Enter your search query at scholar.google.com. On the left-hand side of the search results page, at the bottom of the list of search filters, click on "Create alert."
If you are already logged into Google, Scholar will list your Gmail as the default to receive search alerts, but you can change this to any email you prefer. Additionally, Google Scholar will tell you how many new results for your search query have been created in the past year. You can edit your search terms and keywords based on this information.
Now, when Google Scholar indexes results that match your search query, you will be notified via email.
For more tips on using Google Scholar, see the Google Scholar Research Guide.
