This paper discusses the experience of developing a web resource intended to study argumentation in popular science discourse. Such type of argumentation is, on the one hand, the main mean of achieving a communicative goal and, on the other hand, often not expressed in explicit form. The web resource is built around a corpus of 2256 articles, distributed over 13 subcorpora. The annotation model, which is based on the ontology of argumentation and D. Walton's argumentation schemes for presumptive reasoning, underlies the argument annotation of the corpus. The distinctive features of the argument annotation model are the introduction of weighting characteristics into text markup through assessing the persuasiveness of the argumentation, as well as highlighting argumentative indicators visually. The paper considers a scenario of argument annotation of texts, which allows constructing an argumentative graph based on the typical reasoning schemes. The scenario includes a number of procedures that enable the annotator to check the quality of the text markup and assess the persuasiveness of the argumentation. The authors have annotated 162 texts, using the developed web resource, and as a result, identified the most frequent schemes of argumentation (Example Inference, Cause to Effect Inference, Expert Opinion Inference), as well as described some specific indicators of frequent schemes. Based on the above-mentioned outcomes, the authors listed the indicators of the most frequent schemes of argumentation and made some recommendations for annotators about identifying the main thesis.