Abstract
In this paper we clarified obsolescnce tendencies of the literature of each academic field according to 100 divisions level of NDC classification, by estimating the past of the cited literature appeared in each paper and thesis since they were published. In this investigation we've divided the literature into four groupes such as books and periodicals of domestic and/or overseas publication. On the results, most striking points are as follows : 1) Qualitatively the use-ratio of the literature will climb up to the peak in a few years and then descend down exponentially year by year. These obsolescence tendencies are fairly different among the academic fields and/or literature groupes above-mentioned. 2) The literature on the fields of humanities and social sciences have tendencies to be used longer than those on the fields of sciences and technology. Book literature are used longer than periodical literature, and overseas literature are used longer than domestic ones. 3) Obsolescence tendencies of the literature rather well follow to the exponential curve described as the following formula; Y=A+BR^X X=past years of the cited literature appeared in each paper and thesis Y=cumulated percentage for total number of cited literature according to above-mentioned four groupes in each academic field A, B, and R=constant number We showed the value on the obsolescence tendencies of the literature which made clear relations between aging and cumulated percentage of use in each academic field by calculating from this formula. These values will be useful to academic library and research library planning.
