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分类讨论是中学数学中一种重要的数学思想,也是近几年高考考查的重点内容.同学们解决这类问题最困惑的就是不知如何划分范围,本文结合几个典型例题介绍一种划分范围的简捷方法——零点法. 相似文献
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验证大气压强存在的实验是初中物理中的重要实验,做好本实验对激发学生学习兴趣,培养学生的主动性,使物理课生动、形象、直观、有趣有重要意义,是上好大气压强课成败的关键.通过课堂或课后的探究、启发、分析,培养学生的探究能力和思维能力. 相似文献
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The reformation of nuclei and cells on the basis of yolk granules in vitro has been examined under electron microscope by using the mature ooeytes of the middle female intersex of Chirocephalus nankinensis. And it has been shown that the forms of reformed nuclear and cellular structures vary, which may be related to the developmental stages of the middle female intersex, types of reforming process, culturing times as well as internal and external conditions of yolk granules. We have also studied the structural changes of yolk granules and some transition forms during the reformation of nuclei and cells. The results are fairly in agreement with those of our previous reports, i. e. the time-lapse microcinematographic and phase contrast studies on the cell reformation of yollk granules in vitro and the electron microscopic investigations on the cell reformation of yolk granules of mature oocytes in situ. 相似文献
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纳米TiO2膜用于光催化氧化测定化学需氧量的研究 总被引:4,自引:0,他引:4
A photocatalytic oxidation method for determination of chemical oxygen demand (COD) using nano-TiO2 film, based on the use of a nano-TiO2-Ce(SO4)2 system and electrochemical detection, was proposed. The technique was originated from the direct determination of the Ce(Ⅲ) concentration change resulting from photocatalytic oxidation of organic compounds. Ce(Ⅲ), which was produced by photocatalytic reduction of Ce(SO4)2, could be measured at a multi-walled carbon nanotubes (MWNT) chemically modified electrode (CME). The COD values by this method were calculated from the differential pulse voltammetry (DPV) current of Ce(Ⅲ) at the CME. Under the optimal operation conditions, the detection limit of 0.5 mg·L^-1 COD with the linear range of 1-600 mg·L^-1 was achieved. This method was also applied to determination of various COD of ground water and wastewater samples. The resuits were in good agreement with those from the conventional COD methods, i.e., permanganate and dichromate ones. 相似文献
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1 INTRODUCTION In 1984, thiolate ligand was successfully introduced into molybdenum carbonyl compound by the reaction of Mo(CO)6 with [Et4N]SR( R = C6H5, But) in a moderate condition[1]. From then on, a series of dinuclear molybdenum(0) carbonyl thiolate compounds have been synthesized and characterized by using a variety of thiolate ligands in our research group. It was found that a planar Mo2S2 unit is in the compound [Et4N]2[Mo2(CO)8(SC6H4-CH_3-p)2][2] (2) and a "butterfly" t… 相似文献