Back is a major muscle group, it takes a lot of work to really make your back stand out. A lot more than the pullups and high-rep dumbbell rows.

The major muscles of back

Trapezius
Rhomboids
Latissimus dorsi
Erector spinae

The best exercises for back are

Pull ups

Pull ups target your lats better than any other exercise. They also work your biceps, upper back and forearms. They also work other muscles like your traps, rhomboid, teres major, infraspinatus, pecs, erector spinae and external oblique

lat pull downs

The lat pulldown exercise is a strength training exercise designed to develop the latissimus dorsi muscle. It performs the functions of downward rotation and depression of the scapulae combined with adduction and extension of the shoulder joint.

Back rows

A row is a pull-type, compound exercise which works primarily your middle back, but also works your Latissimus and muscles in your arms

Dead lift

The deadlift is a strength exercise that works several muscle groups, including your back, glutes and legs.Performing a deadlift with good form is imperative to reduce the risk of injury, particularly to the low back.