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11.
Ostashev VE Wilson DK Liu L Aldridge DF Symons NP Marlin D 《The Journal of the Acoustical Society of America》2005,117(2):503-517
Finite-difference, time-domain (FDTD) calculations are typically performed with partial differential equations that are first order in time. Equation sets appropriate for FDTD calculations in a moving inhomogeneous medium (with an emphasis on the atmosphere) are derived and discussed in this paper. Two candidate equation sets, both derived from linearized equations of fluid dynamics, are proposed. The first, which contains three coupled equations for the sound pressure, vector acoustic velocity, and acoustic density, is obtained without any approximations. The second, which contains two coupled equations for the sound pressure and vector acoustic velocity, is derived by ignoring terms proportional to the divergence of the medium velocity and the gradient of the ambient pressure. It is shown that the second set has the same or a wider range of applicability than equations for the sound pressure that have been previously used for analytical and numerical studies of sound propagation in a moving atmosphere. Practical FDTD implementation of the second set of equations is discussed. Results show good agreement with theoretical predictions of the sound pressure due to a point monochromatic source in a uniform, high Mach number flow and with Fast Field Program calculations of sound propagation in a stratified moving atmosphere. 相似文献
12.
Chung P Ajitanand NN Alexander JM Anderson M Best D Brady FP Case T Caskey W Cebra D Chance JL Cole B Crowe K Das A Draper JE Gilkes ML Gushue S Heffner M Hirsch AS Hjort EL Huo L Justice M Kaplan M Keane D Kintner JC Klay J Krofcheck D Lacey RA Lauret J Lisa MA Liu H Liu YM McGrath R Milosevich Z Odyniec G Olson DL Panitkin SY Pinkenburg C Porile NT Rai G Ritter HG Romero JL Scharenberg R Schroeder L Srivastava B Stone NT Symons TJ Wienold T Witt R Whitfield J Wood L Zhang WN;E Collaboration 《Physical review letters》2001,86(12):2533-2536
Directed flow measurements for Lambda hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2A, 4A, and 6A GeV; b<5-6 fm). The measurements indicate that Lambda hyperons flow consistently in the same direction but with smaller magnitudes. A strong positive flow [for Lambdas] has been predicted in calculations which include the influence of the Lambda-nucleon potential. The experimental flow ratio Lambda/p is in qualitative agreement with expectations (approximately 2/3) from the quark counting rule at 2A GeV but is found to decrease with increasing beam energy. 相似文献
13.
14.
Ostashev VE Collier SL Wilson DK Aldridge DF Symons NP Marlin D 《The Journal of the Acoustical Society of America》2007,122(1):107-112
Formulation and implementation of time-domain boundary conditions (TDBCs) at the surface of a reactive porous material are made challenging by the slow decay, complexity, or noncausal nature of many commonly used models of porous materials. In this paper, approaches are described that improve computational efficiency and enforce causality. One approach involves approximating the known TDBC for the modified Zwikker-Kosten impedance model as a summation of decaying exponential functions. A second approach, which can be applied to any impedance model, involves replacing the characteristic admittance with its Padé approximation. Then, approximating fractional derivatives with decaying exponentials, a causal and recursive TDBC is formulated. 相似文献
15.
A. Hudson M.F. Lappert J.J. Macquitty B.K. Nicholson H. Zainal G.R. Luckhurst C. Zannoni S.W. Bratt M.C.R. Symons 《Journal of organometallic chemistry》1976,110(1):C5-C8
The reassignment to a manganese(0) quartet state by C.L. Kwan and J.K. Kochi (J. Organometal. Chem., 101 (1975) C9) of the ESR spectrum obtained during photolysis of Mn2(CO)10 in THF is shown to be in error; computer simulation of the X-band spectrum and observation of the S-band spectrum confirm our previous assignment to sextet manganese(II) and chemical and IR evidence indicate the presence of [Mn(CO)5]? as a counter ion. 相似文献
16.
M.C.R. Symons 《Tetrahedron letters》1973,14(3):207-208
17.
A. Hill S. F. J. Cox R. De Renzi C. Bucci A. Vecli M. C. R. Symons 《Hyperfine Interactions》1984,19(1-4):815-820
The radical (CH3)2 COMu has been studied in pure (CH3)2 CO and in binary aqueous systems. The value of the muon-electron hyperfine coupling constant fell sharply from 25.4 MHz to ca 22.5 MHz on the addition of low concentration of water. It then fell gradually on going to dilute solutions in water. The coupling increased with increasing temperature as expected for a positive hyperfine interaction. The results are compared with esr data for (CH3)2 COH radicals, and the solvent dependence is considered in terms of hydrogen-bonding. The mechanism of formation of these radicals is discussed in the light of reaction rates. It is concluded that their precursor cannot be muonium. 相似文献
18.
L.K. Fifield M.J. Hurst E.F. Garman T.J.M. Symons F. Watt K.W. Allen 《Nuclear Physics A》1980,334(1):109-126
Nine levels in the range 8.7 to 12.5 MeV in 20Ne have been investigated with the 16O(α, γ)20Ne and 16O(α, α')16O1(6.13 MeV) reactions using a differentially pumped windowless gas target. Three of the levels have not been observed previously in these reactions, and new information has been obtained for most of the others. In particular, the 11.27 MeV 1? level is shown to have T = 1, a result of relevance to a proposed parity violation experiment, and the analogue of the 1.97 MeV (3?T = 1) level in 20F is shown to lie at 12.25 MeV in 20Ne rather than at 12.39 MeV as proposed previously. In addition, the 12.25 MeV level has a width Γ < 1 keV, in contrast to the value Γ ~ 5 keV reported in other work. The electromagnetic transition rates for positive parity T = 1 states in 20Ne are compared with shell-model calculations. 相似文献
19.
Martyn C.R. Symons Robert C. Selby Ian G. Smith Stephen W. Bratt 《Chemical physics letters》1977,48(1):100-102
Rigid solution spectra for C6F?6 and C4F?8 are compared, and it is concluded that C6F]t-6 cannot have the planar, σ* structure previously postulated. Instead, a puckered-ring structure with σ and pseudo π delocalisation is postulated. 相似文献
20.