Most databases will allow you to create alerts based your searches. You can get updated results through an email or an RSS feed.
You'll have to create a personal account with that database to save the alert, but this is free. It's often a good idea to create a free personal account for databases you use most often so that you can take advantage of extra features, like alerts, saving citations, and more.
Look in the upper right corner of most databases to create a personal account. Most search alert links are at the top of your result listing.
Most online journals allow you to subscribe to their latest articles and/or table of contents through an RSS feed or email. Below are links to just a few RSS journal feeds for Mathematics.