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排序方式: 共有163条查询结果,搜索用时 15 毫秒
1.
Several models have been developed in order to categorize the numerous expressions that people use in order to describe their emotional experiences. The focus of the present study is on one of these theoretical classifications proposed by Pekrun (1992) specifically concerning emotions which are directly related to learning and achievement in mathematics. In his model, emotions are classified according to their valence (positive vs. negative) and their level of activation. In testing the assumptions of this model, we investigated students' enjoyment, anxiety, anger and boredom experienced before, during, and after the completion of a math test. Correspondence analyses which were used to generate a graphical illustration of structural interrelationships between these emotions provide empirical support for the theoretical classification. 相似文献
2.
Product integration rules generalizing the Fej?r, Clenshaw-Curtis,and Filippi quadrature rules respectively are derived for integralswith trigonometric and hyperbolic weight factors. The Chebyshevmoments of the weight functions are found to be given by well-conditionedexpressions, in terms of hypergeometric functions 0F1. An a priori error estimator is discussed which is shown bothto avoid wasteful invocation of the integration rule and toincrease significantly the robustness of the automatic quadratureprocedure. Then, specializing to extended Clenshaw-Curtis (ECC) rules,three types of a posteriori error estimates are considered andthe existence of a great risk of their failure is demonstratedby large scale validation tests. An empirical error estimator,superseding them for slowly varying integrands, is found toresult in a spectacular increase in the output reliability. Finally, enhancements in the control of the interval subdivisionstrategy aiming at increasing code robustness is discussed.Comparison with the code DQAWO of QUADPACK, with about a hundredthousand solved integrals, is illustrative of the increasedrobustness and error estimate reliability of our computer codeimplementation of the ECC rules. 相似文献
3.
L. Goetz E. Sabbioni E. Marafante J. Edel-Rade C. Birattari M. Bonardi 《Journal of Radioanalytical and Nuclear Chemistry》1981,67(1):183-192
Carrier-free201+202Tl have been produced in the cyclotron by (p, xn) reactions on mercury targets and used as a trcer for thallium in metallobiochemistry
of heavy metal pollution. The separation of201+202Tl radioisotopes from Hg involved a solvent extraction method leading to labelled univalent Tl(I) ions. This radioactive solution
was used to prepare different201+202Tl labelled compounds such as inorganic Tl(III) ions and organic dimethylthallium. Quality controls have been applied directly
on the different radioactive solutions immediately before their administrations to rats in order to ensure that thallium had
the chemical form expected. A summary of the main results concerning different aspects of the metabolic investigations on
rats such as absorption, retention, excretion, transplacental transport and influence of the different chemical forms of thallium
on its metabolism is also reported. 相似文献
4.
Frederick J. Goetz 《Journal of heterocyclic chemistry》1967,4(1):80-84
A definite tautomeric relationship has been found between 2-arylbenzothiazolines (I) and 2-(benzylideneamino)thiophenols (II). In a reaction characteristic of the closed ring structure (I), 2-arylbenzothiazolines were oxidized in high yield with benzoyl peroxide to the corresponding 2-arylbenzothiazoles (III). Reactions characteristic of the open ring structure (II) include the formation of the potassium salt of the open ring structure (IV) by reaction of 2-arylbenzothiazolines with potassium t-butoxide in toluene and oxidation of 2-arylbenzothiazolines to bis-[2-(benzylideneamino)phenyl] disulfides (V) by hydrogen peroxide in methanol. 相似文献
5.
Singh SB Ball RG Bills GF Cascales C Gibbs JB Goetz MA Hoogsteen K Jenkins RG Liesch JM Lingham RB Silverman KC Zink DL 《The Journal of organic chemistry》1996,61(22):7727-7737
Farnesyl-protein transferase (FPTase) is an enzyme responsible for the farnesylation of Ras protein. Farnesylation is required for cell-transforming activity in several tumor-types, and therefore, inhibition of FPTase activity may be a potential target for anticancer drugs. Our continued search for novel inhibitors led to the isolation of a number of bicyclic resorcinaldehyde cyclohexanone derivatives named here cylindrols A(1) to A(4), cylindrols B and B(1), and a number of known compounds, from Cylindrocarpon lucidum. The compounds were isolated by bioassay-guided separation using Sephadex LH-20, silica gel, and reverse phase HPLC. Structures were elucidated by extensive application of 2D NMR and X-ray crystallography. The determination of absolute stereochemistry was accomplished by CD measurements. Chemical transformations of the most abundant compound resulted in a number of key derivatives which were critical for the evaluation of structure activity relationship. These compounds are members of ascochlorin family and showed a wide range of inhibitory activity (0.7 &mgr;M to >140 &mgr;M) against FPTase. The FPTase activity was noncompetitive with respect to both substrates. Isolation, structures, chemical transformations, and FPTase activity are discussed in detail. 相似文献
6.
7.
The reaction of isatoic anhydrides with the anion derived from ethyl o-fluorobenzoylacetate to furnish [1]benzopyrano-[3,2-c]quinolines is described. An analogous reaction with 3-azaisatoic anhydride furnishes 1b , or with tricyclic anhydride 3 , system 4 is isolated. Spectral data is also discussed. 相似文献
8.
The reaction of 2-chloronicotinonitrile with N-methylmethanesulfonamide and subsequent treatment with base furnished the novel pyrido[2,3-c]-1,2-thiazine ring system 7 . Spectrally, it was determined that the predominant tautomer in solution was the 4-amino form 7a . Acidic hydrolysis of 7 furnished the 4-oxo tautomer 8b , compound 8b was alkylated on oxygen with 1-bromopentane in the presence of sodium hydride. Reaction of 8b with isocyanates occurs at the 3 position to produce carboxanilides 10 . Spectral characteristics of these compounds are also discussed. 相似文献
9.
Phytochemistry of genus Gentiana, XXIV. New C-glycosylflavones from the leaves of Gentiana asclepiadea L. p-Hydroxybenzoyl-2″-isoorientin-4′-O-β-D-glucoside ( 1 ) was isolated from the leaves of Gentiana asclepiadea L. by means of column chromatography. This is the first occurrence in nature of a p-hydroxybenzoate of isoorientin. p-Hydroxybenzoyl-2″-isoorientin ( 2 ) was also shown to be present in the same plant. 相似文献
10.
Goetz E. Hardtmann Gabor Koletar Oskar R. Pfister 《Journal of heterocyclic chemistry》1975,12(3):565-572
Three methods for the preparation of N-substituted 2H-3,1-benzoxazine-2,4(1H)diones (isatoic anhydrides) (1) utilizing 2-chloro-, 2-nitrobenzoic acids and N-unsubstituted isatoic anhydrides as starting materials, are described. 相似文献