web crawler，python ，针对puchem，收取化学物质信息，以csv格式记录。采用beautifulsoup 开发，采用lxml解析器，爬取速度较慢，请多等待。可以修改指定爬取范围，也可以根据cid来爬取(Web crawler, python, for puchem, collection of chemical information, recorded in CSV format. Use beautifulsoup development, use lxml parser