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21.
Stable isotope methods are potentially quite useful for validating natural or enhanced mineral degradation of contaminants. For this reason, a continuous flow gas chromatograph (GC), isotope ratio mass spectrometer (IRMS) has been coupled with a quadrupole mass selective detector (MSD) to allow simultaneous mass spectral and stable carbon isotope ratio data to be obtained from a single chromatographic analysis. This allows the target contaminant and any extra-cellular degradation intermediates to be both qualified and quantified. Previously acceptable limits of precision (0.3 parts per mil) are undesirable given the small fractionation observed during aerobic degradation. To further understand the fate of organic contaminants and to gain information about the metabolic degradative pathway employed by a microorganism, routine isotopic analyses on a range of analytes have been performed. Quantities of sample producing mass-44 ion beam signal (I(44)) of 2 x 10(-10) to 1 x 10(-8) A were analysed. When the IRMS was tuned for high sensitivity, ion source nonlinearities were overcome by peak height correction from an algorithm that was produced using known isotopic standards of varying concentrations. This led to sample accuracy of <0.01 per thousand and sample precision of 0.1 per thousand. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
22.
UP Schlunegger M Stoeckli RM Caprioli 《Rapid communications in mass spectrometry : RCM》1999,13(18):1792-1796
An ion trap has been modified for the analysis of high mass ions generated by matrix-assisted laser desorption/ionization. Samples are deposited on a probe tip and introduced directly onto the hyperbolically shaped surface of one endcap. All three electrodes - both the endcaps and the ring electrode - are insulated so that the radio frequency (Rf) voltage may be applied to the center ring electrode and the inverted Rf voltage to the endcaps. By using low frequencies (below 100 kHz) and low amplitudes (below 200 V), high mass singly charged ions may be trapped and analyzed by a frequency sweep at constant amplitude. In the high mass range (60-160 kDa), this instrument showed good sensitivity, signal-to-noise ratios, and mass resolution. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
23.
24.
Downward AM Moore EG Hartshorn RM 《Chemical communications (Cambridge, England)》2011,47(27):7692-7694
Two Ru(II)-Co(III) heterodinuclear complexes have been synthesised as model complexes for photoactivated cytotoxins. Photoinduced ligand release has been demonstrated and the rate shown to depend on dioxygen concentration. Emission lifetimes and quantum yields are reported. These results validate the concept and justify further work to synthesise systems containing cytotoxic ligands. 相似文献
25.
Stephanie S. Peterson Tishal Kirby Mariappan Kadarkaraisamy Richard M. Hartshorn Andrew G. Sykes 《Polyhedron》2009,28(14):3031-3035
Reaction of Ag(I) and Cu(I) [M(NCCH3)4]X (X = BF4− and PF6−) salts with 1,8-bis(nicotinyloxy)anthracene-9,10-dione (1), 1,8-bis(isonicotinyloxy)anthracene-9,10-dione (2), and 1,8-bis(pyrimidine-5-carboxyloxy)anthracene-9,10-dione (3), yield new chelating and bridging complexes and two new coordination polymers. The bridging capabilities of ligands 1 and 2 have not been demonstrated before, and ligand 1, by itself, has the flexibility to produce either chelated or bridged structures and an unusual ladder coordination polymer. The tetradentate ligand 3 also produces a one-dimensional coordination polymer in the presence of one equivalent of Ag(I). All complexes have been characterized by X-ray crystallography. 相似文献
26.
Kinetic and mass spectrometric evidence show that p-anisyl alcohol is acetylated via a carbonium ion intermediate. Other, less activated, benzyl alcohols are acetylated via a mechanism which does not involve C---O fission in the alcohol. 相似文献
27.
The brain is believed to be particularly vulnerable to arsenic due to its high oxygen consumption rate and high level of polyunsaturated fatty acids and relatively high rate of oxygen free radical generate without commensurable level of arsenic. Hence, in the present work an attempt is made to study the changes in the biochemical contents in the brain tissues of edible fish Labeo rohita due to arsenic intoxication using Fourier Transform Infrared (FT-IR) spectroscopy. FT-IR spectra reveal significant differences in absorbance intensities between the control and arsenic intoxicated brain tissues, reflecting an alteration on the major biochemical constituents, such as lipids, proteins and nucleic acids of the brain tissues of L. rohita due to arsenic intoxication. Further, the administration of antidote DMSA improves the protein and lipid contents significantly in the brain tissues when compared to arsenic intoxicated tissues. The decrease in α-helix structure due to arsenic intoxication might be responsible for the increase in β-sheet secondary structures, which is consistent with the mechanism of β-sheet formation. 相似文献
28.
P.A. Bates M.J. Gray M.P. Hartshorn Huong Tuong Ing K.E. Richards W.T. Robinson 《Tetrahedron letters》1981,22(13):1279-1280
In chloroform at 20°, or in tetrachloroethylene at 120°, the title compounds (1) rearrange to give the α-diketone(2), the structure of which was determined by X-ray crystal structure analysis; a possible rearrangement mechanism is outlined. 相似文献
29.
Hojjatie MM Abrams DE Parham TM Balthrop J Beine R Dickinson V Hartshorn J Herald S Latimer G Padmore J Pleasants S Riter K Roser R Schmunck G Sensmeier R Smith V Taylor L Volgas G 《Journal of AOAC International》2004,87(2):346-351
Water soluble urea-formaldehyde (UF) fertilizers, manufactured by complex reaction of urea and formaldehyde, typically contain varying amounts of unreacted urea. A liquid chromatography method for the analysis of urea in these products, and in aqueous urea solutions, was collaboratively studied. An amine chromatography column was used to separate the unreacted urea from numerous UF reaction products present in these liquid fertilizers. Unreacted urea was determined by using external urea standards with UV detection at 195 nm. The standards and test samples were prepared in the mobile phase of 85% (v/v) acetonitrile in water. Ten laboratories analyzed 5 different UF-based commercial products containing unreacted urea in the range of 6 to 17% by weight, and 5 different concentrations of urea in water equivalent to commercial products of that nature. The aqueous urea solutions contained 2-20% urea (w/w). The range of s(R) values for the 5 UF-based commercial fertilizers was 0.49-1.02 and the %RSD(R) was 1.94-6.14. The s(R) range for the 5 urea solutions was 0.10 to 0.79 and the %RSD(R) range was 2.54 to 4.88. The average recovery of urea from the aqueous urea solutions was 96-103%. Therefore, this method is capable of monitoring urea nitrogen manufacturers' label claims and total nitrogen claims in those cases where urea is the sole source of plant food nitrogen. Based on the collaborative study data, the authors recommend this method be approved for AOAC Official First Action status. 相似文献
30.
Lennart Eberson Ola Persson Finn Radner Michael P. Hartshorn 《Research on Chemical Intermediates》1996,22(9):799-820
The generation and reactions of aromatic radical cations by photolysis of ArH-tetranitromethane in 1,1,1,3,3,3-hexfluoropropan-2-ol (HFP) at room temperature has been investigated. The primary radical cations (ArH⊙?) were detectable by EPR spectroscopy in most cases where E o(Ar⊙?/ArH) 1.5 V (vs. Ag/AgCl). Secondary radical cations were obtained from pentamethylbenzene and durene (1,2,3,4,5,6,7,8-octamethyl- and 1,2,4,5,6,8-hexamethyl-anthraceneradical cation), from certain naphthalenes (dehydrodimer radical cations, Ar?Ar⊙?) and from 2,3-dimethylanisole (the radical of a nitroso derivative). The persistence of the radical cations in the presence of trinitromethanide ion is seen as a consequence of the stabilization of the nucleophile by HFP. This assumption was supported by preparative results on 1-methoxynaphthalene and 1,4-dimethylnaphthalene, where the trinitromethanide ion initiated pathway was completely eliminated in HFP, contrary to results earlier obtained in dichloromethane. 相似文献