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61.
By the use of thermal volatilization analysis (TVA), 292°C was chosen as a suitable temperature for a preliminary experimental survey of the thermal degradation of styrene–acrylonitrile copolymers. TVA also indicated that there is no fundamental change in reaction mechanism as the acrylonitrile content of the polymer is increased from zero to 33.4% although there is a progressive increase in the rate of volatilization. The increase in the rate of volatilization over that of polystyrene is directly proportional to the acrylonitrile content of the copolymer. From the changes in molecular weight which occur during the reaction it is clear that the primary effect of the acrylonitrile units on stability is to cause an increased rate of chain scission, but there is a small proportion of “weak links” which are associated with the styrene units and which are broken instantaneously at 292°C. The number of monomer molecules liberated per chain scission, the zip length, is about 40 for polystyrene in the initial stages of degradation and decreases only to the order of 20 even in copolymer containing 24.9% acrylonitrile. Thus the unzipping process is not severely affected by the acrylonitrile units; this is borne out by the fact that acrylonitrile appears among the products in very much greater concentrations than from pure polyacrylonitrile. The proportion of larger chain fragments (dimer, trimer, etc.) also increases with acrylonitrile content. 相似文献
62.
Bain CD 《Advances in colloid and interface science》2008,144(1-2):4-12
The overflowing cylinder (OFC) was developed at Kodak sixty years ago and remains an elegant, precise and versatile tool for studying the dynamic surface properties of surfactant solutions today. The principles and design of the OFC are introduced and the use of the OFC to study adsorption kinetics and Marangoni effects is explained. Examples are provided from the study of pure surfactant solutions, mixed surfactants and polymer-surfactant complexes. 相似文献
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Alex D. Bain Donald W. Hughes Christopher K. Anand Zhenghua Nie Valerie J. Robertson 《Magnetic resonance in chemistry : MRC》2010,48(8):630-641
The INADEQUATE experiment can provide unequalled, detailed information about the carbon skeleton of an organic molecule. However, it also has the reputation of requiring unreasonable amounts of sample. Modern spectrometers and probes have mitigated this problem, and it is now possible to get good structural data on a few milligrams of a typical organic small molecule. In this paper, we analyze the experiment step by step in some detail, to show how each part of the sequence can both contribute to maximum overall sensitivity and can lead to artifacts. We illustrate these methods on three molecules: 1‐octanol, the steroid 17α‐ethynylestradiol and the isoquinoline alkaloid β‐hydrastine. In particular, we show that not only is the standard experiment powerful, but also a version tuned to small couplings can contribute vital structural information on long‐range connectivities. If the delay in the spin echo is long, pairs of carbons with small couplings can create significant double‐quantum coherence and show correlations in the spectrum. These are two‐ and three‐bond correlations in a carbon chain or through a heteroatom in the molecule. All these mean that INADEQUATE can play a viable and important role in routine organic structure determination. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
65.
Beattie DA Fraenkel R Winget SA Petersen A Bain CD 《The journal of physical chemistry. B》2006,110(5):2278-2292
Infrared-visible sum-frequency spectroscopy has been used to record the vibrational spectrum of a zinc arachidate monolayer at the interface between a sapphire prism and a fused silica lens. Spectra have been recorded for the monolayer deposited on the prism before, during, and after contact, and as a function of increasing pressure. Sum-frequency spectra are reported of the monolayer under sliding contact. The monolayer is found to be resistant to pressure- and shear-induced conformational disorder. However, frequency shifts, drops in peak intensities, and changes in peak intensity ratios have been observed as the monolayer is placed in contact between the prism and the lens. Transfer of monolayer material between the two surfaces is observed and is confirmed by spectra obtained with a monolayer deposited on the surface of the lens rather than the prism. On one face of the sapphire prism, the monolayer reconstructs to a low symmetry layer, probably due to epitaxy. The epitaxial structure disappeared in contact. Existing models for calculating sum-frequency spectra have been extended to include unit cells containing two molecules and torsion about the terminal C-C bond. This model can explain some, but not all, of the experimental observations. 相似文献
66.
Marijke WA de Backer Carlos P Fitzsimons Maike AD Brans Mieneke CM Luijendijk Keith M Garner Erno Vreugdenhil Roger AH Adan 《BMC neuroscience》2010,11(1):81
Background
This study compared the transduction efficiencies of an adeno-associated viral (AAV) vector, which was pseudotyped with an AAV1 capsid and encoded the green fluorescent protein (GFP), with a lentiviral (LV) vector, which was pseudotyped with a VSV-G envelop and encoded the discosoma red fluorescent protein (dsRed), to investigate which viral vector transduced the lateral hypothalamus or the amygdala more efficiently. The LV-dsRed and AAV1-GFP vector were mixed and injected into the lateral hypothalamus or into the amygdala of adult rats. The titers that were injected were 1 × 108 or 1 × 109 genomic copies of AAV1-GFP and 1 × 105 transducing units of LV-dsRed. 相似文献67.
Transition Metal Chemistry - 相似文献
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Elisabeth Pereira Ali Youssef Malika El-Ghozzi Daniel Avignant Jennifer Bain Michelle Prudhomme Fabrice Anizon Pascale Moreau 《Tetrahedron letters》2014
Two dipyrrolo[3,4-a:3,4-c]carbazole stereoisomers were unexpectedly obtained by Diels–Alder dimerization of 3-indolylmaleimide. Three dimensional structures of both stereoisomers were confirmed by X-ray analysis. Moreover compound 4 inhibits protein kinases in vitro, especially Pim-3, in the sub-micromolar range. 相似文献
70.