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101.
Richard L. Tolman Roland K. Robins Leroy B. Townsend 《Journal of heterocyclic chemistry》1967,4(2):230-238
The first synthesis of a 7-β-D-ribofuranosylpyrrolo[2,3-d]pyrimidine by direct ribosidation of a preformed pyrrolo[2,3-d]pyrimidine has now been accomplished via the fusion procedure. Subsequent functional group transformations furnished the 6-methyl-thio derivative of the nucleoside antibiotic toyocamycin. Preparation of the 1-, 3- and 7-methyl isomers of 4-amino-5-cyano-6-methylthiopyrrolo[2,3-d]pyrimidine was accomplished and has provided an unequivocal assignment for the actual site of ribosidation by a comparison of ultraviolet absorption spectra. Factors utilized for the assignment of anomeric configuration are discussed. 相似文献
102.
103.
104.
Synthesis of imidazo[1,2-b]pyridazines: Fenbendazole,oxifenbendazole analogs and related derivatives
Alaa E. Mourad Dean S. Wise Leroy B. Townsend 《Journal of heterocyclic chemistry》1993,30(5):1365-1372
A series of imidazo[1,2-b]pyridazines has been prepared and evaluated for macrofilaricidal activity against Brugia pahangi or Acanthocheilonema viteae infections in jirds. The imidazo[1,2-b]pyridazine analogs of fen-bendazole and oxifenbendazole are reported. In addition, several 6-aminoimidazo[1,2-b]pyridazine derivatives have been prepared. None of these compounds possessed significant activity against human cytomega-lovirus (HCMV) or filarial infections. 相似文献
105.
106.
The structure of 5-diazouracil and several closely related derivatives have been revised on the basis of pmr spectroscopy. 5-Diazouracil, 5-diazouracil hydrate, 5-diazouracil methanol adduct, 5-diazouridine and 5-diazo-2′-deoxyuridine have been reassigned the structures 5-diazopyrimidin-2,4(3H)dione (XI), 5-diazo-6-hydroxy-1,6-dihydropyrimidin-2,4(1H,3H,6H)dione (XIII), 5-diazo-6-methoxy-1,6-dihydropyrimidin-2,4(1H,3H,6H)dione (XII), 1 -(β-D-ribofuranosyl)-O5′ -6(S)cyclo-5-diazo-1,6-dihydropyrimidin-2,4(3H,6H)dione (XVII) and 1-(2-deoxy-β-D-ribofuranosyl)-O5′ -6(S)cyclo-5-diazo-1,6-dihydropyrimidin-2,4(3H,6H)dione (XIX), respectively. Treatment of XII with dimethylamine resulted in a coupling of the 5-diazo group with dimethylamine and a concomitant rearomatization of the heterocyclic ring by expulsion of the 6-methoxy group to furnish 5-(3,3-dimethyl-1-triazeno)uracil (XIV). A similar reaction of XIX and XVII with dimethylamine furnished the corresponding 5-(3,3-dimethyl-1-triazeno)derivatives. The effect which certain resonance hybrids of the diazo moiety may exert in reactions of the above hetero-cycles and the assignment of S configuration at C-6 for the nucleoside derivatives is also discussed. 相似文献
107.
(5R)-Carbapenem-3-carboxylic acid is the simplest structurally among the naturally occurring carbapenem beta-lactam antibiotics. It is the produced from (3S,5S)-carbapenam-3-carboxylic acid utilizing a remarkable stereoinversion/desaturation process by CarC (carbapenem synthase), an alpha-ketoglutarate dependent non-heme iron oxygenase. In this communication, we demonstrate for the first time that the epimeric (3S,5R)-carbapenam-3-carboxylic acid is an intermediate in the overall catalytic cycle to the carbapenem antibiotic. The role of alpha-ketoglutarate in the stereoinversion and desaturation processes is also examined. 相似文献
108.
The simple perimeter model combined with PMO theory and semimpirical calculations is used to rationalize the observed MCD spectra of a series of oxo derivatives of azaindoles, such as caffeine and xanthine. The MCD spectra indicate the presence of substantial amounts of the 9-H tautomers in aqueous solutions of xanthines. 相似文献
109.
Livingstone R Schalk O Boguslavskiy AE Wu G Bergendahl LT Stolow A Paterson MJ Townsend D 《The Journal of chemical physics》2011,135(19):194307
Time-resolved photoelectron spectroscopy was used to obtain new information about the dynamics of electronic relaxation in gas-phase indole and 5-hydroxyindole following UV excitation with femtosecond laser pulses centred at 249 nm and 273 nm. Our analysis of the data was supported by ab initio calculations at the coupled cluster and complete-active-space self-consistent-field levels. The optically bright (1)L(a) and (1)L(b) electronic states of (1)ππ? character and spectroscopically dark and dissociative (1)πσ? states were all found to play a role in the overall relaxation process. In both molecules we conclude that the initially excited (1)L(a) state decays non-adiabatically on a sub 100 fs timescale via two competing pathways, populating either the subsequently long-lived (1)L(b) state or the (1)πσ? state localised along the N-H coordinate, which exhibits a lifetime on the order of 1 ps. In the case of 5-hydroxyindole, we conclude that the (1)πσ? state localised along the O-H coordinate plays little or no role in the relaxation dynamics at the two excitation wavelengths studied. 相似文献
110.
The determination of arsenic and selenium in standard reference materials using sector field ICP-MS in high resolution mode 总被引:2,自引:0,他引:2
Ashley T. Townsend 《Fresenius' Journal of Analytical Chemistry》1999,364(6):521-526
Sector field ICP-MS was used to analyse As and Se in a range of standard reference materials (NIST 1643d Water, NIST 1573a
Tomato Leaves, NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine Level 2). A spectral
resolution of m/Δm = 7500 enabled 75As and 77Se to be separated from problematic ArCl interferences. Following microwave acid digestion, solid samples were typically diluted
1 + 99 prior to analysis, while the urine sample was diluted 1 + 9. The water sample was analysed undiluted and diluted 1
+ 9. Despite near baseline spectral separation, 75As and 77Se were still found to be influenced by ArCl at high Cl concentrations, the effect being most pronounced for 77Se. When necessary 82Se was also monitored to determine the accuracy of the 77Se results. Detection limits (LOD, based on 3σ of 10 replicates) for 75As, 77Se and 82Se in ultra-pure water, 1% (w/w) HNO3 and 1% (w/w) HCl were ∼ 0.1, ∼ 0.2 and ∼ 0.5 ng g–1, respectively. Although signal intensities when using high resolution were ∼ 1% of that found when using low resolution mode
(m/Δm = 300), measured As concentrations and certified values were found to agree to within ± 11% for all samples analysed.
The concentration of Se in NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine were found
to be in agreement with certified values to within ± 15– 20%, as measured by 77Se. However, closer agreement (± 5%) was found when these samples were analysed using 82Se. The Se concentration in NIST 1643d Water was found to agree to within ± 5% of the certified value (depending on dilution
factor). Due to the low concentration of Se in NIST 1573a Tomato Leaves, quantitation was not possible (below LOQ, 10σ). As
a consequence of the lower ion transmission when using resolution 7500, analytical precisions were found to be elevated over
that normally observed using low resolution mode, typically ± 5–20% (depending on analyte concentration and isotopic abundance).
Received: 28 December 1998 / Accepted: 9 February 1999 相似文献