Online tool to convert plain text references into list of PubMed IDs or DOIs
You could use CrossRef

Go to this link: 

Paste the references into the box 
and supply an email:
If you want PubMed IDs then click the box:



You'll get results like this:


You could then do some text manipulation to extract the doi or PMID.

Note: the tool requires to register your email.


  Enter the email address you registered for use of Crossref services. If you have >not registered your email address, request an account. [link to register]