全文获取类型
收费全文 | 5489篇 |
免费 | 158篇 |
国内免费 | 26篇 |
专业分类
化学 | 3692篇 |
晶体学 | 33篇 |
力学 | 204篇 |
数学 | 877篇 |
物理学 | 867篇 |
出版年
2023年 | 32篇 |
2022年 | 72篇 |
2021年 | 84篇 |
2020年 | 98篇 |
2019年 | 114篇 |
2018年 | 82篇 |
2017年 | 73篇 |
2016年 | 167篇 |
2015年 | 117篇 |
2014年 | 153篇 |
2013年 | 321篇 |
2012年 | 312篇 |
2011年 | 350篇 |
2010年 | 227篇 |
2009年 | 201篇 |
2008年 | 336篇 |
2007年 | 301篇 |
2006年 | 281篇 |
2005年 | 301篇 |
2004年 | 272篇 |
2003年 | 207篇 |
2002年 | 235篇 |
2001年 | 84篇 |
2000年 | 76篇 |
1999年 | 66篇 |
1998年 | 74篇 |
1997年 | 72篇 |
1996年 | 51篇 |
1995年 | 37篇 |
1994年 | 47篇 |
1993年 | 47篇 |
1992年 | 33篇 |
1991年 | 41篇 |
1990年 | 23篇 |
1989年 | 38篇 |
1988年 | 21篇 |
1986年 | 26篇 |
1985年 | 43篇 |
1984年 | 49篇 |
1983年 | 28篇 |
1982年 | 44篇 |
1981年 | 46篇 |
1980年 | 53篇 |
1979年 | 42篇 |
1978年 | 42篇 |
1977年 | 45篇 |
1976年 | 45篇 |
1975年 | 38篇 |
1974年 | 34篇 |
1973年 | 20篇 |
排序方式: 共有5673条查询结果,搜索用时 15 毫秒
101.
This paper reports on the influence of the sintering temperature and atmosphere and transition-metal doping on the magnetic properties of nanocrystalline and bulk In2O3. Undoped nanocrystalline In2O3 is diamagnetic whatever the sintering temperature and atmosphere. All single-phase transition-metal-doped In2O3 samples are paramagnetic, with a paramagnetic effective moment originating from weakly interacting transition metal ions. No trace of ferromagnetism has been detected even with samples sintered under argon, except extrinsic ferromagnetism for samples with magnetic dopant concentrations exceeding the solubility limit. 相似文献
102.
Saro Memarzadeh Erik D. Tolmachoff Denis J. Phares Hai Wang 《Proceedings of the Combustion Institute》2011,33(2):1917-1924
The properties of TiO2 nanoparticles synthesized using the flame stabilized on a rotating surface method (FSRS) are investigated. The method uses a laminar, premixed, stagnation flame, combining particle synthesis and film deposition in a single step. The current study examines the effects of flame properties on particle characteristics. Synthesized particles were characterized using X-ray diffractometry, Transmission Electron Microscopy and UV–vis spectrometry in order to quantify the effects of equivalence ratio and precursor loading on particle size, crystallinity and optical band-gap. Results show that flame stoichiometry significantly affects crystal phase, but it has little to no effect on particle size and light absorption band edge. In addition, precursor loading impacts both the particle size and the crystal phase. The study demonstrates the potential of the FSRS method for producing tailored nanoscale TiO2 particles for a variety of applications. 相似文献
103.
Yeny A. Tobon Denis Bormann Aurlien Canizares Nicole Raimboux Patrick Simon 《Journal of Raman spectroscopy : JRS》2011,42(5):1109-1113
A time‐resolved intensified charge coupled device‐based Raman microspectrometer system dedicated to the study of solid samples is described, offering good optical, temporal and spatial resolution. The advantages of this approach are demonstrated on Al2O3:Cr3+, obtaining for the first time the temporal evolution of the excited state transition Ē → 2Ā. Moreover, the time dependence of the luminescence due to the chromium ion was also determined by the same Raman device. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
104.
We consider a quantum system in contact with a heat bath consisting in an infinite chain of identical sub-systems at thermal
equilibrium at inverse temperature β. The time evolution is discrete and such that over each time step of duration τ, the
reference system is coupled to one new element of the chain only, by means of an interaction of strength λ. We consider three
asymptotic regimes of the parameters λ and τ for which the effective evolution of observables on the small system becomes
continuous over suitable macroscopic time scales T and whose generator can be computed: the weak coupling limit regime λ → 0, τ = 1, the regime τ → 0, λ2τ → 0 and the critical case λ2τ = 1, τ → 0. The first two regimes are perturbative in nature and the effective generators they determine is such that a
non-trivial invariant sub-algebra of observables naturally emerges. The third asymptotic regime goes beyond the perturbative
regime and provides an effective dynamics governed by a general Lindblad generator naturally constructed from the interaction
Hamiltonian. Conversely, this result shows that one can attach to any Lindblad generator a repeated quantum interactions model
whose asymptotic effective evolution is generated by this Lindblad operator. 相似文献
105.
We consider the question of the existence of stationary solutions for the Navier Stokes equations describing the flow of a
incompressible fluid past a semi-infinite flat plate at zero incidence angle. By using ideas from the theory of dynamical
systems we analyze the vorticity equation for this problem and show that a symmetry-breaking term fits naturally into the
downstream asymptotic expansion of a solution. Finally, in order to check that our asymptotic expressions can be completed
to a symmetry-breaking solution of the Navier–Stokes equations we solve the problem numerically by using our asymptotic results
to prescribe artificial boundary conditions for a sequence of truncated domains. The results of these numerical computations
a clearly compatible with the existence of such a solution.
Mathematics Subject Classification (2000). 76D05, 76D25, 76M10, 41A60, 35Q35
Supported in part by the Fonds National Suisse. 相似文献
106.
Diffraction grating interferometers for mechanical characterisations of advanced fabric laminates 总被引:1,自引:0,他引:1
It is demonstrated that two grating interferometers with high spatial resolutions can successfully be applied for the mechanical characterisation of the advanced fabric composite materials. Based on these two techniques, the mechanical properties of two kinds of fabric laminates are obtained without assumption of uniform strain fields to be used in the characterisation approaches using the local strain sensors. The degree of the yarn crimp effects of the two laminates is compared in terms of the out-of-plane displacement derivatives. Especially, it is shown that the grating shearing interferometer is appropriate for the crimped fabric structure requiring a three-dimensional analysis. The modification from moiré interferometer to grating shearing interferometer is performed by introducing a Michelson interferometer modified for image shearing. 相似文献
107.
Si?Amar?DahoumaneEmail author Claude?Yéprémian Chakib?Djédiat Alain?Couté Fernand?Fiévet Thibaud?Coradin Roberta?Brayner 《Journal of nanoparticle research》2016,18(3):79
Recent years have witnessed a boom in the biosynthesis of a large variety of nanomaterials using different biological resources among which algae-based entities have been gaining much more attention within the community of material scientists worldwide. In our previously published findings, we explored some factors that governed the biofabrication of gold nanoparticles using living cultures of microalgae, such as the utilized microalgal genera, the phylum they belong to, and the impact of tetrachloroauric acid concentrations on the ability of these strains to perform the biosynthesis of gold nanoparticles once in contact with these cations. As a follow-up, we present in this paper an improvement of the features of bioproduced gold colloids using living cells of Euglena gracilis microalga when this species is grown under either mixotrophic or autotrophic conditions, i.e., exposed to light and grown in an organic carbon-enriched culture medium versus under autotrophic conditions. As an outcome to this alteration, the growth rate of this photosynthetic microorganism is multiplied 7–8 times when grown under mixotrophic conditions compared to autotrophic ones. Therefore, the yield, the kinetics, and the colloidal stability of the biosynthesized gold nanoparticles are dramatically enhanced. Moreover, the shape and the size of the as-produced nano-objects via this biological method are affected. In addition to round-shaped gold nanoparticles, particular shapes, such as triangles and hexagons, appear. These findings add up to the amassed knowledge toward the design of photobioreactors for the scalable and sustainable production of interesting nanomaterials. 相似文献
108.
109.
Christian Gruber Nicolas Macris Alain Messager Daniel Ueltschi 《Journal of statistical physics》1997,86(1-2):57-108
The Falicov-Kimball model is a lattice model of itinerant spinless fermions (electrons) interacting by an on-site potential with classical particles (ions). We continue the investigations of the crystalline ground states that appear for various filling of electrons and ions for large coupling. We investigate the model for square as well as triangular lattices. New ground states are found and the effects of a magnetic flux on the structure of the phase diagram are studied. The flux phase problem where one has to find the optimal flux configurations and the nuclei configurations is also solved in some cases. Finally we consider a model where the fermions are replaced by hard-core bosons. This model also has crystalline ground states. Therefore their existence does not require the Pauli principle, but only the on-site hard-core constraint for the itinerant particles. 相似文献
110.
Zs. Podolyák G.F. Farrelly P.H. Regan A.B. Garnsworthy S.J. Steer M. Górska J. Benlliure E. Casarejos S. Pietri J. Gerl H.J. Wollersheim R. Kumar F. Molina A. Algora N. Alkhomashi G. Benzoni A. Blazhev P. Boutachkov A.M. Bruce L. Caceres I.J. Cullen A.M. Denis Bacelar P. Doornenbal M.E. Estevez Y. Fujita W. Gelletly H. Geissel H. Grawe J. Gr?bosz R. Hoischen I. Kojouharov S. Lalkovski Z. Liu K.H. Maier C. Mihai D. Mücher B. Rubio H. Schaffner A. Tamii S. Tashenov J.J. Valiente-Dobón P.M. Walker P.J. Woods 《Physics letters. [Part B]》2009