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31.
Ethanol production from steam-explosion pretreated wheat straw 总被引:1,自引:0,他引:1
Ignacio Ballesteros Ma José Negro José Miguel Oliva Araceli Cabañas Paloma Manzanares Mercedes Ballesteros 《Applied biochemistry and biotechnology》2006,130(1-3):496-508
Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production
from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production
by a simultaneous saccharification and fermentation process were studied, using diluted acid [H2SO4 0.9% (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures
(160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic
digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best
pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after
steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated
biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the
filtrate (300 g/kg wheat straw). 相似文献
32.
Regioselectivity in acylation of oligosaccharides catalyzed by the metalloprotease thermolysin 总被引:2,自引:0,他引:2
Investigation of the acylation scope of carbohydrates by metalloprotease thermolysin immobilized on Celite as biocatalyst has been carried out. The reactions were performed in DMSO, a good solvent for carbohydrates, where the enzyme has previously shown its activity in transesterifications of sucrose, maltose and maltose-containing oligosaccharides. Surprisingly, no reaction was observed for glucose or the glucose-containing disaccharides, trehalose and lactose. In contrast, laurate monoesters of several sucrose-containing tri- and tetrasaccharides were synthetized through a one step transesterification using vinyl laurate as the acylating agent. Enzyme regioselectivity was accurately determined by HPLC/MS and the structure of the main regioisomers was established by a combination of NMR experiments. The preferred position of acylation in all cases was the 2-OH of the α-d-glucopyranose moiety linked 1→2 to the β-d-fructofuranose unit. These results correlate with the regioselectivity observed in the case of the disaccharide sucrose. A general carbohydrate binding motif for catalysis by thermolysin is proposed. 相似文献
33.
C. Testa D. Desideri M. A. Meli C. Roselli A. Bassignani P. B. Finazzi 《Journal of Radioanalytical and Nuclear Chemistry》1993,170(1):117-124
Low specific activity scales consisting of alkaline earth metal carbonates and sulfates are often present in some gaseous and liquid hydrocarbon plants; these scales contain a certain concentration of radium, uranium and thorium, which can cause a risk of -irradiation and of internal radiocontamination when they must be mechanically removed. That being stated,238U,232Th and226Ra were determined in scales, sludges and waters coming from different plants.238U and232Th concentrations were found very low; the isotopes238U and234U resulted in radioactive equilibrium, whilst232Th and228Th were not always in equilibrium.226Ra concentration was higher in scales and sludges than in waters. 相似文献
34.
Grant J. Sherborne Avetik G. Gevondian Ignacio Funes-Ardoiz Amit Dahiya Christoph Fricke Prof. Dr. Franziska Schoenebeck 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(36):15673-15678
Selective C –C couplings are powerful strategies for the rapid and programmable construction of bi- or multiaryls. To this end, the next frontier of synthetic modularity will likely arise from harnessing the coupling space that is orthogonal to the powerful Pd-catalyzed coupling regime. This report details the realization of this concept and presents the fully selective arylation of aryl germanes (which are inert under Pd0/PdII catalysis) in the presence of the valuable functionalities C−BPin, C−SiMe3, C−I, C−Br, C−Cl, which in turn offer versatile opportunities for diversification. The protocol makes use of visible light activation combined with gold catalysis, which facilitates the selective coupling of C−Ge with aryl diazonium salts. Contrary to previous light-/gold-catalyzed couplings of Ar–N2+, which were specialized in Ar–N2+ scope, we present conditions to efficiently couple electron-rich, electron-poor, heterocyclic and sterically hindered aryl diazonium salts. Our computational data suggest that while electron-poor Ar–N2+ salts are readily activated by gold under blue-light irradiation, there is a competing dissociative deactivation pathway for excited electron-rich Ar–N2+, which requires an alternative photo-redox approach to enable productive couplings. 相似文献
35.
Claudio Bianchini Carlo A. Ghilardi Andrea Meli Stefano Midollini Annabella Orlandini 《Journal of organometallic chemistry》1983,255(2):C27-C30
CO2, COS, and SCNPh react under very mild conditions with the copper(I)-tetrahydroborate complexes [(PR3)2Cu(η2-BH4)] (R = Ph, Cy); CO2 and COS give the complexes [(PR3)2Cu(η2-O2CH)] and [(PR3)2Cu(η2-OSCH)] respectively, whereas SCNPh gives the η2-dithiocarbamate complexes [(PR3)2Cu-(η2-S2CNHPh)]. Addition of PPh3 under CO2 to solutions of [(PPh3)2Cu-(η2-BH4)] gives [(PPh3)3Cu(η1-O2CH)] while addition of PPh3 and NBu4ClO4 under CO2 gives [(PPh3)3Cu(η-O2CH)Cu(PPh3)3] ClO4. 相似文献
36.
Octavio Surez-Iglesias Ignacio Medina Consuelo Pizarro Julio L. Bueno 《Fluid Phase Equilibria》2007,260(2):279-286
The Taylor–Aris chromatographic technique was employed for the determination of diffusion coefficients of 2-fluoroanisole, 2-bromoanisole, allylbenzene and 1,3-divinylbenzene at infinite dilution in supercritical carbon dioxide from 313.16 to 333.16 K and pressures between 15 and 35 MPa. As expected, the diffusivities rise when temperature increases and pressure decreases. Numerous predictive equations are compared with experimental data: Lai–Tan, Liu–Ruckenstein cluster formula, Woerlee, Hippler–Schubert–Troe, Catchpole–King, Eaton–Akgerman, He, He–Yu, Liu–Silva–Macedo, Funazukuri and coworkers, Dariva–Coelho–Oliveira, Zhu–Lu–Zhou–Wang–Shi and the Liu–Ruckenstein RHS formula. The equations of He, He–Yu and Catchpole–King are the best of all, but cannot be used in the whole range of temperatures and solvent densities. 相似文献
37.
Viñas P Aguinaga N López-García I Hernandez-Córdoba M 《Journal of AOAC International》2002,85(3):736-743
Procedures were developed for determining cadmium, aluminium, and copper in beer and the products used in its manufacture by electrothermal atomic absorption spectrometry. Beer samples were injected into the furnace and solid samples were introduced as suspensions after preparation in a medium containing hydrogen peroxide, nitric acid, and ammonium dihydrogen phosphate for cadmium atomization. Calibration was performed with aqueous standards, and characteristic masses and detection limits were, respectively, 1 and 0.3 pg for cadmium, 18 and 5.4 pg for aluminium, and 5.6 and 6.8 pg for copper. Different samples of beer, wort, brewer's yeast, malt, raw grain, and hops were analyzed by the proposed procedures. Cadmium was found in low concentrations (0.001-0.08 microg/g and 0-1.3 ng/mL); copper (3-13 microg/g and 25-137 ng/mL) and aluminium (0.6-9 microg/g and 0.1-2 microg/mL) were found at higher levels. The reliability of the procedure was confirmed by comparing the results obtained with others based on microwave oven sample digestion, and by analyzing several certified reference materials. 相似文献
38.
Ignacio H. Sánchez María Isabel Larraza Fernande Basurto Ricardo Yaf?ez Salvador Avila Ricardo Tovar Pedro Joseph-Nathan 《Tetrahedron》1985,41(12):2355-2359
(±)--methylperezone () was obtained by selective oxidative demethylation of (±)-leucoperezone trimethyl ether (). Compound () was prepared by condensation of 2,3,5-trimethoxytoluene () with 6-methyl-5-hepten-2-one, followed by reductive removal of the tertiary alcohol. The aromatic precursor was prepared in four steps from 2,3-dimethoxytoluene () and, alternatively, in three steps from 5-bromoveratraldehyde (). Racemic and were directly compared with the optically active molecules prepared from natural R(-)-perezone (). 相似文献
39.
Ana Cristina Gmez-Herrero Carlos Snchez-Snchez Frdric Chrioux Jose Ignacio Martínez Jos Abad Luca Floreano Alberto Verdini Albano Cossaro Estelle Mazaleyrat Valrie Guisset Philippe David Simone Lisi Jos Angel Martín Gago Johann Coraux 《Chemical science》2021,12(6):2257
Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases.An antioxidant catechol transforms following intramolecular redox reactions into highly reactive oxygen species, a semiquinone and a quinone, on copper. 相似文献
40.