In 1992, he received a doctoral degree with a dissertation comprising the totality of his works, and now heads the group of Slavic glottogenesis.
Nikolaev connects the linguogeography and historical dialectology of Slavic languages with the problems of ethnogenesis of the Slavs [ru].
Reconstruction of the placement of these isoglossae on the territory of the oldest Slavic settlement showed their connection with the archaeological areas of large Proto-Slavic tribal associations.
For more than 20 years, Nikolaev has been the leader and organizer of complex linguistic expeditions to the East Slavic dialects (the Carpathians, the Russian Northwest, Belarus, Polesie) and to the archaic Old Shtokavian dialects of the Serbo-Croatian language (Slavonia, together with Croatian colleagues), author of special field programs on East Slavic historical dialectology.
In 2014, after placing the accents, Nikolaev confirmed (with a significant transformation and many clarifications) Andrei Chernov [ru]'s idea of syncretic polyrhythm in The Tale of Igor's Campaign.