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51.
Pierce CY Barr JR Woolfitt AR Moura H Shaw EI Thompson HA Massung RF Fernandez FM 《Analytica chimica acta》2007,583(1):23-31
Accurate bacterial identification is important in diagnosing disease and in microbial forensics. Coxiella burnetii, a highly infective microorganism causative of the human disease Q fever, is now considered a U.S. category B potential bioterrorism agent. We report here an approach for the confirmatory identification of C. burnetii at the strain level which involves the combined use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and supervised pattern recognition via Partial Least Squares-Discriminant Analysis (PLS-DA). C. burnetii isolates investigated in this study included the following prototype strains from different geographical and/or historical origins and with different antigenic properties: Nine Mile I, Australian QD, M44, KAV, PAV, Henzerling, and Ohio. After culture and purification following standard protocols, linear MALDI-TOF mass spectra of pure bacterial cultures were acquired in positive ion mode. Mass spectral data were normalized, baseline-corrected, denoised, binarized and modeled by PLS-DA under crossvalidation conditions. Robustness with respect to uncontrolled variations in the sample preparation and MALDI analysis protocol was assessed by repeating the experiment on five different days spanning a period of 6 months. The method was validated by the prediction of unknown C. burnetii samples in an independent test set with 100% sensitivity and specificity for five out of six strain classes. 相似文献
52.
53.
Abstract Positive and negative ion laser desorption (LD) mass spectra of organic acids are characterized by the emission of the quasimolecular ions (M+H)+ and (M-H)?. Generation of (M+H)+ ions is interpreted as evidence for the occurence of high pressure proton transfer reactions in LD. Fragment ions can be rationalized by loss of stable neutral molecules from quasimolecular ions although decomposition may also be occuring prior to ionization. Features unique to LD, including the detection of pyrolysis products along with ions characteristic of the sample, are discussed in terms of the internal energy distribution in the irradiated microvolume. Negative ion mass spectra of acids are dominated by (M-H)?, while positive ion spectra contain abundant fragment ions, underlining the utility of detecting negative ions for acidic compounds. 相似文献
54.
Bile acids are important in the diagnosis of certain diseases. Their mass spectra are usually obtained by electron impact or chemical ionization and are dominated by fragment ions. We have investigated laser desorption (LD) as an ionization method for these compounds. The LD mass spectra contain abundant positive and negative quasimolecular ions. Bile acid salts can be successfully analyzed. In addition, the results help to elucidate details of the LD process. 相似文献
55.
The laser microprobe mass analyzer (LAMMA) is a recently developed mass spectroscopic technique for both organic and inorganic microanalysis. LAMMA analysis involves laser ionization of the sample material followed by mass separation in a time of flight (TOF) mass spectrometer. The present application of LAMMA illustrates the characterization of three inorganic perrhenates: NH4ReO4, AgReO4 and Al(ReO4)3. Results clearly show the value of LAMMA for inorganic mass spectrometry, in this study the most useful data originated in the negative-ion mass spectra. 相似文献
56.
Schrenk B Dris S Bakopoulos P Lazarou I Voigt K Zimmermann L Avramopoulos H 《Optics letters》2012,37(15):3222-3224
Optical quadrature amplitude modulation (QAM) is experimentally demonstrated with a low-complexity modulator based on a semiconductor optical amplifier and electroabsorption modulator. Flexible amplitude/phase format transmission is achieved. The applicability of octary QAM for coherent optical access networks with sustainable 3 Gb/s per-user bandwidth is investigated for a long reach of 100 km, and its compatibility with a potentially high split is verified. 相似文献
57.
Kung T. Ng David M. Hercules 《Journal of Electron Spectroscopy and Related Phenomena》1975,7(3):257-268
Variation in ESCA signal intensities for ionic compounds is interpreted in terms of the dependence of photoelectron escape probability on the immediate environment of the emission center. A model has been developed to estimate this escape probability by the fractional solid angle not blocked by the nearest neighbors of the emission center. A linear correlation is found between the normalized intensity ratios for simple alkali halides and the fractional escape solid angle ratios. Absolute intensity measurements have been carried out for alkali perchlorates and alkali chlorides. The chlorine signal intensities were constant for perchlorates but decrease steadily from LiCl to CsCl. These observations are consistent with the chlorine atom in the perchlorate groups always being surrounded by four oxygens; therefore its fractional escape solid angle is independent of the compound. 相似文献
58.
R.C. Gray J.C. Carver D.M. Hercules 《Journal of Electron Spectroscopy and Related Phenomena》1976,8(5):343-357
The silicon 2p electron binding energies have been measured for a series of 33 organosilicon compounds. The binding energies are correlated with partial atomic charges calculated by various electronegativity models and CNDO calculations. Group shifts are reported for various chemical groups attached to silicon and are found to correlate with group shifts reported for carbon and phosphorus compounds. 相似文献
59.
We demonstrate an all-optical circuit capable of generating 40-GHz control signals from flag pulses that can be used to define the switching state of all-optical gates for use with optical packets. The circuit comprises a Fabry-Perot filter and a semiconductor optical amplifier, and with a single pulse it can generate 12 control pulses with 0.64-dB amplitude modulation. With two and three flag pulses the number of control pulses becomes 36 and 54, respectively. 相似文献
60.
Gies AP Hercules DM Gerdon AE Cliffel DE 《Journal of the American Chemical Society》2007,129(5):1095-1104
Electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS) and gel permeation chromatography (GPC) were used to study the synthesis of a series of tiopronin monolayer-protected gold nanoclusters (MPCs) and to monitor their postsynthesis peptide ligand place-exchange reactions. All mass spectra identified the presence of cyclic gold(I)-thiolates with a strong preference for tetrameric species. During the synthesis of pre-monolayer-protected nanoclusters (pre-MPCs), esterified gold(I)-thiolate tetramers were initially observed in minor abundance (with respect to disulfide bridged tiopronin species) before dramatically increasing in abundance and precipitating from solution. After conversion of pre-MPCs to MPCs, ESI-TOF mass spectra demonstrated an overall predominance of tetrameric species with conversion from ester-terminated end groups to carboxyl-terminated end groups. Further modifications were performed through postsynthesis ligand place-exchange reactions to validate the existence of the tetramers. This work suggests that monolayer protection is accomplished by cyclized gold(I)-thiolate tetramers on the gold core surface, and/or that gold(I)-thiolates are a basic building block within the nanoparticles. 相似文献