The phrase "as a single major" is correct and usable in written English.
It can be used when referring to a specific area of study or focus within an academic context, typically in relation to a degree program.
Example: "She decided to pursue her studies as a single major in psychology, dedicating all her efforts to understanding human behavior."
Alternatives: "as a sole major" or "as a primary major".
In humans, 85% of mRNAs studied are predominantly transcribed as a single, major isoform43.
He described the obstacle as "a single, major thing" that would require the intervention of President Clinton.
West of the transform margin, divergent rifting during the Early Cretaceous initiated the development of the Deep Ivorian Basin, essentially, as a single major pull-apart structure.
The chromatogram shows that the protease was eluted as a single major peak (Figure 2).
An IDM functions as a single major and as such, can be combined with a second major; whether such a decision is appropriate or feasible should be carefully evaluated.
Phreatic eruptions often occur during prolonged periods of non-magmatic hydrothermal unrest (e.g., Pisciarelli, Campi Flegrei), and can occur as a single, major event, or as minor events within a phreatic eruption cycle (Rouwet et al. [2014]).
For example, we've had huge debates over the best economic stimulus, with mountains of data, and as far as I know not a single major player in this debate has been persuaded by data to switch sides.
But he goes astray, I think, when he touches on a subject near and dear to my own data-driven heart: For example, we've had huge debates over the best economic stimulus, with mountains of data, and as far as I know not a single major player in this debate has been persuaded by data to switch sides.
Isolated defects were defined as those having a single major defect alone or together with one or more of a list of minor defects used in the National Birth Defects Prevention Study [ 19].
And just to put this state of affairs in perspective, consider that Puerto Rico has less than half the per capita of the nation's poorest state, Mississippi; a murder rate nearly twice as high as Mexico's; and not a single major institution free of corruption and scandal.
As a result, only a single major office tower has been completed in the last eight years, the Conde Nast building in Times Square.
