Journal Citation Reports from Hagerty's web site

Journal Citation Reports is a comprehensive and unique resource that allows you to evaluate and compare journals using citation data drawn from over 7,500 scholarly and technical journals from more than 3,300 publishers in over 60 countries. It is the only source of citation data on journals, and includes virtually all areas of science, technology, and social sciences.

Journal Citation Reports can show you the:
Most frequently cited journals in a field, Highest impact journals in a field and Largest journals in a field

To Access JCR: Click on Electronic Databases Click on Journal Citation Reports
Most frequently cited journals in a field, Highest impact journals in a field
and Largest journals in a field