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341.
Emmanuelle Orhan Marcos Anicete-Santos Fenelon M. Pontes Juan Andrès José A. Varela Carlton A. Taft 《Journal of solid state chemistry》2005,178(4):1284-1291
A joint experimental and theoretical study has been carried out to rationalize for the first time the photoluminescence (PL) properties of disordered CaWO4 (CWO) thin films. From the experimental side, thin films of CWO have been synthesized following a soft chemical processing, their structure has been confirmed by X-ray diffraction data and corresponding PL properties have been measured using the 488 nm line of an argon ion laser. Although we observe PL at room temperature for the crystalline thin films, the structurally disordered samples present much more intense emission. From the theoretical side, first principles quantum mechanical calculations, based on density functional theory at B3LYP level, have been employed to study the electronic structure of a crystalline (CWO-c) and asymmetric (CWO-a) periodic model. Electronic properties are analyzed in the light of the experimental results and their relevance in relation to the PL behavior of CWO is discussed. The symmetry breaking process on going from CWO-c to CWO-a creates localized electronic levels above the valence band and a negative charge transfer process takes place from threefold, WO3, to fourfold, WO4, tungsten coordinations. The correlation of both effects seems to be responsible for the PL of amorphous CWO. 相似文献
342.
A polymeric precursor method based on the Pechini process was successfully used to synthesize zirconia–12 mol% ceria ceramic powders. The influence of the main process variables (citric acid—ethylene glycol ratio, citric acid—total oxides ratio and calcination temperature) on phase formation and powder morphology (surface area and crystallite size) were investigated. The thermal decomposition behavior of the precursor is presented. X‐ray diffraction (XRD) patterns of powders revealed a crystalline tetragonal zirconia single‐phase, with crystallite diameter ranging from 6 to 15 nm. The BET surface areas were relatively high, reaching 95 m2 g−1. Nitrogen adsorption/desorption on the powders suggested that nonaggregated powders could be attained, depending on the synthesis conditions. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
343.
Oberdan Oliveira Ferreira Celeste de Jesus Pereira Franco Everton Luiz Pompeu Varela Sebastio Gomes Silva Mrcia Moraes Cascaes Sandro Percrio Mozaniel Santana de Oliveira Eloisa Helena de Aguiar Andrade 《Molecules (Basel, Switzerland)》2021,26(19)
Eugenia florida DC. belongs to the Myrtaceae family, which is present in almost all of Brazil. This species is popularly known as pitanga-preta or guamirim and is used in folk medicine to treat gastrointestinal problems. In this study, two specimens of Eugenia florida (Efl) were collected in different areas of the same region. Specimen A (EflA) was collected in an area of secondary forest (capoeira), while specimen B (EflB) was collected in a floodplain area. The essential oils (EOs) were extracted from both specimens of Eugenia florida by means of hydrodistillation. Gas chromatography coupled to mass spectrometry (GC/MS) was used to identify the volatile compounds present, and the antioxidant capacity of the EOs was determined by antioxidant capacity (AC-DPPH) and the Trolox equivalent antioxidant (TEAC) assay. For E. florida, limonene (11.98%), spathulenol (10.94%) and α-pinene (5.21%) were identified as the main compounds of the EO extracted from sample A, while sample B comprised selina-3,11-dien-6α-ol (12.03%), eremoligenol (11.0%) and γ-elemene (10.70%). This difference in chemical composition impacted the antioxidant activity of the EOs between the studied samples, especially in sample B of E. florida. This study is the first to report on the antioxidant activity of Eugenia florida DC. essential oils. 相似文献
344.
Tim Mller Fabian Scholten Trung Ngo Thanh Ilya Sinev Janis Timoshenko Xingli Wang Zarko Jovanov Manuel Gliech Beatriz Roldan Cuenya Ana Sofia Varela Peter Strasser 《Angewandte Chemie (International ed. in English)》2020,59(41):17974-17983
The direct electrochemical conversion of carbon dioxide (CO2) into multi‐carbon (C2+) products still faces fundamental and technological challenges. While facet‐controlled and oxide‐derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu2O nanocubes during operation in low‐current H‐Cells and in high‐current gas diffusion electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C2+ Faradaic efficiency of around 60 % for 40 h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C1 products. Operando XAS and time‐resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu‐seeds during the surprisingly slow reduction of bulk Cu2O. The initially (100)‐rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide‐derived generation of under‐coordinated lattice defects, can support the high C2+ product yields. 相似文献
345.
Lisa-Maria Needham Judith Weber Juan A. Varela James W. B. Fyfe Dung T. Do Catherine K. Xu Luke Tutton Rachel Cliffe Benjamin Keenlyside David Klenerman Christopher M. Dobson Christopher A. Hunter Karin H. Müller Kevin O'Holleran Sarah E. Bohndiek Thomas N. Snaddon Steven F. Lee 《Chemical science》2020,11(18):4578
Neurodegenerative diseases such as Alzheimer''s and Parkinson''s are associated with protein misfolding and aggregation. Recent studies suggest that the small, rare and heterogeneous oligomeric species, formed early on in the aggregation process, may be a source of cytotoxicity. Thioflavin T (ThT) is currently the gold-standard fluorescent probe for the study of amyloid proteins and aggregation processes. However, the poor photophysical and binding properties of ThT impairs the study of oligomers. To overcome this challenge, we have designed Thioflavin X, (ThX), a next-generation fluorescent probe which displays superior properties; including a 5-fold increase in brightness and 7-fold increase in binding affinity to amyloidogenic proteins. As an extrinsic dye, this can be used to study unique structural amyloid features both in bulk and on a single-aggregate level. Furthermore, ThX can be used as a super-resolution imaging probe in single-molecule localisation microscopy. Finally, the improved optical properties (extinction coefficient, quantum yield and brightness) of ThX can be used to monitor structural differences in oligomeric species, not observed via traditional ThT imaging.Introducing ThX, a next-generation ThT derivative that allows for the early detection of amyloid aggregates at the bulk and single-aggregate levels. 相似文献
346.
K. P. Lopes L. S. Cavalcante A. Z. Simões R. F. Gonçalves M. T. Escote J. A. Varela E. Longo E. R. Leite 《Journal of Sol-Gel Science and Technology》2008,45(2):151-155
NiTiO3 (NTO) nanoparticles encapsulated with SiO2 were prepared by the sol–gel method resulting on core-shell structure. Changes on isoelectric point as a function of silica
were evaluated by means of zeta potential. The NTO nanoparticles heat treated at 600°C were characterized by X-ray diffraction,
transmission electron microscopy (TEM) and energy dispersive X-ray analysis. TEM observations showed that the mean size of
NTO is in the range of 2.5–42.5 nm while the thickness of SiO2 shell attained 1.5–3.5 nm approximately. 相似文献