URL dump of search sites that just dropped over the transom, if anyone's interested.

No opinion pro or con right now, will peruse later;

https://www.refseek.com/

https://www.worldcat.org/

https://link.springer.com/

http://www.bioline.org.br/

http://repec.org/

https://www.science.gov/

http://www.pdfdrive.com/