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排序方式: 共有199条查询结果,搜索用时 0 毫秒
41.
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43.
Ji Zhang Peter G. Blazecka Joseph Bozelak Norman L. Colbry David C. Boyles Timothy T. Curran Paul Johnson Jacob B. Schwarz Mark Plummer Yun Huang Andrew J. Thorpe 《Tetrahedron letters》2009,50(11):1167-1177
A chiral β-amino acid containing three contiguous chiral centers was synthesized efficiently in 11 steps, employing enantio-enriched β-ketoester as a key intermediate, via stereoselective catalytic hydrogenation of the corresponding enamide. Stereoselective 1,4-addition of a methyl group and protonation were key to the preparation of the desired acid 12. Mild and efficient reaction conditions were applied to the enamine formation and protection to avoid epimerization at C-4 of compounds 13 and 14. The final compound was found to display potent affinity for the α2δ-protein that is a recognized drug target for the treatment of a variety of diseases. 相似文献
44.
Mixed valence in the lowest-energy metal-to-ligand charge-transfer excited state of di-(4-acetylpyridine)tetraammineruthenium(II) complexes is defined and analyzed. The excited state has two interchangeably equivalent ligands with different oxidation states. The electronic absorption band energies, selection rules, and bandwidths are analyzed quantitatively in terms of the signs and orientations of the transition dipole moments, sign and magnitude of the coupling, and resonance Raman analysis of displaced normal modes. 相似文献
45.
Gold nanoparticle synthesis in graft copolymer micelles 总被引:4,自引:0,他引:4
G. Carrot J. C. Valmalette C. J. G. Plummer S. M. Scholz J. Dutta H. Hofmann J. G. Hilborn 《Colloid and polymer science》1998,276(10):853-859
An amphiphilic poly(acrylic acid)/polystyrene graft copolymer (PAA-g-PS) has been used to form “nanoreactors” for the synthesis
of gold clusters. Such copolymers tend to form stable micelles in non-polar organic solvents where the poly(acrylic acid)
chains constitute the core, and the polystyrene chains, the shell. In the present study, the micellar structure of PAA-g-PS
in toluene has been demonstrated by dynamic light scattering and transmission electron microscopy (TEM).
The subsequent preparation of gold-graft copolymer composites involved the introduction of gold chloride (AuCl3), either in powder form or previously dissolved in ether, into the micellar cores of the PAA-g-PS in toluene. The gold salt
was then reduced by ultraviolet (UV) irradiation of the emulsion, or of dried cast films. TEM and ultraviolet-visible (UV/Vis)
spectroscopy were used to characterize the resulting composites. Gold particles of less than 5 nm in diameter were observed
in all cases, but the size distribution and the spatial arrangement of the clusters in the cast films were modified when diethyl
ether was used to introduce AuCl3 into the PAA-g-PS micellar cores. This was thought to be due to enhanced nucleation of the gold particles and partial disruption
of the micellar cores in the presence of diethyl ether.
Received: 21 January 1998 Accepted: 11 June 1998 相似文献
46.
Benjamin F. Plummer W. Gregory Reese William H. Watson Mariusz Krawiec 《Structural chemistry》1993,4(1):53-57
A molecular mechanics simulation of the structure of 7,14-dicarbonylethoxyacenaphth[l,2-k]fluoranthene,1, indicated a preferred geometry for the hindered substituents in which the carbonyl groups were constrained to an anti conformation because of the steric hindrance associated with the in-plane buttressing hydrogen atoms. X-ray crystallographic analysis of1 verifies the correctness of the computation. Compound1 and tetracyanoquinodimethane,2, form a charge transfer complex, and a crystal structure analysis shows a slightly offset, nearly parallel arrangement of the acceptor with the cloud of the donor. The interplanar distance of 3.45 Å between acceptor and donor lies within the statistical limits of the interplanar distance of complexes formed between2 and a variety of PAH donors. The steric hindrance caused by the substituents in1 appears to offer only minimal interference to the formation of the complex. 相似文献
47.
Antoine Tardy Nomie Gil Christopher M. Plummer Didier Siri Didier Gigmes Catherine Lefay Yohann Guillaneuf 《Angewandte Chemie (International ed. in English)》2020,59(34):14517-14526
Radical ring‐opening polymerization (rROP) of cyclic ketene acetals (CKAs) combines the advantages of both ring‐opening polymerization and radical polymerization thereby allowing the robust production of polyesters coupled with the mild polymerization conditions of a radical process. rROP was recently rejuvenated by the possibility to copolymerize CKAs with classic vinyl monomers leading to the insertion of cleavable functionality into a vinyl‐based copolymer backbone and thus imparting (bio)degradability. Such materials are suitable for a large scope of applications, particularly within the biomedical field. The competition between the ring‐opening and ring‐retaining propagation routes is a major complication in the development of efficient CKA monomers, ultimately leading to the use of only four monomers that are known to completely ring‐open under all experimental conditions. In this article we investigate the radical ring‐opening polymerization of model CKA monomers and demonstrate by the combination of DFT calculations and kinetic modeling using PREDICI software that we are now able to predict in silico the ring‐opening ability of CKA monomers. 相似文献
48.
Christopher J. G. Plummer Rudolf Gensler Hans-Henning Kausch 《Colloid and polymer science》1997,275(11):1068-1077
Melt crystallized isotactic polypropylene thin films of thickness between 30 and 100 nm have been investigated by high-resolution
transmission electron microscopy at room temperature. The c-axis projection of the 2*31 helices and their packing in the lattice were clearly visible in flat-on lamellae of the α-phase following reconstruction
from the components of the image Fourier transform corresponding to the (1 1 0) and (0 4 0) lattice planes, and the image
power spectra also indicated contributions from (1 3 0) and (0 6 0) relfections, corresponding to a line resolution of about
0.35 nm. These results are discussed in terms of Bloch wave calculations based on the generally accepted structure for the
α-phase. Attempts to obtain lattice images of the β-phase in isotactic polypropylene and melt crystallized syndiotactic polypropylene
under similar operating conditions are also briefly discussed, although these provided relatively little structural information.
Received: 27 June 1997 Accepted: 15 August 1997 相似文献
49.
Zhang J Ismail Moore RG Wang SC Ding H Jin R Mandrus D Plummer EW 《Physical review letters》2006,96(6):066401
Ca(2-x)Sr(x)RuO4 single crystals with 0.1 < or = x < or = 2.0 have been studied systematically using scanning tunneling microscopy (STM) and spectroscopy, low-energy electron diffraction, and angle resolved photoelectron spectroscopy (ARPES). In contrast with the well-ordered lattice structure, the local density of states at the surface clearly shows a strong doping dependent nanoscale electronic inhomogeneity, regardless of the fact of isovalent substitution. Remarkably, the surface electronic roughness measured by STM and the inverse spectral weight of quasiparticle states determined by ARPES are found to vary with x in the same manner as the bulk in-plane residual resistivity, following the Nordheim rule. For the first time, the surface measurements--especially those with STM--are shown to be in good agreement with the bulk transport results, all clearly indicating a doping-induced electronic disorder in the system. 相似文献
50.