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排序方式: 共有75条查询结果,搜索用时 18 毫秒
1.
Cappa CD Smith JD Wilson KR Messer BM Gilles MK Cohen RC Saykally RJ 《The journal of physical chemistry. B》2005,109(15):7046-7052
Measurements of the oxygen K-edge X-ray absorption spectrum (XAS) of aqueous sodium halide solutions demonstrate that ions significantly perturb the electronic structure of adjacent water molecules. The addition of halide salts to water engenders an increase in the preedge intensity and a decrease in the postedge intensity of the XAS, analogous to those observed when increasing the temperature of pure water. The main-edge feature exhibits unique behavior and becomes more intense when salt is added. Density functional theory calculations of the XAS indicate that the observed red shift of the water transitions as a function of salt concentration arises from a strong, direct perturbation of the unoccupied molecular orbitals on water by anions, and does not require significant distortion of the hydrogen bond network beyond the first solvation shell. This contrasts the temperature-dependent spectral variations, which result primarily from intensity changes of specific transitions due to geometric rearrangement of the hydrogen bond network. 相似文献
2.
The formation of irreversible complexes between carrier ampholyte components and proteins was investigated by gel filtration of mixtures of proteins and radioactively labelled ampholytes. Experiments were performed both with purified proteins (albumin, ferritin, beta-glucuronidase) and with a complex mixture of proteins (serum); in no case was binding of ampholytes to proteins detected. Thus the results argue against the occurrence in isoelectric focusing of proteins of artifacts due to such complex formation. 相似文献
3.
Regulation of polar cap formation in the life cycle of Escherichia coli 总被引:48,自引:0,他引:48
4.
For pure states nonlinear Schrödinger equations, the so-called Schrödinger-Langevin equations are well-known to model quantum dissipative systems of the Langevin type. For mixtures it is shown that these wave equations do not extend to master equations, but to corresponding nonlinear von Neumann equations. Solutions for the damped harmonic oscillator are discussed.Supported by Deutsche ForschungsgemeinschaftSupported by Fonds zur Förderung der wissenschaftlichen Forschung in Österreich, Project no. 3569 相似文献
5.
Zusammenfassung Es werden Hückel-MO-Rechnungen am Borazol und den B-Trihalogenoborazolen durchgeführt und die entsprechenden Parameter an den teils bekannten und teils gemessenen UV-Spektren geeicht. Die für diese Verbindungen bestimmten chemischen Verschiebungen der 11B- und 14N-Kernresonanz lassen sich mit den berechneten -Elektronendichten erklären.
Herrn Professor Dr. H. Hartmann danken wir für sein stetes Interesse und die wohlwollende Förderung dieser Arbeit. Für die Hilfe bei der Aufnahme des Vakuum-UV-Spektrums von Fluoroborazol danken wir Herrn Diplom-Physiker E. Mohler. 相似文献
Hückel-MO calculations are performed for Borazine and the B-Trihalogenoborazines; the parameters used are calibrated with the UV-spectra, which had either been measured here or obtained from the literature. The calculated -electron densities compare favorably well with the 11B- and 14N-nuclear magnetic resonances determined for the above mentioned compounds.
Résumé Le borazole et les B-trihalogenoborazoles sont calculés par la méthode de Hückel en utilisant des paramètres calibrés sur les spectres U.V. mesurés ou obtenus dans la littérature. Les densités électroniques sont en bon accord avec le déplacement chimique de N.M.R. de 11B et 14N déterminé pour les composés cidessus.
Herrn Professor Dr. H. Hartmann danken wir für sein stetes Interesse und die wohlwollende Förderung dieser Arbeit. Für die Hilfe bei der Aufnahme des Vakuum-UV-Spektrums von Fluoroborazol danken wir Herrn Diplom-Physiker E. Mohler. 相似文献
6.
Gray DE Messer D Porter A Ferguson S Harris RK Clark AP Algaier JW Overstreet JD Smith CS 《Journal of AOAC International》2005,88(6):1613-1620
We report here a liquid chromatography (LC) method with inline ultraviolet/evaporative light scattering (UV/ELS) detection for the simultaneous quantification of the terpenelactones and flavonol aglycones in a single sample of hydrolyzed Ginkgo biloba extract (GBE). The sample is hydrolyzed by a rapid and convenient oven heating method for 1 h at 90 degrees C with 10% hydrochloric acid. The 1 h hydrolysis was found to be equivalent to the 2.25 h reflux treatment for dry powder extract, where total flavonol glycosides were 28.4 and 28.1%, respectively. Acceptable precision was achieved for total terpenelactones [relative standard deviation (RSD) = 4.8%] by ELS detection, and total flavonol aglycones (RSD = 2.3%) by UV detection. The analytical range was 1.5 to 7.3% (w/w) for the individual terpenelactones (ELS) and 2.5 to 15.0% (w/w) for the individual glycosides (UV) calculated from the aglycones quercetin, kaempferol, and isorhamnetin. This improved method allows for the first time high throughput sample preparation coupled with the quantification of the predominant compounds generally used for quality control of GBE in a single assay. 相似文献
7.
K. D. Kreuer A. Rabenau R. Messer 《Applied Physics A: Materials Science & Processing》1983,32(3):155-158
The proton conductivity in tetragonal H3OUO2AsO4·(3-)H2O has been measured above the transition temperature at 299 K. The conductivity, calorimetric and spectroscopic data depend on the water content and the transition is suggested to be a peritectic reaction setting free a small amount of solution, which stays strongly adsorbed between the layers of the structure and gives rise to the high conductivity. 相似文献
8.
Armin Dietrich Birgit Maas Wilhelm Messer Günther Bruche Volker Karl Astrid Kaunzinger Armin Mosandl 《Journal of separation science》1992,15(9):590-593
The characteristics of the new chiral stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin are outlined and compared with permethyl- and perethyl-β-cyclodextrins. 相似文献
9.
Photochemical sensing of NO(2) with SnO(2) nanoribbon nanosensors at room temperature 总被引:7,自引:0,他引:7
10.
Langanke K Martínez-Pinedo G Sampaio JM Dean DJ Hix WR Messer OE Mezzacappa A Liebendörfer M Janka HT Rampp M 《Physical review letters》2003,90(24):241102
Supernova simulations to date have assumed that during core collapse electron captures occur dominantly on free protons, while captures on heavy nuclei are Pauli blocked and are ignored. We have calculated rates for electron capture on nuclei with mass numbers A=65-112 for the temperatures and densities appropriate for core collapse. We find that these rates are large enough so that, in contrast to previous assumptions, electron capture on nuclei dominates over capture on free protons. This leads to significant changes in core collapse simulations. 相似文献