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1.
The paper reports the results obtained in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+) by using an Hg(2+)-sensitive membrane-electrode for the end-point indication. The determination of Bi(3+) and Fe(3+) is performed after addition of mercuric complexonate from which these cations release Hg(2+) by means of which the electrode senses the equivalence point. In the case of Cr(3+) an excess of complexone is added and the surplus is titrated with a standard solution of Hg(2+) in the presence of the Hg(2+)-sensitive membrane-electrode. 相似文献
2.
Sorin Mager Ionel Hopârtean Dan Bini§or 《Monatshefte für Chemie / Chemical Monthly》1978,109(6):1393-1401
The spectra of some 9-chloro-6-nitroacridines with methoxy substituents in position 1,4; 2,4; 3,4; 2,3; and ethoxy substituents in positions 1, 2, 3, were recorded. The influence of electron releasing alkoxy groups and electron withdrawing nitro groups on chemical shifts of protons in the 9-chloroacridinic cycle was discussed and PMR parameters were determined, comparatively with those of acridine and 9-chloroacridine. Good agreement between calculated and experimental values is observed. The spectrum of 9-chloro-1,2,3-triethoxyacridine shows for the four protons of the ringC. (H-5, H-6, H-7, H-8) anAMNX coupling pattern whose parameters were determined. 相似文献
3.
The major drawback of liquid chromatography/mass spectrometry (LC/MS) for the analysis of mixtures is the non-quantitative nature of these studies. The ionization efficiency of the various components in the mixture (e.g., a compound and its metabolites) can vary greatly and, therefore, relative intensities of signals cannot be related to relative abundance. A chip-based nanoelectrospray ionization source was used to compare the ionization efficiencies of compounds with different physical-chemical characteristics. The data indicate that the ionization efficiencies vary much less with the chip-based device than by LC/MS. This was ascribed to the generation of a much higher electric field around the nozzles, which supplies a large excess of protons to the small droplets and reduces/eliminates the differences in the ionization efficiency for the analytes. 相似文献
4.
Determination of in vitro permeability of drug candidates through a caco-2 cell monolayer by liquid chromatography/tandem mass spectrometry 总被引:6,自引:0,他引:6
Studying the permeability of compounds across a Caco-2 cell monolayer is an established in vitro model to screen for oral absorption and to evaluate the mechanism of transport. This assay can also be used to evaluate compounds as potential P-glycoprotein substrates and/or inhibitors. The traditional methods of sample analysis (high-performance liquid chromatography (HPLC) with a UV or fluorescence detector) limit the throughput and sensitivity of this assay. Data are presented here describing the use of liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the analysis of samples derived from the Caco-2 cell studies. During the analysis an automatic switching valve was used to divert the flow from the HPLC column to waste for the first minute, preventing the early eluting salts from entering and contaminating the LC/MS interface. This approach allows the rapid and accurate determination of drug transport across the Caco-2 cell monolayer. The high sensitivity and specificity of LC/MS/MS make this technique an ideal candidate for the low concentration and high throughput routine analysis of Caco-2 cell solutions, especially if multiple compounds are administered and analyzed simultaneously. Thus, the use of LC/MS/MS will increase the value of the Caco-2 cell assay as an in vitro screening tool. 相似文献
5.
The low-energy fragmentation characteristics of the [H3,C,N,O2]+· isomers [H3CNO2]+· (a), [H2C?N(O)OH]+· (b), [H3CONO]+· (c), [HC(O)NHOH]+· (d) and [HC(OH)?NOH]+· (e) were studied in detail by metastable ion mass spectrometry. In agreement with most earlier observations, appearance energy measurements established the potential energy surface of the isomers a, b and c, showing the intricate interrelations between them. It was concluded that a isomerizes into b prior to fragmentation by loss of ·OH and H2O and into c before loss of ·H and H3CO· moreover, the reverse reactions do not take place on the metastable time-frame. The dominant metastable process for isomers d and e (obtained via HCN loss from glyoxime) was generation of [H2NOH]+·. For isomer e this process was proposed to involved a rate-determining isomerization into d. It was concluded that isomers d and e do not intercommunicate with ions a, b and c prior to fragmentation. Neutralization-reionization mass spectrometry indicated that the enol form of formohydroxamic acid as well as the keto counterpart are stable in the gas phase. 相似文献
6.
Dovas A. Saulys Cornelis E. C. A. Hop Donald F. Gaines 《Journal of the American Society for Mass Spectrometry》1994,5(6):537-543
Metastable ion (MI) and collision-induced dissociation (CID) mass spectra have been recorded and compared for all nine C4H12Si+. isomers. The (Me)4Si+., t-BuSiH 3 +. , s-BuSiH 3 + , and (Me)2EtSiH+. isomers have unique MI and CID mass spectra. The MI mass spectra, including the kinetic energy release values, of (Me)(i-Pr)SiH 2 +. and (Me)(n-Pr)SiH 2 +. are identical, which implies isomerization. MI data also suggest that a fraction of the n-BuSiH 3 +. ions rearrange into branched (Me)2EtSiH+. ions and a fraction of the n-BuSiH 3 +. ions rearrange into branched s-BuSiH 3 +. ions. A comparison with the isomeric C5H 12 +. pentanes reveals a crucial difference: H2 loss occurs for n-BuSiH 3 +. , i-BuSiH 3 +. , s-BuSiH 3 +. , (Me)(n-Pr)SiH 2 +. , (Me)(i-Pr)SiH 2 +. , and Et2SiH 2 +. , but not for any of the C5Hi 12 +. isomers. Generation of four- or five-membered silicon containing rings is suggested for H2 loss from the C4H12Si+. silanes. 相似文献
7.
Cornelis E. C. A. Hop Dovas A. Saulys Donald F. Gaines 《Journal of the American Society for Mass Spectrometry》1995,6(9):860-865
Two borane salts ([(Me)4N][B3H8] and Cs[B3H8]) were examined by electrospray mass spectrometry in the positive ion mode. Acetonitrile solutions provided the most informative spectra; the salts exhibited a remarkable degree of clustering under electrospray conditions, and virtually all signals corresponded to cationic cluster ions of the general formula {[cation m+] x [anion n?] y }(mx ? ny)+. In contrast, methanol solutions of these salts produced only B(OCH3) 4 ? cluster ions under otherwise identical conditions. 11B NMR analyses corroborate the identities of the methanol solution species that enter the electrospray source and the reaction product generated during the electrospray process. 相似文献
8.
9.
Gerhard Holzmann Johan K. Terlouw Cornelis E. C. A. Hop Peter C. Burgers 《Journal of mass spectrometry : JMS》1986,21(3):105-108
It was concluded from earlier metastable ion and collisional activation experiments that [C13H9]+ ions generated by dissociative ionization of stilbenes and diphenylmethane consist of a mixture of isomeric structures. It is shown in this paper that the methyl loss upon which this conclusion rests originates to a large extent from metastable molecular ions decomposing in the magnetic sector field (interference signal). Our results do not show, nor do they require, that more than one isomeric [C13H9]+ species is present. The importance of recognizing such interference signals is stressed. 相似文献
10.