ACROSS

 1 Use a keyboard
 5 Ursa, to us
 9 Cad
10 Diderot's dream
11 Authorized to act
13 Airships
14 "All ___ is a Miracle" 
   (Mike & the Mechanics song)
15 Freudian self
16 Encircles
17 Tyrannosaurus ___
18 Nuclear device
23 Dickens in disguise
25 "Love Story" author
26 Nest egg component
27 Move and run?
29 Anger
30 Noted Chicago Symphony conductor
31 Tags
32 Fortitude
33 Long. partner
36 Mountaintops
41 "Gross!"
42 Smithy's need
43 African plain
45 Branch of chemistry
46 Lyric poems
47 Sticky stuff
48 Donkey and elephant delineator
49 Brain activity monitors

DOWN

 1 "Cutting a woman in thirds," 
    to magicians
 2 Inhabitant of Sheba, today
 3 Salt's neighbor
 4 Married secretly
 5 Belgian chansonnier
 6 More chilling
 7 Retaliate
 8 Boston sluggers
12 Unites
18 E-mail letters, usually (Abbr.)
19 Vandyke, for one
20 Storytime meanies
21 Chart
22 Bestow approval on
23 Holy book
24 Speechify
28 Tyke
34 To-do list
35 Spasms
36 Sharp pain
37 Put in gear
38 Street crosser
39 Passing bad checks
40 Oil spills
44 Formerly, formerly