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51.
Jacob N. Fairchild Krisztián Horváth Georges Guiochon 《Journal of chromatography. A》2009,1216(34):6210-6217
The theoretical advantages and drawbacks of using a multiple-, parallel column approach in on-line multidimensional liquid chromatography systems were investigated. Much time or peak capacity can be gained with the use of multiple parallel columns at the second-dimension while the aggregate time of separation increases only by the increment of the gradient time of the second-dimension. Multidimensional chromatographic systems are now used to perform many tasks ranging from routine, fast analyses to specialized, arduous separations. In this work, we focus on the advantages of a multiple, parallel columns approach to on-line multidimensional liquid chromatography systems. Calculations of the achievable peak capacities were made as functions of the number of columns operated in parallel. Increasing the number of second-dimension columns from one to two or three causes the largest increase in peak capacity with only a slight increase of aggregate time. We also present some practical aspects to consider when attempting multidimensional separations with multiple columns operated in parallel. 相似文献
52.
Kubanek J Prusak AC Snell TW Giese RA Hardcastle KI Fairchild CR Aalbersberg W Raventos-Suarez C Hay ME 《Organic letters》2005,7(23):5261-5264
[structures: see text] Three diterpene-benzoate natural products, with novel carbon skeletons and an unusual proposed biosynthesis, were isolated from extracts of the Fijian red alga Callophycus serratus and identified by a combination of X-ray crystallographic, NMR, and mass spectral analyses. Bromophycolide A (1) displayed cytotoxicity against several human tumor cell lines via specific apoptotic cell death. This represents the first discovery of natural products incorporating a diterpene and benzoate skeleton into a macrolide system. 相似文献
53.
Bernasconi CF Fairchild DE Montañez RL Aleshi P Zheng H Lorance E 《The Journal of organic chemistry》2005,70(19):7721-7730
[reaction: see text] Acidity constants and rates of reversible deprotonation of acetonyltriphenylphosphonium ion (1H+), phenacyltriphenylphosphonium ion (2H+), N-methyl-4-phenacylpyridinium ion (3H+), and N-methyl-4-(phenylsulfonylmethyl)pyridinium ion (4H+) by amines in water, 50% DMSO-50% water (v/v), and 90% DMSO-10% water (v/v) have been determined. From the respective Br?nsted plots, log k(o) values for the intrinsic rate constants of the various proton transfers were obtained. Solvent transfer activity coefficients of the carbon acids and their respective conjugate bases were also determined which helped in understanding how the pKa values and intrinsic rate constants depend on the solvent. Some of the main conclusions are as follows: (1) The pK(a) values of 1H+, 2H+, and 3H+ are significantly higher than that of 4H+ because of a stronger resonance stabilization of the corresponding conjugate bases 1, 2 and 3, respectively. (2) The electronic effects of the PPh3+ and the N-methyl-4-pyridylium group are similar but the mix between inductive and resonance effect is different. (3) All four acids become more acidic upon addition of DMSO to the solvent. In all cases, the main factor is the stronger solvation of H3O+ in DMSO; for 1H+, 2H+, and 3H+ but not 4H+ this factor is significantly attenuated by stronger solvation of the carbon acid in DMSO. (4) The intrinsic rate constants for proton transfer are relatively high for all four carbon acids and show little solvent dependence; this contrasts with nitroalkanes which have much lower intrinsic rate constants and show a strong solvent dependence. These results can be understood by a detailed analysis of the interplay between inductive, resonance, and solvation effects. 相似文献
54.
K. S. Pramod V. Vijayasundaram N. Krishnakumar PL. RM. Palaniappan 《Journal of Thermal Analysis and Calorimetry》2012,108(1):133-139
This article presents the changes in the thermal properties of the control and titanium dioxide (TiO2), both nano and bulk exposed Zebrafish bones by using thermo analytical techniques. The result shows that the mass loss due
to the thermal decomposition occurs in three distinct steps due to loss of water, organic and inorganic materials. The titanium
dioxide exposed bones present a different thermal behaviour compared to the control bones. The residue masses are found to
be increased due to titanium dioxide exposure. In particular, nano titanium dioxide exposure increases the residue mass level
significantly (three fold) when compared to titanium dioxide bulk exposure. These thermal characteristics can be used as a
qualitative method to check the metal oxide intoxication in biological samples. 相似文献
55.
Metalation of the exterior arene faces of the molecular capsule (+/-)-cryptophane-E with [Cp*Ru]+ moieties results in a pi-acidic cavity capable of encapsulating anions. The [CF3SO3]- and [SbF6]- salts have been crystallographically characterized and demonstrate the encapsulation of these anions by the metalated cryptophane. 1H and 19F NMR spectroscopy establish the binding of anions in NO2CD3 solution and reveal the relative affinity of the cavity for different anions (KX-/KOTf-): [BF4]- approximately 0, [PF6]- = 1.18, [CF3SO3]- identical with 1, [SbF6]- = 0.30. Variable temperature rate studies reveal the activation barrier for triflate encapsulation to be DeltaG298K = 18.0(8) kcal.mol-1 (DeltaH = 17.5(4) kcal.mol-1 and DeltaS = 2(1) cal.mol-1.K-1). 相似文献
56.
Regueiro-Ren A Leavitt K Kim SH Höfle G Kiffe M Gougoutas JZ DiMarco JD Lee FY Fairchild CR Long BH Vite GD 《Organic letters》2002,4(22):3815-3818
[formula: see text] 3-Cyano epothilones 15-18 are the only examples of non-hydroxy C-3-substituted analogues. Their tubulin binding affinity and cytotoxicity provide meaningful structure-activity relationship information on the dependence of C-1/C-3 conformation upon activity. 12-Cyano epothilone 24 has improved pH stability over epothilone B, and its activity further supports the hypothesis that C-12 stereochemistry is not critical for tubulin affinity. 相似文献
57.
Vibrational spectra of oligothiophenes with structural defects are calculated within the density-functional-theory methodology. The effects of the defective αβ linkages on the infrared (IR) and Raman spectra are characterized from calculations of all isomers up to the hexamer. The signatures of αβ linked monomers can be found in IR spectra from broken symmetry arguments which result in absorptions localized in the defective region. The positions of the absorption peaks in the Raman spectra seem to be unaffected by the presence of such defects; however, strong reductions in the intensities are observed because of the shortening of the conjugation length. 相似文献
58.
E. Schulek P. Rózsa H. T. Liem M. Kohout D. A. Webb J. Hamáčková F. Dixon D. C. Jenkins F. W. Gilcreas F. J. Hallinan L. W. Andrews Grigorjewa A. E. Griffin P. W. Frisk A. J. Conrad O. M. Smith J. G. Fairchild J. M. Sanchis D. B. Iochelsson M. Verain J. Franquin St. H. Wilson R. Maucha R. Tengco G. Gad Käte Naumann V. W. Meloche Katherine Pingrey J. B. Romer W. W. Cerna H. F. Hannum K. Šandera W. P. Fedotow R. Vaughn N. B. Mitchell M. Levine Je. M. Nissnewitsch M. M. Rösenblat K. A. Mudretzowa B. S. Alejew J. Krey 《Analytical and bioanalytical chemistry》1943,126(9):354-359
59.
J. G. Fairchild H. Gotô und J. F. Alicino 《Fresenius' Journal of Analytical Chemistry》1941,121(3-4):128-134
Ohne Zusammenfassung 相似文献
60.
J. G. Fairchild 《Fresenius' Journal of Analytical Chemistry》1917,56(6-7):319
Ohne Zusammenfassung 相似文献