There are many archival sources which are accessible on-line, some are free and some require a library log-in or subscription.
Some useful free archives can be found here
Archives requiring a log-in can be found here
Patent searches can be quite useful and sometimes essential,
some useful sites can be found here
Some useful free archives can be found here
Archives requiring a log-in can be found here
Patent searches can be quite useful and sometimes essential,
some useful sites can be found here
