When writing scientific papers, be it journals, theses, theses, or dissertations, it is necessary to look for literature as material for consideration, in determining titles and topics, here are some sources that can be used as references to conduct research.

1. Academia: https://academia.edu/
2. Book yards: https://bookyards.com/
3. Bookboon: https://bookboon.com/
4. Prayer: https://doaj.org/
5. Ebook: https://123dok.com
6. Ebook https://fdocument.com
7. Ebook https://www.googlebook.com
8. Ebook https://www.pdfdrive.com
9. Elsevier: https://www.elsevier.com/search-results/
10. EmeraldInsight: https://www.emeraldinsight.com
11. Free computer books: https://freecomputerbooks.net/
12. Google Scholar: https://scholar.google.co.id/
13. Google Semantic Scholar: https://www.semanticscholar.org/
14. Gutenberg: https://gutenberg.org/
15. IEEE: https://ieeexplore.ieee.org/Xplore/home.jsp
16. International digital children's library: https://en.childrenslibrary.org/
17. Genesis libraries: https://libgen.is/
18. Libri vox: https://Librivox.org/
19. Many Books: https://manybooks.net
20. Mendeley: https://www.mendeley.com/search/
21. Moraref: http://moraref.kemenag.go.id/
22. Research: https://neliti.com/
23. OAPEN: https://oapen.org/
24. Open Library: https://openlibrary.org/
25. National Library: http://e-resources.perpusnas.go.id/
26. Garuda Portal: http://garuda.ristekbrin.go.id
27. Questia Public Library: https://questia.com/
28. Readprint: https://readprint.com/
29. Researchgate: https://researchgate.net/
30. Scihub: https://scihub.org/
31. Sciencedirect : https://sciencedirect.com/
32. Scribd: http://id.scribd.com/
33. Slideshare: https://slideshare.net/
34. Wikibooks: https://Wikibooks.org/
35. Wiley Online Library: https://onlinelibrary.wiley.com

Happy reading, hope it helps...