1.GoogleScholar: This is a free academic search engine, which can search various academic resources including academic papers, books and conference papers.

2.PubMed: This is a free biomedical literature database maintained by the National Library of Medicine, which contains millions of articles related to life sciences and medicine.

3.IEEEXplore: This is an electronic library that provides documents and meeting records in the fields of computer science, electronic engineering and information technology.

4.ScienceDirect: This is the online publishing platform for science, technology and medicine of Elsevier Publishing Group, which contains a large number of journal articles, books and reference books.

5.WebofScience: This is a comprehensive academic citation database, covering the literature and citation information of many disciplines.

6.Scopus: This is another academic citation database of Elsevier Publishing Group, which contains documents in the fields of science, technology, medicine and social sciences all over the world.

7.WorldCat: This is a worldwide library catalogue maintained by the Library of Congress, which contains millions of books and other materials.

8.Data.gov: This is an open data platform provided by the US government, which contains data resources of various government departments and covers information in various fields.

9. Eurostat: This is the official website of Eurostat, which provides economic, social and environmental statistics of EU member states.

10.WorldBankOpenData: This is an open data platform provided by the World Bank, which contains economic, social and environmental data of all countries in the world.