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61.
Kinetics studies are reported of the reactions of benzylidene benzylamine 4a, and of benzylidene allylamine 4b, with cyanide in aqueous buffers to give the corresponding [small alpha]-aminonitriles. The results allow the calculation of values of rate and equilibrium constants for reaction of the iminium ions formed from 4a and 4b with cyanide ions. These values are compared with those, obtained from the hydrolysis reactions, for reaction of the iminium ions with hydroxide ions and with water. Comparison with some other iminium ions reveals that those formed from 4a and 4b are relatively unreactive due to the possibilities of charge delocalisation. 相似文献
62.
Emma Hill Richard R. Lloyd-Williams Richard G. Compton John H. Atherton 《Journal of Solid State Electrochemistry》1999,3(6):327-330
The (100), (010) and (001) faces of monoclinic crystals of the organic solid p-chloranil display contrasting reactivities towards hydrolytic dissolution induced by aqueous hydroxide ions. The differing
behaviour is rationalised in terms of the functional groups exposed in the different faces.
Received: 23 November 1998 / Accepted: 21 January 1999 相似文献
63.
David Thomas Matt Cardarelli Badel L. Mbanga Timothy J. Atherton 《Liquid crystals》2016,43(1):112-123
Nematic liquid-crystalline elastomers (LCEs) are weakly cross-linked polymeric networks that exhibit rubber elasticity and liquid-crystalline orientational order due to the presence of mesogenic groups. Three end-on side-chain nematic LCEs were investigated using real-time synchrotron wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and thermogravimetry (TG) to correlate the thermal behaviour with structural and chemical differences among them. The elastomers differed in cross-linking density and mesogen composition. Thermally reversible glass transition temperature, Tg, and nematic-to-isotropic transition temperature, Tni, were observed upon heating and cooling. By varying the heating rate, Tg0 and Tni0 were determined at zero heating rate. The temperature dependence of the orientational order parameter was determined from the anisotropic azimuthal angular distribution of equatorial reflections seen during real-time WAXS. Results show that the choice of cross-linking unit, its shape, density, and structure of co-monomers, all influence the temperature range over which the thermal transitions take place. Including multi-ring aromatic groups as cross-linkers increased the effective stiffness of the cross-linking, resulting in a higher glass transition temperature. The nematic-to-isotropic transition temperature increased in the presence of multi-ring aromatic structures, as either cross-linkers or mesogens, particularly when the multi-ring structures were larger than the low-molar-mass mesogen common to all three samples. 相似文献
64.
The mechanism of the coupling step in polynucleotide synthesis using 5'-4,4'-dimethoxytritylthymidine-3'-beta-cyanoethyl-N,N-diisopropylphosphoramidite as the phosphitylating agent and catalysed by the salt of saccharin and N-methylimidazole in acetonitrile has been studied by (31)P NMR. Pre- and post-equilibria between the activator salt and released diisopropylamine have been examined by (1)H NMR and ITC, which show that the salt between saccharin and diisopropylamine will be present in acetonitrile. Activation of the phosphoramidite by the salt of saccharin and N-methylimidazole involves nucleophilic catalysis and the formation of a reactive saccharin adduct bonded through its carbonyl oxygen to phosphorus. The rate constants for the reaction of the 4-methoxyphenol with 5'-4,4'-dimethoxytritylthymidine-3'-beta-cyanoethyl-N,N-diisopropylphosphoramidite in the presence of saccharin-N-methylimidazole salt show a non-linear dependence on phenol concentration, becoming independent at high phenol concentrations, compatible with a change in rate limiting step from the alcoholysis step to the activation step. 相似文献
65.
The formation of H-phosphonate diesters is an important step in the synthesis of oligonucleotides. Using diphenylchlorophosphate as the activator for the coupling step is often accompanied by side reactions as a result of self 'capping' and other reactions of the reactive intermediate. In the absence of base, the activation of ethyl H-phosphonate with diphenylchlorophosphate probably occurs through the intermediate formation of bis diethyl pyro-di-H-phosphonate rather than the expected diphenyl ethyl pyro-H-phosphonate. Pyridine acts as a nucleophilic catalyst converting diphenylchlorophosphate to its pyridinium adduct. Several side and unwanted reactions are quantified so that conditions to minimise these can be identified. 相似文献
66.
Döppner T Thomas CA Divol L Dewald EL Celliers PM Bradley DK Callahan DA Dixit SN Harte JA Glenn SM Haan SW Izumi N Kyrala GA LaCaille G Kline JK Kruer WL Ma T MacKinnon AJ McNaney JM Meezan NB Robey HF Salmonson JD Suter LJ Zimmerman GB Edwards MJ MacGowan BJ Kilkenny JD Lindl JD Van Wonterghem BM Atherton LJ Moses EI Glenzer SH Landen OL 《Physical review letters》2012,108(13):135006
We have imaged hard x-ray (>100 keV) bremsstrahlung emission from energetic electrons slowing in a plastic ablator shell during indirectly driven implosions at the National Ignition Facility. We measure 570 J in electrons with E>100 keV impinging on the fusion capsule under ignition drive conditions. This translates into an acceptable increase in the adiabat α, defined as the ratio of total deuterium-tritium fuel pressure to Fermi pressure, of 3.5%. The hard x-ray observables are consistent with detailed radiative-hydrodynamics simulations, including the sourcing and transport of these high energy electrons. 相似文献
67.
Line-shift and line-width parameters for the (J, K) = (3, 3) inversion line of N14H3 have been measured at various temperatures in the range 213 to 373 K, and the results are compared with those predicted theoretically. The line-width parameter decreases with increasing temperature, in qualitative agreement with the theory, but the predicted widths are between 10 and 20% too large. The line-shift parameter is positive, so that the center frequency of the spectral line increases with increasing pressure, and the parameter decreases with increasing temperature. This is also in qualitative agreement with the theory but the predicted results are too large by factors of between 3.8 and 7.2. In addition to the experimental results, details are also given of a number of improvements which have been made to the spectrometer which had been used for earlier shift measurements. 相似文献
68.
Jonathan Booth Giles H.W. Sanders Richard G. Compton John H. Atherton Colin M. Brennan 《Journal of Electroanalytical Chemistry》1997,440(1-2)
A quantitative study of the hydrolytic dissolution of solid p-chloranil at alkaline pH using a combination of the channel flow cell and in situ atomic force microscopy measurements shows that the dissolution is driven by reaction of the substrate with hydroxide ions at, or very close to, the dissolving surface. The dissolution rate equation, deduced from the channel flow cell for single crystals of p-chloranil, is rate/mol cm−2 s−1 = 3.8 × 10−7 [OH−]0 where [OH−]0/M is the hydroxide ion concentration adjacent to the solid surface. An analogous rate law is derived for pressed pellet substrates. The novel application of the atomic force microscope to make absolute measurements of surface averaged dissolution rates is described. Comparison with the independent channel flow cell data reveals good mechanistic agreement and consistency of rate constants provided it is recognised that a thick stagnant diffusion layer can be present under the usual conditions employed for AFM. 相似文献
69.
Joan E. Roberts Stephen J. Atherton James Dillon 《Photochemistry and photobiology》1991,54(5):855-857
Previous steady state and time resolved spectroscopic studies on porphyrins have shown that the triplet lifetimes of those sensitizers that bind to lens proteins are lengthened by several orders of magnitude. Presented here is an extension of this experiment to measure these transients in an intact bovine lens. As demonstrated by steady state fluorescence spectroscopy and flash photolysis, mesotetra (p-sulfonatophenyl)porphyrin (TPPS) binds to lens proteins. In air-saturated aqueous solution, TPPS has a triplet lifetime of 2 microseconds. In an intact bovine lens the triplet state decayed via biexponential kinetics with lifetimes of 0.16 and 1.6 microseconds. In addition to a lengthening of the lifetime there was a red shift in the triplet transient spectra of 10-20 nm of the porphyrin in the intact lenses. 相似文献
70.
-Fluorenylmethoxycarbonyl derivatives of amines are unexpectedly cleaved by catalytic hydrogenation with t 3–33 h. under various conditions. They are also cleaved on standing in the solvents dimethylformamide, dimethylacetamine, and -methylpyrrolidone, but much more slowly. 相似文献