全文获取类型
收费全文 | 6545篇 |
免费 | 224篇 |
国内免费 | 46篇 |
专业分类
化学 | 4818篇 |
晶体学 | 24篇 |
力学 | 208篇 |
数学 | 884篇 |
物理学 | 881篇 |
出版年
2023年 | 67篇 |
2022年 | 87篇 |
2021年 | 127篇 |
2020年 | 118篇 |
2019年 | 149篇 |
2018年 | 92篇 |
2017年 | 82篇 |
2016年 | 197篇 |
2015年 | 166篇 |
2014年 | 205篇 |
2013年 | 369篇 |
2012年 | 467篇 |
2011年 | 501篇 |
2010年 | 271篇 |
2009年 | 239篇 |
2008年 | 425篇 |
2007年 | 435篇 |
2006年 | 394篇 |
2005年 | 362篇 |
2004年 | 339篇 |
2003年 | 301篇 |
2002年 | 252篇 |
2001年 | 86篇 |
2000年 | 82篇 |
1999年 | 68篇 |
1998年 | 57篇 |
1997年 | 60篇 |
1996年 | 74篇 |
1995年 | 51篇 |
1994年 | 36篇 |
1993年 | 27篇 |
1992年 | 32篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 41篇 |
1983年 | 28篇 |
1982年 | 39篇 |
1981年 | 25篇 |
1980年 | 37篇 |
1979年 | 24篇 |
1978年 | 29篇 |
1977年 | 38篇 |
1976年 | 27篇 |
1975年 | 28篇 |
1974年 | 17篇 |
1973年 | 18篇 |
排序方式: 共有6815条查询结果,搜索用时 0 毫秒
101.
Anfosso-Lédée F Dangla P Bérengier M 《The Journal of the Acoustical Society of America》2007,122(2):731-736
Acoustic impedance of an absorbing interface is easily introduced in boundary element codes provided that a local reaction is assumed. But this assumption is not valid in the case of porous road surface. A two-domain approach was developed for the prediction of sound propagation above a porous layer that takes into account the sound propagation inside the porous material. The porous material is modeled by a homogeneous dissipative fluid medium. An alternative to this time consuming two-domain approach is proposed by using the grazing incidence approximate impedance in the traditional single-domain boundary element method (BEM). It can be checked that this value is numerically consistent with the surface impedance calculated at the interface from the pressure and surface velocity solutions of the two-domain approach. The single-domain BEM introducing this grazing incidence impedance is compared in terms of sound attenuation with analytical solutions and two-domain BEM. The comparison is also performed with the single-domain BEM using the normal incidence impedance, and reveals a much better accuracy for the prediction of sound propagation above a porous interface. 相似文献
102.
We report experimental evidence of spatial clustering of dense particles in homogenous, isotropic turbulence at high Reynolds numbers. The dissipation-scale clustering becomes stronger as the Stokes number increases and is found to exhibit similarity with respect to the droplet Stokes number over a range of experimental conditions (particle diameter and turbulent energy dissipation rate). These findings are in qualitative agreement with recent theoretical and computational studies of inertial particle clustering in turbulence. Because of the large Reynolds numbers a broad scaling range of particle clustering due to turbulent mixing is present, and the inertial clustering can clearly be distinguished from that due to mixing of fluid particles. 相似文献
103.
Martins MA Rossatto M Prola LD Pizzuti L Moreira DN Campos PT Frizzo CP Zanatta N Bonacorso HG 《Ultrasonics sonochemistry》2012,19(2):227-231
The synthesis of 14 novel N-propargylic β-enaminones from the reaction of β-alkoxy vinyltrihalomethyl[carboxyethyl] ketones [R3C(O)CHC(R1)OMe, where R3 = CF3, CCl3, CO2Et and R1 = Me, Et, Pr, Bu, i-Pent, CH2CH2CO2Me] with propargyl amines [R2NHCH2CCH, where R2 = Pr, PhCH2] is reported. Yields, solvents and reaction times needed for reaction completion, by microwave irradiation (MW), conventional thermal heating (TH) and under ultrasound irradiation (US) are compared. The best results were obtained under US irradiation in good to excellent yields (70-93%). 相似文献
104.
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
105.
106.
Visarath In Patrick LonghiniAndy Kho Norman LiuSuketu Naik Antonio PalaciosJoseph D. Neff 《Physica D: Nonlinear Phenomena》2011,240(8):701-708
A novel coupling scheme using M≥2 arrays of coupled nonlinear elements arranged in a specific configuration can produce multifrequency patterns or a frequency down-converting effect on an external (input) signal. In such a configuration, each array contains N≥3 nonlinear elements with similar dynamics and each element is coupled unidirectionally within the array. The subsequent arrays in the cascade are coupled in a similar fashion except that the coupling direction is arranged in the opposite direction with respect to that of the preceding array. Previous theoretical work and numerical results have already been reported in [P. Longhini, A. Palacios, V. In, J. Neff, A. Kho, A. Bulsara, Exploiting dynamical symmetry in coupled nonlinear elements for efficient frequency down-conversion, Phys. Rev. E 76 (2007) 026201]. This paper is focused on results of experiments implemented on two distinct systems: the first system is fabricated using discrete component circuits to approximate an overdamped bistable Duffing oscillator described by a quartic potential system, and the second system is built in a microcircuit, where the nonlinearity is described by a hyperbolic tangent function, with the option of applying an external signal to investigate resonant effects. In particular, the circuit implementations for each case use M=2 arrays, but their voltage oscillations already demonstrate that the frequency relations between each of the successive arrays decrease by a rational factor, conforming to earlier theoretical and numerical results for the general case containing M arrays. This behavior is important for efficient frequency down-converting applications which are essential in many communication systems where heterodyning is typically used and it involves multi-step processes with complicated circuitry. 相似文献
107.
Ast CR Henk J Ernst A Moreschini L Falub MC Pacilé D Bruno P Kern K Grioni M 《Physical review letters》2007,98(18):186807
The long-range ordered surface alloy Bi/Ag(111) is found to exhibit a giant spin splitting of its surface electronic structure due to spin-orbit coupling, as is determined by angle-resolved photoelectron spectroscopy. First-principles electronic structure calculations fully confirm the experimental findings. The effect is brought about by a strong in-plane gradient of the crystal potential in the surface layer, in interplay with the structural asymmetry due to the surface-potential barrier. As a result, the spin polarization of the surface states is considerably rotated out of the surface plane. 相似文献
108.
Oleg Lebedev Hans Peter Nilles Stuart Raby Saúl Ramos-Sánchez Michael Ratz Patrick K.S. Vaudrevange Akın Wingerter 《Physics letters. [Part B]》2007
We explore a “fertile patch” of the heterotic landscape based on a Z6-II orbifold with SO(10) and E6 local GUT structures. We search for models allowing for the exact MSSM spectrum. Our result is that of order 100 out of a total 3×104 inequivalent models satisfy this requirement. 相似文献
109.
Salzmann I Heimel G Duhm S Oehzelt M Pingel P George BM Schnegg A Lips K Blum RP Vollmer A Koch N 《Physical review letters》2012,108(3):035502
Current models for molecular electrical doping of organic semiconductors are found to be at odds with other well-established concepts in that field, like polaron formation. Addressing these inconsistencies for prototypical systems, we present experimental and theoretical evidence for intermolecular hybridization of organic semiconductor and dopant frontier molecular orbitals. Common doping-related observations are attributed to this phenomenon, and controlling the degree of hybridization emerges as a strategy for overcoming the present limitations in the yield of doping-induced charge carriers. 相似文献
110.
Patrick Homenya Markus Messerschmidt Muhammad Nawaz Tahir Victor Martinez Yajun Cheng Jochen S. Gutmann Michael Klein Stefan Jung Morris Wolff Reza Saadat Driss Nariaki Roman Bo?a G?star Klingelh?fer Wolfgang Tremel Franz Renz 《Hyperfine Interactions》2012,205(1-3):63-67
The nonanuclear coordination compound [MoIV{(CN)FeIII(3-methyl-saldptn)}8]Cl4 exhibits multiple spin transitions (3-methyl-saldptn = N,N′-bis(3′′-methyl-2′′-hydroxy-benzyliden)-1,7-diamino-4-azaheptane). This spin crossover cluster is bound via a self-assembled monolayer onto a two dimensional array gold surface. M?ssbauer spectroscopy indicates that the thermally and optically induced spin crossover of the compound is maintained. Thereby, the foundation for its potential practical application (e.g. in the field of information storage) was laid. 相似文献