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通过调查,探讨了中学化学教学中开设化学选修课的目的意义,提出了中学化学选修课开设的内容和方式,并对中学化学开设选修课后,如何处理好化学必修课、选修课、课外活动的三者关系进行了初步研究。 相似文献
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The detection of rail surface defects is an important tool to ensure the safe operation of rail transit. Due to the complex diversity of track surface defect features and the small size of the defect area, it is difficult to obtain satisfying detection results by traditional machine vision methods. The existing deep learning-based methods have the problems of large model sizes, excessive parameters, low accuracy and slow speed. Therefore, this paper proposes a new method based on an improved YOLOv4 (You Only Look Once, YOLO) for railway surface defect detection. In this method, MobileNetv3 is used as the backbone network of YOLOv4 to extract image features, and at the same time, deep separable convolution is applied on the PANet layer in YOLOv4, which realizes the lightweight network and real-time detection of the railway surface. The test results show that, compared with YOLOv4, the study can reduce the amount of the parameters by 78.04%, speed up the detection by 10.36 frames per second and decrease the model volume by 78%. Compared with other methods, the proposed method can achieve a higher detection accuracy, making it suitable for the fast and accurate detection of railway surface defects. 相似文献
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A new open-framework copper borophosphate was hydrothermally synthesized and structurally characterized. Its structure may be regarded as a layer forming via vertex-sharing BO3(OH) and PO4 tetrahedra bonded together with CuO2(OH)2(H2O)2 octahedral units. The thermal stability and magnetic properties are also discussed. 相似文献
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Assembly of ordered structures by an external stimulus allows for design of functional materials with enhanced physical and chemical properties. A new side-chain liquid crystal polymer containing strong polar azobenzene mesogens was synthesised. A macroscopically ordered monodomain smectic-like lamellar structure having orientational order and positional order was immediately assembled by linear polarised light irradiation (473 nm, 20 mW/cm2) at room temperature. The lamellar layer with its periodic d-spacing of 1.9 nm and mesogens arranged at an inclination angle of about 75° were characterised by X-ray diffraction and polarising optical microscopy which showed a diffraction peak at 2θ?=?4.53° and an off-centred interference figure. Reversible assembly and disassembly of the lamellar phase were achieved by alternative irradiation with polarised light and non-polarised light. Potential factors influencing the assembly of the ordered lamellar structure were investigated by controlling the mesogens out-of-plane orientation and by changing the polarities of mesogens. The difference in arrangement of the mesogens between the lamellar phase and a thermotropic smectic phase was also compared by heating the selectively exposed film. The light controllable assembly of mesogens provides an easy route to assemble a lamellar phase in azobenzene containing polymers for application in optical and photonic devices. 相似文献