Use sequential trials to continue watching.
This is a turning point. Season 4 introduces Mayim Bialik as Amy Farrah Fowler, Sheldon’s "date" via a dating service set up by Howard and Raj. At first, she is a female Sheldon. By the end of season 4, she becomes a unique character with a desperate need for friendship. the+big+bang+theory+season+1+2+3+4+5+6+7+8+9+10+free
Season 10 is the cut-off for most free streaming libraries. It represents the end of the "early era" before the final two seasons (which are usually locked behind paywalls). Use sequential trials to continue watching