In this paper, we propose a method for detecting temporal trends of technical terms based on importance indices and linear regression methods. In text mining, importance indices of terms such as simple frequency, document frequency including the terms, and tf-idf of the terms, play a key role for finding valuable patterns in documents. As for the documents, they are often published daily, monthly, annually, and irregularly for each purpose. Although the purposes of each set of documents are not changed, roles of terms and the relationship among them in the documents change temporally. In order to detect such temporal changes, we combined a method to extract terms, importance indices of terms, and trend identification based on linear regression analysis. Empirical results show that our method detected emergent and subsiding trends of extracted terms in a corpus of a research domain. By comparing this method with the existing burst detection method, we investigated the trend of phrases consisting of several burst words in the titles of AAAI and IJCAI.