Talvez deva tentar algumas variações de ortografia:
research systems » research synthesis (Expandir a Pesquisa)
dental research » medical research (Expandir a Pesquisa)
center nurse » center nurses (Expandir a Pesquisa), letter nurse (Expandir a Pesquisa), cancer nurse (Expandir a Pesquisa)
cent nerve » bent nerve (Expandir a Pesquisa), recent nerve (Expandir a Pesquisa), crest nerve (Expandir a Pesquisa)
systems di » systems do (Expandir a Pesquisa), systems de (Expandir a Pesquisa), systems d (Expandir a Pesquisa)
nurse cat » nurse can (Expandir a Pesquisa), nurse ca (Expandir a Pesquisa), nurse cadet (Expandir a Pesquisa)
j center » j centner (Expandir a Pesquisa), j centeno (Expandir a Pesquisa), j cestero (Expandir a Pesquisa)
j dental » j dent (Expandir a Pesquisa), j delta (Expandir a Pesquisa), j deal (Expandir a Pesquisa)
cat dis » cat did (Expandir a Pesquisa), cat diets (Expandir a Pesquisa), cat diet (Expandir a Pesquisa)
nerve c » nerve cn (Expandir a Pesquisa), nerve _ (Expandir a Pesquisa), nerve a (Expandir a Pesquisa)
i cent » i cento (Expandir a Pesquisa), ai cent (Expandir a Pesquisa), ii cent (Expandir a Pesquisa)

You can also try:

• Europeana
• Digital Public Library of America
• CORE

Pode obter mais resultados ajustando a pesquisa.

• "As palabras AND, OR e NOT podem gerar pesquisas incorrectas; tente utilizar aspas": "(((( j center nurse cat dis ) OR ( i cent nerve c disch ))) OR ( j dental research systems di ))~".
• Se adicionar um carácter universal pode recuperar variações da palavra pesquisada: (((( j center nurse cat dis ) OR ( i cent nerve c disch ))) OR ( j dental research systems di ))*.