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61.
Development of Polar Order in the Liquid Crystal Phases of a 4‐Cyanoresorcinol‐Based Bent‐Core Mesogen with Fluorinated Azobenzene Wings 下载免费PDF全文
Dr. Mohamed Alaasar Dr. Marko Prehm Dr. Maria‐Gabriela Tamba Dr. Nerea Sebastián Dr. Alexey Eremin Prof. Dr. Carsten Tschierske 《Chemphyschem》2016,17(2):278-287
A bent‐core mesogen consisting of a 4‐cyanoresorcinol unit as the central core and laterally fluorinated azobenzene wings forms four different smectic LC phase structures in the sequence SmA–SmCs–SmCsPAR–M, all involving polar SmCsPS domains with growing coherence length of tilt and polar order on decreasing temperature. The SmA phase is a cluster‐type de Vries phase with randomized tilt and polar direction; in the paraelectric SmCs phase the tilt becomes uniform, although polar order is still short‐range. Increasing polar correlation leads to a new tilted and randomized polar smectic phase with antipolar correlation between the domains (SmCsPAR) which then transforms into a viscous polar mesophase M. As another interesting feature, spontaneous symmetry breaking by formation of a conglomerate of chiral domains is observed in the non‐polar paraelectric SmCs phase. 相似文献
62.
Gabriela A. Grasa Antonio Zanotti-Gerosa Christopher A. Teleha Bruce E. Maryanoff 《Tetrahedron letters》2008,49(36):5328-5331
Enantioselective preparation of a key αvβ3 integrin antagonist intermediate was accomplished via catalytic asymmetric hydrogenation of the corresponding β,β-disubstituted α,β-unsaturated carboxylic acid bearing a 3-quinolinyl moiety. The successful application of a Ru-(R)-XylPhanePhos catalyst to this type of substrate is unprecedented. In situ NMR experiments of pre-catalyst formation/activation by CH3CO2H, and reaction parameter modification, revealed that [Ru(COD)(CF3CO2)2]2/(R)-XylPhanePhos is a highly active and efficient catalytic system. 相似文献
63.
José Luis Fonseca María José Sosa Gabriela Petroselli Rosa Erra-Balsells Matías I. Quindt Sergio M. Bonesi Alexander Greer Edyta M. Greer Andrés H. Thomas Mariana Vignoni 《Photochemistry and photobiology》2023,99(2):593-604
Here, we provide mechanistic insight to the photocleavage of a compound in the folate family, namely pteroic acid. A bis-decyl chain derivative of pteroic acid was synthesized, structurally characterized and photochemically investigated. We showed that, like folic acid, pteroic acid and the decylated derivative undergo a photocleavage reaction in the presence of H2O, while no reaction was observed in methanol solution. Furthermore, density functional theory calculations were carried out to predict relative stabilities of hypothetical mono-, bis- and tris-decylated pteroic acid derivatives to help rationalize the regioselectivity of the bis-decyl pteroic acid product. Additionally, the lipophilicity of the bis-decyl pteroic acid appears to confer a hydrophobic property enabling an interaction with biomembranes. 相似文献
64.
Sajewicz Mieczysław Hauck Heinz-E. Drabik Gabriela Namysło Ewa Głód Bronisław Kowalska Teresa 《平面色谱法杂志一现代薄层色谱法》2006,19(4):278-281
JPC – Journal of Planar Chromatography – Modern TLC - We have previously described unexpected two-dimensionality in the thin-layer chromatographic separation of pairs of enantiomers of... 相似文献
65.
Arráez-Román D Zurek G Bässmann C Segura-Carretero A Fernández-Gutiérrez A 《Electrophoresis》2008,29(10):2112-2116
This short communication describes the characterization of seven tropane alkaloid compounds in Atropa belladonna L. Thus a rapid and easy CE-electrospray interface (ESI)-TOF-MS procedure is developed to analyze these compounds in a pharmaceutical preparations of A. belladonna L. leaf extract. Optimum electrophoretic separation is obtained using an alkaline solution of 60 mM ammonium acetate at pH 8.5 containing 5% isopropanol. Under the optimum CE-ESI-TOF-MS conditions several important compounds such as tropine, belladonnine, norhyoscyamine, apoatropine, hyoscyamine, 6beta-hydroxyhyoscyamine, and scopolamine have been simultaneously identified from A. belladonna L. CE-ESI-IT-MS has been used to discriminate the putative presence of littorine. The sensitivity, together with mass accuracy and true isotopic pattern of the TOF-MS, allowed the identification of a broad series of tropane alkaloid compounds present in pharmaceutical preparations of A. belladonna L. leaf extract. 相似文献
66.
Theoretical and experimental investigation on the oxidation of gallic acid by sulfate radical anions
Caregnato P Gara PM Bosio GN Gonzalez MC Russo N Michelini Mdel C Martire DO 《The journal of physical chemistry. A》2008,112(6):1188-1194
By monitoring the decay of SO4*- after flash photolysis of aqueous solutions of S2O82- at different pH values, the kinetics of the reaction of SO4*- radicals with gallic acid and the gallate ion was investigated. The bimolecular rate constants for the reactions of the sulfate radicals with gallic acid and the gallate ion were found to be (6.3 +/- 0.7) x 10(8) and (2.9 +/- 0.2) x 10(9) M(-1) s(-1), respectively. On the basis of the oxygen-independent second-order decay kinetics and on their absorption spectra, the organic radicals formed as intermediates of these reactions were assigned to the corresponding phenoxyl radicals. DFT calculations in the gas phase and aqueous solution support formation of the phenoxyl radicals by H abstraction from the phenols to the sulfate radical anion. The observed recombination of the phenoxyl radicals of gallic acid to yield substituted biphenyls and quinones is also supported by the calculations. HPLC/MS product analysis showed formation of one of the predicted quinones. 相似文献
67.
Arenas-Alatorre J Gómez-Cortés A Avalos-Borja M Díaz G 《The journal of physical chemistry. B》2005,109(6):2371-2376
The surface properties of bimetallic Ni-Pt/SiO2 catalysts with variable Ni/Ni + Pt atomic ratio (0.75, 0.50, and 0.25) were studied using N2O decomposition and N2O reduction by hydrogen reactions as probes. Catalysts were prepared by incipient wetness impregnation of the silica support with aqueous solutions of the metal precursors to a total metal loading of 2 wt %. For both model reactions, Pt/SiO2 catalyst was substantially more active than Ni/SiO2 catalyst. Mean particle size by TEM was about the same (in the range 6-8 nm) for all catalysts and truly bimetallic particles (more than 95%) were evidenced by EDS in the Ni-Pt/SiO2 catalysts. CO adsorption on the bimetallic catalysts showed differences in the linear CO absorption band as a function of the Ni/Pt atomic ratio. Bimetallic Ni-Pt/SiO2 catalysts showed, for the N2O decomposition, a catalytic behavior that points out an ensemble-size sensitive behavior for Ni-rich compositions. For the N2O + H2 reaction, the bimetallic catalysts were very active at low temperature. The following activity order at 300 K was observed: Ni75Pt25 > Ni25Pt75 approximately Ni50Pt50 > Pt. TOF values for these catalysts increased 2-5 times compared to the most active reference catalyst (Pt/SiO2). The enhancement of the activity in the Ni75Pt25 bimetallic catalysts is explained in terms of the presence of mixed Ni-Pt ensembles. 相似文献
68.
Cabrerizo FM Petroselli G Lorente C Capparelli AL Thomas AH Braun AM Oliveros E 《Photochemistry and photobiology》2005,81(5):1234-1240
Pterins are heterocyclic compounds with important biological functions, and most of them may exist in two acid-base forms in the pH range between 3 and 13 in aqueous solution. In this work, the photophysical properties of acid and basic forms of six compounds of the pterin family (6-hydroxymethylpterin [HPT], 6-methylpterin [MPT], 6,7-dimethylpterin [DPT], rhamnopterin [RPT], N-methylfolic acid [MFA], and pteroic acid [PA]) have been studied. The effects of the chemical nature of the substituents at position 6 of the pterin moiety and the effects of the pH on the absorption and emission properties are analyzed. The fluorescence characteristics (spectra, quantum yields, lifetimes) of these compounds have been investigated using the single-photon-counting technique. Results obtained for pterin derivatives containing small substituents with 1 carbon atom (HPT, MPT, DPT) and short hydrocarbon chain (4 carbon atoms) (RPT) are different from those found for pterin derivatives containing a p-aminobenzoic acid (PABA) moiety in the substituent (MFA and PA). Fluorescence quantum yields (Phi(F)) of the first group of compounds are relatively high (>/=0.4), whereas MFA and PA exhibit very small Phi(F) values (=0.01). 相似文献
69.
Jandera P Skeifíková V Rehová L Hájek T Baldriánová L Skopová G Kellner V Horna A 《Journal of separation science》2005,28(9-10):1005-1022
Methods were developed for the analysis of natural antioxidants including phenolic compounds and flavonoids in beverages and plant extracts using gradient HPLC with multi-channel electrochemical coulometric detection. Suitability of various reversed-phase columns for this purpose was compared; pH and mobile phase gradients were optimized with respect to the separation selectivity and sensitivity of detection. Because of different target compounds in various sample types, the overlapping resolution maps and the normalized resolution product approaches described earlier were used to select optimum columns and gradients to suit the analysis of the individual sample types. The methods were applied to the analysis of phenolic compounds and flavonoids in beer, wine, tea, and yacon extracts. 32 phenolic compounds were identified and determined, including derivatives of benzoic and cinnamic acids, flavones, and a few related glycosides. Eight-channel CoulArray detection offers high selectivity and sensitivity with limits of detection in the low microg L(-1) range, at least an order of magnitude lower than single-channel coulometric detection using the Coulochem detector. No special sample pretreatment is necessary and, because of the compatibility of the CoulArray detector with gradient elution, phenolic antioxidants of different polarities can be determined in a single run. In addition to the retention times, the ratios of the areas of the pre-dominant and post-dominant peaks to the area of the dominant peak can be used for improved identification of natural antioxidants. 相似文献
70.
Petre Ionita Vasile Dinoiu Cornel Munteanu Ioana Maria Turcu Victorita Tecuceanu Traian Zaharescu Eliza Oprea Cornelia Ilie Dan Anghel Gabriela Ionita 《Chemical Papers》2015,69(6):872-880
The rosemary extract was encapsulated in polyethylene or in covalently-based network gels. The covalent gels were obtained by the reaction of isocyanate end-capped polyethylene glycol (PEG) with β-cyclodextrin or glycerol. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was used to evaluate the antioxidant activity (AA) of rosemary extract entrapped in polymeric structures and in ethanol or water solutions. The AA of the rosemary extract was determined using a DPPH radical for samples prepared in ethanol, and a water-soluble derivative, the sulphonated DPPH radical (DPPH-SO3Na), for the rosemary extract in water. Formulation of the rosemary extract in polymeric gels ensures a rapid release which determines the AA values similar to those in solution. 相似文献