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排序方式: 共有210条查询结果,搜索用时 15 毫秒
71.
Ilias S. Zouboulis Fuming Jiang Jue WangThomas S. Duffy 《Journal of Physics and Chemistry of Solids》2014
The six independent elastic constants (C11, C12, C13, C33, C44, and C66) of single-crystal MgF2 in the rutile structure have been measured by Brillouin spectroscopy at room temperature from ambient conditions to 7.4 GPa. Measurements were performed on two monocrystals with perpendicular faces, (001) and (100). A quasi-linear fit from finite strain theory was applied to the experimental data revealing the pressure dependence of the six elastic constants of MgF2. The shear modulus CS=1/2(C11−C12), and the aggregate shear (Voigt–Reuss–Hill) modulus G show a softening with increasing pressure, indicating the approach of the rutile-to-CaCl2-type structural phase transition at P~9 GPa. The adiabatic bulk modulus (Reuss average) and its pressure derivative have been determined: K0S=105.1±0.3 GPa, (∂K0S/∂P)T=4.14±0.05. The pressure–volume equation of state of MgF2 was computed self-consistently from the Brillouin data. Our results are in good agreement with X-ray diffraction data. As the phase transition is approached, MgF2 becomes strongly anisotropic and develops partially auxetic behavior (a negative Poisson's ratio in certain directions). 相似文献
72.
Fluorogel Elastomers with Tunable Transparency,Elasticity, Shape‐Memory,and Antifouling Properties
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Dr. Xi Yao Dr. Stuart S. Dunn Dr. Philseok Kim Meredith Duffy Jack Alvarenga Prof. Joanna Aizenberg 《Angewandte Chemie (International ed. in English)》2014,53(17):4418-4422
Omniphobic fluorogel elastomers were prepared by photocuring perfluorinated acrylates and a perfluoropolyether crosslinker. By tuning either the chemical composition or the temperature that control the crystallinity of the resulting polymer chains, a broad range of optical and mechanical properties of the fluorogel can be achieved. After infusing with fluorinated lubricants, the fluorogels showed excellent resistance to wetting by various liquids and anti‐biofouling behavior, while maintaining cytocompatiblity. 相似文献
73.
Interlaboratory Evaluation of Ultraviolet Radiation Emissions from Compact Fluorescent Lamps
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Sharon Miller Rolf Bergman Mark Duffy David Gross Andrew Jackson Robert James Mihaly Kotrebai Andre Lamontagne Terry Lyon Edward Yandek David Sliney 《Photochemistry and photobiology》2016,92(2):348-354
There have been many recent reports regarding the potential risks of UV emissions from compact fluorescent lamps (CFLs). In some of these reports, the robustness of the measurements was difficult to discern. We conducted round‐robin measurements, involving three lamp manufacturers and two government research laboratories to gather reliable data on the UV emissions from commercially available CFLs. The initial sample of lamps consisted of 71 spiral‐shaped CFLs purchased from local retailers. From the initial sample, 14 “high UV emitting” CFLs were chosen for further evaluation. We compared the UV emissions at a distance of 20 cm with the UV exposure limits (ELs) published by the International Commission on Non‐ionizing Radiation Protection (ICNIRP). We found that the allowable exposure time for measured lamps ranged from 21 to 415 h. This indicates that the emissions would not exceed the short‐term ELs that have been established by the ICNIRP for healthy individuals. We also evaluated the potential long‐term risk and found it to be insignificant. There was a large variation in the UV emissions found, even for lamps from a single package, indicating that it is impossible to predict the UV output of a CFL based on its physical appearance and model designation. 相似文献
74.
This report investigates the effects of sample size on the separation and analysis of individual biological particles using microfluidic devices equipped with an orthogonal LIF detector. A detection limit of 17 +/- 1 molecules of fluorophore is obtained using this orthogonal LIF detector under a constant flow of fluorescein, which is a significant improvement over epifluorescence, the most common LIF detection scheme used with microfluidic devices. Mitochondria from rat liver tissue and cultured 143B osteosarcoma cells are used as model biological particles. Quantile-quantile (q-q) plots were used to investigate changes in the distributions. When the number of detected mitochondrial events became too large (>72 for rat liver and >98 for 143B mitochondria), oversampling occurs. Statistical overlap theory is used to suggest that the cause of oversampling is that separation power of the microfluidic device presented is not enough to adequately separate large numbers of individual mitochondrial events. Fortunately, q-q plots make it possible to identify and exclude these distributions from data analysis. Additionally, when the number of detected events became too small (<55 for rat liver and <81 for 143B mitochondria) there were not enough events to obtain a statistically relevant mobility distribution, but these distributions can be combined to obtain a statistically relevant electrophoretic mobility distribution. 相似文献
75.
Ohkita H Cook S Astuti Y Duffy W Tierney S Zhang W Heeney M McCulloch I Nelson J Bradley DD Durrant JR 《Journal of the American Chemical Society》2008,130(10):3030-3042
We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt % 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C61 (PCBM). Three polymers are observed to give amorphous films, attributed to a nonplanar geometry of their backbone while the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (approximately 100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt % PCBM resulted in 70-90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissociated polymer+ and PCBM- polarons, assayed by the appearance of a long-lived, power-law decay phase assigned to bimolecular recombination of these polarons, was observed to vary by over 2 orders of magnitude depending upon the polymer employed. In addition to this power-law decay phase, the blend films exhibited short-lived decays assigned, for the amorphous polymers, to neutral triplet states generated by geminate recombination of bound radical pairs and, for the more crystalline polymers, to the direct observation of the geminate recombination of these bound radical pairs to ground. These observations are discussed in terms of a two-step kinetic model for charge generation in polythiophene/PCBM blend films analogous to that reported to explain the observation of exciplex-like emission in poly(p-phenylenevinylene)-based blend films. Remarkably, we find an excellent correlation between the free energy difference for charge separation (deltaG(CS)rel) and yield of the long-lived charge generation, with efficient charge generation requiring a much larger deltaG(CS)rel than that required to achieve efficient PL quenching. We suggest that this observation is consistent with a model where the excess thermal energy of the initially formed polaron pairs is necessary to overcome their Coulombic binding energy. This observation has important implications for synthetic strategies to optimize organic solar cell performance, as it implies that, at least devices based on polythiophene/PCBM blend films, a large deltaG(CS)rel (or LUMO level offset) is required to achieve efficient charge dissociation. 相似文献
76.
Nonphotochemical quenching is the photoprotection mechanism by which the excess excitation energy absorbed by the light harvesting complex LHCII is dissipated through the protein scaffold as heat. Using the quenched structure of LHCII obtained from crystallographic experiments, the potential quenching of photoexcited excitons by aggregates of chlorophylls is theoretically investigated. In monomeric LHCII there is a hierarchy of length scales resulting in a hierarchy of energy scales that determine the interpigment direct Coulomb coupling. We propose a model whereby eight chlorophylls are coupled quantum mechanically into four dimers, with exciton transfer between these dimers and the remaining six single chlorophylls proceeding incoherently via Forster transfer. The chlorophyll dimer Chl a604-Chl b606 possesses a quasi-parallel geometry, resulting in a weakly dipole-allowed low-lying excited state. This weakly allowed state is accessible via exciton transfer to a higher, strongly allowed state followed by fast vibrational relaxation. This parallel, H-type aggregate can potentially function as an exciton trap. Calculated Forster transfer rates between single chlorophylls and chlorophyll dimers are used in a simulation of exciton transfer in monomeric LHCII to explore this possibility. It is found that Chl a604-Chl b606 has a short-lived enhanced population (on the time scale of approximately picoseconds), but not a long-time resident population. The fluorescence quantum yield of the model was calculated to be phi F = 0.38. Comparison of this result with phi F approximately 0.26 for unquenched LHCII in dilute solution and phi F approximately 0.06 for the highly quenched LHCII crystal reveals that the proposed model does not account for the quenching observed in the LHCII crystal. We therefore conclude that the formation of chlorophyll dimers is not the main cause of excitonic NPQ in LHCII. 相似文献
77.
A method has been developed to analyse for malachite green (MG), leucomalachite green (LMG), crystal violet (CV) and leucocrystal violet (LCV) residues in salmon. Salmon samples were extracted with acetonitrile:McIIIvain pH 3 buffer (90:10 v/v), sample extracts were purified on a Bakerbond strong cation exchange solid phase extraction cartridge. Aliquots of the extracts were analysed by LC-MS/MS. The method was validated in salmon, according to the criteria defined in Commission Decision 2002/657/EC. The decision limit (CCalpha) was 0.17, 0.15, 0.35 and 0.17 microg kg(-1), respectively, for MG, LMG, CV and LCV and for the detection capability (CCbeta) values of 0.30, 0.35, 0.80 and 0.32 microg kg(-1), respectively, were obtained. Fortifying salmon samples (n=6) in three separate assays, show the accuracy to be between 77 and 113% for MG, LMG, LCV and CV. The precision of the method, expressed as RSD values for the within-laboratory reproducibility, for MG, LMG and LCV at the three levels of fortification (1, 1.5 and 2.0 microg kg(-1)), was less than 13%. For CV a more variable precision was obtained, with RSD values ranging between 20 and 25%. 相似文献
78.
A tungsten oxide-based photoelectrocatalyst for degradation of environmental contaminants 总被引:1,自引:0,他引:1
Donald E. Macphee Daniel Rosenberg Matt G. Skellern Richard P. Wells John A. Duffy Kenneth S. Killham 《Journal of Solid State Electrochemistry》2011,15(1):99-103
The use of photocatalysts in the remediation of contaminated water is now well established in the scientific literature, the
most common photocatalyst being nano-dimensional particulate titanium dioxide. The generation of charge and charge transfer
mechanisms on titanium dioxide are also well described, but this paper addresses the use of tungsten oxide and discusses its
potential in water remediation when supported as a photoelectrocatalytic electrode. A photoelectrocatalytic cell is described
and its performance in the context of the band structure of tungsten oxide is discussed. 相似文献
79.
John A. Duffy 《Journal of Solid State Electrochemistry》2011,15(1):3-4
The results of experiments where Tl+ and Pb2+ ions are electrolysed into a sodium borate glass (35 mol% Na2O and 50 °C) are brought up to date in order to take into account recent developments in the chemistry of borate glasses.
It is first necessary to consider the unique chemistry of the oxide(-II) species in terms of its electronegativity, electronic
polarisability and acid–base properties, and the significant relationship between these is discussed. It is described how
the Lewis basicity of oxidic materials such as glasses can be expressed quantitatively on the optical basicity scale and how
determinations are made by various experimental methods. These methods include optical spectroscopy of ‘probe’ ions such as
Tl+ or Pb2+, measurement of electronic polarisability and far-infrared spectroscopic ‘rattling’ frequencies of constituent metal ions.
When Pb2+ ions are electrolysed into the sodium borate glass, it is found that there is migration of Na+ ions away from and of O2− ions towards the (lead) anode with formation of PbO. There is almost complete depletion of Na2O in the anode region so that the composition of the glass approximates to B2O3. A similar process occurs to a limited degree in the case of thallium, but the Tl+ ions are able to penetrate more deeply into the glass. Their ultraviolet 1S0 → 3P1 frequency indicates that the sites they occupy have much greater basicity than the bulk glass. The two-site model of Kamitsos
proposes that in borate glasses, there are higher and lower basicity sites, and the measured optical basicity of Tl+ indicates occupation of the higher sites. Since it has been shown that BO4 groups in the glass are weakly basic, it is unlikely that they are involved in the higher sites. It is discussed how the
higher site basicity implies greater covalency in the interaction of the Tl+ ion with the oxide(-II)s that constitute the pathway, and it is suggested that this is an important factor in the electromigration
process. 相似文献
80.
Two novel alkaloids, wilsoniamines A and B, both possessing a hexahydropyrrolo[1,2-c]imidazol-1-one ring system that has not previously been found in nature, together with a new alkaloid, amathamide H and a known alkaloid, amathamide C were isolated from the temperate Australian bryozoan, Amathia wilsoni. MS and NMR analysis established the structure of the new compounds and indicated that the structure of amathamide C and several related compounds be revised. Amathamides C and H showed moderate anti-malarial and anti-trypanosomal activity. 相似文献