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991.
Polarized memory, i.e., the memory in which switching between ON and OFF states depends on the polarity of bias voltage has been found in point contact diodes on single crystals of CdSe, CdS, CdTe, GaAs and GaP. The detailed features of switching characteristics depend on the choice of metals for the point contact electrode, on the sharpness of the contact and also on the resistance of the current limiter in the circuit. Observation of the transients between ON and OFF has also been performed. 相似文献
992.
Shosuke Yamamura Seiji Kosemura Shigeru Ohba Masatoki Ito Yoshihiko Saito 《Tetrahedron letters》1981,22(52):5315-5318
Two new toxic substances, euphoscopins A and B, have been isolated from the plant L., and their absolute stereostructures also been elucidated on the basis of their spectral data coupled with an X-ray crystallographic analysis of the -bromobenzoate readily obtained on treatment of euphoscopin A with -bromobenzoyl chloride - pyridine. These antitumor substances belong to a group of jatrophone-type diterpenes. 相似文献
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Ohne Zusammenfassung 相似文献
998.
(2,4-Pentadienyl)- and (2,4-hexadienyl)trimethylsilanes, prepared from the corresponding pentadienylpotassiums and trimethylchlorosilane, react smoothly with various electrophiles such as acetals, aldehydes and acid halides to give pentadienylation products, with regiospecific transposition of the pentadienyl group. 相似文献
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1000.
Kayori Shimada Marina A. Lusenkova Keisuke Sato Takeshi Saito Shigetomo Matsuyama Hisae Nakahara Shinichi Kinugasa 《Rapid communications in mass spectrometry : RCM》2001,15(4):277-282
Mass discrimination effects in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) were quantitatively investigated using equiweight and equimolar mixtures of uniform polystyrene (PS) oligomers. Uniform PS oligomers were separated by preparative super-critical fluid chromatography (SFC) from commercial standard PS samples. The separated PS oligomers, with degrees of polymerization n = 2–25, have absolutely no molecular weight distributions. Equiweight and equimolar mixtures of uniform PS oligomers were accurately prepared by weighing by microbalance, and their spectra were recorded using a MALDI-TOF mass spectrometer. In the lower molecular weight region (less than about 103) the oligomers with lower molecular weights give lower mass spectral intensities, with no correlation with laser power. In contrast, higher laser powers yield a decrease of mass spectral intensities in the higher molecular weight region. These results clearly show that mass discrimination effects occur at lower and higher molecular weights depending on the laser power, and provide quantitative information about the discrimination. Using the data on equiweight and equimolar mixtures of PS oligomers, it was possible to calibrate the MALDI-TOF mass spectral data for an analysis of molecular weight distribution of a standard monodisperse PS sample with number-averaged molecular weight of 103, and to compare it with the molecular weight distribution measured by analytical SFC. The result from the calibrated MALDI-TOF mass spectrum, however, does not agree perfectly with that from the SFC results, because undetectable peaks in MALDI-TOF mass spectra at lower and higher molecular weights could not be included in the calibration of peak intensities. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献