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排序方式: 共有128条查询结果,搜索用时 31 毫秒
1.
During direct liquid introduction (DLI) liquid chromatography-mass spectrometry (LC-MS), the detectability of acetone is shown to be predictable, based on consideration of the gas-phase acidities and basicities of solvents methanol and acetonitrile and modifiers formic acid and ammonium formate. Consequently, ion formation in DLI LC-MS resembles gas-phase chemical ionization processes; since the order of acidities is altered in solution, solution ionization must be much less important than gas-phase. Ion populations could be predicted on the basis of gas-phase proton affinities and acidities: acetone could be detected in all solvent mixture by positive ions, but it was not readily detected by negative ions when acid was also present. In solvents without additives it was always detected. 相似文献
2.
Odile Burlet Chao-Yuh Yang Simon J. Gaskell 《Journal of the American Society for Mass Spectrometry》1992,3(4):337-344
Oxidation of cysteine residues to cysteic acids in C-terminal arginine-eontaining peptides (such as those derived by tryptic digestion of proteins) strongly promotes the formation of multiple members of the Y? series of fragment ions following low energy collision-activated decomposition (CAD) of the protonated peptides, Removal of the arginine residue abolishes the effect, which is also attenuated by conversion of the arginine to dimethylpyrim-idylornithine. The data indicate the importance of an intraionic interaction between the cysteic acid and arginine side-chains. Low energy CAD of peptides which include cysteic acid and histidine residues, also provides evidence for intraionic interactions. It is proposed that these findings are consistent with the general hypothesis that an increased heterogeneity (with respect to location of charge) of the protonated peptide precursor ion population is beneficial to the generation of a high yield of product ions via several charge-directed, low energy fragmentation pathways. Furthermore, these data emphasize the significance of gas-phase conformations of protonated peptides in determining fragmentation pathways. 相似文献
3.
4.
Jiang X Arrington J Benmokhtar F Camsonne A Chen JP Choi S Chudakov E Cusanno F Deur A Dutta D Garibaldi F Gaskell D Gayou O Gilman R Glashauser C Hamilton D Hansen O Higinbotham DW Holt RJ de Jager CW Jones MK Kaufman LJ Kinney ER Kramer K Lagamba L de Leo R Lerose J Lhuillier D Lindgren R Liyanage N McCormick K Meziani ZE Michaels R Moffit B Monaghan P Nanda S Paschke KD Perdrisat CF Punjabi V Qattan IA Ransome RD Reimer PE Reitz B Saha A Schulte EC Sheyor R Slifer K Solvignon P Sulkosky V 《Physical review letters》2007,98(18):182302
We measured the angular dependence of the three recoil-proton polarization components in two-body photodisintegration of the deuteron at a photon energy of 2 GeV. These new data provide a benchmark for calculations based on quantum chromodynamics. Two of the five existing models have made predictions of polarization observables. Both explain the longitudinal polarization transfer satisfactorily. Transverse polarizations are not well described, but suggest isovector dominance. 相似文献
5.
The coupling of the atomic velocity to the transverse current is investigated in a model of liquid rubidium by analyzing the frequency spectra associated with the velocity autocorrelation function in terms of the current correlation functions. 相似文献
6.
W R Mathews T A Runge P E Haroldsen S J Gaskell 《Rapid communications in mass spectrometry : RCM》1989,3(9):314-319
Fast-atom bombardment mass spectrometry of a synthetic renin substrate decapeptide (Pro-His-Pro-Phe-His-Leu-Val-Ile-His-D-Lys) indicated the presence of several side-products, including a component 12 Da higher in mass. Low-energy collisionally activated decomposition analyses were performed using a hybrid tandem instrument and demonstrated that the heavier side product had two components, in which the structural modification was either at the N- or the C-terminus. Additional analyses of the N-acetyl derivative indicated that for each component the structural modification blocked a site of N-acetylation. It is suggested that the formation of these side products is attributable to the generation of formaldehyde, during removal of the histidine protecting group (benzyloxymethyl), which reacts with the N-terminus of the peptide to give an imidazolidinone structure or with the D-lysine epsilon-amine group to yield an imine. While the precise genesis of the side-products remains speculative, it is clear that the combined strategy of derivatization and tandem mass spectrometry has allowed structural conclusions concerning individual components of an isobaric mixture. 相似文献
7.
Qian X Allada K Dutta C Huang J Katich J Wang Y Zhang Y Aniol K Annand JR Averett T Benmokhtar F Bertozzi W Bradshaw PC Bosted P Camsonne A Canan M Cates GD Chen C Chen JP Chen W Chirapatpimol K Chudakov E Cisbani E Cornejo JC Cusanno F Dalton MM Deconinck W de Jager CW De Leo R Deng X Deur A Ding H Dolph PA Dutta D El Fassi L Frullani S Gao H Garibaldi F Gaskell D Gilad S Gilman R Glamazdin O Golge S Guo L Hamilton D Hansen O Higinbotham DW Holmstrom T Huang M Ibrahim HF Iodice M Jiang X Jin G 《Physical review letters》2011,107(7):072003
We report the first measurement of target single spin asymmetries in the semi-inclusive (3)He(e,e'π(±))X reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.16 < x < 0.35 with 1.4 < Q(2) < 2.7 GeV(2). The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The π(±) Collins moments for (3)He are consistent with zero, except for the π(+) moment at x = 0.35, which deviates from zero by 2.3σ. While the π(-) Sivers moments are consistent with zero, the π(+) Sivers moments favor negative values. The neutron results were extracted using the nucleon effective polarization and measured cross section ratios of proton to (3)He, and are largely consistent with the predictions of phenomenological fits and quark model calculations. 相似文献
8.
9.
Navasardyan T Adams GS Ahmidouch A Angelescu T Arrington J Asaturyan R Baker OK Benmouna N Bertoncini C Blok HP Boeglin WU Bosted PE Breuer H Christy ME Connell SH Cui Y Dalton MM Danagoulian S Day D Dodario T Dunne JA Dutta D El Khayari N Ent R Fenker HC Frolov VV Gan L Gaskell D Hafidi K Hinton W Holt RJ Horn T Huber GM Hungerford E Jiang X Jones M Joo K Kalantarians N Kelly JJ Keppel CE Kubarovski V Li Y Liang Y Malace S Markowitz P McGrath E McKee P Meekins DG Mkrtchyan H Moziak B 《Physical review letters》2007,98(2):022001
A large data set of charged-pion (pi+/-) electroproduction from both hydrogen and deuterium targets has been obtained spanning the low-energy residual-mass region. These data conclusively show the onset of the quark-hadron duality phenomenon, as predicted for high-energy hadron electroproduction. We construct several ratios from these data to exhibit the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark-->pion production mechanisms. 相似文献
10.
Park KD Kim D Reamtong O Eyers C Gaskell SJ Liu R Kohn H 《Journal of the American Chemical Society》2011,133(29):11320-11330
We have advanced a useful strategy to elucidate binding partners of ligands (drugs) with modest binding affinity. Key to this strategy is attaching to the ligand an affinity bait (AB) and a chemical reporter (CR) group, where the AB irreversibly attaches the ligand to the receptor upon binding and the CR group is employed for receptor detection and isolation. We have tested this AB&CR strategy using lacosamide ((R)-1), a low-molecular-weight antiepileptic drug. We demonstrate that using a (R)-lacosamide AB&CR agent ((R)-2) 14-3-3 ζ in rodent brain soluble lysates is preferentially adducted, adduction is stereospecific with respect to the AB&CR agent, and adduction depends upon the presence of endogenous levels of the small molecule metabolite xanthine. Substitution of lacosamide AB agent ((R)-5) for (R)-2 led to the identification of the 14-3-3 ζ adduction site (K120) by mass spectrometry. Competition experiments using increasing amounts of (R)-1 in the presence of (R)-2 demonstrated that (R)-1 binds at or near the (R)-2 modification site on 14-3-3 ζ. Structure-activity studies of xanthine derivatives provided information concerning the likely binding interaction between this metabolite and recombinant 14-3-3 ζ. Documentation of the 14-3-3 ζ-xanthine interaction was obtained with isothermal calorimetry using xanthine and the xanthine analogue 1,7-dimethylxanthine. 相似文献