Using the method proposed by Peng (1988) on the basis of density waves theory and the solution of three-dimensional Poisson s equation for a logarithmic disturbance of density,and analyzing the spiral patterns,the sca...Using the method proposed by Peng (1988) on the basis of density waves theory and the solution of three-dimensional Poisson s equation for a logarithmic disturbance of density,and analyzing the spiral patterns,the scale heights of 84 northern spiral galaxies,whose images are taken from the Digitized Sky Survey at Xinglong Observational Station of Beijing Observatory,are measured.The spiral arms of all these galaxies have been fitted on their photographs with some logarithmic spiral curves for getting their correct inclinations.展开更多
Since micropyle of mature eggs of Misgurnus anguillicaudatus and other bony fishes are enclosed by membranes of the eggs, it has been intriguing why spermia are able to enter micropyle of mature eggs in certain direct...Since micropyle of mature eggs of Misgurnus anguillicaudatus and other bony fishes are enclosed by membranes of the eggs, it has been intriguing why spermia are able to enter micropyle of mature eggs in certain directions. Most scholars specializing in fish fertilization cytology guessed that there must be a special kind of chemical substance in cortices of展开更多
基金Project supported by the National Natural Science Foundation of China. National "Climbing Project" of China and the Doctoral Program Foundation of State Education Commission.
文摘Using the method proposed by Peng (1988) on the basis of density waves theory and the solution of three-dimensional Poisson s equation for a logarithmic disturbance of density,and analyzing the spiral patterns,the scale heights of 84 northern spiral galaxies,whose images are taken from the Digitized Sky Survey at Xinglong Observational Station of Beijing Observatory,are measured.The spiral arms of all these galaxies have been fitted on their photographs with some logarithmic spiral curves for getting their correct inclinations.
文摘Since micropyle of mature eggs of Misgurnus anguillicaudatus and other bony fishes are enclosed by membranes of the eggs, it has been intriguing why spermia are able to enter micropyle of mature eggs in certain directions. Most scholars specializing in fish fertilization cytology guessed that there must be a special kind of chemical substance in cortices of
