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11.
Mukil V. Ayyasamy Jeroen A. Deijkers Haydn N.G. Wadley Prasanna V. Balachandran 《Journal of the American Ceramic Society》2020,103(8):4489-4497
Density functional theory (DFT) calculations and machine learning (ML) methods are used to establish a relationship between the crystal structures of rare-earth (RE) disilicates (RE2Si2O7) and their coefficient of thermal expansion (CTE). The DFT total energy data predict the presence of several energetically competing crystal structures, which is rationalized as one of the reasons for observing polymorphism. An ensemble of support vector regression models is trained to rapidly predict the CTE as a function of RE2Si2O7 crystal chemistry. Experiments subsequently validated the structure and CTE predictions for Sm2Si2O7. 相似文献
12.
Front Cover: A Possible Path to Prebiotic Peptides Involving Silica and Hydroxy Acid‐Mediated Amide Bond Formation (ChemBioChem 18/2018) 下载免费PDF全文
13.
《Journal of the European Ceramic Society》2017,37(15):5001-5007
Yttrium monosilicate and disilicate are important materials for environmental barrier coatings. The two silicates were synthesized by sol-gel route and their phase selection upon calcination and thermal exposure was studied. First products of crystallization were the monosilicate and yttria. Amorphous silica precipitated out at 1300 °C as apatite phase. During prolonged high temperature treatment, up to 100 h at 1400 °C, the apatite disappeared and the disilicate appeared, only to disappear itself as the system approached equilibrium. Thermodynamic calculations performed using Thermo-Calc software show the presence of a metastable miscibility gaps in the amorphous (liquid) phase field. As a consequence, phase separation in the amorphous phase prior to crystallization is responsible for the formation of yttria-rich and silica-rich phases during crystallization. Multiple phase formation during both, yttrium monosilicate and disilicate synthesis is consistent with the presence of the amorphous phase miscibility gaps around the silicate compositions. 相似文献
14.
Long lasting afterglow phosphors Sr2MgSi2O7:Eu,Dy and Ca2MgSi2O7:Eu,Dy were prepared by solid-state reaction method. It is revealed by the results that both phosphors show two emission peaks that are caused by the different emitting centers Eu2+ held in the host lattice. Wavelength shift was observed due to the slight differences in the structure parameters of the two hosts. Investigation on afterglow property shows that Sr2MgSi2O7:Eu,Dy phosphor held a better afterglow property than Ca2MgSi2O7:Eu,Dy phosphor. Thermal simulated luminescence study indicates that the long afterglow is generated by a higher trap concentration formed by the co-doped rare earth ions within the host. 相似文献
15.
Shangjun Teng Wei Liang Zhonglei Li Xiaoxia Ma 《Journal of Alloys and Compounds》2008,464(1-2):452-456
Lithium lanthanoid silicate, a high temperature lithium ion conducting solid electrolyte, synthesized by sol–gel method, has been characterized by TGA/DTA, XRD, FTIR and SEM. Conductivity was found to be 0.847 × 10−6 Ω−1 cm−1 at 750 °C and activation energy was 0.5 eV. 相似文献
16.
Alumina Dissolution into Silicate Slag 总被引:1,自引:0,他引:1
Shaowei Zhang Hamid Reza Rezaie Hossain Sarpoolaky William Edward Lee 《Journal of the American Ceramic Society》2000,83(4):897-903
Dissolution of commercial white fused and tabular Al2 O3 grains into a model silicate slag was investigated after 1 h at 1450° and 1600°C. Formation of CA6 and hercynitic spinel layers was observed at all Al2 O3 /slag interfaces. The spinel layer was not always continuous, and so, compared with the CA6 layer, it had a less-significant effect on the dissolution process. The CA6 layer that formed adjacent to the tabular Al2 O3 was incomplete at both temperatures, so that its dissolution was not a totally indirect process. These incomplete CA6 and spinel layers meant that slag penetrated into the tabular Al2 O3 grains, which, thus, were corroded and disintegrated by the penetrating slag. There was evidence of liquid in the CA6 layer adjacent to the fused Al2 O3 after 1 h at 1450°C, which also enabled direct dissolution. After 1 h at 1600°C, fused Al2 O3 revealed a thick (∼60 μm), continuous and unpene-trated CA6 layer, indicating fully indirect dissolution at this temperature. 相似文献
17.
LED用稀土Eu掺杂硅酸盐基荧光粉的研究进展 总被引:3,自引:0,他引:3
由于硅酸盐为基体的光转换材料具有原料来源丰富、工艺适应性广泛及晶体结构稳定性较高等特点,目前已成为白光发光二极管(light-emitting diode,LED)用荧光粉的研究重点之一。本文综述了近年来国内外硅酸盐基稀土荧光粉材料的研究进展,对硅酸盐基稀土荧光粉的材料体系、发光机理及发光特性的改进方面进行了分析与探讨。通过比较固相反应法和溶胶-凝胶法两种不同制备方法的优缺点,阐述了不同制备方法对白光LED质量的影响,并对硅酸盐基荧光粉的发展趋势和应用前景作了简要展望。 相似文献
18.
19.
Tomoki Murata Toru Asaka Sakyo Hirose 《Journal of the American Ceramic Society》2021,104(11):5794-5802
Dielectric tunability has been extensively investigated in ferroelectric materials, which exhibit a negative tunability of dielectric permittivity in an external electric field. In contrast, positive tunability is rare and has been reported only in a few antiferroelectric materials. We present positive (and negative) tunability in the titanite, CaTiSiO5. The dielectric property of CaTiSiO5 was measured up to an extraordinarily high electric field of 40 MV/m. A nonlinear polarization field loop with no hysteresis was obtained. The dielectric permittivity of εr ~ 25 increases up to εr ~ 40 at 20 MV/m and room temperature. Although titanite has an antipolar structure and is expected to be “antiferroelectric,” its dielectric response in high electric fields up to ~40 MV/m differs from that of conventional antiferroelectrics. We demonstrate that the phase-transition temperature and dielectric tunability could be modulated through the chemical substitution of Ca1−xLaxTiSi1−xAlxO5, in which the destabilization of the long-range antipolar order is revealed by transmission electron microscopy analysis. These results indicate that the observed dielectric response to an electric field may originate from the unique features of the antipolar and domain structures in CaTiSiO5. 相似文献
20.
Lucas A. Herweyer Elizabeth J. Opila 《Journal of the American Ceramic Society》2021,104(12):6496-6507
The high-temperature interaction between ~2.5 mg/cm2 of Na2SO4 and an atmospheric plasma sprayed (APS) Yb2Si2O7 topcoat–Si bond coat system on SiC CMC substrates was studied for times up to 240 h at 1000°C–1316°C in a 0.1% SO2–O2 gaseous environment. Yb2Si2O7 reacted with Na2SO4 to form Yb2SiO5 and an intergranular amorphous Na-silicate phase. Below 1200°C, the reaction was sluggish, needing days to cause morphological changes to the “splat microstructure” associated with APS coatings. The reaction was rapid at 1200°C and above, needing only a few hours for the entire topcoat to transform into a granulated microstructure consisting of Yb2SiO5 and Yb2Si2O7 phases. Na2SO4 deposits infiltrated the Yb2Si2O7 topcoat and transformed into an amorphous Na-silicate in less than 1 h at all exposure temperatures. Quantitative assessment of the Yb2SiO5 area fraction in the topcoat showed a linear decrease over time at 1316°C, attributed to reaction with the SiO2 thermally grown oxide (TGO) formed on the Si bond coat and rapid transport through the interpenetrating amorphous Na-silicate grain boundary phase. It was predicted that nearly 2 weeks is needed for complete removal of Yb2SiO5 from the topcoat at 1316°C for a single applied loading of Na2SO4. 相似文献