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11.
Peter A. Beckmann Carolyn A. Buser Clelia W. Mallory Frank B. Mallory Jennifer Mosher 《Solid state nuclear magnetic resonance》1998,12(4):251-256
We have measured the proton spin-lattice relaxation rate as a function of temperature in polycrystalline 3-ethylchrysene at nuclear magnetic resonance Larmor frequencies of 53.0 and 22.5 MHz and in polycrystalline 3-isopropylchrysene at 53.0, 22.5 and 8.50 MHz. The syntheses of these new compounds are presented. The relatively large chrysene backbone creates an ideal and unique environment for the alkyl groups such that methyl group rotation is the only motion on the nuclear magnetic resonance Larmor frequency timescale over a large temperature range. The relaxation rate data are interpreted in terms of the simplest possible dynamical model; that of random hopping for the methyl group(s), all of which are equivalent in the solid state. The barriers of 11–12 kJ mol−1 are typical for methyl groups in ‘isolated' ethyl and isopropyl groups. 相似文献
12.
Christopher Redwood V. K. Ratheesh Kumar Stuart Hutchinson Frank B. Mallory Clelia W. Mallory Ronald J. Clark Olga Dmitrenko Jack Saltiel 《Photochemistry and photobiology》2015,91(3):607-615
cis‐1,2‐Di(1‐methyl‐2‐naphthyl)ethene, c‐ 1,1 , undergoes photoisomerization in methylcyclohexane, isopentane and diethyl ether/isopentane/ethanol glasses at 77 K. On 313 nm excitation the fluorescence of c‐ 1,1 is replaced by fluorescence from t‐ 1,1 . Singular value decomposition reveals that the spectral matrices behave as two component systems suggesting conversion of a stable c‐ 1,1 conformer to a stable t‐ 1,1 conformer. However, the fluorescence spectra are λexc dependent. Analysis of global spectral matrices shows that c‐ 1,1 is a mixture of two conformers, each of which gives one of four known t‐ 1,1 conformers. The λexc dependence of the c‐ 1,1 fluorescence spectrum is barely discernible. Structure assignments to the resolved fluorescence spectra are based on the principle of least motion and on calculated geometries, energy differences and spectra of the conformers. The relative shift of the c‐ 1,1 conformer spectra is consistent with the shift of the calculated absorption spectra. The calculated structure of the most stable conformer of c‐ 1,1 agrees well with the X‐ray crystal structure. Due to large deviations of the naphthyl groups from the ethenic plane in the conformers of both c‐ and t‐ 1,1 isomers, minimal motion of these bulky substituents accomplishes cis → trans interconversion by rotation about the central bond. 相似文献
13.
14.
Frank W. Crow Wayne K. Duholke Chad E. Hadden Richard F. Smith Thomas J. Thamann Brian D. Kaluzny David A. Hahn Christopher S. Mallory Kathleen A. Farley Gary E. Martin 《Journal of heterocyclic chemistry》1999,36(2):365-370
The rigorous structural characterization of novobiocin, is reported using mass spectrometric, infrared and nmr spectroscopic analysis. Complete nmr assignments are reported. Previous reports in the literature had left some quaternary carbon resonances unassigned. Isonovobiocin and decarbamylnovobiocin, although known in the literature for a number of years, have never been completely characterized. Mass spectrometric fragmentation pathways and complete 1H and 13C nmr assignments are reported for these congeners for the first time. The mass spectral fragmentation pathway and nmr assignments are also reported for 2″-(O-carbamyl)novobiocin although the nmr assignments at lower field were reported previously. The structural characterization of novobiocin-2″,3″-carbonate observed in the Test Assay procedure used for Novobiocin is reported for the first time. 相似文献
15.
A visual indicator method is described for titrations of anionic surfactants with 5 × 10-5 M tetraphenylphosphonium solution. Two dyes, the hydrophilic neutral red and the hydrophobic tetrabromophenolphthalein ethyl ester, are used as indicator in the presence of 1,2-dichloroethane. 相似文献
16.
The Whitham equation is a non-local model for nonlinear dispersive water waves. Since this equation is both nonlinear and non-local, exact or analytical solutions are rare except for in a few special cases. As such, an analytical method which results in minimal error is highly desirable for general forms of the Whitham equation. We obtain approximate analytical solutions to the non-local Whitham equation for general initial data by way of the optimal homotopy analysis method, through the use of a partial differential auxiliary linear operator. A method to control the residual error of these approximate solutions, through the use of the embedded convergence control parameter, is discussed in the context of optimal homotopy analysis. We obtain residual error minimizing solutions, using relatively few terms in the solution series, in the case of several different kernels and associated initial data. Interestingly, we find that for a specific class of initial data, there exists an exact solution given by the first term in the homotopy expansion. A specific example of initial data which satisfies the condition producing an exact solution is included. These results demonstrate the applicability of optimal homotopy analysis to equations which are simultaneously nonlinear and non-local. 相似文献
17.
Gregory B. Kharas Youya Gao Jihad Aburas Christina Chintanaphol Mallory L. Davis Hubert Dolubizno 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):593-598
Novel trisubstituted ethylenes, ring-substituted butyl 2-cyano-3-phenyl-2-propenoates, RPhCH=C(CN)CO2C4H9 (where R is 2-C6H5CH2O, 3-C6H5CH2O, 4-C6H5CH2O, 4-CH3COO, 3-CH3CO, 4-CH3CO, 4-CH3CONH, 2-CN, 3-CN, 4-CN, 4-(CH3)2N, 4-(C2H5)2N) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and butyl cyanoacetate, and characterized by CHN analysis, IR, 1H and 13C-NMR. All the ethylenes were copolymerized with styrene (M1) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, 1H and 13C-NMR. The order of relative reactivity (1/r1) for the monomers is 4-C6H5CH2O (6.39) > 2-C6H5CH2O (2.06) > 3-CH3CO (1.86) > 3-C6H5CH2O (1.78) > 4-CH3COO (1.58) > 3-CN (1.47) > 4-CN (1.21) > 4-(C2H5)2N (1.19) > 4-(CH3)2N (1.18) > 2-CN (1.04) > 4-CH3CO (0.71) > 4-CH3CONH (0.63). Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (3.6–9.5% wt), which then decomposed in the 500–800°C range. 相似文献
18.
Melanins are ubiquitous catecholic pigments, formed in organelles called melanosomes within melanocytes, the function of which is to protect skin against harmful effects of UV radiation. Melanosomes within melanoma cells are characteristically abnormal, with fragmented melanin and disrupted membranes. We hypothesize that the disruption of melanosomal melanin might be an early event in the etiology and progression of melanoma, leading to increased oxidative stress and mutation. In this report, we examine the effect of a combination of UV treatment and metal ion exposure on melanosomes within melanocytes, as well as their ability to act as pro-oxidants in ex situ experiments, and assay the effects of this treatment on viability and cell cycle progression. UVB exposure causes morphologic changes of the cells and bleaching of melanosomes in normal melanocytes, both significantly enhanced in Cu(II) and Cd(II)-treated cells, as observed by microscopy. The promoted bleaching by Cu(II) is due to its ability to redox cycle under oxidative conditions, generating reactive oxygen species; verified by the observed enhancement of hydroxyl radical generation when isolated melanosomes were treated with both Cu(II) ions and UVB, as assayed by DNA clipping. Single-dose UVB/Cu treatment does not greatly affect cell viability or cell cycle progression in heavily pigmented cells, but did so in an amelanotic early stage melanoma cell line. 相似文献
19.
Jenny Triptow Dr. André Fielicke Prof. Gerard Meijer Dr. Mallory Green 《Angewandte Chemie (International ed. in English)》2023,62(1):e202212020
Photoelectron Circular Dichroism (PECD) is a forward-backward asymmetry in the photoemission from a non-racemic sample induced by circularly polarized light. PECD spectroscopy has potential analytical advantages for chiral discrimination over other chiroptical methods due to its increased sensitivity to the chiral potential of the molecule. The use of anions for PECD spectroscopy allows for mass-selectivity and provides a path to simple experimental schemes that employ table-top light sources. Evidence of PECD for anions is limited, and insight into the forces that govern PECD electron dynamics in photodetachment is absent. Here, we demonstrate a PECD effect in the photodetachment of mass-selected deprotonated 1-indanol anions. By utilizing velocity map imaging photoelectron spectroscopy with a tunable light source, we determine the energy-resolved PECD over a wide range of photon energies. The observed PECD reaches up to 11 %, similar to what has been measured for neutral species. 相似文献
20.
Emily Oakley David Bellnier Alan Hutson Hannah Cooper Michael Habitzruther Sandra Sexton Leslie Curtin Lawrence Tworek Matthew Mallory Barbara Henderson Gal Shafirstein 《Photochemistry and photobiology》2020,96(2):397-404
The objective of the present study was to develop a predictive model for Photofrin®-mediated interstitial photodynamic therapy (I-PDT) of locally advanced tumors. Our finite element method was used to simulate 630-nm intratumoral irradiance and fluence for C3H mice and New Zealand White rabbits bearing large squamous cell carcinomas. Animals were treated with light only or I-PDT using the same light settings. I-PDT was administered with Photofrin® at 5.0 or 6.6 mg kg−1, 24 h drug-light interval. The simulated threshold fluence was fixed at 45 J cm−2 while the simulated threshold irradiance varied, intratumorally. No cures were obtained in the mice treated with a threshold irradiance of 5.4 mW cm−2. However, 20–90% of the mice were cured when the threshold irradiances were ≥8.6 mW cm−2. In the rabbits treated with I-PDT, 13 of the 14 VX2 tumors showed either local control or were cured when threshold irradiances were ≥15.3 mW cm−2 and fluence was 45 J cm−2. No tumor growth delay was observed in VX2 treated with light only (n = 3). In the mouse studies, there was a high probability (92.7%) of predicting cure when the initial tumor volume was below the median (493.9 mm3) and I-PDT was administered with a threshold intratumoral irradiance ≥8.6 mW cm−2. 相似文献