Background and Objectives: Abstract is a compact that introduces an academic paper with the least possible words. The number of people who read the abstracts is much broader than those who read the full text of articles. Most readers usually decide upon going through the full text of the article after reading the abstract. In fact, after the title, the abstract is of great importance. Unfortunately, it seems that the majority of authors and scholars - despite their care for the body of their paper - write the abstract hastily using copy and paste method. Since the abstract is brief and informatively condensed, it is necessary to observe all linguistic considerations in order to increase its readability. Cohesion is one of the factors that contributes to the improvement and readability of the text. Abstract as one of the important components of the article should represent the content of the article. But due to the length limitations, the authors find it difficult to write the abstract, because they should display the content with the least words. Most writers use copy and paste method; they get different sentences from different sections of the article, such as introduction, methodology, analysis of the results and conclusion. This method, in spite of the presentation of the article, usually reduces its readability, because of the lack of cohesive ties. This shows the importance of studying abstracts based on Halliday-Hasan cohesion theory. In this research, Persian abstracts of the ISC top journals in 7 areas were investigated based on the Halliday-Hasan cohesion theory. Also, in the present study, the possibility of adding to the linguistic guidelines of the ISO 214-1976 abstracting was examined. In research was conducted to answer the following questions:
1. How are ISC top journals of the 7 subject areas of science ranked based on the Halliday-Hasan cohesive theory?
2. What cohesive ties are used by the authors in Persian abstracts?
3. is there any possibility of adding any linguistic direction to the ISO 214-1976 abstracting Guidelines, based on cohesion theory?
Methodology: Since the present study was conducted by content analysis and comparative analysis, the sampling method was collecting data based on available resources. A checklist was developed based on Halliday-Hasan cohesion theory (1976). 21 ISC top journals- 3 in every subject area of science- with the highest impact factors were selected for the study. 24 articles from the latest available issues of every journal were downloaded from its website. The abstracts were extracted and investigated by the researcher to find cohesive ties.
Findings: The most frequent cohesive devices used in the abstracts of the papers of ISC top journals are respectively reference, conjunction, ellipsis and substitution. In addition, in the abstracts of basic sciences and humanities, more cohesive devices are used than in the other 5 areas.  With regard to the findings, it is possible to add to the linguistic directions of the guidelines of the ISO 214-1976 abstracting not only for writing Persian abstracts, but also for writing abstracts in general. They are as follows:
1. Use conjunctions to create causal, temporal, additive… relationship between the sentences.
2. Use transparent cohesive words and avoid the ambiguous ones.
4. Use ellipsis, both for nominal and verbal to shorten sentences.
5. Take care of the position of cohesive ties and their frequency should be in proportion to the number of sentences to make abstracts more transparent and readable
Discussion: Since abstracts play a key role in introducing an academic paper and can play a key role in its retrieval, the present study investigates abstracts in terms of Halliday-Hasan cohesive theory. Findings showed that in many abstracts, the lack of cohesive ties have led into semantic ambiguity and thus less readability. This finding is consistent with the findings of the Milky study (2002). Another finding was that the most frequent cohesive ties were reference and conjunction, which confirmed the findings of Hoseinzadeh (2001). This finding, of course, is not consistent with Rai Dehghi (1380), because in the latter, ellipsis was more used than reference and conjunction. In the abstracts of subject areas of science, except for agriculture, reference has been used more than conjunction. The present study showed that abstracts of quarterly journal of Biomedical Engineering, quarterly journal of Interdisciplinary Studies in the Humanities and quarterly journal of Political and International Approaches have the highest number of cohesive ties. The findings showed that in the abstracts of the basic sciences and humanities, more cohesive ties were used in comparison to other five subject areas, and the field of medical sciences stands in the last position. Of course, most of the investigated abstracts of medical sciences were structured abstracts. It is likely that the abstract type had influenced the findings. Therefore, it is suggested that this issue be investigated in another study.   In addition, the present study added a few linguistic directions to the guidelines for writing abstracts, based on the Halliday-Hasan cohesive theory.