I am asking this question specifically for the subject of Mathematics. What are some efficient ways of searching papers on two different broad topics, say number theory and graph theory. Also, if I want to be more specific and search for papers involving phrases from number theory and graph theory? I am aware of MathScinet, Google Scholar and arXiv. However, I do not know if there are ways to serve my query in these sites. Thanks in advance.
Scopus advanced search might be good. It is much better than Google Scholar in some ways.
This shows an example of a search that is much more complicated than yours.
This is not a free service, so you will need access through your university or some other way.
I would do this using Scopus as well but I would also use another method. Look up first article on topic. Click the link for articles that cite that article. Extract all the results as a list of articles. Do the same thing for 2nd article. Compare the two lists to identify common articles. My current solution is to download many highly-cited papers (without reading) and index them.
Web of Science has a SAME operator, which matches “records where the terms separated by the operator appear in the same sentence”. Given that Web of Science supports four search operators (AND, OR, NOT, and SAME), it is safe to assume that this is the extent of its context-sensitive search capabilities. Then connect this to Scopus searches.