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731.
Noel P. McLaughlin Paul Evans Nigel P. Brunton Anastasios Koidis Dilip K. Rai 《Tetrahedron》2010,66(51):9681-9687
A short, practical synthesis of the bis-acetylenic natural product falcarinol 1 is reported. This method relies on the alternate functionalisation of bis-trimethylsilylbutadiyne 10. This may be achieved in one-pot, however, better yields were obtained more conventionally. Lipase mediated enzymatic kinetic resolution of the racemic adduct in an organic solvent afforded (+)-1 in 97% enantiomeric excess. The analogous process performed with racemic 3-acetoxy falcarinol 11 under aqueous conditions gave (−)-1. Oxidation of 1 with Dess-Martin periodinane gave falcarinone 2. 相似文献
732.
Geoffrey C. Kite Nigel C. Veitch 《Rapid communications in mass spectrometry : RCM》2009,23(19):3125-3132
Kaempferol 3‐O‐β‐glucopyranoside, kaempferol 3‐O‐β‐galactopyranoside and higher glycosides of these two flavonoids with α‐rhamnose at C‐2 and/or C‐6 of the primary sugar were studied by negative ion electrospray ionisation and serial mass spectrometry in a three‐dimensional (3D) ion trap mass spectrometer. Kaempferol 3‐O‐β‐glucopyranoside and kaempferol 3‐O‐α‐rhamnopyranosyl(1→6)‐β‐glucopyranoside could be distinguished from their respective galactose analogues by differences in the ratio of the radical aglycone ion [Y0 – H]?? to the rearrangement aglycone ion Y following MS/MS of the deprotonated molecules. Kaempferol 3‐O‐rhamnopyranosyl(1→2)‐β‐glucopyranoside and kaempferol 3‐O‐α‐rhamnopyranosyl(1→2)[α‐rhamnopyranosyl(1→6)]‐β‐glucopyranoside could be distinguished from their respective galactose analogues by differences in the product ion spectra of the [(M – H) – rhamnose]? ion following serial mass spectrometry. In the triglycoside, it was deduced that this ion resulted from the loss of the rhamnose substituted at 2‐OH of the primary sugar by observing that MS/MS of deprotonated kaempferol 3‐O‐β‐glucopyranosyl(1→2)[α‐rhamnopyranosyl(1→6)]‐β‐glucopyranoside showed the loss of glucose and not rhamnose. Thus the class of sugar (hexose, deoxyhexose, pentose) at C‐2 and C‐6 of the primary sugar can be determined. These observations aid the assignment of kaempferol 3‐O‐glycosides, having glucose or galactose as the primary glycosidic sugar, in LC/MS analyses of plant extracts, and this can be done with reference to only a few standards. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
733.
Visualizing macromolecular complexes with in situ liquid scanning transmission electron microscopy 总被引:1,自引:0,他引:1
Evans JE Jungjohann KL Wong PC Chiu PL Dutrow GH Arslan I Browning ND 《Micron (Oxford, England : 1993)》2012,43(11):1085-1090
A central focus of biological research is understanding the structure/function relationship of macromolecular protein complexes. Yet conventional transmission electron microscopy techniques are limited to static observations. Here we present the first direct images of purified macromolecular protein complexes using in situ liquid scanning transmission electron microscopy. Our results establish the capability of this technique for visualizing the interface between biology and nanotechnology with high fidelity while also probing the interactions of biomolecules within solution. This method represents an important advancement towards allowing future high-resolution observations of biological processes and conformational dynamics in real-time. 相似文献
734.
Falk BruckmannFlorian Gruber Nigel Cundy Andreas SchäferThomas Lippert 《Physics letters. [Part B]》2012,707(2):278-285
We investigate how the topological charge density in lattice QCD simulations is affected by violations of chiral symmetry caused by the fermion action. To this end we compare lattice configurations generated with a number of different actions including first configurations generated with exact dynamical overlap quarks. We visualize the topological profiles after mild smearing. In the topological charge correlator we measure the size of the positive core, which is known to shrink to zero extension in the continuum limit. To leading order we find the core size to scale linearly with the lattice spacing with the same coefficient for all actions, even including quenched simulations. In the subleading term the different actions vary over a range of about 10%. Our findings suggest that non-chiral lattice actions at current lattice spacings do not differ much for observables related to topology, both among themselves and compared to overlap fermions. 相似文献
735.
Xinghua Li Guoguo Tan Wei Chen Baofan Zhou Desheng Xue Yong Peng Fashen Li Nigel J. Mellors 《Journal of nanoparticle research》2012,14(3):751
This study presents a comprehensively and systematically structural, chemical and magnetic characterization of ~9.5 nm virtually
monodispersed nickel ferrite (NiFe2O4) nanoparticles prepared using a modified liquid–solid-solution (LSS) assisted hydrothermal method. Lattice-resolution scanning
transmission electron microscope (STEM) and converged beam electron diffraction pattern (CBED) techniques are adapted to characterize
the detailed spatial morphology and crystal structure of individual NiFe2O4 particles at nano scale for the first time. It is found that each NiFe2O4 nanoparticle is single crystal with an fcc structure. The morphology investigation reveals that the prepared NiFe2O4 nanoparticles of which the surfaces are decorated by oleic acid are dispersed individually in hexane. The chemical composition
of nickel ferrite nanoparticles is measured to be 1:2 atomic ratio of Ni:Fe, indicating a pure NiFe2O4 composition. Magnetic measurements reveal that the as-synthesized nanocrystals displayed superparamagnetic behavior at room
temperature and were ferromagnetic at 10 K. The nanoscale characterization and magnetic investigation of monodispersed NiFe2O4 nanoparticles should be significant for its potential applications in the field of biomedicine and magnetic fluid using them
as magnetic materials. 相似文献
736.
A multilinear version of the Boyd interpolation theorem is proved in the context of quasi-normed rearrangement-invariant
spaces. A multilinear Marcinkiewicz interpolation theorem is obtained as a corollary. Several applications are given, including
estimates for bilinear fractional integrals.
Received January 31, 1999 / Accepted February 27, 2000 / Published online December 8, 2000 相似文献
737.
Farrington Dennis J. Jones John G. Robinson Nigel D. Twigg Martyn V. 《Transition Metal Chemistry》1999,24(6):697-702
The kinetics of the replacement of dmso in FePc(dmso)2 by piperidine and 11 substituted pyridines, to form FePc(base)2 species, have been studied by stopped-flow techniques. For the first step a linear free energy relationship (LFER) exists between the rate constant for fission of base from FePc(base)(dmso) and the gas phase proton affinity of the base, from bases with low proton affinity (CO) to high proton affinity (CN–). The rate constant for dmso fission from FePc(dmso)2 was estimated to be ca. 420,000 s–1, and this fission process largely governs the rate of the first step for neutral bases. The slow first step for the reaction with cyanide ion as base can be explained when the energy needed to de-pair cyanide and potassium ions is taken into account.In the second step the formation rate constants of FePc(base)2 species cover one order of magnitude for neutral bases, and the base dissociation rate constants cover two orders of magnitude, with a good LFER between these constants and the pKBH of the leaving group. There is also a good LFER between the equilibrium constant for bis-base complex formation and these same dissociation rate constants. 相似文献
738.
739.
Small angle X-ray scattering (SAXS) has been used to investigate density fluctuations occurring in amorphous semiconductors prepared by sputtering, evaporation and electrodeposition. Correlations of the total number of dangling bonds determined by SAXS, optical absorption, and ESR signals have been made. The density deficits from the density of the FC-2 crystal are in some cases accounted for by the voids. It is argued that models based on domains 10–15 Å in size are not supported by the SAXS data. 相似文献
740.