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作文教学是语文教学中不可或缺的一个环节,是对学生进行语文素质训练的主要阵地。写作水平和写作能力的高低,是一个人能否较好地运用语文知识及其语文素质的综合体现。随着语文教学改革的不断深入和发展,新课程标准对当前的作文教学改革的发展方向提出了明确的目标和要求,如何改进作文教学是我们教育上作者所要面对的重大难题。 相似文献
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Titanium silicalite-1(TS-1)was synthesized by a hydrothermal synthesis method with different amounts of tetrapropyl ammonium hydroxide(TPAOH)as template. The as-prepared TS-1 was characterized by scanning electron microscopy, X-ray powder diffraction, Fourier-transform infrared resonance spectroscopy, ultravioletvisible diffuse reflectance spectroscopy and nitrogen physical adsorption and desorption, and studied in the propylene epoxidation with hydrogen peroxide in a fixed bed reactor. The results showed that the amount of TPAOH had a strong influence on the grain morphology, the amount of framework Ti, and the average particle sizes of TS-1. With the increase of TPAOH amount in the synthesis(the molar ratio of TPAOH/SiO2 increasing from 0.25 to 0.45), the morphology changed gradually from ellipsoids to cubes, the particle sizes of TS-1 decreased slightly, the amount of the framework Ti increased appreciably, and the catalytic stability in the propylene epoxidation increased markedly. Moreover, all the catalysts had the same selectivity to propylene epoxide. However, when the molar ratio of TPAOH/SiO2 was further increased to 0.55, the particles became large hexagons with the size distribution in a wide range, and the catalytic stability decreased sharply although the amount of the framework Ti increased further, which can be attributed to the long diffusion paths of the reactants in the zeolite. 相似文献
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小班是森林资源规划设计调查、统计和经营管理的基本单位。小班区划方法上的分歧,是导致森林经理不能主动地对森林经营发挥其指导作用的内在原因。 相似文献
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针对我国森林资源现状,探讨了增加森林资源总量、提高森林资源质量、调整森林资源结构和对森林资源实施有效保护的措施。 相似文献
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Mesoporous titanium silicalite-1(TS-1)was hydrothermally synthesized with the addition of triethanolamine( TEA)in the conventional process, and used in the cyclohexanone ammoximation in a continuous slurry reactor. The as-prepared TS-1 was characterized with X-ray diffraction(XRD), scanning electron microcopy( SEM), N2 adsorption-desorption, Fourier transform infrared (FT-IR)spectroscopy, UV-Visible(UV-Vis) diffuse reflectance spectra and UV Raman spectroscopy. The results indicated that the addition of TEA resulted in the formation of mesopores and the slight increase of framework titanium in TS-1. TS-1 synthesized with the addition of TEA exhibited a higher stability in the cyclohexanone ammoximation than that without the addition of TEA, attributing to the increase of mesopore volumes and the slight increase of the framework titanium in TS-1. However, when the addition of TEA was up to TEA/SiO2 ratio of 0.24, the crystallinity and framework titanium of TS-1 decreased markedly, and the average crystal sizes of TS-1 increased, with the catalyst stability becoming poor. 相似文献
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