lock What's available for free?

Unfortunately, not too much. You can search some segments of the journal literature using free discovery tools such as Google Scholar and PubMed, which are fine within their own limits. (Google Scholar covers mainly recent literature across many disciplines; PubMed covers the biomedical literature very thoroughly.) But that's about it as far as free indexes go.

Once you identify an article in a journal, you will realize that the vast bulk of scientific journal literature is locked behind paywalls and available only via institutional subscriptions or pricey pay-per-view. If you are not currently affiliated with an institution that subscribes, you will not have access to most of the restricted content you discover on the Web. (Sorry, alumni don't qualify.)

What to do? If you are nearby and the UT Libraries has a print copy of the journal (search for it in our Catalog), you are welcome to visit and make a photocopy. If you prefer, you can order a copy via our Document Express service. If UT subscribes to the content online, you can also visit and use one of our workstations to view the article, but there are significant bureaucratic hurdles in getting temporary guest access to these machines. And don't forget that there's lots of stuff that UT can't afford to subscribe to in the first place.

Be sure to check out all your options before getting out your credit card.