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排序方式: 共有142条查询结果,搜索用时 31 毫秒
71.
Mattias Kalén Elisabet Wallgard Noomi Asker Aidas Nasevicius Elisabet Athley Erik Billgren Jon D. Larson Shannon A. Wadman Elizabeth Norseng Karl J. Clark Liqun He Linda Karlsson-Lindahl Ann-Katrin Häger Holger Weber Hellmut Augustin Tore Samuelsson Chelsy K. Kemmet Carly M. Utesch Jeffrey J. Essner Perry B. Hackett Mats Hellström 《Chemistry & biology》2009,16(4):432-441
72.
73.
Maxwell D. Cummings Jimmy Lindberg Tse‐I Lin Herman de Kock Oliver Lenz Elisabet Lilja Sara Felländer Vera Baraznenok Susanne Nyström Magnus Nilsson Lotta Vrang Michael Edlund Åsa Rosenquist Bertil Samuelsson Pierre Raboisson Kenneth Simmen 《Angewandte Chemie (International ed. in English)》2010,49(19):3250-3250
74.
Maxwell D. Cummings Jimmy Lindberg Tse‐I Lin Herman de Kock Oliver Lenz Elisabet Lilja Sara Felländer Vera Baraznenok Susanne Nyström Magnus Nilsson Lotta Vrang Michael Edlund Åsa Rosenquist Bertil Samuelsson Pierre Raboisson Kenneth Simmen 《Angewandte Chemie (International ed. in English)》2010,49(9):1510-1510
75.
Dr. Julien Godeau Dr. Fabien Fontaine‐Vive Dr. Sylvain Antoniotti Dr. Elisabet Duñach 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(52):16815-16822
Cycloisomerisation of polyenes such as diethyl geranylprenylmalonate [(E)‐ 1 a ], diethyl geranylphenylmalonate [(E)‐ 2 a ] and diethyl cinnamylgeranylmalonate [(E,E)‐ 3 a ] catalysed by bismuth triflate was studied from experimental and theoretical viewpoints. Several intermediates were isolated and characterised, and calculated transition‐state structures are proposed for the three reactions. The diastereoselectivity observed during the reaction of (E)‐ or (Z)‐ 2 a in favour of the formation of trans‐fused bicyclic products is discussed in detail. The nature of the active catalytic species derived from bismuth triflate was also investigated, and the formation of a hybrid Lewis acid/Brønsted acid catalyst with water molecules is proposed, supported by experimental and theoretical data. 相似文献
76.
Ana Ferrer Elisabet Quintana Ilari Filpponen Iina Solala Teresa Vidal Alejandro Rodríguez Janne Laine Orlando J. Rojas 《Cellulose (London, England)》2012,19(6):2179-2193
Unbleached (UN), oxygen-delignified and fully-bleached (FB) birch fibers with a residual lignin content of ca. 3, 2 and <1 %, respectively, were used to produce nanofibrillated cellulose (NFC) and nanopaper by using an overpressure device. The tensile index, elongation and elastic modulus of nanopaper were compared and the effect of residual cell wall components accessed. Under similar manufacturing conditions, UN NFC produced nanopaper with a density of 0.99 g/cm3, higher than that from FB NFC (0.7 g/cm3). This translated in much lower air permeability in the case of UN nanopaper (1 and 11 mL/min for UN and FB samples, respectively). Fundamentally, these observations are ascribed to the finer fibrils produced during microfluidization of UN fibers compared to those from lower yield counterparts (AFM roughness of 8 and 17 nm and surface areas of 124 and 98 m2/g for NFC from UN and FB fibers, respectively). As a result, values of stress at break and energy absorption of nanopaper from high yield fibers are distinctively higher than those from fully bleached NFC. Interactions of water with the surface and bulk material were affected by the chemical composition and structure of the nanofibrils. While UN nanopaper presented higher water contact angles their sorption capacity (and rate of water absorption) was much higher than those measured for nanopaper from FB NFC. These and other observations provided in this contribution are proposed to be related to the mechanoradical scavenging capacity of lignin in high shear microfluidization and the presence of residual heteropolysaccharides. 相似文献
77.
Monfardini I Massi L Duñach E Olivero S Gal JF 《Chemical communications (Cambridge, England)》2010,46(44):8472-8474
The relative Lewis basicity of a series of phosphoryl compounds toward cations M(n+)(OTf)(n-1) derived from triflate salts, M(OTf)(n), is ranked using electrospray mass spectrometry according to competitive adduct formation. 相似文献
78.
Mateos-Martín ML Fuguet E Quero C Pérez-Jiménez J Torres JL 《Analytical and bioanalytical chemistry》2012,402(3):1327-1336
The inner bark of Ceylon cinnamon (Cinnamomum zeylanicum L.) is commonly used as a spice and has also been widely employed in the treatment and prevention of disease. The positive
health effects associated with the consumption of cinnamon could in part be due to its phenolic composition; proanthocyanidins
(PA) are the major polyphenolic component in commercial cinnamon. We present a thorough study of the PA profile of cinnamon
obtained using matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) mass spectrometry. In addition
to the advantages of MALDI-TOF as a sensitive technique for the analysis of high-molecular-weight compounds, the tandem arrangement
allows the identification of the compounds through their fragmentation patterns from MS/MS experiments. This is the first
time that this technique has been used to analyze polymeric PA. The results show that cinnamon PA are more complex than was
previously thought. We show here for the first time that they contain (epi)gallocatechin and (epi)catechingallate units. As
gallates (galloyl moieties) and the pyrogallol group in gallocatechins have been related to the biological activity of grape
and tea polyphenols, the presence of these substructures may explain some of the properties of cinnamon extracts. MALDI-TOF/TOF
reveals that cinnamon bark PA include combinations of (epi)catechin, (epi)catechingallate, (epi)gallocatechin, and (epi)afzelechin,
which results in a highly heterogeneous mixture of procyanidins, prodelphinidins, and propelargonidins. 相似文献
79.
Two in-line preconcentration capillary zone electrophoresis (CZE) methods (field amplified sample injection (FASI) and stacking with sample matrix removal (LVSS)) have been evaluated for the analysis of acrylamide (AA) in foodstuffs. To allow the determination of AA by CZE, it was derivatized using 2-mercaptobenzoic acid. For FASI, the optimum conditions were water at pH > or = 10 adjusted with NH3 as sample solvent, 35 s hydrodynamic injection (0.5 psi) of a water plug, 35 s of electrokinetic injection (-10 kV) of the sample, and 6s hydrodynamic injection (0.5 psi) of another water plug to prevent AA removal by EOF. In stacking with sample matrix removal, the reversal time was found to be around 3.3 min. A 40 mM phosphate buffer (pH 8.5) was used as carrier electrolyte for CZE separation in both cases. For both FASI and LVSS methods, linear calibration curves over the range studied (10-1000 microg L(-1) and 25-1000 microg L(-1), respectively), limit of detection (LOD) on standards (1 microg L(-1) for FASI and 7 microg L(-1) for LVSS), limit of detection on samples (3 ng g(-1) for FASI and 20 ng g(-1) for LVSS) and both run-to-run (up to 14% for concentration and 0.8% for time values) and day-to-day precisions (up to 16% and 5% for concentration and time values, respectively) were established. Due to the lower detection limits obtained with the FASI-CZE this method was applied to the analysis of AA in different foodstuffs such as biscuits, cereals, crisp bread, snacks and coffee, and the results were compared with those obtained by LC-MS/MS. 相似文献
80.
Conjugate additions of non-nucleophilic N-containing compounds such as amides, thioamides, sulfonamides, and electron-poor anilines with different Michael acceptors can be promoted through the use of tributylphosphine. The range of useful pKa's of nucleophiles has been established (pKa<25) and new insights into the mechanism proposed. 相似文献