全文获取类型
收费全文 | 236617篇 |
免费 | 2299篇 |
国内免费 | 605篇 |
专业分类
化学 | 123126篇 |
晶体学 | 4074篇 |
力学 | 10118篇 |
综合类 | 4篇 |
数学 | 26840篇 |
物理学 | 75359篇 |
出版年
2021年 | 1957篇 |
2020年 | 2215篇 |
2019年 | 2511篇 |
2018年 | 3351篇 |
2017年 | 3511篇 |
2016年 | 5021篇 |
2015年 | 2750篇 |
2014年 | 4572篇 |
2013年 | 10444篇 |
2012年 | 8166篇 |
2011年 | 9578篇 |
2010年 | 7210篇 |
2009年 | 7240篇 |
2008年 | 9044篇 |
2007年 | 8814篇 |
2006年 | 8418篇 |
2005年 | 7481篇 |
2004年 | 6964篇 |
2003年 | 6315篇 |
2002年 | 6228篇 |
2001年 | 7074篇 |
2000年 | 5259篇 |
1999年 | 4033篇 |
1998年 | 3468篇 |
1997年 | 3285篇 |
1996年 | 3005篇 |
1995年 | 2822篇 |
1994年 | 2786篇 |
1993年 | 2700篇 |
1992年 | 3048篇 |
1991年 | 3036篇 |
1990年 | 2933篇 |
1989年 | 2872篇 |
1988年 | 2801篇 |
1987年 | 2763篇 |
1986年 | 2614篇 |
1985年 | 3370篇 |
1984年 | 3502篇 |
1983年 | 3076篇 |
1982年 | 3194篇 |
1981年 | 2922篇 |
1980年 | 2885篇 |
1979年 | 3055篇 |
1978年 | 3204篇 |
1977年 | 3165篇 |
1976年 | 3130篇 |
1975年 | 3028篇 |
1974年 | 2993篇 |
1973年 | 3139篇 |
1972年 | 2126篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
A model proposed in the literature for fish schools of relatively large size is studied for mathematical and qualitative properties. Existence, uniqueness and positivity of solutions are established and bifurcation properties relative to diffusion and alignment parameters are studied. 相似文献
942.
B. Sun Yu. A. Litvinov P. M. Walker K. Beckert P. Beller F. Bosch D. Boutin C. Brandau L. Chen C. Dimopoulou H. Geissel R. Knöbel C. Kozhuharov J. Kurcewicz S. A. Litvinov M. Mazzocco J. Meng C. Nociforo F. Nolden W. R. Plass C. Scheidenberger M. Steck H. Weick M. Winkler 《The European Physical Journal A - Hadrons and Nuclei》2007,31(3):393-394
A new long-lived isomeric state in the near proton dripline nucleus 125Ce has been identified with Schottky mass spectrometry at GSI. The excitation energy E
* = 103(12)keV and the decay time of 193(1)s have been obtained from a single stored fully ionized 125m
Ce58+ ion. The data implies an E3 transition and a 1/2+ assignment for the spin of the isomer. 相似文献
943.
Charge density fluctuation of low frequency in a dusty plasma 总被引:2,自引:0,他引:2
The charge density fluctuation of low frequency in a dusty plasma, which is derived from the longitudinal dielectric permittivity
of the dusty plasma, has been studied by kinetic theory. The results show that theP value, which describes the relative charge density on the dust in the plasma, and the charging frequency of a dust particle
Ω
c
, which describes the ratio of charge changing of the dust particles, determine the character of the charge density fluctuation
of low frequency. For a dusty plasma ofP≪1, when the charging frequency Ω
c
, is much smaller than the dusty plasma frequency ωd, there is a strong charge density fluctuation which is of character of dust acoustic eigenwave. For a dusty plasma ofP≫1, when the frequency Ω
c
, is much larger than ω
d
there are weaker fluctuations with a wide spectrum. The results have been applied to the ionosphere and the range of radius
and density of dust particles is found, where a strong charge density fluctuation of low frequency should exist. 相似文献
944.
In this paper we establish a sharp result concerning integral mean estimates for self-reciprocal polynomials. 相似文献
945.
946.
Results are presented of an experimental investigation of vortex ring formation by a fluid drop contacting a free surface
with negligible velocity. The pool fluid is mixed with fluorescein dye, and a laser sheet is used to illuminate a plane of
the flow. A series of representative images is recorded by a CCD camera and speculation is made regarding specific sources
of vorticity flux through the free surface. Two scaling analyses previously presented by other investigators are demonstrated
to be equivalent under the assumptions of this experiment, and they provide the motivation for a series of test runs in which
the duration of the coalescence process, τ*, is related to variations in drop diameter L and fluid surface tension σ. Experimental results are in agreement with the analyses, showing τ*∼σ-1/2 and τ*∼L
3/2.
Received: 22 December 1995 / Accepted: 15 October 1996 相似文献
947.
The paper presents an exact analysis of the dispersion of an immiscible solute in a non-Newtonian fluid (known as an incompressible second-order fluid which shows viscoelastic behaviour) flowing slowly in a parallel plate channel in the presence of a periodic pressure gradient. Using a generalized dispersion model which is valid for all times after the solute injection, the diffusion coefficients K i (τ)(i=1,2,3,…) are obtained as functions of time τ in the case when the initial solute distribution is in the form of a slug of finite extent. The analysis leads to the novel result that K 2(τ) (which is a measure of the longitudinal dispersion coefficient of the solute) has a steady part S in addition to a fluctuating part D 2(τ) due to the pulsatility of the flow. It is found that S decreases with increase in the viscoelastic parameter M for given values of the amplitude λ and frequency ω of the pressure pulsation. On the other hand, it is found that at a fixed instant τ, the amplitude of D 2(τ) increases with increase in M for given values of λ and ω. Further it is shown that at a given instant τ, the amplitude of D 2(τ) decreases with increase in ω for given λ and M and the profile for D 2(τ) becomes progressively flatter with increase in ω. Finally the axial distribution of the average concentration θ m of the solute over the channel cross-section is determined at different instants after the solute injection for several values of M, λ and ω. The present study is likely to have important bearing on the problem of dispersion of tracers in blood flow through arteries. 相似文献
948.
949.
We study the evolution of radiating and viscous fluid spheres assuming an additional homothetic symmetry on the spherically symmetric space-time. We match a very simple solution to the symmetry equations with the exterior one (Vaidya). We then obtain a system of two ordinary differential equations which rule the dynamics, and find a self-similar collapse which is shear-free and with a barotropic equation of state. Considering a huge set of initial self-similar dynamics states, we work out a model with an acceptable physical behavior. 相似文献
950.
In the case of number fields the embedding problem of a p-extension with non-Abelian kernel of order p4 is studied. The two kernels of order 34 with generators α, γ and relations α9 = 1, [α,α]3=1,[α,αγγ]==1,[αγγ]=α3,γ3=1 or γ3=α3 and the kernel of order 24 with generators α, β, γ and relations α4=1 β2,[αγ]=1, [α,γ]=1,[βγ]=α2 are considered. For kernels of odd order the embedding problem is always solvable. For the kernel of order 16 the solvability
conditions are reduced to those for the associated problems at the Archimedean points, and to the compatibility condition.
Bibliography: 9 titles.
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 227, 1995, pp. 74–82. 相似文献