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Coffman D DeJongh F Dubois GP Eigen G Hitlin DG Matthews CG Mincer A Richman J Weinstein AJ Wisniewski WJ Zhu Y Bolton T Bunnell KO Cassell RE Coward DH Kim PC Labs J Odian A Pitman D Schindler RH Toki W Wasserbaech S Drinkard JJ Gatto C Heusch CA Lockman WS Scarlatella M Sadrozinski HF Schalk TL Seiden A Weseler S Eisenstein BI Freese T Gladding G Izen JM Stockdale IE Tripsas B Mallik U Wang MZ Brown J Burnett TH Li AD Mir R Mockett PM Nemati B Parrish L Willutzki H 《Physical review D: Particles and fields》1992,45(7):2196-2211
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Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems. The photoresolution of the enantiomers of helical-shaped, sterically overcrowded alkene 1 with circularly polarized light and the transduction of the stereochemical information by triggering the helical arrangement of a large collection of achiral molecules in a twisted nematic liquid crystalline phase (2) are examples of control and amplification of chirality. 相似文献
54.
Adler J Bai Z Blaylock GT Bolton T Brient J Browder TE Brown JS Bunnell KO Burchell M Burnett TH Cassell RE Coffman D Cook V Coward DH DeJongh F Dorfan DE Drinkard J Dubois GP Eigen G Einsweiler KF Eisenstein BI Freese T Gatto C Gladding G Grab C Hauser J Heusch CA Hitlin DG Izen JM Kim PC Köpke L Labs J Li A Lockman WS Mallik U Matthews CG Mincer AI Mir R Mockett PM Nemati B Odian A Parrish L Partridge R Pitman D Plaetzer SA Richman JD Sadrozinski HF Scarlatella M Schalk TL Schindler RH 《Physical review letters》1990,64(22):2615-2618
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Numerous organic and inorganic laboratory standards were gathered from nine European and North American laboratories and were analyzed for their delta(18)O values with a new on-line high temperature pyrolysis system that was calibrated using Vienna standard mean ocean water (VSMOW) and standard light Antartic precipitation (SLAP) internationally distributed reference water samples. Especially for organic materials, discrepancies between reported and measured values were high, ranging up to 2 per thousand. The reasons for these discrepancies are discussed and the need for an exact and reliable calibration of existing reference materials, as well as for the establishment of additional organic and inorganic reference materials is stressed. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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L. Bertanza A. Bigi P. Calafiura M. Calvetti R. Carosi M. C. Carrozza R. Casali C. Cerri R. Fantechi I. Mannelli V. M. Marzulli A. Nappi G. M. Pierazzini L. Tassi G. D. Barr P. Buchholz D. Coward D. Cundy N. Doble L. Gatignon P. Grafström R. Hagelberg H. Wahl K. J. Peach T. Beier H. Blümer R. Heinz K. Kleinknecht B. Panzer-Steinde B. Renk H. Rohrer J. Scheidt J. Staeck A. Wagner E. Augé D. Fournier L. Iconomidou-Fayard O. Perdereau A. C. Schaffer L. Serin M. Holder A. Kreutz R. Werthenbach 《Zeitschrift fur Physik C Particles and Fields》1997,73(4):629-632
A precision measurement of the K S mean lifetime has been performed by comparing, in the same experimental setup, the distributions of two-pion decays of neutral kaons produced by high energy proton-beryllium interactions in two targets at a relative distance variable between 112 and 160 m. The value obtained combining the results from π+π? and π0π0 decays is τs = (0.8971 ± 0.0021) 10?10 s. 相似文献
58.
A review is presented of the calculation of photoionization spectra, particularly in the spectral range where electron autoionization of diatomic molecules takes place. In addition to some interesting results obtained over years that compare favourably with experiment, the emphasis here is put on the relation between the methods developed for the calculation of observables associated with the continuum energy spectrum of the electrons and the Alchemy system of programs. This system of programs serves as a basis for initial and intermediate calculations. The examples presented show that diatomic molecules not only in gas phase but also oriented in space or physisorbed at surfaces may be studied readily. 相似文献
59.
Since 2-amino-5-benzamidopropyl-6-methyl-4-pyrimidinol (VII) was a reasonably good reversible inhibitor of dihydrofolic reductase, the benzamido group was substituted with p-bromomethyl (XVIIa), m-bromomethyl (XVIIIa), and p-bromoacetyl (XIXa) groups; these compounds, and the corresponding 6-phenylpyrimidines, were synthesized from the proper 2-amino-5-aminopropyl-4-pyrimidinol (V) by devising methods that were compatible with the high reactivity of the halogen. Compounds XVII-XIX showed in-activation of dihydrofolic reductase; the fact that p-nitrobenzyl bromide inactivated the enzyme as rapidly as XVII and XVIII and phenacyl bromide inactivated the enzyme as rapidly as XIX indicated that these inactivations proceeded by a random bimolecular mechanism and not the desired active-site-directed mechanism. 相似文献
60.
[formula: see text] An enantiomerically pure bicyclic lactam proved to be an excellent substrate for electrophilic difluorination using N-fluorobenzenesulfonimide. The resulting difluorinated lactam can be easily converted into L-4,4-difluoroglutamic acid. To the best of our knowledge, this is the first example of a synthetically useful electrophilic difluorination of an unactivated lactam. 相似文献