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91.
Tomáš Skála Nataliya TsudKevin C. Prince Vladimír Matolín 《Applied Surface Science》2011,257(8):3682-3687
Interaction of aluminium with cerium oxide was studied by photoelectron spectroscopy of Al/CeO2(1 1 1) and CeO2/Al(1 1 1) model systems. It was found in both cases that metallic aluminium was immediately oxidized, CeO2 was partially reduced and a mixed oxide with cerium present as Ce3+ was formed. The compound is probably cerium aluminate CeAlO3 mixed with Al2O3 or Ce2O3. In both cases the intermixing was limited by the diffusion of aluminium into ceria. The excess of deposited material above this limit formed AlOx and CeO2 overlayers on the top of the mixed oxide + aluminate/CeO2 and mixed oxide + aluminate/Al films, respectively. 相似文献
92.
Niobium diffusion in niobium-doped titanium dioxide 总被引:1,自引:0,他引:1
L. R. Sheppard A. J. Atanacio T. Bak J. Nowotny M. K. Nowotny K. E. Prince 《Journal of Solid State Electrochemistry》2009,13(7):1115-1121
The present work studied the self-diffusion coefficient of 93Nb in Nb-doped TiO2 single crystal (4.3 at.% Nb) at high oxygen activity [p(O2) = 21 kPa] over the temperature range 1,073 to 1,573 K. The diffusion-induced 93Nb concentration profile was determined by using secondary ion mass spectrometry (SIMS). The subsequently determined self-diffusion
coefficient of 93Nb exhibits the following temperature dependence:. This study builds upon a similar study performed previously for 93Nb tracer diffusion in undoped TiO2, and identifies the effect of compositional change on self-diffusion behaviour. The obtained activation energy has been considered
in terms of migration and formation enthalpies of titanium vacancies.
The present work is dedicated to Professor John Bockris on the occasion of his 85th birthday. His contribution to the progress
of modern electrochemistry is well-known to several generations of students and researchers who have been using his textbooks.
His specific contribution to the theory of photoelectrochemical water splitting is known to all working in this fascinating
area. 相似文献
93.
Takács AF Neumann M Postnikov AV Kuepper K Scheurer A Sperner S Saalfrank RW Prince KC 《The Journal of chemical physics》2006,124(4):044503
The electronic structure of the single molecule magnet system {M[Fe(L(1))(2)](3)}4CHCl(3) [M=Fe,Cr;L(1)=CH(3)N(CH(2)CH(2)O)(2) (2-)] has been studied using x-ray photoelectron spectroscopy, x-ray-absorption spectroscopy, soft-x-ray emission spectroscopy, as well as theoretical density-functional-based methods. There is a good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarization yielding effective spin S=52 per iron atom, giving a high-spin state molecule with a total S=5 effective spin for the case of M=Fe. 相似文献
94.
Jirka I Plsek J Sutara F Matolín V Cháb V Prince KC 《The journal of physical chemistry. B》2006,110(47):23837-23844
A model catalyst system, palladium on tungsten oxide, has been examined by temperature-programmed desorption and photoemission spectroscopy. The samples were prepared by evaporation of palladium onto an oxidized tungsten foil under ultrahigh vacuum conditions. Mostly three-dimensional (3-D) palladium (Pd) clusters were found to be present on oxidized tungsten (WOx) surfaces at room temperature. Upon annealing to 670 K, the palladium clusters are redispersed and decorated by the WOx surface layer. The nature of the WOx phase on top of the palladium clusters is dependent on the mode of oxidation of the tungsten foil prior to palladium deposition. Mainly W(2+) species decorate palladium deposits on tungsten oxidized at room temperature, while mainly W(4+) species are on top of palladium deposits on the surface oxidized at 1300 K. The appearance of a Pd(n+)-O-W(4+) mixed oxide phase with n < 2 was observed on the oxidized tungsten surface. The substantial reduction (relative to nonannealed samples) of molecular CO coverage induced by annealing is discussed in terms of the changes in chemical composition and morphology of the outermost surface. 相似文献
95.
Conrads T Hemann C George GN Pickering IJ Prince RC Hille R 《Journal of the American Chemical Society》2002,124(38):11276-11277
Arsenite oxidase, a member of the DMSO reductase family of molybdenum enzymes, has two molecules of guanosine dinucleotide molybdenum cofactor coordinating the molybdenum at the active site. X-ray absorption spectroscopy indicates that the Mo-S bonds shorten from 2.47 to 2.37 A upon reduction with the physiological substrate. It also indicates the presence of an oxo ligand at 1.70 A in both oxidized and reduced forms of the enzyme, together with a short, 1.83 A, Mo-O bond in the oxidized form that is lost upon reduction. Resonance Raman spectroscopy indicates that the two pterin dithiolene moieties have different aromaticities, with one, the Q-pterin, having a more discrete dithiolate structure while the other, the P-pterin, has considerable pi-delocalization. Our results indicate that the structure of arsenite oxidase is intermediate between that seen in other molybdenum enzymes, in which one ligand to the metal is provided by the polypeptide (serine, cysteine, or selenocysteine), and tungsten enzymes that lack a peptide ligand. 相似文献
96.
Metal ion function in carbonic anhydrase 总被引:1,自引:0,他引:1
The purpose of this review is to present an up-to-date account of the chemistry of the metal ion in the enzyme carbonic anhydrase. The interest lies in how the study of the metal may lead to deductions concerning the chemistry of the enzyme's action and in the way that metalloenzyme chemistry seems to demand a new appraisal of some aspects of the established chemistry of metal complexes. 相似文献
97.
Arsköld SP Masters VM Prince BJ Smith PJ Pace RJ Krausz E 《Journal of the American Chemical Society》2003,125(43):13063-13074
We report and compare highly resolved, simultaneously recorded absorption and CD spectra of active Photosystem II (PSII) samples in the range 440-750 nm. From an appropriately scaled comparison of spinach membrane fragment (BBY) and PSII core spectra, we show that key features of the core spectrum are quantitatively represented in the BBY data. PSII from the cyanobacterium Synechocystis 6803 display spectral features in the Qy region of comparable width (50-70 cm(-1) fwhm) to those seen in plant PSII but the energies of the resolved features are distinctly different. A comparison of spectra taken of PSII poised in the S1QA and S2QA(-) redox states reveals electrochromic shifts largely attributable to the influence of QA(-) on Pheo(D1). This allows accurate determinations of the Pheo(D1) Qy absorption positions to be at 685.0 nm for spinach cores, 685.8 nm for BBY particles, and 683.0 nm for Synechocystis. These are discussed in terms of earlier reports of the Pheo(D1) energies in PSII. The Qx transition of Pheo(D1) undergoes a blue shift upon Q(A) reduction, and we place a lower limit of 80 cm(-1) on this shift in plant material. By comparing the magnitude of the Stark shifts of the Qx and Qy bands of Pheo(D1), the directions of the transition-induced dipole moment changes, Deltamu(x) and Deltamu(y), for this functionally important pigment could be determined, assuming normal magnitudes of the Deltamu's. Consequently, Deltamu(x) and Deltamu(y) are determined to be approximately orthogonal to the directions expected for these transitions. Low-fluence illumination experiments at 1.7 K resulted in very efficient formation of QA(-). This was accompanied by cyt b(559) oxidation in BBYs and carotenoid oxidation in cores. No chlorophyll oxidation was observed. Our data allow us to estimate the quantum efficiency of PSII at this temperature to be of the order 0.1-1. No Stark shift associated with the S1-to-S2 transition of the Mn cluster is evident in our samples. The similarity of Stark data in plants and Synechocystis points to minimal interactions of Pheo(D1) with nearby chloropyll pigments in active PSII preparations. This appears to be at variance with interpretations of experiments performed with inactive solubilized reaction-center preparations. 相似文献
98.
William S Kerwin Jerry L Prince 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,142(2):313
We present a k-space approximation that directly relates a pulse sequence to its residual pattern of z-directed magnetization Mz, in a manner akin to the k-space approximation for small tip-angle excitation. Our approximation is particularly useful for the analysis and design of tagging sequences, in which Mz is the important quantity—as opposed to the transverse magnetization components Mx and My considered in selective excitation. We demonstrate that our approximation provides new insights into tagging, can be used to design novel tag patterns, and, more generally, may be applied to selective presaturation sequences for purposes other than tagging. 相似文献
99.
100.