The phrase 'has been earlier' is grammatically correct and can be used in written English.
You can use it to refer to something that happened in the past. Example: She had mentioned the issue before, but it has been earlier this year that she became really concerned.
Therefore, it is plausible that the HA0 with intact polybasic cleavage site expressed in Flp-In system, which was cleaved into HA1 and HA2 forms provided better immunogenicity than what has been earlier reported for HA with mutated cleavage site [3].
This tendency has been earlier observed in [38].
This method has been earlier used in many studies [19 21].
There has been earlier evidence of a plan for a 'six-stage' notification system.
The other gene (Affymetrix probe set ID, Os.7678.1.S1_at) has been earlier shown to be involved in JA biosynthesis in rice (Mei et al. 2006).
High18F-activity accumulation was seen in the locus coeruleus, a brain region with high NET density as has been earlier shown by Burchett et al. [34].
As has been earlier probed in the absorption spectra, further increase in the AgNO3 added decreased the aspect ratio of the nanonetworks.
The compound 2 has been earlier derived from DHEA (dehydroepiandrosterone) by the action of 17β-hydroxysteroid dehydrogenase type 7 enzyme [12].
This data has been earlier published in the context of the negative influence of terminally differentiated CD8+ T cells in bone healing [13].
The analysis of recombinant proteins fused with GST in biological assays has been earlier described, with no interference of the targeted protein's activity.
However, it has been earlier noticed that the overall pedestrian kinematics response may vastly differ if the lower legform impactor hits a car with a high bumper.
