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6. If you want to read the full retrieved in books digital databases, you must download and install the PDF browser. I 7. Secondary literature is the processing, sorting, refining and concentration of primary literature, and according to its external characteristics and content characteristics in order, to form a new form of literature. 8. Advanced search of full-texts of Chinese journals in CNKI series databases is combined search 9. Mixed row document: some attributes or feature of the literature is used as a literature identification, that is, as a retrievable field, subject word, author's name, classification number, etc. 10. Journal papers, abstracts, dissertations, and conference documents are all primary documents. 11. In the Chinese Journal Full-text Database CNKI, the full-text format of the literature provided is divided into two formats: CAJ and PDF