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1.
2.
Simultaneous DTA and dilatometric measurements were made and the derivatives of the dilatometric curves were taken for three glasses by means of a derivatograph. Glass blocks were used as test pieces with a boring for the thermoelement. A maximum was observed in the rate of length change, which can be explained by overheating phenomena. A comparison with DTA curves of glass powders published by Yamamoto showed that the break points in the DTA curves of glass blocks do not coincide with the Tg points, but under identical conditions they can serve for the rapid characterization of the transformation range. 相似文献
3.
Journal of Algebraic Combinatorics - It is well known that linear rank-metric codes give rise to q-polymatroids. Analogously to matroid theory, one may ask whether a given q-polymatroid is... 相似文献
4.
Uulke A. van der Heide Marc A. M. J. Zandvoort Ernst van Faassen Gijs van Ginkel Yehudi K. Levine 《Journal of fluorescence》1993,3(4):271-279
Measurements of fluorescence depolarization decays are widely used to obtain information about the molecular order and rotational dynamics of fluorescent probe molecules in membrane systems. This information is obtained by least-squares fits of the experimental data to the predictions of physical models for motion. Here we present a critical review of the ways and means of the data analysis and address the question how and why totally different models such as Brownian rotational diffusion and wobble-in-cone provide such convincing fits to the fluorescence anistropy decay curves. We show that while these models are useful for investigating the general trends in the behavior of the probe molecules, they fail to describe the underlying motional processes. We propose to remedy this situation with a model in which the probe molecules undergo fast, though restricted local motions within a slowly rotating cage in the lipid bilayer structure. The cage may be envisaged as a free volume cavity between the lipid molecules, so that its position and orientation change with the internal conformational motions of the lipid chains. This approach may be considered to be a synthesis of the wobble-in-cone and Brownian rotational diffusion models. Importantly, this compound motion model appears to provide a consistent picture of fluorescent probe behavior in both oriented lipid bilayers and lipid vesicle systems. 相似文献
5.
E. Hartung K. Heide R. Naumann K. H. Jost W. Hilmer 《Journal of Thermal Analysis and Calorimetry》1983,26(2):277-284
In spite of numerous investigations the literature data on the thermal decomposition of borax are contradictory. On the basis of thermal, X-ray, gas analytical and optical investigations this fact can be attributed to the complex decomposition mechanism. After the release of about 8 mole water the reaction product is an X-ray amorphous phase, having the thermal behaviour of glass. From this glass sodium diborate (Na2O.2B2O3) crystallizes between 500–600? with further mass loss. Sodium diborate decomposes from about 700? incongruently yielding NaBO2 vapor and B2O3 glass phase. After evaporation of NaBO2 is completed the rate of evaporation of B2O3 increases considerably. 相似文献
6.
Clorobiocin (clo) and novobiocin (nov) are potent inhibitors of bacterial DNA gyrase. The two substances differ in the substitution pattern at C-8' of the aminocoumarin ring, carrying a chlorine atom or a methyl group, respectively. By gene inactivation, clo-hal was identified as the gene of the halogenase responsible for the introduction of the chlorine atom of clorobiocin. Inactivation of cloZ did not affect clorobiocin formation, showing that this ORF is not essential for clorobiocin biosynthesis. Expression of the methyltransferase gene novO in the clo-hal(-) mutant led to the very efficient formation of a hybrid antibiotic containing a methyl group instead of a chlorine atom at C-8'. Comparison of the antibacterial activity of clorobiocin analogs with -Cl, -H, or -CH(3) at C-8' showed that chlorine leads to 8-fold higher activity than hydrogen and to 2-fold higher activity than a methyl group. 相似文献
7.
Thermal decomposition of K2SiF6 is a complicated process depending on several parameters, the combination of which cause difficulty in comparing the results obtained from different methods. An experimental method for the study of small quantities of material is described. This allows direct comparison with thermoanalytical results. The influence of experimental conditions is discussed. The decomposition of K2SiF6 is a model for other complexes which produce easily hydrolysed products during thermal reaction. The course of thermal decomposition of K2SiF6 is described up to complete vaporisation of the products at 1200°C. 相似文献
8.
K. Heide 《Journal of Thermal Analysis and Calorimetry》1991,37(7):1593-1603
Degassing experiments showed that a remarkable difference exists between glasses from a range of geological environments. The released gases were thermally analysed by a simultaneous thermogravimetric, mass spectrometric (partial pressure), and total pressure measurements of evolved gases by heating from room temperature to 1450°C. Detailed degassing studies on natural glasses from various terrestrial environments show that the degassing behaviour of glasses differs strongly, also in respect of the manmade glasses. The gas release profiles of natural glasses can be divided into three groups: 1) volcanic glasses, 2) impact glasses and 3) silica glasses and tectites.The degassing behaviour of manmade glasses is determined by the melting technique, the raw materials, and the fining agents. Gas release curves are suitable tools for the identification of vitreous samples of unknown origin but it is impossible to gain data of physico-chemical conditions of the glass formation process or for the polymerization state of the melt.
Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60th birthday 相似文献
Zusammenfassung Entgasungsexperimente zeigen, daß zwischen Gläsern von einer Reihe von geologischen Umfeldern bemerkenswerte Unterschiede bestehen. Die beim Erhitzen von Raumtemperatur auf 1450°C freigesetzten Gase wurden thermisch mittels simultanen thermogravimetrischen, massenspektrometrischen (Partialdruck) und Gesamtdruckmessungen analysiert. Ausführliche Entgasungsstudien an natürlichen Gläsern aus verschiedenen Landschaftsgebieten zeigen, daß sich das Entgasungsverhalten der Gläser stark unterscheidet, auch im Vergleich zu künstlich erzeugten Gläsern. Die Gasfreisetzungsprofile natürlicher Gläser können in drei Gruppen unterteilt werden: 1.) vulkanische Gläser, 2.) Aufschlaggläser und 3. Silikatgläser und Tektite.Das Entgasungsverhalten künstlich hergestellter Gläser wird durch die Schmelztechnik, die Rohstoffe und die Läutermittel bestimmt. Entgasungskurven sind ein geeignetes Mittel zur Identifizierung glasähnlicher Proben unbekannten Ursprunges. Es ist jedoch nicht möglich, Daten über physikalisch-chemische Bedingungen der Glasbildungsprozesse oder über den Polymerisationsgrad der Schmelze zu erhalten.
Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60th birthday 相似文献
9.
Correlation of structure parameters of glasses and related crystals formed in homogeneous or heterogeneous nucleation processes by thermal treatment is discussed on the basis of DTA, TG and EGA measurements in relation to the textural patterns of the materials. For cordierite glass, crystallization of metastable disordered cordierite polymorphs is related to an exothermic heat evolution and simultaneous with a small weight loss (appr. 0.025%). By MS-EGA, evolution of water was determined during the transformation of the metastable melt to a metastable intermediate crystalline phase. Interpretation of the crystallization by comparing the available structure parameters of cordierite glasses and crystals alone is insufficient to explain the role of water in the kinetics of crystallization. Optical and electron microscopy of the primary crystallization phenomena show the metastable solid solution with low quartz-type structure. Interpretation of the crystallization behaviour in terms of conventional theory of nucleation and crystal growth is impossible. 相似文献
10.
The processes, which influence the decomposition of 4MgCO3 ·-Mg(OH)2 · 4H2O, could be determined by systematical variation of the analytical parameters. The original crystal structure exists in a wide temperature range during the decomposition. The formation of magnesite is a secondary reaction of the gaseous phase with the reaction product.H2O and CO2, are released simultaneously in different proportions during the decomposition to 500°C. Stoichiometric intermediates were not found. The original crystal structure collapsed, when the last H2O escapes. The ratio of MgCO3: MgO can be influenced by partial pressure of CO2 in a wide range. 相似文献