Development of science and academic knowledge has led to changes in academic language and transfer of information and knowledge. In this regard, the present study is an attempt to investigate lexico-grammaticality in academic abstracts and their full research papers in Linguistics, Chemistry and Electrical engineering papers published during 1991-2015 in academic journals from a diachronic perspective through quantitative research design. The focus of this paper is on transitivity, mood and theme analysis in the corpus according to Halliday's (1994) systemic functional linguistics model. So, all the attempts are to find the changes in abstracts and research papers of these disciplines and how they are to be positioned in different linguistic contexts over time. The results revealed that research papers employ the spectrum of possible lexical realization quite differently as compared to general English, especially concerning the use of specific lexical items. Also, the results of chi-squares of each discipline showed that there are significant differences between papers over time at .05 level of significance (.000< .05) with regard to the transitivity, mood, and theme.
