This article reports a diachronic study carried out on a sample of medicine research articles in order to determine variations in evaluation resources. The attitude relates to certainty, obligation and other sets of values. It includes affect, judgement and appreciation and the evaluation can be positive or negative. Based on the analysis of twenty research articles of a medical journal, Medicina, (ten from 1941-1942, and ten from 2002-2003) the analysis shows that lexical items, specially quantifiers, are typically used to evaluate. Verbs as 'appreciate', 'prefer', are evaluative, like 'increase', 'reduce', which express evaluation related to the context. We have observed differences between the texts of the first group and the texts of the second one. In particular, the first group shows an important number of verbs of obligation, as well as the presence of the agent, responsible of the evaluation. The second group of texts shows lesser explicit evaluation and display strategies for hiding the author of the text.