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61.
X Shi Y Huang Y Mao H Naimy J Zaia 《Journal of the American Society for Mass Spectrometry》2012,23(9):1498-1511
Heparan sulfate (HS) is a polysaccharide modified with sulfation, acetylation, and epimerization that enable its binding with protein ligands and regulation of important biological processes. Tandem mass spectrometry has been employed to sequence linear biomolecules e.g., proteins and peptides. However, its application in structural characterization of HS is limited due to the neutral loss of sulfate (SO(3)) during collisional induced dissociation (CID). In this report, we studied the dissociation patterns of HS disaccharides and demonstrate that the N-sulfate (N-S) bond is especially facile during CID. We identified factors that influence the propensities of such losses from precursor ions and proposed a Free Proton Index (FPI) to help select ions that are able to produce meaningful backbone dissociations. We then investigated the thermodynamics and kinetics of SO(3) loss from sulfates that are protonated, deprotonated, and metal-adducted using density functional theory computations. The calculations showed that sulfate loss from a protonated site was much more facile than that from a deprotonated or metal-adducted site. Further, the loss of SO(3) from N-sulfate was energetically favored by 3-8?kcal/mol in transition states relative to O-sulfates, making it more prone to this process by a substantial factor. In order to reduce the FPI, representing the number of labile sulfates in HS native chains and oligosaccharides, we developed a series of chemical modifications to selectively replace the N-sulfates of the glucosamine with deuterated acetyl group. These modifications effectively reduced the sulfate density on the HS oligosaccharides and generated considerably more backbone dissociation using on-line LC/tandem MS. 相似文献
62.
Oualid Berkani Khelil Latrous Hicham El Hamzaoui Bruno Capoen Mohamed Bouazaoui 《Journal of luminescence》2012,132(11):2979-2983
The photoluminescence properties of Eu3+-doped TiO2–SiO2 thin films were investigated. The films were deposited on silicon substrates by the sol–gel process using the dip-coating method. The molar ratio of TiO2 content was varied from 25% to 100%, while Europium concentration was fixed to 1%. The obtained films were calcinated at various temperatures ranging from 400 °C to 1300 °C, which allowed determining the optimal conditions for the Eu3+ luminescence. Meanwhile, the structure of TiO2–SiO2 powders, prepared in the same conditions as the films, was also studied by Raman spectroscopy. It revealed the role of Europium and SiO2 on the stabilization of the anatase phase and the importance of the silica matrix in the control of titania particle size. 相似文献
63.
The high-resolution Fourier transform infrared spectrum of phosphorus trifluoride (PF3) has been reinvestigated in the v2?=?1 vibrational excited state near 487?cm?1 (at a resolution of 3?×?10–3?cm–1). Thanks to our new accurate rotational ground-state C 0 value, 0.159970436(69)?cm–1, and to recent pure rotational measurements, 318 new infrared transitions of the ν 2 fundamental band have been assigned, extending the rotational quantum number values up to K max?=?71 and J max?=?72. A merge, for the first time, of 135 reported microwave data (K max?=?42 and J max?=?49) within the v2?=?1 excited level and 2860 rovibrational transitions yielded improved constants of ν 2. Parameters of this band have been obtained, up to sextic centrifugal distortion constants, by least-squares fits, σ IR?=?3.60?×?10–4?cm–1 and σ MW?=?5.53?×?10–6?cm–1 (166?kHz). Comparison of these constants with those measured previously by infrared spectroscopy reveals orders of magnitude higher accuracy of these new values. 相似文献
64.
Using strain energy-based prediction of effective elastic properties in topology optimization of material microstructures 总被引:1,自引:0,他引:1
Weihong Zhang Gaoming Dai Fengwen Wang Shiping Sun Hicham Bassir 《Acta Mechanica Sinica》2007,23(1):77-89
An alternative strain energy method is proposed for the prediction of effective elastic properties of orthotropic materials
in this paper. The method is implemented in the topology optimization procedure to design cellular solids. A comparative study
is made between the strain energy method and the well-known homogenization method. Numerical results show that both methods
agree well in the numerical prediction and sensitivity analysis of effective elastic tensor when homogeneous boundary conditions
are properly specified. Two dimensional and three dimensional microstructures are optimized for maximum stiffness designs
by combining the proposed method with the dual optimization algorithm of convex programming. Satisfactory results are obtained
for a variety of design cases.
The project supported by the National Natural Science Foundation of China (10372083, 90405016), 973 Program (2006CB601205)
and the Aeronautical Science Foundation (04B53080). The English text was polished by Keren Wang. 相似文献
65.
66.
Degradations have been carried out under programmed heating conditions to 500 in racuo for the three copolymer systems based upon methyl methacrylate with lithium, sodium and potassium methacrylate respectively. Products have been analyzed quantitatively and the mode of variation in the yields of the principal degradation products with copolymer composition has been established. As the salt content increases, methyl methacrylate monomer production declines and the amount of solid residue increases, in both cases non-linearly. Methanol and carbon dioxide productions however, pass through maxima in the intermediate composition range. The relationships between these product yields and copolymer structure and degradation mechanism are discussed. 相似文献
67.
Patrick Farquet Celestino Padeste Martin Börner Hicham Ben youcef Selmiye Alkan Gürsel Günther G. Scherer Harun H. Solak Volker Saile Alexander Wokaun 《Journal of membrane science》2008
Selective exposures of poly(ethylene-alt-tetrafluoroethylene) (ETFE) films with hard X-rays through high aspect ratio Ni-masks were performed at the LIGA3 beamline of the “Angström Quelle Karlsruhe” (ANKA) to create patterns of radicals used as initiators for the grafting of styrene into the bulk of the ETFE films. Grafted films were then sulfonated to obtain proton-conducting membranes. The structure definition, as investigated by scanning electron microscopy (SEM), showed a perfect discrimination between exposed and shaded areas through all the film thickness. Structuring results in a more homogeneous appearance of the membrane without affecting the degree of grafting and proton conductivity in the grafted areas. In fuel cell tests the structured membranes showed slightly lower performance due to 10% lower active area, but had a significantly higher lifetime. 相似文献
68.
Tikhomirov G Yamazaki T Kovalenko A Fenniri H 《Langmuir : the ACS journal of surfaces and colloids》2008,24(9):4447-4450
Supramolecular synthesis emerged recently as a new formalism to devise complex architectures held through noncovalent forces. Much of the research endeavor has been devoted to the use of H-bonds as the alphabet for chemical information encoding, and the structures expressed have spanned the range of dimensions and shapes, from discrete to infinite networks. Here we describe the synthesis and characterization of a GwedgeC base bearing two C12 alkyl chains, which undergoes a solvent-controlled multistep hierarchical self-assembly process into lamellar prolate nanospheroids. These assemblies were characterized by AFM, SEM, TEM, XRD, and SAXS, and a mechanism for their formation is proposed. 相似文献
69.
Noémi Feillée Maurizio De Fina Arnaud Ponche Cyril Vaulot Séverinne Rigolet Leandro Jacomine Hicham Majjad Christian Ley Abraham Chemtob 《Journal of polymer science. Part A, Polymer chemistry》2017,55(1):117-128
This report introduces a novel UV‐curing technology based on thiol–thiol coupling for polydisulfide network formation. Beginning with a model tris(3‐mercaptopropionate) trithiol monomer and xanthone propionic acid‐protected guanidine as photobase generator, a comprehensive characterization based on spectroscopic techniques supports the reaction of thiols into disulfides without side reactions. The best experimental conditions are described as regards to film thickness, irradiance, emission wavelength, and atmosphere composition. The results shed light on a step‐growth photopolymerization mechanism involving two steps: first, the formation of thiyl radicals by thiolate air oxidation or/and thiol photolysis, and second, their recombination into disulfide. By varying thiol functionality and structure, oligomer chain length and monomer/oligomer ratio, the network architecture can be finely tuned. The molecular mobility of the polydisulfide network is crucial to high thiol conversion rates and yields as revealed by 1H T2 NMR relaxation measurements. Ultimately, spatial control enables the formation of a photopatterned poly(disulfide) film, used as next‐generation high refractive index photoresist. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 117–128. 相似文献
70.
Mohammed Lahcini Hicham Qayouh Takao Yashiro Peter Simon Hans R. Kricheldorf 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):503-509
The usefulness of bismuth, calcium, magnesium and zinc salts for the preparation of poly(butylene succinate), PBSu, was studied. Two different approaches were compared. Firstly, 1,4-butanediol (or in a few experiments ethanediol) dimethyl succinate were condensed at temperatures up to 240°C in the presence of Bi2O3. Regardless of the feed ratio, only low molar mass polyesters having two diol endgroups were obtained. Secondly, 1,4-butanediol and succinic anhydride were polycondensed in refluxing decalin with azeotropic removal of water. BiCL3, BiBr3, BiI3, and Bi-triflate were used as catalyst and the monomer/catalyst ratio was varied. The highest molar masses were achieved with BiCl3. Analogous polycondensations catalysed with ZnCl2, Zn-triflate, MgCl2, Mg-triflate and CaCl2 were unsuccessful. Yet the BiCl3, decalin method was also successfully applied to the combination of succinic anhydride and 1,5-pentanediol. 相似文献