Scroll down the page to the icons below the search box and click on 'First Research'.
Type in your DU email and hit submit.
Enter your SIC code and hit enter
There will be a link that shows up that says 'Would you like to search by SIC code, click here'. Click on that and it will change over to SIC codes.
Type in your SIC code and look for it on the result list.

If you want a list of companies under that SIC code, click on the word 'Industry' under the search box and type in the code and hit search.

Select 'Industry' from the dropdown menu next to the search box.
Type in your SIC code and hit search.
This database searches by NAICS code, but will recognize the 4 digit SIC code when you hit enter. The wording might be a bit different, so look for the report that resembles the code you entered.

You should also be able to get a list of companies from that report.

Find companies by SIC codes under the 'Classification Search' box.
Either enter a code or use the 'lookup' link to find one.