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排序方式: 共有122条查询结果,搜索用时 26 毫秒
1.
J. L. Cotter 《Journal of mass spectrometry : JMS》1973,7(1):11-16
The pyrolysis of some perfluoroalkylene-linked aromatic and heteroaromatic polymer precursors and a poly(1,3-phenylenehexafluorotrimethylene) has been studied using a combined pyrolysis-gas chromatographic-mass spectrometric method. Whereas the electron-impact induced fragmentations of the polymer precursors are almost exclusively controlled by cleavage β to the aromatic or heteroaromatic ring, thermolysis of these compounds yields products whose formation is consistent with the occurrence of primary cleavage processes that are not confined β to the ring. 相似文献
2.
The reaction of epibromohydrin with hydroxyquinazolin-2-(1H)one derivatives. Novel oxazine formation
Mary Lou Cotter Victor Bandurco Elizabeth Wong Zoltan G. Hajos 《Journal of heterocyclic chemistry》1979,16(3):623-624
Epibromohydrin was found to react with 7-hydroxy-2-methylpyrrolo[1,2-c]quinazolin-5(6H)-one ( 4 ) in the presence of sodium hydroxide to form the novel oxazine 5 . The structure of compound 5 was proven by cmr and pmr analysis. 相似文献
3.
The electron-impact induced loss of CO2 from phthalanil and 4-phthalimidobiphenyl is paralleled by the formation of large amounts of CO2 on pyrolysis. CO is also a major pyrolysis product, but the loss of CO from these compounds under electron-impact is not an important fragmentation process. The mass spectra of meta and para-chlorophthalanils show prominent [M ? CO2] peaks but the corresponding peak for the ortho isomer is of relatively low intensity. CO and CO2 are the principal gaseous products of the thermal decomposition of o-chlorophthalanil. 相似文献
4.
J. L. Cotter 《Journal of mass spectrometry : JMS》1972,6(10):1071-1075
The principal electron-impact fragmentation patterns of 3,4,5-triphenyl-1,2,4-triazole, 2,5-diphenyl-1,3,4-thiadiazole, their perfluorinated analogues and 2,5-di(pentafluorophenyl)-1,3,4-oxadiazole have been established from metastable ion evidence and precise mass measurements. Although ions produced by expulsion of nitrogen from the molecular-ions of these compounds are of low abundance, the simultaneous expulsion of nitrogen and a C7X5 radical (X = H or F) gives rise to abundant ions. 相似文献
5.
Ron Orlando Catherine Fenselau Robert J. Cotter 《Journal of the American Society for Mass Spectrometry》1991,2(3):189-197
Endothermic ion-molecule reactions in a tandem mass spectrometer have been used for a number of years for determining thermodynamic quantities, such as heats of formation and proton affinities, for gaseous ions. Recently, the reactive, endothermic collision has been exploited as an analytical technique for the structural analysis of peptides and other biomolecules. The technique is based upon the endothermic transfer of protons associated with amide bonds to ammonia. This reaction proceeds via a long-lived collision complex. When additional beam energy is supplied, other dissociation channels are opened up, leading to the production of sequence ions for the mass-selected, protonated analyte that are normally observed in high energy collision-induced dissociation spectra. The advantage, however, is that such spectra can be produced at very low beam energies. In this article, the rationale for developing this scheme, and its roots in previous ion-molecule studies, are explored. 相似文献
6.
7.
Dr. Benjamin Frank Dr. Thomas P. Cotter Dr. Manfred E. Schuster Prof. Dr. Robert Schlögl Dr. Annette Trunschke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):16938-16945
The effect of the gas‐phase chemical potential on surface chemistry and reactivity of molybdenum carbide has been investigated in catalytic reactions of propane in oxidizing and reducing reactant mixtures by adding H2, O2, H2O, and CO2 to a C3H8/N2 feed. The balance between surface oxidation state, phase stability, carbon deposition, and the complex reaction network involving dehydrogenation reactions, hydrogenolysis, metathesis, water‐gas shift reaction, hydrogenation, and steam reforming is discussed. Raman spectroscopy and a surface‐sensitive study by means of in situ X‐ray photoelectron spectroscopy evidence that the dynamic formation of surface carbon species under a reducing atmosphere strongly shifts the product spectrum to the C3‐alkene at the expense of hydrogenolysis products. A similar response of selectivity, which is accompanied by a boost of activity, is observed by tuning the oxidation state of Mo in the presence of mild oxidants, such as H2O and CO2, in the feed as well as by V doping. The results obtained allow us to draw a picture of the active catalyst surface and to propose a structure–activity correlation as a map for catalyst optimization. 相似文献
8.
Pitch perception by cochlear implant subjects 总被引:9,自引:0,他引:9
B Townshend N Cotter D Van Compernolle R L White 《The Journal of the Acoustical Society of America》1987,82(1):106-115
Direct electrical stimulation of the auditory nerve can be used to restore some degree of hearing to the profoundly deaf. Percepts due to electrical stimulation have characteristics corresponding approximately to the acoustic percepts of loudness, pitch, and timbre. To encode speech as a pattern of electrical stimulation, it is necessary to determine the effects of the stimulus parameters on these percepts. The effects of the three basic stimulus parameters of level, repetition rate, and stimulation location on subjects' percepts were examined. Pitch difference limens arising from changes in rate of stimulation increase as the stimulating rate increases, up to a saturation point of between 200 and 1000 pulses per second. Changes in pitch due to electrode selection depend upon the subject, but generally agree with a tonotopic organization of the human cochlea. Further, the discriminability of such place-pitch percepts seems to be dependent on the degree of current spread in the cochlea. The effect of stimulus level on perceived pitch is significant but is highly dependent on the individual tested. The results of these experiments are discussed in terms of their impact on speech-processing strategies and their relevance to acoustic pitch perception. 相似文献
9.
10.
Summary Summary
The assigned chirality at each center of the synthetic nonapeptide histrelin (L-pyroglutamyl-L-histidyl-L-tryptophyl-L-seryl-L-tyrosyl-D-Nim-benzyl-histidyl-L-leucyl-L-arginyl-L-proline-ethylamide) was verified using chiral gas chromatography. The procedure involved
acid hydrolysis of histrelin to the constituent amino acids, derivatization as the N-pentafluoropropionyl/isopropyl esters
and the analysis of the mixture using a commercially available 25m chiral capillary column (Chirasil-L-Val). There was no
significant difference in the retention time of the amino acids obtained from the hydrolysate mixture when compared to the
appropriate standards. Additionally, the hydrolysate was spiked with the D and L amino acids to prove the identity of closely
eluting peaks.
Luteinizing hormone-releasing hormone 相似文献