The phrase "first line of research" is correct and can be used in written English.
It is often used to describe the initial or primary area of investigation in a research project. Here is an example: "The first line of research for this study will focus on the effects of diet on blood pressure levels."
The first line of research is already yielding results, thanks to micro-electrodes just 40 microns across implanted in the brain.
The first line of research suggests that there are no separate learning systems for acquiring mental rules and storing exceptions to these rules.
Our first line of research is focused on determining the cellular and molecular components crucial to the neural representation of external space by functionally defined cell types in entorhinal cortex (grid, border and head direction cells).
The first line of research examines patterns of career mobility among bureaucrats in the Jiangsu Province in its entirety from 1990 to 2016, while China experienced rapid economic growth.
The first line of research investigates how social, economic, and psychosocial determinants influence racial/ethnic- and geography-related disparities in HIV care continuum indicators (e.g. diagnosis, linkage to care, viral suppression).
Segregation at the extremes: The first line of research addresses the need to better monitor segregation at the extremes, including (a) the possible rise of enclave-style segregation at the very top (the "one percent") and (b) the yet more troubling possibility of a resurgence of extreme segregation among the very poor.
In an attempt to confirm or refute the lipid bilayer postulate, one of the first lines of research to be explored was the measurement of membrane thickness.
The second line of research is the development of a consensus among researchers regarding best practices in determining the difference to be detected by a clinical trial, as stated above.
The second line of research focuses on recovery, and shows that an enhancing cognitive style interacts with positive life events to reduce depression.
