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81.
Dweck J. Buchler P. M. Cartledge F. K. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):1011-1016
In the present work, a Portland cement blended with calcium carbonate is being used to study the solidification/stabilization
(S/S) of a Brazilian tanning waste arising from leather production. Chromium is the element of greatest concern in this waste,
but the waste also contains a residual organic material. Using thermogravimetry (TG) and derivative thermogravimetry (DTG)
to identify and quantify the main hydrated phases present in the pastes, this paper presents a comparative study between the
effects of Wyoming and Organophilic bentonites (B and OB) on cement hydration. Samples containing combinations of cement, B, OB and waste have been subjected to thermal analysis after different setting times during the first 28 days of the waste S/S
process. Both bentonites affect the cement hydration, with no significant differences in hydration degree after 1 week. This
work shows further examples of the great utility of thermal analysis techniques in the study of very complex systems containing
both crystalline and amorphous mineral materials as well as organics.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
82.
The present article describes the synthesis, spectral, coordination and thermal aspects of N,N′-polymethylene bis(1-phenyl-3-methyl-4-trifluoroacetylimino-2-pyrazoline-5-ol)oxovanadium(IV) or copper(II) Schiff base complexes with alkyl
backbones ranging from two to four carbons have been characterized on the basis of elemental analysis, magnetic moments, molar
conductivity measurements, spectra (FTIR, ESR, UV-Visible, MS), VPO and thermal studies. The vapour pressure osmometry (VPO)
and mass spectral studies indicate that the complexes are monomeric. An ESR study of all these complexes of VO(IV) and Cu(II)
are consistent with the square pyramidal and square planar geometries of these metal ions, respectively. In addition, the
kinetics and thermodynamic parameters for the different thermal decomposition steps of the complexes have been studied employing
Horowitz-Metzger and Freemen-Carroll methods. 相似文献
83.
Patrícia R. Pinto Luis C. Mendes Marcos L. Dias C. Azuma 《Colloid and polymer science》2006,284(5):529-535
Silica was obtained by sol–gel process through hydrolysis and condensation of tetraethyl orthosilicate (TEOS) using molar
fraction of H2O/TEOS=9 under alkaline catalysis, at different reaction times (5 min to 24 h). At the end of each time, the reaction medium
appeared as a suspended microparticle system. After solvent evaporation, the yield was calculated to be around 100% and practically
independent of the time of reaction. The silica had its surface modified through the condensation reaction with acryloyl chloride
forming organically modified silica. The unmodified and modified silica were characterized by thermogravimetry and derivative
thermogravimetry (TG/DTG), infrared spectrometry (FT-IR), size particle and optical microscopy (OM). The acrylic content was
independent of the reaction time. The methodology represents an alternative route to obtain silica with an unsaturated organic
group, able to polymerize and stabilize up to 300–400°C. The modified material has a potential application as compatibilizing
filler in dental composite. 相似文献
84.
Dranca I. Lupascu T. Vogelsang K. Monahova L. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):945-953
Thermoanalytical methods (TG, DTG and DTA) were used to determine the temperature interval (140–350°C) in which p-nitroaniline undergoes thermal desorption from the surface of activated carbons obtained from the shells of oxidized plum
stones and impregnated with aqueous solutions of Cu, Fe and Ti salts, which simulate the processes of activated carbon regeneration.
It was established that the impregnation of the activated carbons facilitated the regeneration processes in the sense that
they can occur at lower temperatures: 135–320 (Cu), 150–340 (Ti) and 130–320°C (Fe). The utilized activated carbons were preliminarily
characterized by BET surface area, DSC and scanning electron microscopic methods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
85.
Nano- and submicrometer zinc(II) oxide particles were synthesized by the polyol method and were used for the preparation of ZnO/poly(methyl methacrylate) (ZnO/PMMA) composite materials by the chain polymerization of methyl methacrylate (MMA) in bulk. ZnO particles with an organophilic surface layer were homogeneously dispersed in the PMMA matrix. Very low concentrations (0.1 wt.%) of nano zinc oxide absorbed over 98% of UV light as determined by UV-vis spectroscopy. Nano zinc oxide (75 nm) increased the initial decomposition temperature of the PMMA matrix by 30-40 °C at concentrations of 0.1% and above. This was explained by the changes in the termination mechanism of MMA polymerization resulting in a reduced concentration of vinylidene chain ends. Nano ZnO also increased the MMA polymerization reaction rate and reduced the activation energy. Submicrometer ZnO showed lower UV absorption, thermal stabilization and no influence on the reaction kinetics indicating that average particle size is of vital importance for the properties of PMMA nanocomposites and for MMA polymerization. 相似文献
86.
Florian Bausch Dickson D. Owusu Paul Jusner Mario J. Rosado Jorge Rencoret Sabine Rosner Jos C. del Río Thomas Rosenau Antje Potthast 《Molecules (Basel, Switzerland)》2021,26(14)
Papyri belong to the oldest writing grounds in history. Their conservation is of the highest importance in preserving our cultural heritage, which is best achieved based on an extensive knowledge of the materials’ constituents to choose a tailored conservation approach. Thermogravimetric Analysis (TGA) has been widely employed to quantify cellulose and lignin in papyrus sheets, yielding reported lignin contents of 25% to 40%. In this work, the TGA method conventionally used for papyrus samples was repeated and compared to other lignin determination approaches (Klason-lignin and acetyl bromide-soluble lignin). TGA can lead to a large overestimation of the lignin content of commercial papyrus sheets (~27%) compared to the other methods (~5%). A similar overestimation of the lignin content was found for the pith and rind of the native papyrus plant. We concluded that the TGA method should, therefore, not be used for lignin quantification. 相似文献
87.
88.
Synthesis and degradation profile of cast films of PPG-DMPA-IPDI aqueous polyurethane dispersions based on selective catalysts 总被引:1,自引:0,他引:1
Suzana M. Cakic Jakov V. Stamenkovic Dragan M. Djordjevic Ivan S. Ristic 《Polymer Degradation and Stability》2009,94(11):2015-2022
Waterborne polyurethane (WBU) dispersions synthesized from poly(propylene glycol) (PPG), dimethylolpropionic acid (DMPA), and isophorone diisocyanate (IPDI) with catalysts of different selectivity were prepared via by the conventional prepolymer isocyanate process. Two types of chain extenders were used, ethylene glycol (EG) and propylene glycol (PG), producing polyurethanes. The dispersions were neutralized by the addition of triethylamine. The thermal stability of the materials, obtained as cast films prepared from aqueous dispersions was evaluated by thermogravimetry (TG). It was observed that initial degradation temperatures were above 140 °C, with two-step degradation profiles. The use of a more selective catalyst in the formulations led to materials with higher thermal stability. DTG curves exhibited stages not perceptible in the curves of weight loss, which were mainly influenced by the differences in the formulations. Thermal decomposition of the obtained polyurethanes was followed by TG coupled with FTIR spectroscopy. 相似文献
89.
采用热分析(TG-DTA/DTG)、X射线衍射(XRD)研究了固态物质NH4Al(SO4)2.12H2O在氩气中的热分解过程。热分析结果表明,NH4Al(SO4)2.12H2O在氩气中分5步分解,其质量变化率与理论计算相吻合。XRD结果表明,NH4Al(SO4)2.12H2O热分解的最终产物为Al2O3。用Friedman法对各步分解过程的活化能Ea进行了计算,依此为初始值,采用多元非线性回归法得到各个分解步骤可能的动力学模型和参数。 相似文献
90.
草酸亚铁在氩气中的热分解机理和动力学研究 总被引:2,自引:0,他引:2
用热分析(TG/DTG/DTA)、X射线衍射(XRD)技术研究了固态物质FeC2O4·2H2O在氩气中热分解的过程.热分析结果表明,FeC2O4·2H2O在氩气中分两步分解,其失重率与理论计算失重率相吻合.XRD结果表明FeC2O4·2H2O分解产物为Fe3O4用Friedman法和Flynn-Wall-Ozawa(FWO)法求取了分解过程的活化能,并用多元线性回归法给出了可能的机理函数,由这些方法得到的动力学数据相互比较吻合. 相似文献