Most journals use a conventional IMRD structure: An abstract followed by Introduction, Methods, Results, and Discussion.
Abstract: The abstract should be a concise overview of how the researchers/authors conducted their study.
It should contain
The abstract is always at the beginning of the paper but is typically written by the researchers after completing the paper.
Introduction: Presents the current state of knowledge about the topic, what is known about the topic and what is not known about the topic. Then the researchers describe the hypothesis they are testing and their conclusions.
Methods: The methods section explains the what experiments were done and should be detailed enough for another scientist to replicate the work. This section revels the design of the study and is crucial to evaluate the validity of the results. Questions to ask yourself while reading this section:
Results: Describes the outcome of the experiment. Figures and tables are often utilized the convey the results clearly.
Discussion/Conclusion: Conveys the authors interpretation of their findings and discuses the results within the broader context of the field.
Summarized from:
Purugganan, M., & Hewitt, J. (2004) How to read a scientific article.