These studies, besides influencing his original work, led to his important monograph on the etched work of Rembrandt.

He wrote alone, and in collaboration, four important monographs:

On the occasion of that retrospective an important monograph is published.

He published an important monograph on the sculptor Jean-Baptiste Carpeaux in 1987.

The art scholar A. B. de Vries then excluded this painting from an important monograph.

He authored several important monographs over his 30-year career.

Sidney also wrote an important monograph on the Bodos.

The period most dense in exhibitions and retrospectives, with the publication of important monographs, was the 1980s.

In 1940 the group was reviewed in detail and every species known at the time described (and many illustrated) in an important monograph.

He was author of more than 100 scientific-research articles and many important monographs.