This set is formated for Launch Center Pro, I tested the first one.
http://www.openproblemgarden.org/search/[prompt:URL]
http://mathworld.wolfram.com/search/?query=[prompt:URL]&x=0&y=0
http://math.wikia.com/wiki/Special:Search?search=[prompt:URL]&fulltext=Search
https://tqft.net/mlp_wiki/index.php?search=[prompt:URL]&go=Go&title=Special%3ASearch
http://groupprops.subwiki.org/w/index.php?search=[prompt:URL]&title=Special%3ASearch&go=Go
http://www.encyclopediaofmath.org/index.php?title=Special%3ASearch&search=[prompt:URL]&button=
http://timescalewiki.org/index.php?search=[prompt:URL]&button=&title=Special%3ASearch
http://ncatlab.org/nlab/search?query=[prompt:URL]
http://plato.stanford.edu/search/searcher.py?query=[prompt:URL]
https://archive.org/search.php?query=[prompt:URL]
https://proofwiki.org/w/index.php?search=[prompt:URL]&title=Special%3ASearch&go=Go
https://scholar.google.com/scholar?hl=en&q=[prompt:URL]&btnG=&as_sdt=1%2C16&as_sdtp=