Has Bruce ever partially transformed into the Hulk i.e, has he transformed a part of his body into the Hulk, while still remaining human? For example, transforming just his arm to punch someone really hard (something similar to what Eddie Brock does in the Venom movie when he is attacked by Treece and his thugs at his apartment)?
Way back in Incredible Hulk Vol. 1 Issue 6 when Banner still uses the Gamma Ray Projector to switch between Banner and Hulk the machine starts malfunctioning. At one point it leaves him still strong for a while after transforming back to Banner, another it has a delayed reaction and at one point it delays his head transforming to Hulk while his body is the Hulk's.
He "solves" this issue by wearing a mask of the Hulk's face over his own. Later on when he is unmasked his face has finally changed over to Hulk's.
Whilst you are looking for answers from the comics it is worth mentioning about the scene in Avengers: Infinity War when Hulk refuses to come out. Banner turns partially green and so he does appear to have done a partial transformation.
I offer this as a supplement to TheLethalCarrot's answer.
Incredible Hulk #376 (1990), is a bountiful source of whacky partial transformation. The mind of Bruce Banner is a turbulent mess and three identities are battling for control: Banner, Green Hulk, and Grey Hulk. That battle takes on strange results...
Ultron Forever: New Avengers (2015) is the second part of a trilogy that makes a direct callback to the Incredible Hulk #6 (1963) reference. The Hulk's head was cut clean off and Banner's head erupted from the big green chest. And then the Hulk's head was successfully re-attached. (Whew)