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The extent of urban specialization is closely related to urban development level. This paper distinguishes relative specialization and absolute specialization in terms of their connotations and measurement methods, and examines functional specialization in general. Using data on prefecture-and-above cities in China, this paper also reviews the characteristics of indicators of urban specialization in China. The findings are as follows. There exists a $U$-shaped relationship between the relative specialization index and city size and income level; the absolute specialization index shows a significant negative correlation with city size and a significant positive correlation with income level. Functional specialization coefficient and city size manifest a significant positive correlation; there is clear division of functions among city clusters, and functional specialization coefficient is significantly related to administrative level of cities. Finally, from the perspective of functional division and specialization of cities (city clusters), this paper makes the proposition of coordinating the spatial, scale and industrial structures of Chinese cities.

In order to study the diversity of intestinal aerobic bacteria in the 3rd instar larvae of Dendrolimus kikuchii Matsumura, 16S rDNA was PCR amplified by the generic primers. The 16S rDNA amplicons (about 1.5 kb) were digested by four restriction enzymes, and the characteristic ARDRA fingerprint was obtained. The results of digestion showed that the diversity of intestinal bacteria could be reflected by the results of all four restriction enzyme digestions. Phylogenetic analysis based on sequencing showed that Klebsiella pneumoniae and Bacillus cereus were the dominant microflora, and Enterobacter sp., Bacillus sp., Citrobacter sp. and Staphylococcus sp. were not abundant microflora in the intestinal tract of 3rd instar larvae of Dendrolimus kikuchii.