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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.
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
63.
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
64.
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
65.
C. Suárez-Pantaleón A.C. Huet O. Kavanagh H. Lei G. Dervilly-Pinel B. Le Bizec C. Situ Ph. Delahaut 《Analytica chimica acta》2013
The administration of recombinant methionyl bovine somatotropin (rMbST) to dairy cows to increase milk yield remains a common practice in many countries including the USA, Brazil, Mexico, South Africa and Korea, whereas it has been forbidden within the European Union (EU) since 1999. A rapid screening immunoanalytical method capable of the unequivocal determination of rMbST in milk would be highly desirable in order to effectively monitor compliance with the EU-wide ban for home-made or imported dairy products. For decades, the production of specific antibodies for this recombinant isoform of bovine somatotropin (bST) has remained elusive, due to the high degree of sequence homology between both counterparts (e.g. methionine for rMbST in substitution of alanine in bST at the N-terminus). In this study, we compared several immunizing strategies for the production of specific polyclonal antibodies (pAbs), based on the use of the full-length recombinant protein, an rMbST N-terminus peptide fragment and a multiple antigen peptide (MAP) which consists of an oligomeric branching lysine core attached to the first two N-terminus amino acids of rMbST, methionine and phenylalanine (MF-MAP). The immunization with KLH-conjugated MF-MAP led to the production of the pAb with the highest rMbST/bST recognition ratio amongst the generated battery of antibodies. The pAb exhibited a specific binding ability to rMbST in a competitive antigen-coated ELISA format, which avidity was further improved after purification by rMbST N-terminus peptide-based affinity chromatography. These results suggest that immunodiscrimination between structurally related proteins can be achieved using immuno-enhanced immunogens such as MAPs. 相似文献
66.
Cirtog M Asselin P Soulard P Tremblay B Madebène B Alikhani ME Georges R Moudens A Goubet M Huet TR Pirali O Roy P 《The journal of physical chemistry. A》2011,115(12):2523-2532
A series of hydrogen bonded complexes involving oxirane and water molecules have been studied. In this paper we report on the vibrational study of the oxirane-water complex (CH(2))(2)O-H(2)O. Neon matrix experiments and ab initio anharmonic vibrational calculations have been performed, providing a consistent set of vibrational frequencies and anharmonic coupling constants. The implementation of a new large flow supersonic jet coupled to the Bruker IFS 125 HR spectrometer at the infrared AILES beamline of the French synchrotron SOLEIL (Jet-AILES) enabled us to record first jet-cooled Fourier transform infrared spectra of oxirane-water complexes at different resolutions down to 0.2 cm(-1). Rovibrational parameters and a lower bound of the predissociation lifetime of 25 ps for the v(OH)(b) = 1 state have been derived from the rovibrational analysis of the ν(OH)(b) band contour recorded at respective rotational temperatures of 12 K (Jet-AILES) and 35 K (LADIR jet). 相似文献
67.
Stoeffler C Darquié B Shelkovnikov A Daussy C Amy-Klein A Chardonnet C Guy L Crassous J Huet TR Soulard P Asselin P 《Physical chemistry chemical physics : PCCP》2011,13(3):854-863
Originating from the weak interaction, parity violation in chiral molecules has been considered as a possible origin of biohomochirality. We have proposed the observation of molecular parity violation using the two-photon Ramsey fringes technique on a supersonic beam. As a first step in this direction, a detailed spectroscopic study of methyltrioxorhenium (MTO) has been undertaken. It is an ideal test molecule as the achiral parent molecule of chiral candidates for a parity violation experiment. For the (187)Re MTO isotopologue, a combined analysis of Fourier transform microwave and infrared spectra as well as ultra-high resolution CO(2) laser absorption spectra enabled the assignment of 28 rotational lines and 71 rovibrational lines, some of them with a resolved hyperfine structure. A set of spectroscopic parameters in the ground and first excited state, including hyperfine structure constants, was obtained for the ν(as) antisymmetric Re=O stretching mode of this molecule. This result validates the experimental approach to be followed once a chiral derivative of MTO is synthesized, and shows the benefit of the combination of several spectroscopic techniques in different spectral regions, with different set-ups and resolutions. The first high resolution spectra of jet-cooled MTO, obtained on a set-up being developed for the observation of molecular parity violation, are shown, which constitutes a major step towards the targeted objective. 相似文献
68.
The hyperfine structure of methyl formate was recorded in the 2-20 GHz range. A molecular beam coupled to a Fourier transform microwave spectrometer having an instrumental resolution of 0.46 kHz and limited by a Doppler width of a few kHz was used. A-type lines were found split by the magnetic hyperfine coupling while no splittings were observed for E-type lines. Symmetry considerations were used to account for the internal rotation of the methyl top and to derive effective hyperfine coupling Hamiltonians. Neglecting the spin-rotation magnetic coupling, the vanishing splittings of the E-type lines could be understood and analyses of the hyperfine patterns of the A-type lines were performed. The results are consistent with a hyperfine structure dominated by the magnetic spin-spin coupling due to the three hydrogen atoms of the methyl group. 相似文献
69.
70.
We propose a simple model of first impression bias (FIB), where agents tend to ignore features which contradict their initial view. We consider a population of agents which are all in contact with a media, communicating randomly chosen features of an object. In some cases, we observe on simulations that FIB is significantly more frequent when the agents interact with each other than when they are only in contact with the media. We design an analytical aggregated model of the global agent‐based model behavior, which helps to explain the higher number of FIB due to the interactions. © 2009 Wiley Periodicals, Inc. Complexity, 2010 相似文献