iScienceSearch is an internet search portal for scientists that allows you to perform a search across multiple data sources with a single query. I wrote a review a while back but it has undergone several updates since then and has been significantly expanded.

iScienceSearch allows both text and structure based searches, but the really interesting thing is that when you do a search using a single query item it automatically searchs in the background for other synonyms, structure, CAS Registry Number, InChI etc.

The screenshot below (click to enlarge) was generated using a structure-based query, as you can see the search results also include the results from text-based queries using synonyms. The filters on the left-hand side allow you to sort and filter the results to allow you to focus on the most relevant information.

The searching is free and requires no registration.