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71.
S. A. Dodds G. A. Gist R. H. Heffner M. Leon D. E. MacLaughlin J. A. Mydosh G. J. Nieuwenhuys M. E. Schillaci 《Hyperfine Interactions》1984,18(1-4):467-471
Positive-muon (
+) spin relaxation experiments have been carried out in the dilute ferromagnetic alloy Pd+2 at.% Mn (T
c=5.8 K). In the paramagnetic state the inhomogeneous
+ linewidth is proportional to the bulk magnetization. BelowT
c the
+ linewidth and the width of the
+ local field distribution in zero applied field are both in qualitative accord with the Sherrington-Kirkpatrick theory of disordered magnets.This work was performed under the auspices of the U.S. Department of Energy, and was supported by the U.S. National Science foundation, grant nos. DMR-7909223 and DMR-8115543, and by the Netherlands Stichting voor Fundamenteel Onderzoek der Materie (FOM). 相似文献
72.
Mino R. Caira Devric R. Dodds 《Journal of inclusion phenomena and macrocyclic chemistry》2000,38(1-4):75-84
Single crystals of a 1 : 1 complex between-cyclodextrin (-CD) and the analgesicacetaminophen (paracetamol) have been prepared and themode of inclusion of the drug has been determined fromX-ray data collected at 293 K. Complexcharacterization by UV and thermogravimetric analysesyielded the composition-(CDacetaminophen13.3H2O. The complex crystallizes in the space group C2 with a =19.207(7), b = 24.48(1), c =15.700(4)Å, = 109.52(2)° and Z = 4complex units in the crystal unit cell. The hostmolecules form dimeric motifs withC2 crystallographic symmetry which pack in thechannel mode. Guest molecules residing in the hostdimer are disordered, each acetaminophen moleculebeing statistically distributed over two sites withequal occupancy. In each case, the guest hydroxylgroup is located at the host primary face while theacetamide residue lies at the dimer interface. TwoC2-related water molecules are trapped inside thehost cavity, being hydrogen bonded to theC2-related carbonyl groups of one of thedisordered guest conformers. Structural features ofthe complex are discussed with reference to recentspectroscopic and other studies aimed at elucidatingthe nature of the interaction between acetaminophenand -CD. 相似文献
73.
Enzymatic kinetic resolution of piperidine atropisomers: synthesis of a key intermediate of the farnesyl protein transferase inhibitor, SCH66336 总被引:1,自引:0,他引:1
Morgan B Zaks A Dodds DR Liu J Jain R Megati S Njoroge FG Girijavallabhan VM 《The Journal of organic chemistry》2000,65(18):5451-5459
The resolution of secondary amines via enzyme-catalyzed acylation is a relatively rare process. The kinetic resolution of a series of intermediates of SCH66336 (1), by either enzymatic acylation of the pendant piperidine (4, 5) or hydrolysis of the corresponding carbamate 3, was investigated. In the case of 4, the molecule exists as a pair of enantiomers due to atropisomerism about the exocyclic double bond. The enzymatic acylation of (+/-)-4 was optimized in terms of acylating agent, solvent, and moisture content. The use of lipase, Toyobo LIP-300, and trifluoroethyl isobutyrate as acylating agent resulted in isobutyrylation of the (+)-enantiomer, which is easily separated from the unwanted (-)-4. Hydrolysis of the isobutyramide 6c yielded the desired (+)-4 in high enantiomeric excess. (-)-4 may be recovered from the resolution step, racemized, and resubjected to enzymatic acylation to increase material throughput. 相似文献
74.
Reaction of sodium hydrotris(methimazolyl)borate (NaTm(Me)) with cobalt halides leads to the formation of paramagnetic pseudotetrahedral [Co(Tm(Me))X] (X = Cl, Br, I), of which the bromide has been crystallographically characterized. Mass spectrometry reveals the presence of higher molecular weight fragments [Co(Tm(Me))(2)](+) and [Co(2)(Tm(Me))(2)X](+) in solution. Aerial oxidation in donor solvents (e.g. MeCN) leads to formation of the [Co(Tm(Me))(2)](+) cation, which has been crystallographically characterized as the BF(4)(-), ClO(4)(-), Br(-), and I(-), salts. Attempts to prepare the mixed sandwich complex, [Co(Cp)(Tm(Me))](+), resulted in ligand decomposition to yield [Co(mtH)(3)I]I (mtH = 1-methylimidazole-2-thione), but with the more electron donating methylcyclopentadienyl (Cp(Me)) ligand, [Co(Cp(Me))(Tm(Me))]I was isolated and characterized. Electrochemical measurements reveal that the cobalt(III) Tm(Me) complexes are consistently more difficult to reduce than their Tp and Cp congeners. 相似文献
75.
Venkata Kolli Heidi A. Roth Gabriela De La Cruz Ganga S. Fernando Eric D. Dodds 《Analytica chimica acta》2015
Site-specific glycoproteomic analysis largely hinges on the use of tandem mass spectrometry (MS/MS) to identify glycopeptides. Experiments of this type are usually aimed at drawing connections between individual oligosaccharide structures and their specific sites of attachment to the polypeptide chain. These determinations inherently require ion dissociation methods capable of interrogating both the monosaccharide and amino acid connectivity of the glycopeptide. Collision-induced dissociation (CID) shows potential to satisfy this requirement, as the vibrational activation/dissociation of protonated N-glycopeptides has been observed to access cleavage of either glycosidic bonds of the glycan or amide bonds of the peptide in an energy-resolved manner. Nevertheless, the relative energy requirement for these fragmentation pathways varies considerably among analytes. This research addresses the influence of proton mobility on the vibrational energy necessary to achieve either glycan or peptide cleavage in a collection of protonated N-glycopeptide ions. While greater proton mobility of the precursor ion was found to correlate with lower energy requirements for precursor ion depletion and appearance of glycosidic fragments, the vibrational energy deposition necessary for appearance of peptide backbone fragments showed no relation to the precursor ion proton mobility. These results are consistent with observations suggesting that peptide fragments arise from an intermediate fragment which is generally of lower proton mobility than the precursor ion. Such findings have potential to facilitate the rational selection of CID conditions which are best suited to provide either glycan or peptide cleavage products in MS/MS based N-glycoproteomic analysis. 相似文献
76.
Dreyfus MA Tolocka MP Dodds SM Dykins J Johnston MV 《The journal of physical chemistry. A》2005,109(28):6242-6248
Fine particles of cholesterol were reacted with ozone under pseudo-first-order conditions in an aerosol bag reactor. Gas-phase ozone was monitored using an ozone meter. Particle size distribution functions were determined using a scanning mobility particle sizer, which selected particle sizes for introduction into a photoionization aerosol mass spectrometer (PIAMS). PIAMS was used to determine the concentration of cholesterol in the aerosol as a function of reaction time. Dilution corrected rate coefficients were used to calculate the reactive uptake coefficient for ozone onto cholesterol particles as (2.8 +/- 0.4) x 10(-6). Uptake was found to be independent of particle diameter for the sizes studied (100 and 200 nm), suggesting that the uptake is surface mediated. The reaction products were also collected on filters and analyzed by electrospray ionization (ESI) mass spectrometry with both direct infusion and liquid chromatography sample introduction. The main primary reaction products contained one, two, or three oxygens added to the cholesterol moiety. Secondary oligomeric products were also observed, consisting of covalently bound dimers and trimers. Tandem mass spectrometry was used to confirm the expected structures of these compounds. The dimers appear to be acyl hydroperoxides, consistent with a previously reported mechanism for the reaction in a nonparticipating solvent. Finally, the magnitude of the uptake coefficient confirms that cholesterol is suitable as a local source tracer for source apportionment of ambient organic aerosol. 相似文献
77.
B. Dodds 《Annali di Matematica Pura ed Applicata》1973,96(1):243-254
Summary The spin transforming matrices of all types in three dimensions are obtained, explicitly, in each of two alternative forms,
together with corresponding formulae for the inverse matrices. Similar results are obtained for the spin transforming matrices
and their inverses corresponding to the symmetric irreducible spinors in 4-dimensional space-time.
Entrata in Redazione il 16 maggio 1972. 相似文献
78.
J. W. Schneider H. Keller W. Odermatt B. Pümpin I. M. Savić H. Simmler S. A. Dodds T. L. Estle R. C. Duvarney K. Chow R. Kadono R. F. Kiefl Q. Li T. M. Riseman H. Zhou R. L. Lichti C. Schwab 《Hyperfine Interactions》1991,64(1-4):543-549
Datailed muon level-crossing resonance measurements of Mu1 and Mu11 centres in single crystals of CuCl are presented. The hyperfine and nuclear hyperfine parameters of the closest two shells
of nuclei are remarkably similar for the two centres, indicating that both are located at the same tetrahedral interstitial
site with four Cu nearest neighbours and six Cl next-nearest neighbours. About 30% of the total unpaired-electron spin density
is located on the muon, about 60% on the four nearest neighbours and the rest on the six next-nearest neighbours, with nothing
observable for any other shell. 相似文献
79.
R. L. Hutson D. W. Cooke R. H. Heffner M. E. Schillaci S. A. Dodds G. A. Gist 《Hyperfine Interactions》1986,32(1-4):893-900
In order to reduce pileup limitations on μSR data rates, a fast chopper for surface muon beams was built and tested at LAMPF.
The system allowed one muon at a time to be stopped in a μSR sample in the following way: A surface beam from the LAMPF Stopped
Muon Channel was focused through a crossed-field beam separator and onto a chopper slit. With the separator E and B fields
adjusted properly, the beam could pass through the slit. The beam to the μSR sample was turned on or off (chopped) rapidly
by switching the high voltage applied to the separator plates on or off within approximately 500 ns; with the E field off,
the B field deflected the beam, dumping it near the slit. We demonstrated that, with improved electronics, we will be able
to stop a single muon in a μSR sample as frequently as once every 20 μs and that data rates for the system can be a factor
of five higher than is attainable with unchopped beams. The observed positron contamination of the beam was less than five
percent, and the ratio of the muon rate with beam on to the rate with beam off was 1540. 相似文献
80.
We show the existence of a spectral shift function in the sense of Krein for bounded trace class perturbations of a self-adjoint
operator affiliated with a semifinite von Neumann algebra 相似文献