Which tools can identify scholarly papers that use the same types of equations? Many types of equations are being used in multiple contexts, so a search for specific formulas might be one way to identify scholarly papers that are conceptually related.
Is any website or tool actually providing recommendations of related content on that basis?
The closest I can think of is Springer's LaTeX Search, which allows to identify papers containing similar TeX strings, e.g. $\nabla [(k(T)\nabla T]$.
However, they seem to match the string as a whole, which gives undue weight to things like variable names or formatting, and while it is possible to identify related papers that way, they do not seem to use it to recommend related articles, nor have I seen this used anywhere else at publishers' sites, at arXiv or on Google Scholar, nor in readers like Papers or Mendeley.
Also, their system is proprietary, and I would be interested in a system that is open source and openly licensed. Any pointers appreciated.
 A: Approach0 is able to find expressions with different variables:
https://approach0.xyz/search/?q=%24%5Cnabla%5Cleft(k(T)%5Cnabla%20T%5Cright)%24&p=1
However, its index does not include academic papers, it is only indexing Math StackExchange now.
That being said, I think this is still an option since Approach0 is open-source, and you can use it freely to index whatever content you want to perform search on. And in the near future, approach0.xyz is very likely to further include academic PDFs into its index. Just keep an eye on it!
A: I know this is already answered, but searchOnMath looks interesting too. Maybe it suits your needs.
A: There is MathWebSearch; from the site: 

The MathWebSearch system (MWS) is a content-based search engine for mathematical formulae. It indexes ​MathML formulae, using a technique derived from automated theorem proving: Substitution Tree Indexing. 

Indeed, zbMATH, already uses it to provide MathSearch. The interface uses LaTeX syntax. (MWS itself seems to support different interfaces.)
