Hi Compton, welcome to the forum.
Yours is an excellent suggestion that would find application in many other areas than the specialized one of journal articles. The short answer is that PB does not have this feature built into it, so if you need it you might have to design your own workaround.
Similar requests for this type of feature have been made previously. If you search the forum under metadata you will find a few. There's also at least one UserGroup thread on this.
I understand v6 now supports filtering by thought type in Instant Search, so if you were prepared to go to the trouble of creating several child thoughts of different types for each journal article, you could have a thought with the author's name of type author, etc.
Instead of first entering the search term, then deciding what type of field to apply it in, you could first narrow the search to a particular type by using Reports filter set to Normal or Inverse, then that would limit Instant Search results to that type.
Alternatively, without needing to create a whole bunch of typed child thoughts for each article which would slow down your Brain, you could decide on a set of non-english keyword codes for each field, such as xau for author, xti for title, etc. Prefix them to keywords and hide them in the thought's label field so that you could look up a paper by Bill Bones on bone marrow by typing xaubones xtibone xtimarr into the search edit field and pressing Enter to invoke Extended Search but exclude false positives (by using non-English codes) since it searches all fields. You get the idea.
(Since this is a Feature Suggestions thread, I would like to reiterate the suggestions that the sooner Instant Search can be enabled to search Thought Labels, and Extended Search be given user-customizable, preset filters equivalent to Advanced Search, the better.)