Because copyright issues are involved, completely free resources are limited. There used to be a free online library such as Yifan Public Library and Million Books, but it seems to have been closed now because of copyright reasons. Isn't the free information in Baidu library also a lawsuit for copyright reasons?

Now I know the free resources:

1, Superstar Digital Library. Its resources include philosophy, politics, economy, law and other social sciences. And natural sciences such as mathematical physics, industrial technology, transportation, architecture and other categories have free e-books.

2. I am now in Guangzhou, and I know that Zhongshan Library in Guangdong Province can register an account for free and see some of its resources. I wonder if other provincial libraries have free electronic resources.

3. If you are doing scientific research, there are many unpublished papers by researchers on the domestic internet, and foreign websites such as DOAJ and OPEN J-GATE can read periodical papers, including many papers included in SCI and EI.