are the main component which may be excitated by the mass redistribution of Earth’s fluid layer, e.g.
ocean, atmosphere and continental water. The inter-annual variations are also found in the GCM series measured with CHAMP.
Supported by the International S&T Cooperation Program of China (Grant No. 2006DFA21980), the National Hi-tech R&D Program
of China (Grant No. 2006AA12z303), the National Natural Science Foundation of China (Grant No. 40774009), and the Natural
Science Foundation of Shandong Province, China (Grant No. Y2003E01) 相似文献
134.
介绍了用自然坐标分析平面运动刚体上各点加速度的方法,并用该方法直是明地讨论了瞬心的加速度和刚体绕瞬心的转动方程。 相似文献
135.
本文提出了分析速调管束波互作用能量转换的二维模型和假设,详细描述了在能量转换过程中的电子运动方程,并指出了能量转换的二维数值分析可能会对速调管基础理论的发展有所贡献的方面。 相似文献
136.
An analysis is made of the effects on the diffusion of Brownian particles whose Knudsen number is large compared to unity, of nonuniformities in the host gas. As examples, in one type of nonuniformity of the host gas, the Chapman-Enskog velocity distribution function for the gas molecules is used; in the other, the host gas is a free-molecule Couette flow. In both cases, a new force on the Brownian particles appears. Two techniques are used (extending Kramers' method and utilizing the Chapman-Enskog method) to transform the new Fokker-Planck equation into generalized Smoluchowski and convective diffusion equations. In these equations, the diffusion coefficient appears as a second-order tensor. Thus, it is demonstrated that Brownian diffusion in a nonuniform gas is anisotropic.The work of Slinn was financially supported in part by Battelle Memorial Institute and in part by U.S. Atomic Energy Commission Contract AT(45-1)-1830. The work of Shen was supported in part by U.S. Air Force Office of Scientific Research Contract 49(638)-1346. 相似文献
137.
Two models are given of branching transport processes that converge to branching Brownian motion starting with one initial particle. The martingale problem method is used. 相似文献
138.
Michael Nauenberg 《Physics in Perspective (PIP)》2005,7(1):4-34
During the second half of the seventeenth century, the outstanding problem in astronomy was to understand the physical basis for Keplers laws describing the observed orbital motion of a planet around the Sun. In the middle 1660s,Robert Hooke (1635–1703) proposed that a planets motion is determined by compounding its tangential velocity with the change in radial velocity impressed by the gravitational attraction of the Sun, and he described his physical concept to Isaac Newton (1642–1726) in correspondence in 1679. Newton denied having heard of Hookes novel concept of orbital motion, but shortly after their correspondence he implemented it by a geometric construction from which he deduced the physical origin of Keplers area law,which later became Proposition I, Book I, of his Principia in 1687.Three years earlier, Newton had deposited a preliminary draft of it, his De Motu Corporum in Gyrum (On the Motion of Bodies), at the Royal Society of London, which Hooke apparently was able to examine a few months later, because shortly there-after he applied Newtons construction in a novel way to obtain the path of a body under the action of an attractive central force that varies linearly with the distance from its center of motion (Hookes law). I show that Hookes construction corresponds to Newtons for his proof of Keplers area law in his De Motu. Hookes understanding of planetary motion was based on his observations with mechanical analogs. I repeated two of his experiments and demonstrated the accuracy of his observations.My results thus cast new light on the significance of Hookes contributions to the development of orbital dynamics, which in the past have either been neglected or misunderstood.Michael Nauenberg is Professor Emeritus of Physics at the University of California, Santa Cruz. His primary research has been in theoretical physics, but he also has written several articles and coedited a book on the historical development of dynamics by Huygens, Newton, and Hooke. 相似文献
139.
We first derive the relation between the eikonal approximation to the Maxwell wave equations in an inhomogeneous anisotropic medium and geodesic motion in a three dimensional Riemannian manifold using a method which identifies the symplectic structure of the corresponding mechanics. We then apply an analogous method to the five dimensional generalization of Maxwell theory required by the gauge invariance of Stueckelbergs covariant classical and quantum dynamics to demonstrate, in the eikonal approximation, the existence of geodesic motion for the flow of mass in a four dimensional pseudo-Riemannian manifold. No motion of the medium is required. These results provide a foundation for the geometrical optics of the five dimensional radiation theory and establish a model in which there is mass flow along geodesics. Finally, we discuss the interesting case of relativistic quantum theory in an anisotropic medium as well. In this case the eikonal approximation to the relativistic quantum mechanical current coincides with the geodesic flow governed by the pseudo-Riemannian metric obtained from the eikonal approximation to solutions of the Stueckelberg-Schrödinger equation. This construction provides a model for an underlying quantum mechanical structure for classical dynamical motion along geodesics on a pseudo-Riemannian manifold. The locally symplectic structure which emerges is that of Stueckelbergs covariant mechanics on this manifold.This revised version was published online in April 2005. The publishing date was inserted. 相似文献
140.
Pilot-Wave Theory and Financial Option Pricing 总被引:1,自引:0,他引:1
This paper tries to argue why pilot-wave theory could be of use in financial economics. We introduce the notion of information
wave. We consider a stochastic guidance equation and part of the drift term of that equation makes reference to the phase
of the wave. In order to embed information in financial option pricing we could use such a drift. We also briefly argue how
we could embed information in the pricing kernel of the option price.
PACS: 03, 89.65.Gh. 相似文献