Python Join String to Produce Combinations For All Words in String

If my string is this: 'this is a string', how can I produce all possible combinations by joining each word with its neighboring word?

What this output would look like:

this is a string
thisis a string
thisisa string
thisisastring
this isa string
this isastring
this is astring

What I have tried:

s = 'this is a string'.split()    
for i, l in enumerate(s):
        ''.join(s[0:i])+' '.join(s[i:])

This produces:

'this is a string'
'thisis a string'
'thisisa string'
'thisisastring'

I realize I need to change the s[0:i] part because it's statically anchored at 0 but I don't know how to move to the next word is while still including this in the output.