a b s t r a c tResearch networks play a crucial role in the production of new knowledge since collaboration contributes to determine the cognitive and social structure of scientific fields and has a positive influence on research. This paper analyses the structure of co-authorship networks in three different fields (Nanoscience, Pharmacology and Statistics) in Spain over a three-year period (2006)(2007)(2008) and explores the relationship between the research performance of scientists and their position in co-authorship networks. A denser co-authorship network is found in the two experimental fields than in Statistics, where the network is of a less connected and more fragmented nature. Using the g-index as a proxy for individual research performance, a Poisson regression model is used to explore how performance is related to different co-authorship network measures and to disclose interfield differences. The number of co-authors (degree centrality) and the strength of links show a positive relationship with the g-index in the three fields. Local cohesion presents a negative relationship with the g-index in the two experimental fields, where open networks and the diversity of co-authors seem to be beneficial. No clear advantages from intermediary positions (high betweenness) or from being linked to well-connected authors (high eigenvector) can be inferred from this analysis. In terms of g-index, the benefits derived by authors from their position in co-authorship networks are larger in the two experimental fields than in the theoretical one.

a b s t r a c tIn 2008, the type of document "proceedings paper" (PP) was assigned in the WoS database to journal articles which were initially presented at a conference and later adapted for publication in a journal. Since the use of two different labels ("article" and "proceedings paper") might lead to infer differences in their relevance and/or quality, this paper presents a comparative study of standard journal articles and PP in journals to explore potential differences between them. The study focuses on the Library and Information Science field in the Web of Science database and covers the 1990-2008 period. PP approximately account for 9% of the total number of articles in this field, two-thirds of which are published in monographic issues devoted to conferences, which tend to be concentrated in specific journals. Proceedings papers emerge as an heterogeneous set comprising PP in ordinary issues, similar to standard articles in structure and impact of research; and PP in monographic issues, which seem to be less comprehensive and tend to receive less citations. Faster publication of PP in monographic than in ordinary issues may conceal differences in the review process undergone by either type of paper. The main implications of these results for authors, bibliometricians, journal editors and research evaluators are pointed out.

A positive influence of international collaboration on the impact of research has been extensively described. This paper delves further into this issue and studies to what extent the type of collaborating country-high, medium or low R&D intensive countryand which country is the leader in the research may influence the impact of the final scientific output. Among 9,961 papers co-authored by scientists from Spain and from another country (bilateral collaboration) during 2008-2009, papers with high R&D intensive countries predominated (60 %) and received the highest number of citations. This holds true in eight out of nine fields, being Social Sciences the one which benefited the most from partnerships with high R&D intensive countries. Mathematics emerges as a special case where other factors such as the partner's specialisation in the field may have a greater influence on research impact than the level of investment in R&D of the collaborating country. No significant influence of the type of country leading the research on the impact of the final papers is observed in most fields. Research policy implications are finally discussed.