While you won’t find much of a clue in your google searching, ISI does offer some limited APIs and direct-linking-syntaxes for the Web of X products.
It seems you can use many of them with an existing ISI subscription, no additonal charge.
You do need to register/request access.
Here’s one that looks particularly useful that I plan to use in Umlaut:
If it works as I have been told, it will allow me to look up a particular citation in ISI, and get links to the ‘cited by’ page for that citation, ISI-computed ‘similar articles’ for that citation, and perhaps others.
I don’t want to display any of these links to my users unless I know clicking on them is going to give non-zero hits. Hopefully the API will tell me that, otherwise my app will just have to do a request in the background first and screen-scrape the HTML to make sure there are non-zero hits.
Either way, it’s going to be a LOT easier than trying to simulate user interaction with ISI’s actual end-user web site, requiring lots of session cookies and lots of slowness.