It is possible in Australia to see basic bibliographic information and get the patent application number for a provisional patent application. It is also possible to search on useful fields like inventor names, applicant and titles for provisional patent applications.
Using data mined from published non-provisional specifications, academic papers and news articles, this can provide some intelligence around the type of invention in the provisional.
It is not possible to get a copy of the actual provisional specification unless this had already been used to found priority in a later non-provisional application that is published.
In some other jurisdictions, not even basic bibliographic information is available.
In summary, some limited searching is available depending on the jurisdiction.