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51.
Colin L. Weeks Hyunil Jo Brandon Kier William F. DeGrado Thomas G. Spiro 《Journal of Raman spectroscopy : JRS》2012,43(9):1244-1249
Nitriles introduced into peptides and proteins can serve as useful vibrational spectroscopic probes, because the nitrile C ≡ N stretch is well isolated from backbone and sidechain vibrational bands. Aromatic nitriles offer large νC ≡ N absorption intensity in infrared spectra and resonance enhancement in Raman spectra with ultraviolet excitation. We report the ultraviolet resonance Raman spectra of cyanophenylalanine attached to cysteine, through linkage reactions that are applicable to cysteine residues in proteins. Excitation profiles are reported, and the νC ≡ N detection limit is estimated to be 5 µ m . The band position is sensitive to solvent polarity and especially to strong H‐bonding. The derivatization of mastoparan X peptide at introduced cysteine residues demonstrated the effectiveness of a cyanophenylcysteine probe in reporting the lowered environmental polarity when the peptide was incorporated into liposomes. For an asymmetrical cyanophenyl derivative, 2‐CBCys, the intensity ratio of asymmetric and symmetric ring modes, ν8b and ν8a, was found to respond to solvent polarity and not to H‐bonding. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
52.
Shu I Stewart JM Scian M Kier BL Andersen NH 《Journal of the American Chemical Society》2011,133(5):1196-1199
The (13)C chemical shifts measured for designed β-hairpins indicate that the structuring shifts (upfield for Cα and C', downfield for Cβ) previously reported as diagnostic for β-structuring in proteins appear only at the H-bonded strand residues. The resulting periodicity of structuring shift magnitudes is not, however, a consequence of H-bonding status; rather, it reflects a previously unrecognized alternation in the backbone torsion angles of β-strands. This feature of hairpins is also likely to be present in proteins. The study provides reference values for the expectation shifts for (13)C sites in β-structures that should prove useful in the characterization of the folding equilibria of β-sheet models. 相似文献
53.
54.
MJ Lazaro AA Herod M Domin Y Zhuo CA Islas R Kandiyoti 《Rapid communications in mass spectrometry : RCM》1999,13(14):1401-1412
Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
55.
The CNDO/2 method is used to study the hydrogen bond strength in several representative systems. Enthalpies of hydrogen bond formation are generally predicted fairly well although some exceptions are noted. The proton-proton acceptor distances are predicted to be about 10 percent too small in all cases where comparison with experiment can be made.
Zusammenfassung Mit Hilfe der CNDO/2-Methode wird in verschiedenen repräsentativen Systemen die Stärke von Wasserstoffbrücken untersucht. Die Enthalpien werden bis auf wenige Ausnahmen recht gut vorausgesagt. In allen Fällen, in denen experimentelle Unterlagen vorhanden sind, werden die Abstände der Proton-Proton-Akzeptoren urn etwa 10% zu klein vorausgesagt.
Résumé La méthode CNDO/2 est utilisée pour étudier le force de la liaison hydrogène dans quelques systèmes représentatifs. Les enthalpies de formation de la liaison hydrogène sont en général convenablement prédites à quelques exceptions près. La distance entre le proton et l'accepteur de proton est prédite avec une erreur par défaut d'environ 10% dans les cas où le résultat expérimental est connu.相似文献
56.
57.
Van Bael MJ Bekaert J Temst K Van Look L Moshchalkov VV Bruynseraede Y Howells GD Grigorenko AN Bending SJ Borghs G 《Physical review letters》2001,86(1):155-158
A scanning Hall probe microscope is used to study flux pinning in a thin superconducting Pb film covering a square array of single-domain Co dots with in-plane magnetization. We show that single flux quanta of opposite sign thread the superconducting film below T(c) at the opposite poles of these dipoles. Depending on the polarity of the applied field, flux lines are attracted to a specific pole of the dipoles, due to the direct interaction with the vortexlike structures induced by the local stray field. 相似文献
58.
The molecular connectivity indices are shown to be the numerical possibilities of a molecule encountering another identical molecule, derived from the bond accessibilites of each. The meaning of the delta values and the significance of all suppressed X-H bonds is described. A new concept of the meaning of molecular connectivity, built around bimolecular encounter accessibility, is presented. 相似文献
59.
The organization of water around a solute molecule with surface features of varying hydropathic states is studied. A stationary solute molecule and mobile water solvent molecules are modeled using cellular automata dynamics. It is shown that varying hydropathic states of solute molecule surface features influence the relative affinities of water for these features. In the case of a simulated chiral solute, a chiral pattern of associated water molecules binding to the surface is produced. This finding is in agreement with published simulations and circular dichroism measurements. A pattern of water molecules at locations beyond the surface of the solute molecules is detected, evidence of an emergent property in this solvent-solute system. 相似文献
60.