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231.
The regiochemistry of the cyclization reations of some ω-lithioepoxides as a function of chain length and substitution pattern has been examined. Striking changes in regiochemistry have been observed in the presence of certain Lewis acids and metal halides. 相似文献
232.
符合Ore条件的简单图称为Ore图,Ore条件指图的两个不相邻的顶点的度数之和不小于图的顶点数。本文搞清了Ore图的泛连通性,同时得到了Ore图的点(边)泛圈性的结果,推广了Bondy的一个结论。 相似文献
233.
E. A. Boucher D. J. Langdon R. J. Manning 《Journal of Polymer Science.Polymer Physics》1972,10(7):1285-1296
As part of a study of chemical and physical changes accompanying the formation of carbons by the pyrolysis of polymers, conventional electron microscopy, electron diffraction, and scanning electron microscopy techniques have been used to examine structural and morphological features of polyacrylonitrile (PAN) crystals, powder, and fibers, and of Saran and poly(vinylidene chloride) (PVDC) powder. Changes accompanying the heating of these polymers in air and in nitrogen have been investigated. PAN crystals grown from propylene carbonate were similar to those obtained by Klement and Geil. When heated in air at 220°C they retained their morphology, and electron diffraction gave the same reflections as PAN. On further heating to 400°C in nitrogen the morphology was retained, but the diffraction was lost. Crystals treated in nitrogen alone at 200°C showed morphology similar to that of the polymer. PAN powders and fibers retained discernable external features of their morphology on heating to 800°C. These results are discussed with reference to changes which take place when poly(vinylidene chloride) and Saran are heated in the range 150–180°C, which results in the loss of one hydrogen chloride per monomer unit, and are subsequently carbonized at 800°C. The development of pore structure and the adsorptive properties of Saran carbons are also discussed. 相似文献
234.
Siddharth V. Patwardhan Joseph R.H. Manning Mauro Chiacchia 《Current Opinion in Green and Sustainable Chemistry》2018
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235.
The determination of aluminum in the presence of perchloric acid is shown to depend upon the quality of the pyrolytic coating of furnace tubes. With new pyrolytically coated tubes, no interference was found from 0.5 M HClO4 on 0.5 ng Al and no decrease in signal or deterioration of the pyrolytic coating was found after more than 150 firings. Very little interference was found in the determination of thallium in perchloric acid. In both cases the literature reported severe interferences. The determination of thallium and aluminum in perchloric acid appears to be more sensitive to the quality of the pyrolytic graphite coating than any of the materials studied previously here. 相似文献
236.
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238.
A procedure is described for quality-control in graphite-furnace atomic-absorption spectrometry. It uses an NBS standard reference material to avoid errors in standard preparation, and very simple instrumental conditions, with no matrix modifier or pyrolysis step. The characteristic mass and the Zeeman ratio are calculated for Ag, Cu, and Cr, and deviations from the expected values for these quantities are correlated with potential instrumental malfunctions. 相似文献
239.
Michael D. Brown Joanna M. Manning Gillian Reid 《Journal of organometallic chemistry》2005,690(6):1540-1548
The synthesis and characterisation of complexes of two distibinopropanes R2Sb(CH2)3SbR2 (R = Me or Ph) with a variety of metal carbonyls is described. These include cis-[M(CO)4{R2Sb(CH2)3SbR2}] (M = Cr, Mo or W), [{Fe(CO)4}2{μ-R2Sb(CH2)3SbR2}], [{Ni(CO)3}2{μ-R2Sb(CH2)3SbR2}], [Co2(CO)6{Ph2Sb(CH2)3SbPh2}], [Co2(CO)4{Me2Sb(CH2)3SbMe2}3][Co(CO)4]2 and [Mn2(CO)8{Ph2Sb(CH2)3SbPh2}]. The complexes have been characterised by analysis, mass spectrometry, IR and multinuclear NMR spectroscopy as appropriate. Comparison of the spectroscopic data on these complexes with those of other stibine complexes and with complexes of Group 16 ligands has been used to establish the relative electronic properties of the distibines. 相似文献
240.
A study undertaken following recent reports of deaths in neonatal children associated with the use of benzyl alcohol resulted in the development of a stability-indicating high-performance liquid chromatographic assay of benzyl alcohol in plasma using benzocaine as internal standard. Thawed plasma samples were diluted and subjected to solid-phase extraction using Extrelut and eluted with ethyl acetate. The evaporated eluate was reconstituted with mobile phase and chromatographed on a C18 column with water-acetonitrile-glacial acetic acid as mobile phase and detection at 254 nm. Baseline separation was achieved within 12 min for benzyl alcohol, benzaldehyde, benzoic acid, hippuric acid and benzocaine. Peak-height ratios were linear over 80-640 ng of benzyl alcohol injected (r = 0.998) and over 10-80 ng of benzoic acid injected (r = 0.999). Benzaldehyde and hippuric acid were not quantitated because these compounds were not detectable in actual dog plasma. Validation studies by spiking dog plasma with benzyl alcohol and benzoic acid gave overall percent recoveries (+/- relative standard deviation, n = 4) of 98.3 +/- 3.0 and 101.4 +/- 7.6%, respectively. The method was applied to the assay of actual plasma samples. Since benzyl alcohol is very susceptible to oxidation to benzaldehyde and benzoic acid, its purity in bulk liquid samples can be determined by this method. 相似文献