全文获取类型
收费全文 | 411202篇 |
免费 | 5357篇 |
国内免费 | 1328篇 |
专业分类
化学 | 219900篇 |
晶体学 | 6271篇 |
力学 | 16793篇 |
综合类 | 5篇 |
数学 | 50095篇 |
物理学 | 124823篇 |
出版年
2020年 | 3363篇 |
2019年 | 3599篇 |
2018年 | 4483篇 |
2017年 | 4455篇 |
2016年 | 7323篇 |
2015年 | 4847篇 |
2014年 | 7212篇 |
2013年 | 19188篇 |
2012年 | 14010篇 |
2011年 | 17160篇 |
2010年 | 11523篇 |
2009年 | 11354篇 |
2008年 | 15745篇 |
2007年 | 15665篇 |
2006年 | 14590篇 |
2005年 | 13366篇 |
2004年 | 12060篇 |
2003年 | 10664篇 |
2002年 | 10460篇 |
2001年 | 11737篇 |
2000年 | 8886篇 |
1999年 | 6947篇 |
1998年 | 5853篇 |
1997年 | 5744篇 |
1996年 | 5558篇 |
1995年 | 5185篇 |
1994年 | 5032篇 |
1993年 | 5151篇 |
1992年 | 5567篇 |
1991年 | 5427篇 |
1990年 | 5188篇 |
1989年 | 5085篇 |
1988年 | 5157篇 |
1987年 | 4984篇 |
1986年 | 4775篇 |
1985年 | 6493篇 |
1984年 | 6656篇 |
1983年 | 5629篇 |
1982年 | 6040篇 |
1981年 | 5796篇 |
1980年 | 5666篇 |
1979年 | 5803篇 |
1978年 | 6070篇 |
1977年 | 5872篇 |
1976年 | 6043篇 |
1975年 | 5534篇 |
1974年 | 5673篇 |
1973年 | 6127篇 |
1972年 | 3846篇 |
1971年 | 3071篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The diffusion of carbon atoms between the volume and the surface of (100) molybdenum is directly studied at temperatures between 1400 and 2000 K (i.e., at process temperatures) for the first time. The balance of carbon atoms in the system is determined. The difference in the activation energies of carbon dissolution and precipitation, ΔE=E s 1-E1s, is found for the case when the diffusion fluxes of dissolved and precipitated carbon atoms are in equilibrium. This difference defines the enrichment of the surface by carbon relative to the bulk. The experimentally found activation energy of carbon dissolution is Es1=3.9 eV. The activation energy of carbon precipitation is estimated at E 1 s=1.9 eV. The latter value is close to the energy of bulk diffusion of carbon in molybdenum. 相似文献
992.
We study the propagation of the light mesons σ,ω,ρ, and a0(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible
to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric
nuclear matter with fixed isospin asymmetry, and then we pay particular attention to hypermatter in β-equilibrium. The equation
of state and the potential contribution to the symmetry coefficient arising from the mean-field approximation are investigated.
Received: 16 October 2001 / Accepted: 10 January 2002 相似文献
993.
R. Adhikari A. Sil A. Raychaudhuri 《The European Physical Journal C - Particles and Fields》2002,25(1):125-130
We present a solution of the solar neutrino deficit using three flavors of neutrinos and R-parity non-conserving supersymmetry. In this model, in vacuum, the is massless and unmixed, mass and mixing being restricted to the - sector only, which we choose in consistency with the requirements of the atmospheric neutrino anomaly. The flavor changing
and flavor diagonal neutral currents present in the model and the three-flavor picture together produce an energy dependent
resonance-induced - mixing in the sun. This mixing plays a key role in the new solution to the solar neutrino problem. The best fit to the solar
neutrino rates and spectrum (1258-day SK and 241-day SNO data) requires a mass square difference of eV2 in vacuum between the two lightest neutrinos. This solution cannot accommodate a significant day-night effect for solar neutrinos
nor CP violation in terrestrial neutrino experiments.
Received: 26 December 2001 / Revised version: 16 February 2002 / Published online: 26 July 2002 相似文献
994.
995.
In this paper, we review and unify some classes of generalized convex functions introduced by different authors to prove minimax results in infinite-dimensional spaces and show the relations between these classes. We list also for the most general class already introduced by Jeyakumar (Ref. 1) an elementary proof of a minimax result. The proof of this result uses only a finite-dimensional separa- tion theorem; although this minimax result was already presented by Neumann (Ref. 2) and independently by Jeyakumar (Ref. 1), we believe that the present proof is shorter and more transparent. 相似文献
996.
The object of the present investigation is to introduce a new trigonometric method of summation which is both regular and
Fourier effective and determine its status with reference to other methods of summation (see §2-§4) and also give an application
of this method to determine the degree of approximation in a new Banach space of functions conceived as a generalized Holder
metric (see §5). 相似文献
997.
By an elementary calculation we obtain the exact mean values of Minkowksi functionals for a standard model of percolating sets. In particular, a recurrence theorem for the mean Euler characteristic recently put forward is shown to be incorrect. Related previous mathematical work is mentioned. We also conjecture bounds for the threshold density of continuum percolation, which are associated with the Euler characteristic. 相似文献
998.
Rafael R. del Río Castillo 《Communications in Mathematical Physics》1991,142(2):421-431
In this work we study the behavior of embedded eigenvalues of Sturm-Liouville problems in the half axis under local perturbations. When the derivative of the spectral function is strictly positive, we prove that the embedded eigenvalues either disappear or remain fixed. In this case we show that local perturbations cannot add eigenvalues in the continuous spectrum. If the condition on the spectral function is removed then a local perturbation can add infinitely many eigenvalues. 相似文献
999.
The stationary and the time-dependent homogeneous ordered states in convection may both become unstable against localized perturbations. Defects are then created and they may contribute to the disorganization of the homogeneous state. We present an experimental study of defects in some homogeneous stationary structures as well as in the traveling-wave states of convection of a nematic liquid crystal. We show that the core of the defects is a germ of the unstable state and it can become unstable under the external stress. Then, either fully homogeneous states with the symmetry of the core, or complex disordered states can develop from the local instability of defects in processes quite similar to displacive transitions in solids. Some of the main features are qualitatively similar to numerical simulations of an appropriate Landau-Ginzburg equation. 相似文献
1000.
R. Németh 《Journal of statistical physics》1991,63(1-2):419-424
We calculate the site occupation probabilities of one-dimensional lattice gas models within the canonical and grand canonical ensembles. The appearing differences do not vanish if we increase the system size keeping the site energies discrete. In this way one can explain the surprising numerical results of Barszczak and Kutner. This effect in the single-site occupation number disappears in higher dimensions. 相似文献