CiNii (https://ci.nii.ac.jp/ja): a database of articles in Japanese research journals, some of which are available online. Not as good as JStor, as many articles are not available online, but nonetheless invaluable.

 

National Diet Library: (1) Research Navigator (https://rnavi.ndl.go.jp/rnavi/)—introductions to performing research in various fields and a collection of databases  (2) Digital Collections (http://dl.ndl.go.jp)—scans of premodern and early modern texts (up to pre-war 20th century) in the collection of the NDL.