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排序方式: 共有168条查询结果,搜索用时 15 毫秒
61.
62.
Christian Marquardt Oliver Hegen Matthias Hautmann Dr. Gábor Balázs Dr. Michael Bodensteiner Dr. Alexander V. Virovets Prof. Dr. Alexey Y. Timoshkin Prof. Dr. Manfred Scheer 《Angewandte Chemie (International ed. in English)》2015,54(44):13122-13125
The synthesis of the Lewis base stabilized monomeric parent compound of stibanylboranes, “H2Sb? BH2”, is reported. Through a salt metathesis route, the silyl‐substituted compounds (Me3Si)2Sb? BH2?LB (LB=NMe3, NHCMe) were synthesized as representatives of derivatives with a Sb? B σ bond. Under very mild conditions, they could be transformed into the target compounds Me3N?H2B? HSb? BH2?NMe3 and H2Sb? BH2?NHCMe, respectively. The products were characterized by X‐ray structure analysis, NMR spectroscopy, IR spectroscopy, and mass spectrometry. DFT calculations give further insight into the stability and bonding of these unique compounds. 相似文献
63.
Jung JE Pierson NA Marquardt A Scheffner M Przybylski M Clemmer DE 《Journal of the American Society for Mass Spectrometry》2011,22(8):1463-1471
Modification of ubiquitin, a key cellular regulatory polypeptide of 76 amino acids, to polyubiquitin conjugates by lysine-specific
isopeptide linkage at one of its seven lysine residues has been recognized as a central pathway determining its biochemical
properties and cellular functions. Structural details and differences of distinct lysine-isopeptidyl ubiquitin conjugates
that reflect their different functions and reactivities, however, are only partially understood. Ion mobility spectrometry
(IMS) combined with mass spectrometry (MS) has recently emerged as a powerful tool for probing conformations and topology
involved in protein interactions by an electric field-driven separation of polypeptide ions through a drift gas. Here we report
the conformational characterization and differentiation of Lys63- and Lys48-linked ubiquitin conjugates by IMS–MS. Lys63-
and Lys48-linked di-ubiquitin conjugates were prepared by recombinant bacterial expression and by chemical synthesis using
a specific chemical ligation strategy, and characterized by high-resolution Fourier transform ion cyclotron resonance mass
spectrometry, circular dichroism spectroscopy, and molecular modeling. IMS–MS was found to be an effective tool for the identification
of structural differences of ubiquitin complexes in the gas phase. The comparison of collision cross-sections of Lys63- and
Lys48-linked di-ubiquitin conjugates showed a more elongated conformation of Lys63-linked di-ubiquitin. In contrast, the Lys48-linked
di-ubiquitin conjugate showed a more compact conformation. The IMS-MS results are consistent with published structural data
and a comparative molecular modeling study of the Lys63- and Lys48-linked conjugates. The results presented here suggest IMS
techniques can provide information that complements MS measurements in differentiating higher-order polyubiquitins and other
isomeric protein linkages. 相似文献
64.
Gerd Kaupp Jens Schmeyers Michael Haak Thorsten Marquardt Andreas Herrmann 《Molecular Crystals and Liquid Crystals》2013,570(1-2):315-337
Abstract Organic solid-state reactions are probed with the atomic force microscope (AFM). In all cases phase rebuilding gives rise to characteristic submicroscopic features which change in shape due to phase transformation in later stages of the chemical reaction. Photo-(E/Z)-isomerization of olefin 1 occurs in the crystal, photodimerization of 9-chloroanthracene 3 is used as a probe for characterizing the luminosity distribution of SNOM-tips. Gas/solid imbibition in chiral host 5 proceeds enantiospecifically. Histidine crystals form the dihydrochloride with HC1, ammonia and methylamine react face-selectively with crystalline adipic acid 8, furane-2-carboxylic acid 10 and 2-mercaptobenzothiazole 12. Crystals of olefin 14 add chlorine. Solid-state diazotations and subsequent transformations of the solid diazonium nitrates into triazenes occur quantitatively. Solid/solid pinacol- and benzilic acid rearrangements are probed with the AFM. The features formed by long range molecular movements relate to the crystal packing and are thus different on different faces. Correlations with X-ray structural data are demonstrated. All reactions proceed to completion on a preparative scale and do not produce wastes as do their less selective counterparts if performed in solution. 相似文献
65.
We analyze the nonlinear dynamics of a high-finesse optical cavity in which one mirror is mounted on a flexible mechanical element. We find that this system is governed by an array of dynamical attractors, which arise from phase locking between the mechanical oscillations of the mirror and the ringing of the light intensity in the cavity. We develop an analytical theory to map out the diagram of attractors in parameter space, derive the slow amplitude dynamics of the system, including thermal fluctuations, and suggest a scheme for exploiting the dynamical multistability in the measurement of small displacements. 相似文献
66.
Nidhu L. Banik Boris Brendebach Christian M. Marquardt 《Journal of Radioanalytical and Nuclear Chemistry》2014,300(1):177-183
The speciation of redox sensitive trivalent actinides Pu(III), Np(III), and U(III) has been studied in aqueous solution. The redox preparation, stabilization, and speciation of these trivalent actinides in aqueous systems are discussed here. The reductants investigated were rongalite, hydroxylamine hydrochloride, and acetohydroxamic acid and the An(III) species have been characterized by UV–Vis and XANES spectroscopy. The results show that the effectiveness of stabilization decreases generally in the order Pu(III) > Np(III) > U(III) and that the effectiveness of each reducing agent depends on the experimental conditions. More than 80 % of Pu(III) aquo species have been stabilized up to pH 5.5, whereas the Np(III) aquo ion could be stabilized in a pH range 0–2.5, and U(III) aquo ion is sufficiently stable at pH 1.0 and below over time periods suitable for experiments. However, this study gives a basis for the characterisation of the trivalent lighter actinides involved in complexation, sorption, and solid formation reactions in the future. 相似文献
67.
Quarles Gregory J. Rosenbaum Annette Abella Isaac D. Marquardt Charles L. Esterowitz Leon 《Optical and Quantum Electronics》1990,22(1):S141-S152
Utilizing the results of Cr3+ → Tm3+ transfer efficiency studies, we have demonstrated that yttrium aluminium garnet (YAG) is the preferred host for room-temperature, flashlamp-pumped solid-state lasers operating in the 2.0 µm spectral range. We report data on two different sensitizer-activator combinations in YAG and yttrium scandium gallium garnet (YSGG) laser materials: one is doped with Cr:Tm:Ho and operates on the Ho3+5I7 →5I8 transition at 2.097 µm; the other is doped only with Cr:Tm, which lases on the Tm3+3F4 →3H6 transition at 2.014 µm. We have achieved a slope efficiency of 5.1% with the Cr:Tm:Ho:YAG laser, which is the highest slope efficiency yet reported for a room-temperature, flashlamp-pumped, 2 µm solid-state laser. We have measured thresholds as low as 38 J and output energies >1.5 J for that system. We also report the first room-temperature operation of an efficient flashlamp-pumped Cr:Tm:YAG laser at 2.014 µm. Thresholds as low as 43 J, output energies exceeding 2 J, and slope efficiencies as high as 4.5% have been achieved. This is an order of magnitude higher than the efficiency previously reported for a 2.01 µm Cr:Tm:YAG laser operated at cryogenic temperatures. These two efficient 2 µm laser systems (Cr:Tm:Ho:YAG and Cr:Tm:YAG) are discussed in terms of their potential for Q-switched operation. 相似文献
68.
69.
L. Asch B. D. Dunlap R. Marquardt W. Potzel F. J. Litterst G. D. Werner F. Weigel J. C. Spirlet G. M. Kalvius 《Hyperfine Interactions》1988,40(1-4):279-282
Mössbauer spectra of hexavalent neptunyls X2(NpO2)Cl4 and X4(NpO2)(CO3)3 with X=Na, K, Cs, (NH4) and [C2H5)4N] are discussed and compared to EPR data. In cases where reliable values of hyperfine parameters can be extracted, the Mössbauer spectra give fine details of bonding structure. It is found that the O–Np–O bond is not linear and that exchanging the cation results in small but definite changes.Work supported by the Bundesministerium für Forschung und Technologie and the U.S. Department of Energydeceased 相似文献
70.
Arylboronate esters bearing a pendant Michael-type acceptor olefin or acetylene linkage undergo transmetalation with a rhodium-based catalytic complex to generate a functionalized organorhodium intermediate which can cyclize onto nonterminal acetylenes in good to excellent yields. The catalytic system involves the use of electron-rich, sterically bulky ligands as tri-tert-butylphosphonium tetrafluoroborate stabilizing the organorhodium intermediates and reduces the incidence of protodeboronation in aqueous media. 相似文献