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81.
Jiwha Lee Ciaran P. Hanrahan Jose Arias Richard M. Martin Horia Metiu 《Surface science》1985,161(1):L543-L548
We show that at low potassium coverage the K/Ni(111) surface has two kinds of sites: one whose local work function is close to that of Ni(111) and another whose local work function is much smaller. The evidence is provided by the metastable quenching spectrum of K/Ni(111) and Xe covered K/Ni(111). 相似文献
82.
William L. Manner Jane A. Lloyd Robert J. Hanrahan Jr. Mark T. Paffett 《Applied Surface Science》1999,150(1-4):73-88
The corrosion resistance of uranium is greatly enhanced by alloying with niobium. In this study the initial stages of corrosion of a specific uranium-base alloy (U–14.1 at.% Nb) by O2 or D2O have been examined using the surface specific techniques of X-ray photoelectron spectroscopy (XPS), thermal programmed desorption (TPD), static secondary-ion mass spectroscopy (SSIMS), and sputtered neutrals mass spectroscopy (SNMS). XPS studies of the U–14.1 at.% Nb surface following oxidation using O2 at 300 K indicate production of a thin oxide overlayer of stoichiometric UO2.0 intermixed with Nb2O5. The same stoichiometry is exhibited for uranium when the oxide is prepared at 500 K with O2; although, niobium is much less oxidized exhibiting a mixture of NbO and Nb. Contrary to previous XPS literature, SNMS depth profiling studies reveal that oxidation by O2 is much greater (as judged by oxide layer thickness) than that exhibited by D2O. An oxide layer thickness of less than 20 Å was created using D2O as an oxidant at 300 K with exposures >3500 L (oxide layers created from O2 are significantly greater at much smaller exposures). Formation of a critical density of Nb2O5 is suggested to be responsible for the enhanced corrosion resistance by preventing diffusion of O− (O2−) or OD−/OH− into the oxide/metal interface region. The domains of stability of hydroxyl formation have also been followed using TPD, SSIMS and XPS. Maximal surface hydroxyl concentrations (Θrel=0.30) are obtained at a surface temperature of 175 K for these experimental conditions. 相似文献
83.
Duarte A Slutsky M Hanrahan G Mello CM Bazan GC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(3):756-759
Electrostatic nanoassemblies were employed to identify bacterial growth conditions. They comprise a cationic conjugated oligoelectrolyte and fluorescein-tagged ssDNA and were optimized with a hybrid, computational neural network model. The photoluminescence spectra contained the oligomer and sensitized fluorescein emission. The spectra changed depending on the growth history of the bacteria introduced (see figure). 相似文献
84.
The time and magnetic field dependent magnetization of polarized signals in the presence of chemically induced magnetization transfer is described by means of a kinetic matrix incorporated into the Bloch equations. The approach is transformed into a computer algorithm accounting for all hyperfine lines present in the system. Solutions are readily obtained by numerical methods. Calculations are applied to the time resolved EPR (TR-EPR) spectroscopic signals of p-benzoquinone after laser flash photolysis. In an aqueous alcoholic solution at pH 2.0, chemical exchange via intermolecular proton transfer is found present between neutral semiquinones. At pH 8.3, the TR-EPR spectrum shows only a uniform signal of the semiquinone. At pH 5.4, a superposition of neutral and anionic radicals is observed together with a protonation-deprotonation equilibrium. A two-step hydrogen atom transfer, consisting of electron transfer followed by protonation, is proposed to account for the formation of both neutral and anionic semiquinone species prior to observation. Experiments in partly deuterated solvent mixtures indicate the existence of three semiquinone forms: BQH?, BQ?-, and BQD? prior to observation. The origin of the proton/deuteron transferred to the anion radical in the precursor state is discussed. 相似文献
85.
MINHHUY HÔ VEDENE H. SMITH JR. ROBIN P. SAGAR RODOLFO O. ESQIVEL 《Molecular physics》2013,111(20):1727-1728
The asymptotic behaviour of the negative ratio of the density gradient to the electron density, q(r), for neutral and singly charged atoms has been investigated. The results show that, for large r, q(r) can approach its limit √8?, where ? is the first ionization potential, from either above or below depending on the specific system considered. 相似文献
86.
JR Henderson 《Molecular physics》2013,111(17-18):2345-2352
The confinement of fluids in pores and wedges is associated with exponentially damped oscillatory packing structure, as observed with the surface forces apparatus. This paper reviews the statistical mechanics of confined fluids and then illustrates the results with density functional data for hard-sphere solvent. The free energy of the pore fluid and its functional derivatives with respect to thermodynamic fields all oscillate, as a function of pore width, with a wavelength close to the solvent diameter. In contrast, the density at the centre of pores oscillates with twice this wavelength, as a function of pore width. The development of a unified physics of confined fluids is considered. Approximations based on one-dimensional physics do extraordinarily well in planar symmetry at three-dimensions. 相似文献
87.
INTRODUCTION In this third part of a review on chemometrics in spectroscopy we will describe a recent methodology that has attracted increasing interest in spectroscopy. namely multi-way analysis. The application of multi-way analysis in spectroscopy is still relatively new. hence many methodological improvements are being investigated currently. Part of thls review will also be used to describe the algorithmic improvements gained the last decade. 相似文献
88.
William N. Anderson JR. E. James Harner George E. Trapp 《Linear and Multilinear Algebra》2013,61(3-4):295-299
There is an isomorphism between the matrices over the Boolean algebra of subsets of a k-element set and the k-tuples of Boolean binary (i.e. zero-one) matrices. This isomorphism allows many problems concerning nonbinary Boolean matrices to the referred to the binary ease. However, there are some features of the general (i.e. nonbinary) case that have not been mentioned, although they differ somewhat from the binary case. We exhibit characterizations of the linear operators that preserve several invariants of matrices over finite Boolean algebras to illustrate the differences and similarities of the general vs. the binary cases. We employ a canonical form that is useful in applying the isomorphism. 相似文献
89.
Michael A. Jansen Jacqueline Kiwata Jennifer Arceo Kym F. Faull Grady Hanrahan Edith Porter 《Analytical and bioanalytical chemistry》2010,397(6):2367-2374
Cholesteryl esters have antimicrobial activity and likely contribute to the innate immunity system. Improved separation techniques
are needed to characterize these compounds. In this study, optimization of the reversed-phase high-performance liquid chromatography
separation of six analyte standards (four cholesteryl esters plus cholesterol and tri-palmitin) was accomplished by modeling
with an artificial neural network–genetic algorithm (ANN-GA) approach. A fractional factorial design was employed to examine
the significance of four experimental factors: organic component in the mobile phase (ethanol and methanol), column temperature,
and flow rate. Three separation parameters were then merged into geometric means using Derringer’s desirability function and
used as input sources for model training and testing. The use of genetic operators proved valuable for the determination of
an effective neural network structure. Implementation of the optimized method resulted in complete separation of all six analytes,
including the resolution of two previously co-eluting peaks. Model validation was performed with experimental responses in
good agreement with model-predicted responses. Improved separation was also realized in a complex biological fluid, human
milk. Thus, the first known use of ANN-GA modeling for improving the chromatographic separation of cholesteryl esters in biological
fluids is presented and will likely prove valuable for future investigators involved in studying complex biological samples. 相似文献
90.
Alves GA Amato S Anjos JC Appel JA Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Kaplan D Karchin PE Kwan S Leedom I Lueking LH Luste GJ Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A d'Olivera AB Rafatian A dos Reis AC Reucroft S Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wu Z 《Physical review letters》1992,69(22):3147-3150