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Do C Hatfield J Patel S Vasudevan D Tirla C Mills NS 《The Journal of organic chemistry》2011,76(1):181-187
Oxidation of m- and p-substituted benzylidene fluorenes to antiaromatic dications was attempted by electrochemical and chemical means. Electrochemical oxidation to dications was successful for benzylidene fluorenes with p-methoxy, p-methyl, p-fluoro, and unsubstituted phenyl rings in the 3-position; attempts to oxidize the m-substituted derivatives via electrochemistry were unsuccessful. Chemical oxidation with SbF(5)/SO(2)ClF gave the dication of 9-[(4-methoxyphenyl)methylene]-9H-fluorene cleanly; oxidation of all other substituted benzylidene fluorenes resulted in mixtures of products. The excellent linear relationship between the chemical shifts calculated by the GIAO method and the experimental shifts for the p-methoxy-substituted benzylidene fluorene dication suggests that the calculations satisfactorily reflect the magnetic properties of this dication and potentially those of the other dications studied. The redox potentials from electrochemical oxidation, a measure of the stability of the dications, showed a good linear relationship with another measure of stability, the calculated difference in energy between each dication and its neutral precursor. The dications of benzylidene fluorenes were less stable than the dications of diphenylmethylidene fluorenes; within each type of compound, dications with p-substituted phenyl rings were more stable than dications with m-substituted phenyl rings and dications with phenyl rings substituted with electron-donating groups were more stable than dications with phenyl rings substituted with electron-withdrawing groups. The antiaromaticity of the fluorenyl system was assessed through the nucleus-independent chemical shift (NICS) that was also calculated by the GIAO method. The plot of the NICS values per square area versus the calculated energy difference for the dications showed a moderate degree of linearity; the plot of NICS values per square area versus the oxidation potentials was less linear. Thus, a suggestive, but not conclusive, relationship between magnetic and energetic measures of antiaromaticity was observed. 相似文献
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B.F. Hatfield 《Physics letters. [Part B]》1984,147(6):435-440
The ground state wave functional for pure SU(2) Yang-Mills in the temporal gauge is calculated to first order in the coupling constant. The standard formula for the perturbed wave function fails to give the correct form. The wave functional may be obtained by applying the Gauss law constraint. 相似文献
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The bioaccumulation of paralytic shellfish toxins in mussels, oysters, cockles, hard clams, razors, and king scallops is monitored in England, Scotland, and Wales by AOAC Official Method 2005.06 LC-with fluorescence detection (FLD). One of the commonly perceived disadvantages of using this method is the long turnaround time and low throughput in a busy laboratory environment. The chromatographic analysis of each sample typically utilizes a 15 min cycle time to achieve toxin oxidation product separation and column equilibration prior to subsequent analysis. A standard RP C18 analytical column, used successfully in recent years, achieves good separation with a long column lifetime. The analysis of a 40 sample qualitative screening batch takes approximately 18 h, including blanks, standards, and other QC samples. The availability of superficially porous column technology has offered the potential to reduce analysis time while retaining column performance on existing hardware. In this study, AOAC Official Method 2005.06 with LC-FLD was transferred to two different commercially available superficially porous columns, and the method performance characteristics were evaluated. Both columns separated all toxins adequately with cycle times less than half that of the existing method. Linearity for each toxin was acceptable up to two times the European maximum permitted limit of 800 microg di-HCl saxitoxin equivalent/kg flesh. LOD and LOQ values were substantially improved for the majority of toxins, with gonyautoxin 1&4 and neosaxitoxin showing up to a two- and fourfold improvement, respectively, depending on the column used. Quantification results obtained from parallel analysis of contaminated samples were acceptable on both columns. Comparative screen results gave a slight increase in the occurrence of contaminated samples, which was attributed to the improved detection limit for most toxins. Issues with rapidly increasing back pressure, however, were identified with both columns, with a limit of around 500 injections. This compares to the >3000 cycles routinely obtained with the standard RP-C18 HPLC columns currently in use. Overall, the gain achieved with these columns through shorter analysis time and improved analytical sensitivity is potentially of benefit in a high-throughput environment. For the routine high-throughput screening of shellfish samples, however, an improved column lifetime is desirable. 相似文献
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Iodination of the bicyclic enone hydrazone in excess triethylamine gave, in addition to the expected vinyl iodide , the rearranged aromatic product . 相似文献
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Tom Otieno Jaime R. Blanton M. Jason Hatfield Sherry L. Asher Sean Parkin 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m182-m185
The reaction of Cu(ClO4)2·6H2O, NaAsF6 and excess pyrazole yields hexakis(pyrazole‐κN2)copper(II) bis(hexafluoroarsenate), [Cu(C3H4N2)6](AsF6)2 or [Cu(pzH)6](AsF6)2 (pzH is pyrazole), (I). The analogous hexakis(pyrazole‐κN2)copper(II) hexafluorophosphate perchlorate complex, [Cu(C3H4N2)6](PF6)1.29(ClO4)0.71 or [Cu(pzH)6](PF6)1.29(ClO4)0.71, (II), is obtained in a similar fashion, using KPF6 in place of NaAsF6. Both compounds contain the hitherto unknown [Cu(pzH)6]2+ complex cation, in which the copper(II) ion lies at the center of a regular octahedron of coordinated N atoms. The cation has crystallographically imposed symmetry. The X‐ray data indicate that the lack of the expected distortion can be accounted for by the presence of either static Jahn–Teller disorder or dynamic Jahn–Teller distortion. 相似文献