as a promotional genre has been an increasing interest in recent years, leading to an intriguing debate on the objectivity of scientific writing. The present study investigated the promotion and caution in research article abstracts through the use of positive, negative and hedge words across disciplines and rankings based on a large and principled dataset (more than 12.6 million words). The corpus was designed and built with full consideration of representativeness, structure, balance, and size in terms of discipline and ranking. The results showed that positive words were more frequently used than negative words in terms of both discipline and ranking, positive and negative words were more frequently used in hard sciences than those in soft sciences and high ranking journals than those in low ranking journals, and hedge words were more frequently used in high ranking journals and soft sciences. Further investigation also found a complexity of frequency patterns when two disciplines were broken down into specific categories. The more frequent use of positive words in abstracts to promote scientific research was discussed from the perspective of disciplinary knowledge construction in addition to the publication bias, the outcome reporting bias, and universal linguistic positivity bias.