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101.
102.
A fluorous prolinol precatalyst bearing only 34 fluorine atoms has been immobilized in the hydrofluoroether solvent HFE-7500. The CBS reduction of acetophenone proceeded rapidly, in high yield and in high ee in the absence of any organic solvent. The organic product was stripped from the HFE-7500 phase with a polar solvent, and the HFE-7500 phase was reused "as is" with satisfactory results through eight runs. This process is an attractive prototype for the large-scale use, recovery, and reuse of fluorous organocatalysts. 相似文献
103.
Wenlin Huang Qian Zhao Zuohua Huang Henry J. Curran Yingjia Zhang 《Proceedings of the Combustion Institute》2021,38(1):601-609
Though the combustion chemistry of dimethyl ether (DME) has been widely investigated over the past decades, there remains a dearth of ignition data that examines the low-temperature, low-pressure chemistry of DME. In this study, DME/‘air’ mixtures at various equivalence ratios from lean (0.5) to extremely rich (5.0) were ignited behind reflected shock waves at a fixed pressure (3.0 atm) over the temperature range 625–1200 K. The ignition behavior is different from that at high-pressures, with a repeatable ignition delay time fall-off feature observed experimentally in the temperature transition zone from the negative temperature coefficient (NTC) regime to the high-temperature regime. This could not be reproduced using available kinetic mechanisms as conventionally homogeneous ignition simulations. The fall-off behavior shows strong equivalence ratio dependence and disappears completely at an equivalence ratio of 5.0. A local ignition kernel postulate was implemented numerically to quantifiably examine the inhomogeneous premature ignition. At low temperature, no pre-ignition occurs in the mixture. A conspicuous discrepancy was observed between the measurements and constrained UV simulations at temperatures beyond the NTC regime. A third O2 addition reaction sub-set was incorporated into AramcoMech 3.0, together with related species thermochemistry calculated using the G3/G4/CBS-APNO compound method, to explore the low-temperature deviation. The new reaction class does not influence the model predictions in IDTs, but the updated thermochemistry does. Sensitivity analyses indicate that the decomposition of hydroperoxy-methylformate plays a critical role in improving the low-temperature oxidation mechanism of DME but unfortunately, the thermal rate coefficient has never been previously investigated. Further experimental and theoretical endeavors are required to attain holistic quantitative chemical kinetics based on our understanding of the low-temperature chemistry of DME. 相似文献
104.
Shashank S. Nagaraja Jennifer Power Goutham Kukkadapu Shijun Dong Scott W. Wagnon William J. Pitz Henry J. Curran 《Proceedings of the Combustion Institute》2021,38(1):881-889
A single-pulse shock tube study of the four pentene isomers is carried out at 2 ± 0.16 bar and 900–1600 K. C1 to C6 species profiles were recorded using gas chromatography mass spectrometry analyses. The species are identified using mass spectrometry and quantified by flame ionization detection. High-pressure limiting and pressure-dependent rate constants for 2M1B, 2M2B and 3M1B + ? were calculated using RRKM theory with a Master Equation (ME) analysis using the Master Equation System Solver, MESS. A mechanism was formulated based on rate rules and theoretical calculations. Comparisons between experimental results and model simulations are provided for all of the five pentene isomers investigated with satisfactory agreement. Furthermore, an insight is provided into the influence of molecular structure on the reactivity of pyrolysis chemistry. Interestingly, it is found that the HACA mechanism is much less prominent for benzene formation compared to the role of cyclopentadienyl radical recombination with methyl radicals and also the recombination of propargyl radicals. 相似文献
105.
A. Abd El-Sabor Mohamed Snehasish Panigrahy Amrit Bikram Sahu Gilles Bourque Henry J. Curran 《Proceedings of the Combustion Institute》2021,38(1):365-373
Ignition delay time measurements for multi-component natural gas mixtures were carried out using a rapid compression machine at conditions relevant to gas turbine operation, at equivalence ratios of 0.5–2.0 in ‘air’ in the temperature range 650–1050 K, at pressures of 10–30 bar. Natural gas mixtures comprising C1–C7 n-alkanes with methane as the major component (volume fraction: 0.35–0.98) were considered. A design of experiments was employed to minimize the number of experiments needed to cover the wide range of pressures, temperatures and equivalence ratios. The new experimental data, together with available literature data, were used to develop and assess a comprehensive chemical kinetic model. Replacing 1.875% methane with 1.25% n-hexane and 0.625% n-heptane in a mixture containing C1–C5 components leads to a significant increase in a mixture's reactivity. The mixtures containing heavier hydrocarbons also tend to show a strong negative temperature coefficient and two-stage ignition behavior. Sensitivity analyses of the C1–C7 blends have been performed to highlight the key reactions controlling their ignition behavior. 相似文献
106.
Teodor Banica Stephen Curran Roland Speicher 《Probability Theory and Related Fields》2011,149(3-4):435-462
We consider several orthogonal quantum groups satisfying the ??easiness?? assumption axiomatized in our previous paper. For each of them we discuss the computation of the asymptotic law of Tr(u k ) with respect to the Haar measure, u being the fundamental representation. For the classical groups O n , S n we recover in this way some well-known results of Diaconis and Shahshahani. 相似文献
107.
Y Wang L Davidow AC Arvanites J Blanchard K Lam K Xu V Oza JW Yoo JM Ng T Curran LL Rubin AP McMahon 《Chemistry & biology》2012,19(8):972-982
Highlights? Screened compound libraries for modulation of Smo movement to the primary cilium ? Identified glucocorticoids inducing Smo ciliary accumulation without activation ? They sensitize cells to Hh input and potentially modify the efficacy of Smo antagonists ? Identified a glucocorticoid inhibitor effective in inhibiting drug-resistant Smo mutants 相似文献
108.
109.
Selenide ions have been shown to catalyze the Tishchenko reaction for the first time. These catalysts are superior to previously reported thiolate analogues and promote the disproportionation of aldehydes with increased reaction rates and broader scope at lower catalyst loadings and temperatures. Significantly improved catalyst performance was also observed in the aryl selenide mediated crossed intermolecular Tishchenko reaction. 相似文献
110.
Murphy MC Curran GL Glaser KJ Rossman PJ Huston J Poduslo JF Jack CR Felmlee JP Ehman RL 《Magnetic resonance imaging》2012,30(4):535-539
The increasing prevalence of Alzheimer's disease (AD) has provided motivation for developing novel methods for assessing the disease and the effects of potential treatments. Magnetic resonance elastography (MRE) is an MRI-based method for quantitatively imaging the shear tissue stiffness in vivo. The objective of this research was to determine whether this new imaging biomarker has potential for characterizing neurodegenerative disease. Methods were developed and tested for applying MRE to evaluate the mouse brain, using a conventional large bore 3.0T MRI system. The technique was then applied to study APP-PS1 mice, a well-characterized model of AD. Five APP-PS1 mice and 8 age-matched wild-type mice were imaged immediately following sacrifice. Brain shear stiffness measurements in APP-PS1 mice averaged 22.5% lower than those for wild-type mice (P = .0031). The results indicate that mouse brain MRE is feasible at 3.0T, and brain shear stiffness has merit for further investigation as a potential new biomarker for Alzheimer's disease. 相似文献