全文获取类型
收费全文 | 88243篇 |
免费 | 3149篇 |
国内免费 | 1040篇 |
专业分类
化学 | 46594篇 |
晶体学 | 659篇 |
力学 | 3049篇 |
综合类 | 65篇 |
数学 | 19777篇 |
物理学 | 22288篇 |
出版年
2023年 | 526篇 |
2022年 | 551篇 |
2021年 | 807篇 |
2020年 | 1134篇 |
2019年 | 988篇 |
2018年 | 2397篇 |
2017年 | 2544篇 |
2016年 | 2882篇 |
2015年 | 2467篇 |
2014年 | 2440篇 |
2013年 | 4789篇 |
2012年 | 6671篇 |
2011年 | 5869篇 |
2010年 | 4209篇 |
2009年 | 3653篇 |
2008年 | 3738篇 |
2007年 | 3403篇 |
2006年 | 3180篇 |
2005年 | 6713篇 |
2004年 | 5893篇 |
2003年 | 3978篇 |
2002年 | 2084篇 |
2001年 | 1511篇 |
2000年 | 1324篇 |
1999年 | 1103篇 |
1998年 | 874篇 |
1997年 | 728篇 |
1996年 | 858篇 |
1995年 | 654篇 |
1994年 | 702篇 |
1993年 | 629篇 |
1992年 | 778篇 |
1991年 | 686篇 |
1990年 | 704篇 |
1989年 | 575篇 |
1988年 | 574篇 |
1987年 | 479篇 |
1986年 | 462篇 |
1985年 | 560篇 |
1984年 | 515篇 |
1983年 | 433篇 |
1982年 | 418篇 |
1981年 | 438篇 |
1980年 | 364篇 |
1979年 | 377篇 |
1978年 | 358篇 |
1977年 | 345篇 |
1976年 | 422篇 |
1974年 | 358篇 |
1973年 | 364篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
72.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献
73.
Addition of aqueous hydrogen peroxide significantly accelerates the substitution reactions of hydroxide salts with haloarenes bearing electron withdrawing substituents. A similar effect is observed in the reactions of hydroxide salts with halogenated heteroarenes. Reactions are carried out in water or water-THF at ambient temperature or at 50-60 °C. 相似文献
74.
J. Kudrna I. Pelant J. Štěpánek F. Trojánek P. Malý 《Applied Physics A: Materials Science & Processing》2002,74(2):253-256
We have studied ultra-fast carrier dynamics of photo-excited carriers in hydrogenated microcrystalline silicon prepared by
a very high frequency glow-discharge technique. We report on direct observation of two types of dynamics using selective photo-excitation
in picosecond pump and probe measurements. One type of the observed dynamics has been found to be independent of the sample
preparation, while the other reflects the relative weights of crystalline and amorphous fractions. We propose a simple rate-equation
model that describes the carrier dynamics in microcrystalline silicon in terms of the composition of those in Si microcrystallites
and in the a-Si:H tissue which surrounds the microcrystallites. The model without any fitting parameters reproduces the experimental
data very well when the dynamics are scaled with relative volume fractions as obtained from Raman spectra.
Received: 23 November 2000 / Accepted: 17 March 2001 / Published online: 23 May 2001 相似文献
75.
T. Temesvári C. De Dominicis I.R. Pimentel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):361-372
Symmetry considerations and a direct, Hubbard-Stratonovich type, derivation are used to construct a replica field-theory relevant
to the study of the spin glass transition of short range models in a magnetic field. A mean-field treatment reveals that two
different types of transitions exist, whenever the replica number n is kept larger than zero. The Sherrington-Kirkpatrick critical point in zero magnetic field between the paramagnet and replica
magnet (a replica symmetric phase with a nonzero spin glass order parameter) separates from the de Almeida-Thouless line,
along which replica symmetry breaking occurs. We argue that for studying the de Almeida-Thouless transition around the upper
critical dimension d = 6, it is necessary to use the generic cubic model with all the three bare masses and eight cubic couplings. The critical
role n may play is also emphasized. To make perturbative calculations feasible, a new representation of the cubic interaction is
introduced. To illustrate the method, we compute the masses in one-loop order. Some technical details and a list of vertex
rules are presented to help future renormalisation-group calculations.
Received 9 October 2001 相似文献
76.
We describe a new algorithm which uses the trajectories of a discrete dynamical system to sample the domain of an unconstrained objective function in search of global minima. The algorithm is unusually adept at avoiding nonoptimal local minima and successfully converging to a global minimum. Trajectories generated by the algorithm for objective functions with many local minima exhibit chaotic behavior, in the sense that they are extremely sensitive to changes in initial conditions and system parameters. In this context, chaos seems to have a beneficial effect: failure to converge to a global minimum from a given initial point can often be rectified by making arbitrarily small changes in the system parameters. 相似文献
77.
Chunguang Du Hongyi Chen Shiqun Li 《量子光学学报》2006,12(B08):70-71
Recently, research on left-handed materials (LHMs) has attracted considerable attentions. The LHMs are a kind of metameterial which have negative permittivity and negative permeability, which lead to negative refractive index in a frequency range. The LHMs that have been available so far are in the microwave range and are usually composed of classical particles, such as split-ring resonators. Some quantum phenomena such as spontaneous emission of atoms in the LHMs which are considered to be 'classical background' have also been investigated. Many potential applications of LHMs have been proposed, such as superlenses which, in principle, can achieve arbitrary subwavelength resolution. 相似文献
78.
Lubomír Kubáček 《Applications of Mathematics》2006,51(6):565-582
Some remarks to problems of point and interval estimation, testing and problems of outliers are presented in the case of multivariate
regression model.
This work was supported by the Council of Czech Government J14/98:153100011. 相似文献
79.
带干扰的多险种风险模型 总被引:2,自引:0,他引:2
由于保险公司风险经营规模不断扩大,用单一险种的模型来描述风险过程存在局限性,本文讨论了带干扰多险种风险模型,应用鞅论方法,得出伦德伯格不等式和最终破产概率公式。 相似文献
80.
Dušan Hemzal 《Czechoslovak Journal of Physics》2006,56(12):1467-1479
In this article, general idea of focusing is studied within the framework of optics extension into general relativity (covariant optics). In a configuration of static spacetime, the general, mathematically rigorous treatment of rays, wavefronts and caustics
of spherical symmetry is presented, particularly with regard to problems of obtaining them within general relativity. An original
result is the aberration formulation to covariant optics, whose application is given in this paper; a particular solution
of Einstein equations is finally chosen to provide concrete, exact results of cluster focal length and its aberration structure.
In this way, a gravitational lensing situation is shown to be a true lens. 相似文献