This is the 6665th most frequent Spanish word.
científicas
"Scientist" (feminine plural).
Here, 'científicas' is used as an adjective describing 'investigaciones', meaning 'scientific' in a feminine plural form as it agrees in gender and number.
Las investigaciones científicas son fundamentales para el avance del conocimiento.
Scientific research is fundamental for the advancement of knowledge.
In this case, 'científicas' is a noun used to refer to female scientists.
Dos científicas recibieron el premio por sus descubrimientos.
Two female scientists received the award for their discoveries.
This usage of 'científicas' as an adjective modifies 'teorías', describing them as 'scientific', maintaining agreement in gender and number.