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151.
Soft ambient ionization sources generate reactive species that interact with analyte molecules to form intact molecular ions, which allows rapid, sensitive, and direct identification of the molecular mass. We used a dielectric barrier discharge ionization (DBDI) source with nitrogen at atmospheric pressure to detect alkylated aromatic hydrocarbon isomers (C8H10 or C9H12). Intact molecular ions [M]•+ were detected at 2.4 kVpp, but at increased voltage (3.4 kVpp), [M + N]+ ions were formed, which could be used to differentiate regioisomers by collision-induced dissociation (CID). At 2.4 kVpp, alkylbenzene isomers with different alkyl-substituents could be identified by additional product ions: ethylbenzene and -toluene formed [M-2H]+, isopropylbenzene formed abundant [M-H]+, and propylbenzene formed abundant C7H7+. At an operating voltage of 3.4 kVpp, fragmentation of [M + N]+ by CID led to neutral loss of HCN and CH3CN, which corresponded to steric hindrance for excited state N-atoms approaching the aromatic ring (C-H). The ratio of HCN to CH3N loss (interday relative standard deviation [RSD] < 20%) was distinct for ethylbenzene and ethyltoluene isomers. The greater the number of alkyl-substituents (C-CH3) and the more sterically hindered (meta > para > ortho) the aromatic core, the greater the loss of CH3CN relative to HCN was. 相似文献
152.
Rapid classification of perfumes by extractive electrospray ionization mass spectrometry (EESI-MS) 总被引:1,自引:0,他引:1
Chingin K Gamez G Chen H Zhu L Zenobi R 《Rapid communications in mass spectrometry : RCM》2008,22(13):2009-2014
Extractive electrospray ionization mass spectrometry (EESI-MS) was applied to rapid fingerprinting of various perfumes for quality classification. Unique EESI-MS fingerprints of ten famous brands were obtained. This technique was shown to be applicable to rapid forgery detection on the example of an authentic and a counterfeit 'Miss Dior' fragrance by Christian Dior. We believe that the high throughput and simplicity of this sample-preparation-free method can be advantageous in the perfume industry, for instance when applied to online quality control. 相似文献
153.
Mädler S Barylyuk K Boeri Erba E Nieckarz RJ Zenobi R 《Journal of the American Society for Mass Spectrometry》2012,23(2):213-224
Chemical cross-linking in combination with high-mass MALDI mass spectrometry allows for the rapid identification of interactions
and determination of the complex stoichiometry of noncovalent protein–protein interactions. As the molecular weight of these
complexes increases, the fraction of multiply charged species typically increases. In the case of homomeric complexes, signals
from multiply charged multimers overlap with singly charged subunits. Remarkably, spectra recorded in negative ion mode show
lower abundances of multiply charged species, lower background, higher reproducibility, and, thus, overall cleaner spectra
compared with positive ion mode spectra. In this work, a dedicated high-mass detector was applied for measuring high-mass
proteins (up to 200 kDa) by negative ion mode MALDI-MS. The influences of sample preparation and instrumental parameters were
carefully investigated. Relative signal integrals of multiply charged anions were relatively independent of any of the examined
parameters and could thus be approximated easily for the spectra of cross-linked complexes. For example, the fraction of doubly
charged anions signals overlapping with the signals of singly charged subunits could be more precisely estimated than in positive
ion mode. Sinapinic acid was found to be an excellent matrix for the analysis of proteins and cross-linked protein complexes
in both ion modes. Our results suggest that negative ion mode data of chemically cross-linked protein complexes are complementary
to positive ion mode data and can in some cases represent the solution phase situation better than positive ion mode. 相似文献
154.
A method for enhancing positive analyte ion signal in MALDI is described. The idea is based on influencing the kinetic energy of free electrons emitted from the organic/metal interface. It has been recently shown that free electrons in MALDI have energies around 1 eV. This energy is close to the maximum capture cross-section of most common MALDI matrices, leading to the efficient formation of negative matrix ions. This results in the reduction of the positive analyte ion yield. The effect can be minimized by shifting the kinetic energy of the electrons away from the maximum of the matrix capture cross-section by choosing a different substrate material. 相似文献
155.
Konstantin Chingin Huanwen Chen Gerardo Gamez Renato Zenobi 《Journal of the American Society for Mass Spectrometry》2009,20(9):1731-1738
An instrument for fluorescence spectrometry and FTICR-MS has been developed to study ions produced by a commercial ESI source.
156.
Carolin Blum Thomas Schmid Lothar Opilik Simon Weidmann Stephan R. Fagerer Renato Zenobi 《Journal of Raman spectroscopy : JRS》2012,43(12):1895-1904
Although conventional Raman, surface‐enhanced Raman (SERS) and tip‐enhanced Raman spectroscopy (TERS) have been known for a long time, a direct, thorough comparison of these three methods has never been carried out. In this paper, spectra that were obtained by conventional Raman, SERS (on gold and silver substrates) and TERS (in ‘gap mode’ with silver tips and gold substrates) are compared to learn from their differences and similarities. Because the investigation of biological samples by TERS has recently become a hot topic, this work focuses on biologically relevant substances. Starting from the TER spectra of bovine serum albumin as an example for a protein, the dipeptides Phe–Phe and Tyr–Tyr and the tripeptide Tyr–Tyr–Tyr were investigated. The major findings were as follows. (1) We show that the widely used assumption that spectral bands do not shift when comparing SER, TER and conventional Raman spectra (except due to binding to the metal surface in SERS or TERS) is valid. However, band intensity ratios can differ significantly between these three methods. (2) Marker bands can be assigned, which should allow one to identify and localize proteins in complex biological environments in future investigations. From our results, general guidelines for the interpretation of TER spectra are proposed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
157.
Frankevich V Nieckarz RJ Sagulenko PN Barylyuk K Zenobi R Levitsky LI Agapov AY Perlova TY Gorshkov MV Tarasova IA 《Rapid communications in mass spectrometry : RCM》2012,26(13):1567-1572
The ionization mechanisms of several atmospheric pressure ion sources based on desorption and ionization of samples deposited on a surface were studied. Home-built desorption electrospray ionization (DESI), laserspray ionization (LSI), and atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) sources were characterized using low-molecular-weight compounds, in particular fluorescent dyes. Detection of the desorbed and ionized species was performed by laser-induced fluorescence and ion cyclotron resonance mass spectrometry. The dependences of the signal intensities on various experimental parameters were studied. The data obtained reveals common features, such as formation of solvated species and clusters in the ionization processes, in all of the techniques considered. 相似文献
158.
159.
160.
Faster than with conventional solution-phase methods , mass spectrometry can be used to recognize the formation of noncovalent complexes. This is shown by the detection of the specific triple complex between an 18-residue zinc finger peptide from the gag protein p55 of HIV-1, Zn2+, and the oligodeoxynucleotide d(TTGTT) by MALDI-MS (see the spectrum). The results also indicate that MALDI mass spectra can qualitatively reflect solution-phase chemistry. 相似文献