"core of the study" is a correct and usable phrase in written English.
You could use it to refer to the main focus or primary aspect of a particular study. For example, you could say, "The core of the study was an analysis of the economic impacts of the policy."
At the core of the study was a survey of more than 2,000 affluent people around the world conducted in January and February by Ledbury Research, a market research firm based in London.
The core of the study includes semi-structured interviews material.
The research that formed the core of the study consisted of the authors observing initial due diligence between 140 investors (40percentt of whom were women) and 189 entrepreneurs at TechCrunch Disrupt New York.
In the proposed model, demotivators constitute the core of the study and their direct and indirect roles in the other four variables are investigated.
Few attempts were made to reconsider which texts represented the core of the study of natural philosophy in the universities; one remarkable exception was Pierre de la Ramée (1515 1572), who put a distinctive emphasis on particular sciences at the expense of study of the Physics.
NKU conceived the core of the study design.
We searched publication titles in PubMed to identify relevant studies using terms sufficient to identify a reasonable core of the studies on a topic.
At the core of this study are the language ideologies which are outlined in more detail below.
Regarding ERTMS specifications, FRS (Functional Requirement Specifications) and SRS (System Requirement Specifications) contain functional requirements at system level, which place the core of this study in the functional testing field.
At the core of this study was creation of gold-standards of transcriptional regulation in humans that can be compared with target genes reported in transcriptional regulatory pathways.
