Unfortunately not.
to get the national pokedex you have to complete the shiono pokedex, then go to Prof. Birch's lab and their should be a cut scence where Prof. Birch comes and gives you the national pokedex.
you have to trade them from a game that has the national dex.
it's immpossable to get the national dex without seeing all 150 sinnoh Pokemon (this doesn't include manaphy, which is just extra if u see it)
The sinnoh dex has 210 pokemon, and the national dex has 493 pokemon. It has an entire 664 pokemon (I think)
Pokemon 1-150 national dex 1-386
Sinnoh Dex #152 -- Rotom National Dex #152 -- Chikorita
Pokemon Platinum has two different Pokedexes: the Sinnoh dex and the National Pokedex. In the Sinnoh dex, #152 is Rotom. In the National Pokedex, it's Chikorita.
you have to catch 151 Pokemon and then go to professor oak . He will ask you to take one Pokemon from the three Pokemon , the Pokemon are chikorita , cyndaquil and totdile.
There is no number 152 in the Sinnoh Pokedex however number 152 in the National Pokedex is Chikorita.
to get the national pokedex you have to complete the shiono pokedex, then go to Prof. Birch's lab and their should be a cut scence where Prof. Birch comes and gives you the national pokedex.
you have to trade them from a game that has the national dex.
Chikorita, its the grass type starter Pokemon for the Johto Region.
You can have the national dex, but you can't complete it without transferring Pokemon from GBA games. Therefore, it's impossible to complete the national dex using only a DSi (without cheating with an Action Replay.)
it's immpossable to get the national dex without seeing all 150 sinnoh Pokemon (this doesn't include manaphy, which is just extra if u see it)
The last Pokemon on the national dex is Arceus.
The only way to get chikorita is to migrate it from Emerald or XD to the Gamepak, though you need the national dex and you need to go to pal park.
NO, that is impossible. You need to trade and migrate Pokemon to complete the national dex.