Foreign databases, that is, half of foreign databases, are generally priced according to the number of documents downloaded or the annual usage. Generally speaking, when downloading foreign literature, you don't need to use tools such as Thunder and Express to download it in batches, otherwise your account may be blocked.

Domestic databases generally take the form of mirror image or annual fee of package library. If it is a mirror image, you open the download and there is no traffic limit. However, if it is a package library, the general website will have account monitoring, so don't use the download tool to download in large quantities.

For more specific requirements, you can ask the technical teacher of the library, because the specific requirements of each database will be different. I hope my answer can help you.