Theses are final projects made by students of universities of applied sciences or academic universities. Doctoral dissertation is the highest level of a final project.
Most of theses are published online. You can find theses of Finnish Universities of Applied Sciences in open repository Theseus.
Academic universities in Finland have their own portals for theses. You can find the links to them beneath (Online theses of academic universities).
There are a lot of theses and dissertations in libraries' online catalog Melinda as well to be read online.
Melinda is the union catalogue of Finnish Libraries, including university libraries, libraries of universities of applied sciences, and some special and public libraries. In Melinda you can find final theses and dissertations in open access format as well. You can limit your search to dissertations and theses, or to publications in e-format.