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291.
James Y. Katekaru Gerald A. Garwood John F. Hershberger Arthur T. Hubbard 《Surface science》1982,121(3):396-410
Studies are reported of the interaction of vapor of typical polar solvents and electrolytes at electrodes having Pt(111) or Pt(100) single-crystal surfaces: water, pyridine, acetonitrile, dimethyl-sulfoxide, hydrogen bromide, iodine, sulfur dioxide, acrylic acid, and ammonia. Exposure was extended from low pressures (about 10?5 Torr) to pressures approaching the vapor pressure of the pure liquid. The results indicate that these typical electrochemical materials adsorb strongly to the clean Pt surface but once adsorbed tend not to react with each other. However, analysis of LEED patterns and Auger intensities suggests that exposure of an adsorbed layer of solvents such as dimethylsulfoxide to iodine results in adsorption of the halogen and molecular re-orientation of the adsorbed solvent. 相似文献
292.
293.
Optimum control of bobsled steering 总被引:1,自引:0,他引:1
Y. L. Zhang M. Hubbard R. K. Huffman 《Journal of Optimization Theory and Applications》1995,85(1):1-19
Minimum-time and smooth-steering control algorithms are developed for bobsled optimal control. Numerical solutions are obtained both for one-curve optimal control and whole-course piecewise optimal control with application to realistic three-dimensional track surface shapes. Specific results are calculated for the Lillehammer Olympic Track. 相似文献
294.
Ezz -Eldin A. Abu-Gharib Michael J. Blandamer John Burgess Nrinder Gosal Pilar Guardado Francisco Sanchez Colin D. Hubbard 《Transition Metal Chemistry》1984,9(8):306-308
Summary Solubilities of perchlorate and thiocyanate salts of several iron(II)-diimine complexes of Schiff base ligands in methanolwater mixtures are reported. From these results and published values for transfer chemical potentials of the perchlorate and thiocyanate anions, transfer chemical potentials for the complex cations are calculated. Trends with solvent composition suggest that preferential solvation varies from negligible to very strongly by methanol, depending on the size and hydrophilic-hydrophobic character of the complex.On leave from the Faculty of Science, Sohag, Egypt. 相似文献
295.
Nija A. Ellis Colin D. Hubbard Shailaja M. Shirodkar Pilar Guardado Maria-Luisa Moya Francisco Sanchez-Burgos John Burgess 《Transition Metal Chemistry》1989,14(6):466-470
Summary The kinetics of formation of the NiII and CoII complexes of pyridine 2-azo-p-dimethylaniline have been studied in aqueous ethylene glycol, aqueous glycerol and in moderate (up to 2.5 mol dm–3) concentrations of NaCl at 298.2K.Mole fractions of 0.24 and 0.12 respectively for ethylene glycol and glycerol effect a lowering of the formation rate constant Kf of Ni(PADA)2+ to about 50% of the value in water. A concentration of 2.0 mol dm–3 NaCl doubles kf for both the Ni and Co complexes. These findings are discussed within the framework of the dissociative interchange mechanism; the possible effects upon each step of the mechanistic pathway are considered. 相似文献
296.
Abstract— Flavone, polyhydroxyflavones (apigenin, fisetin, kaempferol, luteolin, myricetin, quercetin, resokaempferol and robinetin), polymethoxyflavones and acetylated and benzylated flavones were tested for photodynamic activity using Tetrahymena pyriformis T as the test organism. Among these compounds, polymethoxyflavones showed the highest order of activity, followed by flavone and then flavone derivatives with OH and OCH3 groups. Resokaempferol was the only active polyhydroxyflavone, the remainder being inactive such as the benzyl-derivative. The methoxyl group in the 5–position and an increase in number of methoxyl groups from one to three in the phenolic portion of the flavonoid tended to decrease photodynamic activity. Tetrahymena killed photodynamically by polymethoxyflavones were morphologically altered by blister-like blebs. Polymethoxyflavones showed the lowest cytotoxicity and the greatest photodynamic activity among those flavonoids tested. The majority of the favonoids in this series have absorption spectra in the 320–370 nm region. 相似文献
297.
Hubbard PL McGrath KM Callaghan PT 《Langmuir : the ACS journal of surfaces and colloids》2005,21(10):4340-4346
The correlation of molecular diffusion coefficients obtained via a novel two-dimensional pulsed gradient spin-echo (PGSE) NMR method has been shown to reveal detailed structural information on the mesophases of lyotropic liquid crystals. A four-component system containing both nonionic (pentaethylene glycol monododecyl ether) and ionic (sodium dodecyl sulfate) surfactants, water, and decane was prepared and left to equilibrate. In the temperature region around 309 K, a lamellar mesophase forms. A two-dimensional Laplace inverse transformation was performed on the (gammadeltag)2(delta - delta/3) domain data to separate any multiexponential behavior that resulted from local anisotropy. The results of the double PGSE experiment with contiguous gradient pulse pairs, applied both collinearly and orthogonally, clearly show the presence of local anisotropic self-diffusion of the water molecules and suggest a preferred orientation of the lamellae. Information about defects/domain size was obtained by the insertion of a mixing time (t(m)') between the successive gradient pulse pairs. This work highlights the value of this new NMR correlation method in the study of surfactant systems. 相似文献
298.
SANTOS JUAN ENRIQUE; DOUGLAS JIM JR; MORLEY MARY E.; LOVERA OSCAR M. 《IMA Journal of Numerical Analysis》1988,8(4):415-433
A model is defined to simulate the propagation of waves in aradially symmetric, isotropic, composite system consisting ofa fluid-filled well bore f through a fluid-saturated poroussolid p. Biot's equations of motion are chosen to describe thepropagation of waves in p, while the standard equation of motionfor compressible inviscid fluids is used for f, with appropriateboundary conditions at the contact surface between f and p.Also, absorbing boundary conditions for the artificial boundariesof p are derived for the model, their effect being to make themtransparent for waves arriving normally First, results on the existence and uniqueness of the solutionof the differential problem are given and then a discrete-time,explicit finite element procedure is defined and analysed, withfinite element spaces suited for radially symmetric problemsbeing used for the spatial discretisation. 相似文献
299.
The energies of reaction of XeF6(c), XeF4(c), and XeF2(c) with PF3(g) were measured in a bomb calorimeter. These results were combined with the enthalpy of fluorination of PF3(g), which was redetermined to be −(151.98 ± 0.07) kcalth mol−1, to derive (at 298.15 K) ΔHfo(XeF6, c, I) = −(80.82 ± 0.53) kcalth mol−1, ΔHfo(XeF4, c) = −(63.84 ± 0.21) kcalth mol−1, and ΔHfo(XeF2, c) = −(38.90 ± 0.21) kcalth mol−1. The enthalpies of formation of the solid xenon fluorides were combined with reported enthalpies of sublimation to derive (at 298.15 K) ΔHfo(XeF6, g) = −(66.69 ± 0.61) kcalth mol−1, ΔHfo(XeF4, g) = −(49.28 ± 0.22) kcalth mol−1, and ΔHfo(XeF2, g) = −(25.58 ± 0.21) kcalth mol−1. The average bond dissociation enthalpies,〈Do〉(XeF, 298.15 K), are (29.94 ± 0.16), (31.15 ± 0.13), and (31.62 ± 0.16) kcalth mol−1 in XeF6(g), XeF4(g), and XeF2(g), respectively. The enthalpy of formation of PF3(g) was determined to be −(228.8 ± 0.3) kcalth mol−1. 相似文献
300.
W. A. SUMMERS JR. C. ENWALL J. G. BURR R. L. LETSINGER 《Photochemistry and photobiology》1973,17(5):295-301
Abstract— Quantum yields for 254 nm ultraviolet photoaddition of the nucleophiles hydrazine, HCN, HSO3 - , methyl amine, and BH4 - to uracil have been measured; the quantum yields for hydrazine, HCN, and HSO3 - additions are pH-dependent. The nucleophiles sulfide, azide, chloride, bromide, iodide, nitrite and thiocyanate failed to photo–add under similar conditions. These reactions are interpreted as 1,4-additions to the conjugated enone system of the anti-aromatic compound, uracil; as suggested by S. Y. Wang (Wang and Nnadi, 1968). The nuclear magnetic resonance (NMR) spectrum of the photohydrate of uracil-5-d-showed that the proton was added to the 5-position in a stereochemically random manner. The photoaddition of HSO3 - takes place at much lower concentrations than required for the thermal addition of this anion and is also stereochemically random. 相似文献