Literature citation is a very important part of academic research and paper writing. In order to facilitate readers to find and read relevant literature, it is usually necessary to add icons or symbols to the cited literature. The following are some common document icon formats:

1.APA (American Psychological Association) format: APA format is one of the most commonly used citation formats in social sciences. It uses the author-date system to cite documents, and provides the author and publication year for each citation in brackets. For example, (Smith, 20 10).

2.MLA (Modern Language Association) format: MLA format is mainly used for writing papers in the humanities field. It uses the author-title-publisher system to cite documents, and provides the author, title and publisher for each citation in brackets. For example, (Smith's Great Book, Penguin Book).

3. Chicago format: Chicago format is a citation format widely used in various disciplines. It uses the author-title system to cite documents, and provides the author and publication year for each citation in brackets. For example, (Smith, 20 10). In addition, the Chicago format also requires complete publication information in the bibliography.

4. Harvard format: Harvard format is similar to APA format, and it also uses the author-date system to cite documents. However, the Harvard format only provides the author and publication year in brackets, excluding the page number. For example, (Smith, 20 10).

5.IEEE (Institute of Electrical and Electronics Engineers) format: IEEE format is mainly used for paper writing in engineering and technology fields. It uses the author-title-publisher system to cite documents, and provides the author, title and publisher for each citation in brackets. For example, (Smith's Great Book, Penguin Book).

6. Natural format: Natural format is a commonly used citation format in Nature magazine. It uses the author-title-publisher system to cite documents, and provides the author, title and publisher for each citation in brackets. For example, (Smith's Great Book, Penguin Book).

7.ScienceDirect format: ScienceDirect format is a commonly used citation format of Elsevier publishing house. It uses the author-title-publisher system to cite documents, and provides the author, title and publisher for each citation in brackets. For example, (Smith's Great Book, Penguin Book).