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1.
2.
Treatment of 2,3-diketo-cholestane (1) with thallium triacetate in acetic acid afforded mainly 3α-carbomethoxy-A-nor-5α-cholestan-2-one (2). Under similar conditions, the 3,4-diketo steroids (3 and 4) underwent extensive rearrangement affording spiro-lactones (9 and 10), in low yields. The structural assignment of the spiro-cholestane derivative was supported by crystallographic X-ray analysis. This product was the result of A and B-ring contractions followed by acid-catalysed cyclization of an unsaturated carboxy intermediate. 相似文献
3.
Daniele Mazza Maria Lucco-Borlera Esterina Lepore Silvia Ronchetti 《Journal of Thermal Analysis and Calorimetry》1996,46(6):1625-1632
A calorimetric method is proposed to evaluate the catalytic activity of a solid catalyst with respect to the exothermic oxidation of Volatile Organic Compounds (VOC).This method employs a differential thermal analyzer in which an inert reference and a catalytically active sample are both fluxed at a constant rate with a reactive gaseous mixture composed of an inert gas (N2 90% vol.), oxygen and VOC, the last typically 900 to 5000 ppm. While the temperature is varied according to a predefined cycle, the output signal due to the exothermic reaction on the catalyst is continuously recorded. The design of the test chamber, the amount of catalyst, the shape of the holders and finally the flow rate and composition of the gaseous mixture should be carefully selected in order to achieve reproducible results. 相似文献
4.
Bacillus thuringiensis and recombinant Escherichia coli proteinaceous protoxins were subject to proteolysis and analyzed by capillary electrokinetic chromatography. Three resulting toxins (65 kDa) were baseline-resolved within 22 min using a 10 mM borate, pH 11 separation buffer consisting of 25 mM sodium dodecyl sulfate (SDS) and 30 mM phytic acid. The toxins displayed differential interactions with the SDS and phytic acid phases to effect their separation. The ion-pairing interaction between the analyte and phytic acid was also useful in preventing adsorption to the capillary walls and thus enhanced separation resolution and efficiency. The use of electrokinetic chromatography allows achievement of the separation in a significantly shorter time than conventional high-performance liquid chromatography (HPLC) using a diethylaminoethyl (DEAE) weak-anion exchanger. 相似文献
5.
Aschi M Lucente G Mazza F Mollica A Morera E Nalli M Paglialunga Paradisi M 《Organic & biomolecular chemistry》2003,1(11):1980-1988
The conformational study of a new group of synthetic peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt), a cysteine-related achiral residue, has been carried out through a joint application of computational and experimental methodologies. Molecular Dynamics simulations clearly suggest the tendency of this molecule to adopt a gamma-turn conformation in vacuum and help in analyzing the complex and crucial conformational behaviour of the dithiolane ring which appears to preferentially adopt a C(S)-like structure. Electronic structure calculations carried out in solution using the Density Functional Theory also indicate the preservation of the gamma-like folding in apolar solvents and the helix-like one in more polar solvents. A comparison with the achiral 1-aminocycloalkane-1-carboxylic acid (Ac5c) has been carried out using the same computational tools. NMR and IR data on dipeptide derivatives containing the Adt or Ac5c residue show that in chloroform solution all the models prefer a gamma-turn structure, centered at the cyclic residue, stabilized by an intramolecular H-bond, whereas in a more polar solvent, i.e. dimethyl sulfoxide, this folding is not maintained. The experimental conformational studies, extended to N-Boc protected tripeptides, clearly indicate the remarkable tendency of both the five-membered C(alpha)-tetrasubstituted cyclic amino acids Adt and Ac5c to induce the gamma-turn structure also in models able to adopt the beta-bend conformation. 相似文献
6.
The polymerization of the system indene-titanium tetrachloride-methylene chloride gave irreproducible kinetics which have been attributed to variable concentrations of impurities in the solvent. Incomplete yields sometimes observed at ?70° are also caused by impurities, but introduction of water and hydrochloric acid then gives complete yields. A new method of solvent purification has been used giving reproducible yields and rates. In such cases, monomer consumption at ?70° follows the rate law log [M]o/[M] = kt. 相似文献
7.
P Leroy A Nicolas C Gavriloff M Matt P Netter B Bannwarth B Hercelin M Mazza 《Journal of chromatography. A》1991,564(1):258-265
A simple and fast high-performance liquid chromatographic method was developed for the simultaneous measurement of 2-mercaptopropionylglycine (Tiopronine) and its metabolite (2-mercaptopropionic acid) in human plasma after the administration of a pharmaceutical dosage form (Acadione). The sample treatment before high-performance liquid chromatographic analysis consisted of the reduction of the corresponding disulphides by tri-n-butylphosphine and protein precipitation with ethanol. Separation was achieved by ion-pair high-performance liquid chromatography on a reversed-phase column (LiChrospher RP 18e) with cetrimonium bromide as counter ion and detection by fluorimetry after post-column derivatization with a selective thiol reagent, i.e. pyrenemaleimide. The high frequency of the analyzed samples and validation results make the method suitable for pharmacokinetic studies, and this was demonstrated by the first results obtained after the administration of an oral dose of 500 mg of Tiopronine to two healthy subjects. 相似文献
8.
Anthony Winston Edward T. Mazza 《Journal of polymer science. Part A, Polymer chemistry》1975,13(9):2019-2030
A polymer bearing hydroxamic acid groups and having a high affinity for iron(III) was prepared through the following procedure. Acryloylalanine (III), prepared by the reaction of acryloyl chloride with alanine, was treated with N-hydroxysuccinimide in the presence of dicyclohexylcarbodiimide to give the N-hydroxysuccinimide ester (IV). The ester IV was polymerized by using AIBN in dioxane to give polymer V. Treatment of polymer V with methylhydroxylamine in DMF gave the hydroxamic acid polymer II. The water-soluble polymer II was purified by dialysis or by gel-permeation chromatography (GPC) on Sephadex G-25. Analytical GPC on Sephadex G-200 and Sepharose 4B indicate that the average molecular weight of the polymer is in the range of 5 × 105 to 1 × 106. The presence of hydroxamic acid groups is confirmed by the intense red-brown color produced by the addition of iron(III) to a 50% aqueous DMF solution of the polymer under acidic conditions. In pure water the polymer-iron complex precipitates as a tan solid. Iron-binding studies of the polymer reveal that the iron(III) trihydroxamic acid complex FeA3 forms at low concentrations of iron. At higher iron levels a lower order of stability is apparent, which can be accounted for by the conversion of FeA3 to FeA2+. In contrast, the FeA3 complex of the trihydroxamic acid deferoxamine-B is stable at all iron levels. These results are consistent with the polymer structure, which for steric reasons would favor a stable complex, FeA2+, between iron and two adjacent hydroxamic acid groups. An FeA3 complex would be expected to have a lower stability as a result of either bond angle strain and atomic compression, or a lower probability in bringing a third hydroxamic acid into position to form the octahedral complex. 相似文献
9.
Najoua Ouerfelli Daniele Mazza Mohamed Faouzi Zid 《Journal of solid state chemistry》2007,180(4):1224-1229
A new solid solution TlFe0.22Al0.78As2O7 has been synthesized by a solid-state reaction. The structure of the title compound has been determined from a single-crystal X-ray diffraction and refined to final values of the reliability factors: R(F2)=0.030 and wR(F2)=0.081 for 1343 independent reflections with I>2σ(I). It crystallizes in the triclinic space group P-1, with a=6.296(2) Å, b=6.397(2) Å, c=8.242(2) Å, α=96.74(2)°, β=103.78(2)°, γ=102.99(3)°, V=309.0(2) Å3 and Z=2. The structure can be described as a three-dimensional framework containing (Fe/Al)O6 octahedra connected through As2O7 groups. The metallic units and diarsenate groups share oxygen corners to form a three-dimensional framework with interconnected tunnels parallel to the a, b and c directions, where Tl+ cations are located. The ionic conductivity measurements are performed on pellets of the polycrystalline powder. At 683 K, The conductivity value is 5.23×10−6 S cm−1 and the ionic jump activation energy is 0.656 eV. The bond valence analysis reveals that the ionic conductivity is ensured by Tl+ along the [001] direction. 相似文献
10.
Jan-Christoph Eichler Robert A. Skutnik Anupam Sengupta Marco G. Mazza Martin Schoen 《Molecular physics》2019,117(23-24):3715-3733
Anisotropic fluids (e.g. liquid crystals) offer a remarkable promise as optofluidic materials owing to the directional, tunable, and coupled interactions between the material, flow, and the optical fields. Here we present a comprehensive in silico treatment of this anisotropic interaction by performing nonequilibrium molecular dynamics simulations. We quantify the response of a nematic liquid crystal (NLC) undergoing a Poiseuille flow in the Stokes regime, while being illuminated by a laser beam incident perpendicular to the flow direction. We adopt a minimalistic model to capture the interactions, accounting for two features: first, the laser heats up the NLC locally; and second, the laser polarises the NLC and exerts an optical torque that tends to reorient molecules of the nematic phase. Because of this reorientation the liquid crystal exhibits small regions of biaxiality, where the nematic director is one symmetry axis and the axis of rotation for the reorientation of the molecules is the other one. We find that the relative strength of the viscous and the optical torques mediates the flow-induced response of the biaxial regions, thereby tuning the emergence, shape and location of the regions of enhanced biaxiality. The mechanistic framework presented here promises experimentally tractable routes toward novel optofluidic applications based on material-flow-light interactions. 相似文献