全文获取类型
收费全文 | 353844篇 |
免费 | 5981篇 |
国内免费 | 1136篇 |
专业分类
化学 | 196461篇 |
晶体学 | 3833篇 |
力学 | 14308篇 |
综合类 | 7篇 |
数学 | 43847篇 |
物理学 | 102505篇 |
出版年
2021年 | 2180篇 |
2020年 | 2599篇 |
2019年 | 2569篇 |
2018年 | 2907篇 |
2017年 | 2669篇 |
2016年 | 5269篇 |
2015年 | 4518篇 |
2014年 | 5713篇 |
2013年 | 16601篇 |
2012年 | 13717篇 |
2011年 | 16487篇 |
2010年 | 10223篇 |
2009年 | 9809篇 |
2008年 | 14968篇 |
2007年 | 15138篇 |
2006年 | 14500篇 |
2005年 | 13399篇 |
2004年 | 11931篇 |
2003年 | 10346篇 |
2002年 | 9989篇 |
2001年 | 10731篇 |
2000年 | 8304篇 |
1999年 | 6536篇 |
1998年 | 5238篇 |
1997年 | 4941篇 |
1996年 | 4713篇 |
1995年 | 4494篇 |
1994年 | 4314篇 |
1993年 | 4163篇 |
1992年 | 4657篇 |
1991年 | 4465篇 |
1990年 | 4152篇 |
1989年 | 3998篇 |
1988年 | 4237篇 |
1987年 | 3901篇 |
1986年 | 3768篇 |
1985年 | 5543篇 |
1984年 | 5616篇 |
1983年 | 4503篇 |
1982年 | 4937篇 |
1981年 | 4991篇 |
1980年 | 4694篇 |
1979年 | 4827篇 |
1978年 | 4840篇 |
1977年 | 4764篇 |
1976年 | 4789篇 |
1975年 | 4648篇 |
1974年 | 4529篇 |
1973年 | 4679篇 |
1972年 | 2628篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
Phononic band gaps and vibrations in one- and two-dimensional mass-spring structures 总被引:1,自引:0,他引:1
J.S. Jensen 《Journal of sound and vibration》2003,266(5):1053-1078
The vibrational response of finite periodic lattice structures subjected to periodic loading is investigated. Special attention is devoted to the response in frequency ranges with gaps in the band structure for the corresponding infinite periodic lattice. The effects of boundaries, viscous damping, and imperfections are studied by analyzing two examples; a 1-D filter and a 2-D wave guide. In 1-D the structural response in the band gap is shown to be insensitive to damping and small imperfections. In 2-D the similar effect of damping is noted for one type of periodic structure, whereas for another type the band gap effect is nearly eliminated by damping. In both 1-D and 2-D it is demonstrated how the free structural boundaries affect the response in the band gap due to local resonances. Finally, 2-D wave guides are considered by replacing the periodic structure with a homogeneous structure in a straight and a 90° bent path, and it is shown how the vibrational response is confined to the paths in the band gap frequency ranges. 相似文献
992.
The Hawking radiation of Dirac particles on the event horizon of a nonuniformly rectilinearly accelerating black hole is studied in this paper. First, we construct the symmetrized null tetrad from which the spin coefficients and Dirac equation are derived. Next, by proposing generalized tortoise coordinate transformation, the decoupling problem of the Dirac equation with nonzero rest mass is solved. Finally, by analytic continuation, the Hawking thermal spectrum formula of Dirac particle for nonuniformly rectilinearly accelerating black hole is obtained. 相似文献
993.
The effect of dynamical exchange interactions on the dielectric function of a two-dimensional electron gas is studied using a variational approach. Exchange effects are introduced via the local-field correction. The variationally obtained local-field factor is compared to the earlier perturbative result to first order in the electron-electron interaction. 相似文献
994.
L. G. Lumbreras R. Gebhard W. Häusler F. Kauffmann-Doig J. Riederer G. Sieben U. Wagner 《Hyperfine Interactions》2003,150(1-4):51-72
Ceramic finds from the Galería de las Ofrendas at Chavín de Huántar and surface finds from the settlement of Chavín were characterised by combining the results of archaeological typology with archaeometric studies using neutron activation analysis, Mössbauer spectroscopy, X-ray diffraction and thin-section microscopy. Sherds from the pyramid Tello are included in the study as representative of local material. The analyses show that the vessels were made from different raw materials and that different firing procedures were used in their production. Sherds of certain styles largely exhibit similar types of Mössbauer patterns and in many instances also have similar element compositions. This supports the archaeological notion that the vessels were brought to Chavín from the provinces, perhaps on the occasion of a festivity. 相似文献
995.
Siegfried Grossmann Denis Jérome Antonio Paoletti 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):447
We mourn the death of Professor Dr. Gilbert Grynberg, April 17, 1948 - January 27, 2003. We have lost an excellent and highly esteemed scientist, an outstanding character and a good friend. He has been a very active colleague in the merger of Zeitschrift für Physik and Journal de Physique in the early days. As one of the Co-Editors-in-Chief of The European Physical Journal D, from its start, he has formed the scienti.c standards of EPJ. Untiringly he has served our Journal with greatest dedication. We are grateful that he has been with us. The editorial board and o.ce of EPJ B Siegfried Grossmann, Denis Jérome, Antonio Paoletti 相似文献
996.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献
997.
The kinetics of oxygen exchange are of primary importance for the application of titanates as fast resistive oxygen sensors.
The sensor’s conductivity is correlated with the oxygen partial pressure pO2 of the surrounding atmosphere: Due to oxygen surface transfer and subsequent diffusion of oxygen vacancies V
O
··
, a pO2 change gives rise to a conductivity change of the sample. While bulk diffusion usually occurs very fast, the surface transfer
reaction becomes the rate determining step for thin samples and for low temperatures. We have shown that in the case of acceptor
doped SrTiO3 the kinetics of the surface transfer reaction can be strongly influenced through stoichiometric changes brought about by
thin coatings of alkaline earth metal oxides (e.g. SrO). In contrast to the commonly used jump method (conductivity response
to a sudden pO2 change in the time domain), a model is presented which is based on the frequency-domain analysis of amplitude and phase shift
of the response signal obtained from a pO2 modulation in a fast kinetic measurement set-up. This method allows not only for measuring response times in the sub-millisecond
range but also for distinguishing between behaviour either controlled by volume diffusion or by surface transfer reaction.
Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002. 相似文献
998.
999.
C.H Chung S.D KimH.J Kim F.O AdurodijaK.H Yoon J Song 《Solid State Communications》2003,126(4):185-190
The dependence of structural properties and surface morphology of Cu-In alloy layers on the composition and sputtering deposition sequence were investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The properties of the co-sputtered alloy layers changed abruptly around the composition boundary when the Cu/In ratio reached 1/2. This can be explained by the effective heat of formation (EHF) model, which has been used to predict the sequence of phase formation for metal diffusion couples. The use of a co-sputtered alloy layer with a high In concentration was not suitable for fabricating solar cells, because the film had a very rough morphology due to large In islands formed on the CuIn2 phase. However, it was possible to minimize this phase by In sputtering followed by co-sputtering with a Cu/In ratio of 1 (Cu-In/In/Glass). This permitted the fabrication of a homogeneous Cu-In alloy layer, which was not possible through the simple co-sputtering. 相似文献
1000.
This Note deals with the sensitivity analysis of a newtonian incompressible fluid driven by the Navier–Stokes equations with respect to the dynamic of the fluid domain boundary. The structure of the gradient with respect to the velocity of the domain for a given cost function is established. This result is obtained using new shape derivation tools for Eulerian functionals and the Min–Max derivation principle. To cite this article: R. Dziri et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献