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101.
Queueing Systems - We study the tight upper bound of the transient mean waiting time in the classical GI/GI/1 queue over candidate interarrival-time distributions with finite support, given the... 相似文献
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Thomas OD Soo KJ Peckham TJ Kulkarni MP Holdcroft S 《Journal of the American Chemical Society》2012,134(26):10753-10756
A stable hydroxide-conducting membrane based on benzimidazolium hydroxide and its analogous anion-exchange polymer is reported for the first time. The molecular and polymeric analogues possess unprecedented hydroxide stability in neutral and KOH solutions as the soluble benzimidazolium salt, made possible by steric crowding around the benzimidazolium C2 position, which is usually susceptible to nucleophilic attack by OH(-). The polymers were cast and insolubilized for the purpose of forming membranes by blending with a poly(benzimidazole) followed by hydroxide-activated electrostatic interactions. The resulting membranes possess ionic (OH(-)) conductivities of up to 13.2 mS cm(-1) and represent a new class of anion-exchange polymers and membranes. 相似文献
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Wren SW Vogelhuber KM Garver JM Kato S Sheps L Bierbaum VM Lineberger WC 《Journal of the American Chemical Society》2012,134(15):6584-6595
The negative ion chemistry of five azine molecules has been investigated using the combined experimental techniques of negative ion photoelectron spectroscopy to obtain electron affinities (EA) and tandem flowing afterglow-selected ion tube (FA-SIFT) mass spectrometry to obtain deprotonation enthalpies (Δ(acid)H(298)). The measured Δ(acid)H(298) for the most acidic site of each azine species is combined with the EA of the corresponding radical in a thermochemical cycle to determine the corresponding C-H bond dissociation energy (BDE). The site-specific C-H BDE values of pyridine, 1,2-diazine, 1,3-diazine, 1,4-diazine, and 1,3,5-triazine are 110.4 ± 2.0, 111.3 ± 0.7, 113.4 ± 0.7, 107.5 ± 0.4, and 107.8 ± 0.7 kcal mol(-1), respectively. The application of complementary experimental methods, along with quantum chemical calculations, to a series of nitrogen-substituted azines sheds light on the influence of nitrogen atom substitution on the strength of C-H bonds in six-membered rings. 相似文献
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The mechanisms of high-molecular-weight polyacrylamide nonionic homopolymer and 25 mol% anionic acrylate-substituted copolymer adsorption onto iron oxide particles were investigated via DRIFT and UV-vis spectroscopies at three pH values (6, 8.5, and 11). While electrostatic interactions play an important role in charged polymer adsorption, this information is not spectroscopically available. At pH values above and below pH 8.5 (the isoelectric point for the anionic polymer), bidentate chelation and hydrogen bonding were the main adsorption mechanisms. At the isoelectric point, monodentate chelation was observed to be the main mode of adsorption, along with hydrogen bonding. For the nonionic polymer, in all cases, hydrogen bonding through the carbonyl group was the main mode of adsorption. The adsorption of both polymers conformed well to the Freundlich model, suggesting that the adsorbed polymer amount increases with increasing polymer concentration up to 7500 g/t solid, rather than approaching monolayer coverage. Spectroscopic evidence was found to suggest that hydrolysis of nonionic polyacrylamide occurs at high pH. 相似文献
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Weinert EE Dondi R Colloredo-Melz S Frankenfield KN Mitchell CH Freccero M Rokita SE 《Journal of the American Chemical Society》2006,128(36):11940-11947
Electronic perturbation of quinone methides (QM) greatly influences their stability and in turn alters the kinetics and product profile of QM reaction with deoxynucleosides. Consistent with the electron-deficient nature of this reactive intermediate, electron-donating substituents are stabilizing and electron-withdrawing substituents are destabilizing. For example, a dC N3-QM adduct is made stable over the course of observation (7 days) by the presence of an electron-withdrawing ester group that inhibits QM regeneration. Conversely, a related adduct with an electron-donating methyl group is very labile and regenerates its QM with a half-life of approximately 5 h. The generality of these effects is demonstrated with a series of alternative quinone methide precursors (QMP) containing a variety of substituents attached at different positions with respect to the exocyclic methylene. The rates of nucleophilic addition to substituted QMs measured by laser flash photolysis similarly span 5 orders of magnitude with electron-rich species reacting most slowly and electron-deficient species reacting most quickly. The reversibility of QM reaction can now be predictably adjusted for any desired application. 相似文献
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Fritsch JM Thoreson KA McNeill K 《Dalton transactions (Cambridge, England : 2003)》2006,(40):4814-4820
An acyclic monoanionic tetradentate nitrogen ligand was prepared through the condensation of 2-(4-tolyl)-malondialdehyde and 8-aminoquinoline to give (BDI(QQ))H where (BDI(QQ))H = (8-quinolyl)-NCHC(4-tolyl)CHNH-(8-quinolyl). Metal complexes, (BDI(QQ))MX, were prepared where MX = MgBr 2, ZnCl 3, and CdOAc 4. The spectroscopic and crystallographic properties of compounds 2, 3, and 4 were explored. Structures of complexes 2, 3, 4, and the tridentate ligand, (BDI(Q))OH, 5, are reported. 相似文献
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