<正>于2005至2007年对江苏南京紫金山地区的蜻蜓资源进行了调查，经过对采集标本的鉴定，初步确定南京紫金山地区蜻蜓目昆虫有30种，隶属8科24属，其中8种是江苏省新纪录。该地区蜻蜓目区系组成的特点是：广布种所占的比例较大，东洋种次之，古北种最少。

The woodworking band saw blades had complex forces when it worked. In order to ensure its cutting precision and efficiency, its vibration property of the structure system was studied in this paper. The natural frequency pn of the woodworking band saw blades system was computed using chordal vibration theory. The approximate values of the system’s natural frequency were obtained through finite element methods. The values through the random frequency spectrum method were measured and analysed. The results showed that the maximum difference between the test results and the theoretical values doesnt exceed 10% and between the approximate values and theoretical the error values is less than 3% at the low-frequency stage tests.