MOSAIC search interface to OpenWebSearch:
https://mosaic.ows.eu/service/webinterface/
To read more on howMOSAIC uses index fractions, read "Enriching science search with the open search framework MOSAIC." Index partitions are small or medium sized indices containing web documents related to a certain topic or for a particular purpose, such as geo-coordinates.
For my purposes, I find utilities like LitSift more useful for post-processing on the 1st query pass.