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51.
A preparation of 4,4-diphenylcyclohexanol 2 is described from benzoin in five synthetic steps. The process uses readily available reagents and is suitable for manufacturing. 相似文献
52.
John Fountain 《Semigroup Forum》2010,81(1):2-25
We give an account of some of the highlights of the mathematical research of Douglas Munn. 相似文献
53.
Fast ignition by intense laser-accelerated proton beams 总被引:12,自引:0,他引:12
Roth M Cowan TE Key MH Hatchett SP Brown C Fountain W Johnson J Pennington DM Snavely RA Wilks SC Yasuike K Ruhl H Pegoraro F Bulanov SV Campbell EM Perry MD Powell H 《Physical review letters》2001,86(3):436-439
The concept of fast ignition with inertial confinement fusion (ICF) is a way to reduce the energy required for ignition and burn and to maximize the gain produced by a single implosion. Based on recent experimental findings at the PETAWATT laser at Lawrence Livermore National Laboratory, an intense proton beam to achieve fast ignition is proposed. It is produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF. 相似文献
54.
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56.
Ion-pair reversed-phase high-performance liquid chromatography (IP-RP-HPLC) was utilized in tandem with negative-ion electrospray ionization time-of-flight mass spectrometry (ESI-TOFMS) for the analysis of native and chemically modified oligonucleotides. Separation was performed on a 1.0 x 50 mm column packed with porous C(18) sorbent with a particle size of 2.5 microm and an average pore diameter of 140 A. A method was developed which maximizes both chromatographic separation and mass spectrometric sensitivity using an optimized buffer system containing triethylamine and 1,1,1,3,3,3-hexafluoro-2-propanol with a methanol gradient. The ESI-TOFMS tuning parameters were also optimized in order to minimize in-source fragmentation and achieve the best sensitivity. Analyses of native, phosphorothioate, and guanine-rich oligonucleotides were performed by LC/MS. Detection limits were at sub-picomole levels with an average mass accuracy of 125 ppm. The described method allowed for the LC/MS analysis of oligonucleotides up to 110mer in length with little alkali cation adduction. Since sensitive detection of oligonucleotides was achieved with ultraviolet (UV) detection, we utilized a combination of UV-MS for quantitation (UV) and characterization (MS) of oligonucleotides and their failure sequence fragments/metabolites. 相似文献
57.
Sophia J. Yu Michael L. Gross Kenneth R. Fountain 《Journal of the American Society for Mass Spectrometry》1993,4(2):117-124
The distonic radical cation C5H5N+?·CH2 can be generated by the reactions of neutral pyridine with the radical cations of cyclopropane, ethylene oxide, and ketene, as well as with the [C3H6]+ ion from fragmentation of tetrahydrofuran. The distonic product ion can be distinguished from isomeric methylpyridine radical cations because the former gives characteristic [M?CH2]+, [M ? CH2NCH]+, and a doubly charged ion, all of which are produced on collisional activation. Furthermore, the distonic species completely transfers CH2 + to more nucleophilic, substituted pyridines. These properties are all consistent with the assigned distonic structure. Another distonic isomer, the (3-methylene) pyridinium ion, can be distinguished from the (1-methylene)pyridinium ion on the basis of their different fragmentation behaviors. The latter ion exhibits higher stability (lower reactivity) than the prototypal [·CH2NH3 +], making available a distonic species whose bimolecular reactivity can be readily investigated. 相似文献
58.
Yeong Choi Heewon Lee Scott T. Fountain David M. Lubman 《Journal of the American Society for Mass Spectrometry》1994,5(2):106-112
Trace quantities of laser ablated organic polymers were analyzed by using commercial capillary column gas chromatography/mass spectrometry; the instrument was modified so that the iaser ablation products could be introduced into the capillary column directly and the constituents of each peak in the chromatogram were identified by using a mass spectrometer. The present study takes advantage of the selective ion monitoring mode for significantly improving the sensitivity of the mass spectrometer as a detector, which is critical in anatyzing the trace quantities and confirming the presence or absence of the species of interest in laser ablated polymers. The initial composition of the laser ablated polymers was obtained by using an electron impact reflectron time-of-flight mass spectrometer and the possible structure of the fragments observed in the spectra was proposed based on the structure of the polymers. 相似文献
59.
JUDYTA CIELECKA‐PIONTEK PRZEMYSŁAW ZALEWSKI PIOTR GARBACKI EWELINA JURA ALICJA TALACZYŃSKA 《国际化学动力学杂志》2014,46(8):443-450
The kinetic and thermodynamic analysis of biapenem degradation was conducted during acid–base hydrolysis, under the influence of buffer components and in the solid state at increased temperature (dry air) and relative air humidity (RH > 50%). The effects of the initial concentration of biapenem and the formation of degradation products on its stability were investigated. 相似文献
60.
Kenneth J. Fountain Uwe D. NeueEric S. Grumbach Diane M. Diehl 《Journal of chromatography. A》2009,1216(32):5979-5988
The effects of extra-column band spreading, LC system operating pressure, and separation temperature were investigated for sub-2-μm particle columns using both a conventional HPLC system as well as a UPLC® system. The contributions of both volume- and time-based extra-column effects were analyzed in detail. In addition, the performance difference between columns containing 2.5 and 1.7-μm particles (same stationary phase) was studied. The performance of these columns was compared using a conventional HPLC system and a low dead volume UPLC system capable of routine operation up to 1000 bar. The system contribution to band spreading and the pressure limitations of the conventional HPLC system were found to be the main difficulties that prevented acceptable performance of the sub-2-μm particle columns. Finally, an increase in operating temperature needs to be accompanied by an increase in flow rate to prevent a loss of separation performance. Thus, at a fixed column length, an increase in temperature is not a substitute for the need for very high operating pressures. 相似文献