<s>
PubMed	B-Library
is	O
a	O
free	O
search	B-Library
engine	I-Library
accessing	O
primarily	O
the	O
MEDLINE	O
database	B-Library
of	O
references	O
and	O
abstracts	O
on	O
life	O
sciences	O
and	O
biomedical	O
topics	O
.	O
</s>
<s>
The	O
United	O
States	O
National	O
Library	O
of	O
Medicine	O
(	O
NLM	O
)	O
at	O
the	O
National	O
Institutes	O
of	O
Health	O
maintain	O
the	O
database	B-Library
as	O
part	O
of	O
the	O
Entrez	O
system	O
of	O
information	B-Library
retrieval	I-Library
.	O
</s>
<s>
From	O
1971	O
to	O
1997	O
,	O
online	O
access	O
to	O
the	O
MEDLINE	O
database	B-Library
had	O
been	O
primarily	O
through	O
institutional	O
facilities	O
,	O
such	O
as	O
university	O
libraries	O
.	O
</s>
<s>
PubMed	B-Library
,	O
first	O
released	O
in	O
January	O
1996	O
,	O
ushered	O
in	O
the	O
era	O
of	O
private	O
,	O
free	O
,	O
home	O
-	O
and	O
office-based	O
MEDLINE	O
searching	O
.	O
</s>
<s>
The	O
PubMed	B-Library
system	O
was	O
offered	O
free	O
to	O
the	O
public	O
starting	O
in	O
June	O
1997	O
.	O
</s>
<s>
In	O
addition	O
to	O
MEDLINE	O
,	O
PubMed	B-Library
provides	O
access	O
to	O
:	O
</s>
<s>
Many	O
PubMed	B-Library
records	O
contain	O
links	O
to	O
full	O
text	O
articles	O
,	O
some	O
of	O
which	O
are	O
freely	O
available	O
,	O
often	O
in	O
PubMed	B-Library
Central	O
and	O
local	O
mirrors	O
,	O
such	O
as	O
Europe	B-Application
PubMed	I-Application
Central	I-Application
.	O
</s>
<s>
Information	O
about	O
the	O
journals	O
indexed	O
in	O
MEDLINE	O
,	O
and	O
available	O
through	O
PubMed	B-Library
,	O
is	O
found	O
in	O
the	O
NLM	O
Catalog	O
.	O
</s>
<s>
,	O
PubMed	B-Library
has	O
more	O
than	O
30	O
million	O
citations	O
and	O
abstracts	O
dating	O
back	O
to	O
1966	O
,	O
selectively	O
to	O
the	O
year	O
1865	O
,	O
and	O
very	O
selectively	O
to	O
1809	O
.	O
,	O
20	O
million	O
of	O
PubMed	B-Library
's	O
records	O
are	O
listed	O
with	O
their	O
abstracts	O
,	O
and	O
21.5	O
million	O
records	O
have	O
links	O
to	O
full-text	O
versions	O
(	O
of	O
which	O
7.5	O
million	O
articles	O
are	O
available	O
,	O
full-text	O
for	O
free	O
)	O
.	O
</s>
<s>
Approximately	O
12%	O
of	O
the	O
records	O
in	O
PubMed	B-Library
correspond	O
to	O
cancer-related	O
entries	O
,	O
which	O
have	O
grown	O
from	O
6%	O
in	O
the	O
1950s	O
to	O
16%	O
in	O
2016	O
.	O
</s>
<s>
In	O
2016	O
,	O
NLM	O
changed	O
the	O
indexing	O
system	O
so	O
that	O
publishers	O
are	O
able	O
to	O
directly	O
correct	O
typos	O
and	O
errors	O
in	O
PubMed	B-Library
indexed	O
articles	O
.	O
</s>
<s>
PubMed	B-Library
has	O
been	O
reported	O
to	O
include	O
some	O
articles	O
published	O
in	O
predatory	O
journals	O
.	O
</s>
<s>
MEDLINE	O
and	O
PubMed	B-Library
policies	O
for	O
the	O
selection	O
of	O
journals	O
for	O
database	B-Library
inclusion	O
are	O
slightly	O
different	O
.	O
</s>
<s>
Weaknesses	O
in	O
the	O
criteria	O
and	O
procedures	O
for	O
indexing	O
journals	O
in	O
PubMed	B-Library
Central	O
may	O
allow	O
publications	O
from	O
predatory	O
journals	O
to	O
leak	O
into	O
PubMed	B-Library
.	O
</s>
<s>
The	O
National	O
Library	O
of	O
Medicine	O
had	O
respond	O
that	O
individual	O
journal	O
articles	O
can	O
be	O
included	O
in	O
PMC	O
to	O
support	O
the	O
public	O
access	O
policies	O
of	O
research	O
funders	O
and	O
that	O
rigorous	O
policies	O
about	O
journals	O
and	O
publishers	O
ensure	O
integrity	O
of	O
NLM	O
literature	B-Library
databases	I-Library
.	O
</s>
<s>
A	O
new	O
PubMed	B-Library
interface	O
was	O
launched	O
in	O
October	O
2009	O
and	O
encouraged	O
the	O
use	O
of	O
such	O
quick	O
,	O
Google-like	O
search	O
formulations	O
;	O
they	O
have	O
also	O
been	O
described	O
as	O
'	O
telegram	O
 '	O
searches	O
.	O
</s>
<s>
The	O
PubMed	B-Library
website	O
design	O
and	O
domain	O
was	O
updated	O
in	O
January	O
2020	O
and	O
became	O
default	O
on	O
15	O
May	O
2020	O
,	O
with	O
the	O
updated	O
and	O
new	O
features	O
.	O
</s>
<s>
PubMed/MEDLINE	O
can	O
be	O
accessed	O
via	O
handheld	O
devices	O
,	O
using	O
for	O
instance	O
the	O
"	O
PICO	O
"	O
option	O
(	O
for	O
focused	O
clinical	O
questions	O
)	O
created	O
by	O
the	O
NLM	O
.	O
</s>
<s>
A	O
"	O
PubMed	B-Library
Mobile	O
"	O
option	O
,	O
providing	O
access	O
to	O
a	O
mobile	O
friendly	O
,	O
simplified	O
PubMed	B-Library
version	O
,	O
is	O
also	O
available	O
.	O
</s>
<s>
Simple	O
searches	O
on	O
PubMed	B-Library
can	O
be	O
carried	O
out	O
by	O
entering	O
key	O
aspects	O
of	O
a	O
subject	O
into	O
PubMed	B-Library
's	O
search	O
window	O
.	O
</s>
<s>
PubMed	B-Library
translates	O
this	O
initial	O
search	O
formulation	O
and	O
automatically	O
adds	O
field	O
names	O
,	O
relevant	O
MeSH	O
(	O
Medical	O
Subject	O
Headings	O
)	O
terms	O
,	O
synonyms	O
,	O
Boolean	O
operators	O
,	O
and	O
'	O
nests	O
 '	O
the	O
resulting	O
terms	O
appropriately	O
,	O
enhancing	O
the	O
search	O
formulation	O
significantly	O
,	O
in	O
particular	O
by	O
routinely	O
combining	O
(	O
using	O
the	O
OR	O
operator	O
)	O
textwords	O
and	O
MeSH	O
terms	O
.	O
</s>
<s>
The	O
examples	O
given	O
in	O
a	O
PubMed	B-Library
tutorial	O
demonstrate	O
how	O
this	O
automatic	O
process	O
works	O
:	O
</s>
<s>
For	O
optimal	O
searches	O
in	O
PubMed	B-Library
,	O
it	O
is	O
necessary	O
to	O
understand	O
its	O
core	O
component	O
,	O
MEDLINE	O
,	O
and	O
especially	O
of	O
the	O
MeSH	O
(	O
Medical	O
Subject	O
Headings	O
)	O
controlled	O
vocabulary	O
used	O
to	O
index	O
MEDLINE	O
articles	O
.	O
</s>
<s>
The	O
search	O
into	O
PubMed	B-Library
's	O
search	O
window	O
is	O
only	O
recommended	O
for	O
the	O
search	O
of	O
unequivocal	O
topics	O
or	O
new	O
interventions	O
that	O
do	O
not	O
yet	O
have	O
a	O
MeSH	O
heading	O
created	O
,	O
as	O
well	O
as	O
for	O
the	O
search	O
for	O
commercial	O
brands	O
of	O
medicines	O
and	O
proper	O
nouns	O
.	O
</s>
<s>
On	O
the	O
other	O
side	O
,	O
articles	O
more	O
recently	O
incorporated	O
into	O
the	O
database	B-Library
to	O
which	O
descriptors	O
have	O
not	O
yet	O
been	O
assigned	O
will	O
not	O
be	O
found	O
.	O
</s>
<s>
For	O
clinical	O
trials	O
,	O
PubMed	B-Library
extracts	O
trial	O
IDs	O
for	O
the	O
two	O
largest	O
trial	O
registries	O
:	O
ClinicalTrials.gov	O
(	O
NCT	O
identifier	O
)	O
and	O
the	O
International	O
Standard	O
Randomized	O
Controlled	O
Trial	O
Number	O
Register	O
(	O
IRCTN	O
identifier	O
)	O
.	O
</s>
