Talvez deva tentar algumas variações de ortografia:
aircraft observations » direct observations (Expandir a Pesquisa), first observations (Expandir a Pesquisa), airborne observations (Expandir a Pesquisa)
observations system » observation system (Expandir a Pesquisa), observational system (Expandir a Pesquisa), observation systems (Expandir a Pesquisa)
system delay » system data (Expandir a Pesquisa), system der (Expandir a Pesquisa)
mental nerve » ventral nerve (Expandir a Pesquisa), central nerve (Expandir a Pesquisa)
22 aircraft » _ aircraft (Expandir a Pesquisa), 1 aircraft (Expandir a Pesquisa), 16 aircraft (Expandir a Pesquisa)
nerve cyst » nerve cystic (Expandir a Pesquisa), nerve case (Expandir a Pesquisa), nerve cat (Expandir a Pesquisa)
j mental » j mengual (Expandir a Pesquisa), j mena (Expandir a Pesquisa), j mehta (Expandir a Pesquisa)

You can also try:

• Europeana
• Digital Public Library of America
• CORE

Pode obter mais resultados ajustando a pesquisa.

• Se usar operadores Booleanos, por favor insira-os com letras MAIÚSCULAS: (( 22 aircraft observations system delay ) OR ( j mental nerve cyst _ ))~.
• Se adicionar um carácter universal pode recuperar variações da palavra pesquisada: (( 22 aircraft observations system delay ) or ( j mental nerve cyst _ ))*.