Talvez deva tentar algumas variações de ortografia:
research systems » research synthesis (Expandir a Pesquisa)
mental research » dental research (Expandir a Pesquisa), central research (Expandir a Pesquisa), neonatal research (Expandir a Pesquisa)
center nurse » center nurses (Expandir a Pesquisa), better nurse (Expandir a Pesquisa), letter nurse (Expandir a Pesquisa)
cento nerve » bent nerve (Expandir a Pesquisa), central nerve (Expandir a Pesquisa), mental nerve (Expandir a Pesquisa)
systems di » systems doi (Expandir a Pesquisa), systems do (Expandir a Pesquisa), systems de (Expandir a Pesquisa)
nurse can » nurses can (Expandir a Pesquisa), nurse care (Expandir a Pesquisa), nurse case (Expandir a Pesquisa)
j center » j centner (Expandir a Pesquisa), 2 center (Expandir a Pesquisa), 19 center (Expandir a Pesquisa)
can diet » can direct (Expandir a Pesquisa)
j mental » j mengual (Expandir a Pesquisa), j mena (Expandir a Pesquisa), j mehta (Expandir a Pesquisa)
i cento » a cento (Expandir a Pesquisa), i censo (Expandir a Pesquisa), i centeno (Expandir a Pesquisa)
nerve c » nerve cn (Expandir a Pesquisa), nerve co (Expandir a Pesquisa), nerve ct (Expandir a Pesquisa)
c dis » c dias (Expandir a Pesquisa), c disc (Expandir a Pesquisa), c dos (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 can diet ) OR ( i cento nerve c dis ))) OR ( j mental research systems di ))~".
• Se adicionar um carácter universal pode recuperar variações da palavra pesquisada: (((( j center nurse can diet ) OR ( i cento nerve c dis ))) OR ( j mental research systems di ))*.