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51.
52.
Herbert H. Hill Robert H. St Louis Mark A. Morrissey Christopher B. Shumate William F. Siems Dennis G. McMinn 《Journal of separation science》1992,15(7):417-422
Ion mobility monitoring has been used for detection in gas, supercritical fluid, and liquid chromatography, illustrating its potential as a method of detection for unified chromatography. Applications presented include GC-IMD of dioxins in fly ash, SFC-IMD of vitamin E, and HPLC-IMD of alkylamines. Ion mobility spectra of several mixed supercritical fluid mobile phases are also presented. Use of methanol, acetonitrile, and dichloromethane as modifiers of supercritical carbon dioxide, and use of supercritical dichlorodifluoromethane and chlorodifluoromethane as mobile phases had little effect on the reactant ion pattern at the flow rates and concentrations used in this study. Only when acetone was used as a modifier of carbon dioxide did the positive reactant ions change significantly. No effect of modifiers or mobile phase was observed for the negative reactant ions. 相似文献
53.
Summary During the transition of Ehrlich mouse ascites tumour cells from the proliferating to the resting state of growth a large loss of purine and pyrimidine compounds occurs. This decrease is accompanied by a change in the amount of protein in the supernate of ascites fluid, which is known from the study of the ATP-consumption during protein synthesis. The ascites fluid was investigated by anion-exchange and size-exclusion chromatography (SEC). SDS-PAGE (sodium, dodecyl sulfate-polyacrylamide gel electrophoresis) data were compared with SEC data. The total amount of protein increased by 50% between day 5 and 12 of growth. At least 5 new peaks are observed in the chromatograms of an ion-exchange separation of Ehrlich ascites fluid at day 12 postinoculation. The amounts of transferrin, albumin and IgG (immunoglobulin G) were increased to 132, 134, 157%, respectively duringin vivo growth. 相似文献
54.
A microscopic theory of solids is presented which allows the calculation of lattice properties from first principles. The method is based on the Density-Functional-Theory and a new version of the Linear-Muffin-Tin-Orbital method, which includes nonspherical charge distributions in the total energy calculations. Explicit results for BaTiO3 and SrTiO3 are reported. The deformations of the charge density due to a homogeneous volume change and due to a soft mode deformation were determined. Differences between BaTiO and SrTiO3 and the nature of the chemical bonding are discussed. Calculated cohesive energies and lattice constants agree well with experimental data.Dedicated to Prof. Dr. H.E. Müser on the occasion of his 60th birthday 相似文献
55.
An ion mobility detector has been designed and constructed for direct axial interfacing with capillary gas chromatography. The principle advantages of this detector were the following: (1) Direct concentric introduction of the capillary column into the ionization region, eliminating peak broadening in the transfer line and improving the efficiency with which neutral molecules were swept from the detector. (2) A variable capillary insertion distance, providing a sensitivity/resolution interplay that could be modified in response to the needs of the assay. (3) An inert gas flow external to the drift cylinder, preventing atmospheric impurities from infiltrating the ultratrace detector. Qualitative and quantitative capabilities of the detector were evaluated using standard preparations of n-hexyl ether. 相似文献
56.
Wan W Zhao G Al-Saad K Siems WF Zhou ZS 《Rapid communications in mass spectrometry : RCM》2004,18(3):319-324
We report here an isotopic labeling and mass spectrometric method to rapidly identify S-adenosylmethionine (AdoMet)-dependent methylation products. In the presence of CH(3)- and CD(3)-labeled AdoMet, a methyl transfer product appears as a doublet separated by 3 Da in a mass spectrum, while other compounds show their normal isotopic distribution. Based on this unique isotopic pattern, methylation product(s) can be easily detected even from a mixture of cellular components. To validate our method, the product of human thiopurine methyltransferase (TPMT, EC 2.1.1.67) has been successfully identified from both an in vitro assay and a whole-cell assay. This method is generally applicable to AdoMet-dependent transmethylation and other group-transfer reactions, and constitutes the first example of a general strategy of enzyme-transferred isotope patterns (ETIPs) analysis. 相似文献
57.
There are peroxidative changes during the reperfusion of the rat small intestine following a 1h period of total ischaemia. That is demonstrated by the increases of the concentrations of glutathione disulphide and of thiobarbituric acid-reactive substances. An important source of the active oxygen species leading to peroxidations is the degradation of purine nucleotides. The nucleotides and their derivatives were measured by an ion-pair reversed-phase high-performance liquid chromatographic separation in a single analysis within 40 min. Modification of the elution gradient resulted in a high resolution of nucleosides and nucleobases, including allopurinol and oxypurinol. The decrease of the nucleoside triphosphate concentration and the increase of nucleoside monophosphate concentration, followed by accumulations of nucleosides and nucleobases in the course of the ischaemia were measured. During reperfusion the nucleotide pools are filled up. Restoration of adenosine triphosphate and guanosine triphosphate can be accelerated by application of the xanthine oxidoreductase inhibitor allopurinol. Pretreatment of the animals with allopurinol also diminished the formation of glutathione disulphide and thiobarbituric acid-reactive substances. 相似文献
58.
Electrospray ionization-voltage sweep-Ion mobility spectrometry for biomolecules and complex samples
Eric J. Davis Kristopher F. Grows William F. Siems Herbert H. Hill Jr. 《International Journal for Ion Mobility Spectrometry》2014,17(3-4):147-156
Voltage Sweep Ion Mobility Spectrometry (VSIMS) has been applied to complex samples using electrospray ionization (ESI). The usable range of VSIMS has been extended from that obtained in previous studies where only volatile compounds were investigated. Using ESI, VSIMS was evaluated with compounds with reduced mobility values as low as 0.3 V2cm?1 s?1. The primary advantage of VSIMS is to enable a drift time ion mobility spectrometer (DTIMS) to detect both fast and slow moving ions at optimal resolving power, thus improving the peak capacity. In this work ESI-VSIMS was applied to a series of small peptides and drugs spanning a large range of reduced mobility values in order to demonstrate ESI-VSIMS to separation. To demonstrate improved peak capacity of IMS with voltage scan operation, oligomers of silicone oil provided a series of evenly-spaced peaks, ranging in reduced mobility values from 0.85 to 0.3 V2cm?1 s?1. The peak capacity of 61 for a standard IMS was improved to 102 when voltage sweep operation was employed. In addition, VSIMS increased the average resolving power of the DTIMS from 66 to 106 for silicone oil. 相似文献
59.
Larry A. Viehland Tamar Skaist Chetana Adhikari William F. Siems 《International Journal for Ion Mobility Spectrometry》2017,20(1-2):1-9
The zero-field mobilities of many atomic ions in rare gases are calculated from highly accurate, ab initio potential energy curves. They are expected to be accurate to at least 0.05%, thus allowing them to be used to calibrate mobility measurements in different drift-tube and ion mobility mass spectrometers. 相似文献
60.