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61.
Jack Huet 《Tetrahedron》1981,37(4):731-741
13C NMR chemical shifts of ethylenic carbon atom Cβ of α alkoxy-indenes and α-alkoxy-styrenes are affected by the conformation of the OR group with respect to the double bond and hence the efficiency of p- Π conjugation but, contrary to previous results, δCα is not affected. The phenyl group exerts a diamagnetic Π- effect on Cα and Cβ which is a function of its dihedral angle with the double bond. Although δCβ is especially sensitive to the Π-electron density, the chemical shifts of the ethylenic carbons are best understood by considering the total charge density. The σ and Π contributions to the total charge density are discussed using the preferred conformation of the molecules. This approach strongly suggests that the correlation between the gradual shift of δCα to low frequency and the gradual shift of δCβ to high frequency (relative to TMS) as R changes from RCH3 to RtC4H9 in certain series of enol-ethers is not due to pΠ conjugation variations. This method of interpreting 13C NMR shifts, as opposed to previous methods, is compatible with explanations of other physico-chemical properties of alkyl vinyl ethers. Although it is sometimes possible to correlate the gradual shifts of δCβ with (σ + Π) electron density variations in a homogeneous series, it seems impossible to predict the relation. In all cases, there is no evident correlation between gradual shifts of δCβ(orδCα) and the reactivity of enol ethers because one cannot consider the role of the out-of-plane conformation of the alkoxy group (which increases from RCH3 to RtC4H9); however, the out of plane conformation does not have an identical effect on δCβ and the reactivity. 相似文献
62.
Servais AC Fillet M Chiap P Dewé W Hubert P Crommen J 《Journal of chromatography. A》2005,1068(1):143-150
The influence on the enantiomeric resolution of the nature of the cationic BGE component (sodium, ammonium or potassium) and that of the anionic component (chloride, formate, methanesulfonate or camphorsulfonate) as well as the concentration of heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD), the selected chiral selector, was studied in nonaqueous capillary electrophoresis (NACE). For this purpose, two D-optimal designs with 33 and 26 experimental points were applied. Three beta-blockers (atenolol, celiprolol and propranolol) and three local anesthetics (bupivacaine, mepivacaine and prilocaine) were selected as basic model compounds. Both cationic and anionic BGE components were found to have a deep impact on the enantiomeric resolution of the investigated analytes but it is the cationic component that has shown the strongest influence. Indeed, in some cases, the change of the latter led to a complete loss of enantioresolution. Based on the observed results, two NACE systems were recommended, namely ammonium formate and potassium camphorsulfonate in a methanolic solution containing HDMS-beta-CD and acidified with formic acid, in order to separate efficiently the enantiomers of basic drugs. 相似文献
63.
Carbon-13 relaxation times, T1, have been measured for ten cobalt(III)–cyclohexanedione dioxime complexes: CH3CH2? Co(Niox)2-p-R-pyridine [R?H, N(CH3)2, CH3, C2H5, C(CH3)3, Cl, Br, CN and COCH3] and CH3CH2? Co(Niox)2-3-N-methylimidazole. The values obtained have been rationalized by making assumptions on the length of the metal—hetrocyclic nitrogen bond. The internal rotation around the axial Co? N (heterocyclic) bond is faster for the 3-N-methylimidazole ligand than for the pyridine ligands. Correlations of the T1 values with the σ-donor and π-acceptor character of the pyridine ligands were attempted. The interpretation of the results suggests the existence of π-back-bonding from the metal to the N-1 pyridine nitrogen atom, in agreement with the results of other workers. This conclusion, however, was not supported by the use of the para-C chemical shift as a criterion for back-bonding in pyridine–transition metal complexes. 相似文献
64.
The 1H NMR spectra of the protonated and unprotonated forms of cis- and trans-N-methylhexahydroisoindoline, of 1,3,3,4,4-pentamethylpyrrolidine and of 1,3,3-trimethylpyrrolidine were analyzed. The coupling constants between the NH⊕ and the CH protons α to the nitrogen allowed the study of the conformation of the cyclic systems in pseudorotation. 相似文献
65.
66.
An antibody was generated that can bind metronidazole (MNZ), a nitroimidazole drug used in veterinary medicine to treat poultry for coccidiosis and histomoniasis. A direct competitive enzyme-linked immunosorbent assay (cELISA) is described. It was used to characterise binding of this antibody to a number of nitroimidazole drugs. It displayed cross-reactivity with dimetridazole (DMZ), ronidazole (RNZ), hydroxydimetridazole (DMZOH), and ipronidazole (IPZ).Egg and chicken muscle samples were extracted with acetonitrile and de-fatted by washing with hexane. Detection capabilities (CCβ) were determined: dimetridazole, <1 ppb (egg) and <2 ppb (muscle); metronidazole, <10 ppb; ronidazole and hydroxydimetridazole, <20 ppb; ipronidazole, <40 ppb. 相似文献
67.
68.
S. Le Blond E. Guilminot G. Lemoine N. Huet J.Y. Mevellec 《Vibrational Spectroscopy》2009,51(2):363-161
The degreasing methods currently used for osteological collections are not always completely satisfactory. Numerous natural history museums encounter the problem of grease seeping to the surface of bones. FT-Raman spectroscopy was used to characterise cetacean bones, before and after degreasing treatment, in order to evaluate the efficacy of treatment and the impact thereof on bone constituents. The Raman spectra made it possible to monitor the changes in the main bone constituents: the mineral component with the apatite band at 960 cm−1, the organic component with the collagen amide III band at 1270 cm−1 and fat with the lipid CH2 band at 2850 cm−1. The band associated with lipids decreased and even disappeared with degreasing treatment containing chlorinated solvents. This type of treatment enables fat to be extracted both from the surface and from the bone core; however, it debases the organic component of bone by denaturing collagen. Alternative types of treatment (acetone or enzyme baths) were tested over a limited period, which did not enable their true efficacy to be demonstrated. During the alternative treatments, no bone degradation was observed. Only the acetone solution was able to extract fat, though only from the surface. 相似文献
69.
Multiplex dipstick immunoassay for semi-quantitative determination of Fusarium mycotoxins in cereals
Veronica M.T. Lattanzio Noan Nivarlet Vincenzo Lippolis Stefania Della Gatta Anne-Catherine Huet Philippe Delahaut Benoit Granier Angelo Visconti 《Analytica chimica acta》2012
A multiplex dipstick immunoassay based method for the simultaneous determination of major Fusarium toxins, namely zearalenone, T-2 and HT-2 toxins, deoxynivalenol and fumonisins in wheat, oats and maize has been developed. The dipstick format was based on an indirect competitive approach. Four test lines (mycotoxin–BSA conjugates) and one control line were located on the strip membrane. Labelled antibodies were freeze-dried within the microwell. Two matrix-related sample preparation protocols have been developed for wheat/oats (not containing fumonisins) and maize (containing fumonisins) respectively. The use of a methanol/water mixture for sample preparation allowed recoveries in the range 73–109% for all mycotoxins in all tested cereals, with relative standard deviation less than 10%. The optimized immunoassay was able to detect target mycotoxins at cut off levels equal to 80% of EU maximum permitted levels, i.e. 280, 400, 1400 and 3200 μg kg−1, respectively, for zearalenone, T-2/HT-2 toxins, deoxynivalenol and fumonisins in maize, and 80, 400 and 1400 μg kg−1, respectively, for zearalenone, T-2/HT-2 toxins and deoxynivalenol in wheat and oats. Analysis of naturally contaminated samples resulted in a good agreement between multiplex dipstick and validated confirmatory LC–MS/MS. The percentage of false positive results was less than or equal to 13%, whereas no false negative results were obtained. Data on the presence/absence of 6 mycotoxins at levels close to EU regulatory levels were obtained within 30 min. The proposed immunoassay protocol is rapid, inexpensive, easy-to-use and fit for purpose of rapid screening of mycotoxins in cereals. 相似文献
70.
Lamalle C Servais AC Fradi I Crommen J Fillet M 《Journal of separation science》2012,35(15):1933-1939
In this study, the migration behavior of charged and uncharged analytes was investigated under different conditions. Effective mobilities - electrophoretic mobilities under the influence of micelles - of cations, anions, and neutrals were measured at neutral, basic, and acidic pH (7.5, 11, and 2.2) using background electrolytes containing different sodium dodecyl sulfate (SDS) concentrations (0-90 mM) and acetonitrile (ACN) proportions (0-75%). SDS concentration and ACN proportion were found to have a tremendous effect on the effective mobilities and migration order of the model compounds. Although the SDS micelles preferably interact with neutrals and cations, hydrophobic bonds can also occur with anions. Cations, anions, and neutrals having rather different migration behaviors, it is possible to considerably enhance the selectivity of the method by adjusting properly the SDS concentration and the ACN proportion. These observations confirm the interest of using micellar electrokinetic chromatography not only for the separation of neutral substances but also to analyze charged compounds. 相似文献