NwebCrawler是用C#写的一款多线程网络爬虫程序，它的实现原理是先输入一个或多个种子URL到队列中，然后从队列中提取URL（先进先出原则），分析此网页寻找相应标签并获得其href属性值，爬取有用的链接网页并存入网页库中，其中用爬取历史来记录爬过的网页，这样避免了重复爬取。提取URL存入队列中，进行下一轮爬取。所以NwebCrawler的搜索策略为广度优先搜索。采用广度优先策略有利于多个线程并行爬取而且抓取的封闭性很强。-NwebCrawler is a multi-threaded web crawler program written in C#, it is the realization of the principle of the first to enter one or more seed URL to the queue, and then extracted from the queue URL (FIFO principle), analysis of this page to find the appropriate label and get the href attribute value, useful links page crawling and deposited in the web library, with crawling history to record climbed pages, so to avoid a repeat of crawling. Extract URL stored in the queue, and the next one crawling. NwebCrawler search strategy is breadth-first search. Breadth-first strategy is conducive to multiple threads parallel crawling and crawling closed strong.