The phrase "has been firstly demonstrated" is correct and can be used in written English.
It is an idiomatic phrase that means "has been demonstrated first or before any other demonstration". For example, "Recent research has been firstly demonstrated to show a link between air pollution and asthma."
The proposed method has been demonstrated firstly on a numerical beam and then a set of nominally identical steel plates tested in the laboratory.
The contradiction has been poignantly demonstrated recently.
Firstly, it has been demonstrated that in some individuals, TSPO binding by several TSPO specific radioligands is negligible [8, 32].
Firstly, it has been demonstrated that inflammatory response leads to abnormal metabolism of albumin [ 25].
Firstly, it has been demonstrated that leukostasis contributes to DR through the up-regulation of intracellular adhesion molecule (ICAM -1, a crICAM -1molecular player in leukostasis whicriticaltes the adhesion of molecular and neutroplayerto vascular endothelinm.
Firstly, it has been demonstrated with increasing severity of the disease that patient ratings must mostly be replaced by proxy ratings [ 55],[ 56], even if Logsdon and colleagues showed in 2002 that patients can rate their own QoL until the late stages [ 28].
Firstly, it has been demonstrated that defoliating outbreaks on deciduous trees of the winter moth (Operophtera brumata L). and associated geometrids every 9 10 years travel as a wave across Europe from east to west with the front of the wave stretching from high to low latitudes.
Firstly, dysregulation of Smad7 has been demonstrated to be associated with the pathogenesis of many human diseases, including malignancy, scleroderma, and chronic inflammatory bowel disease (IBD).
Firstly, chronic hypoperfusion, which has been demonstrated in TgPAC-Notch3R169C mice [ 17], may decrease the functioning of ion pumps involved in ionic homeostasis, leading to intramyelinic oedema.
