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961.
A short sequential synthesis of pyrrolidino- pyridines and pyrimidines illustrates the potential of combining Ugi-Smiles couplings with radical tin-free processes. 相似文献
962.
Josef T. Boronski Laurence R. Doyle John A. Seed Ashley J. Wooles Stephen T. Liddle 《Angewandte Chemie (International ed. in English)》2020,59(1):295-299
Despite there being numerous examples of f‐element compounds supported by cyclopentadienyl, arene, cycloheptatrienyl, and cyclooctatetraenyl ligands (C5–8), cyclobutadienyl (C4) complexes remain exceedingly rare. Here, we report that reaction of [Li2{C4(SiMe3)4}(THF)2] ( 1 ) with [U(BH4)3(THF)2] ( 2 ) gives the pianostool complex [U{C4(SiMe3)4}(BH4)3][Li(THF)4] ( 3 ), where use of a borohydride and preformed C4‐unit circumvents difficulties in product isolation and closing a C4‐ring at uranium. Complex 3 is an unprecedented example of an f‐element half‐sandwich cyclobutadienyl complex, and it is only the second example of an actinide‐cyclobutadienyl complex, the other being an inverse‐sandwich. The U?C distances are short (av. 2.513 Å), reflecting the formal 2? charge of the C4‐unit, and the SiMe3 groups are displaced from the C4‐plane, which we propose maximises U?C4 orbital overlap. DFT calculations identify two quasi‐degenerate U?C4 π‐bonds utilising the ψ2 and ψ3 molecular orbitals of the C4‐unit, but the potential δ‐bond using the ψ4 orbital is vacant. 相似文献
963.
Thierry Fouquet Valérie Toniazzo David Ruch Laurence Charles 《Journal of the American Society for Mass Spectrometry》2013,24(7):1123-1129
Collision-induced dissociation of doubly charged poly(dimethylsiloxane) (PDMS) molecules was investigated to provide experimental evidence for fragmentation reactions proposed to occur upon activation of singly charged oligomers. This study focuses on two PDMS species holding trimethylsilyl or methoxy end-groups and cationized with ammonium. In both cases, introduction of the additional charge did not induce significant differences in dissociation behavior, and the use of doubly charged precursors enabled the occurrence of charge-separation reactions, allowing molecules always eliminated as neutrals upon activation of singly charged oligomers to be detected as cationized species. In the case of trimethylsilyl-terminated oligomers, random location of the adducted charge combined with rapid consecutive reactions proposed to occur from singly charged precursors could be validated based on MS/MS data of doubly charged oligomers. In the case of methoxy-terminated PDMS, favored interaction of the adducted ammonium with both end-groups, proposed to rationalize the dissociation behavior of singly charged molecules, was also supported by MS/MS data obtained for molecules adducted with two ammonium cations. Figure
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964.
Nicolas Staelens Laurence Leherte Daniel P. Vercauteren 《Supramolecular chemistry》2013,25(1-2):90-109
Experimental data about 3D arrangements and building modes of cyclodextrin (CD) tubes are scarce, though investigations of such assemblies are particularly interesting for a vast array of applications related to organic tubes in general. Opting for a theoretical approach, we studied the organisation of CD tubes by three schemes: a structural examination of geometries from the Cambridge Structural Database, simulated annealing studies based on classical force fields to evaluate the stability of tubular arrangements, and an incremental construction procedure of the tubes by molecular dynamics. For β-CDs, the investigations pointed to a head-to-head configuration, while γ-CDs favoured a head-to-head+tail-to-head triplet. The position and interactions of water molecules inside the obtained tubular arrangements were studied as well. Various complexes for diphenylpolyenes and styrene included in the β- and γ-CDs tubes were considered and compared based on structural, energetic and dynamic criteria. 相似文献
965.
Chen J Kim JY Kurtis KE Jacobs LJ 《The Journal of the Acoustical Society of America》2011,130(5):2728-2737
This paper presents a theoretical and experimental study of the nonlinear flexural vibration of a cement-based material with distributed microcracks caused by an important deterioration mechanism, alkali-silica reaction (ASR). The general equation of motion is derived for the flexural vibration of a slender beam with the nonlinear hysteretic constitutive relationship for consolidated materials, and then an approximate formula for excitation-dependent resonance frequency is obtained. A downward shift of the resonance frequency is related to the nonlinearity parameters defined in the constitutive relationship. Vibration experiments are conducted on standard mortar bar samples undergoing progressive ASR damage. The absolute nonlinearity parameters are determined from these experimental results using the theoretical solution in order to investigate their dependence on the damage state of the material. With the progress of the ASR damage, the absolute value of the hysteresis nonlinearity parameter increases by as much as six times from the intact (undamaged) state in the sample with highly reactive aggregate; this is in contrast to a change of about 16% in the linear resonance frequency. It is demonstrated that the combined theoretical and experimental approach developed in this research can be used to quantitatively characterize ASR damage in mortar samples and other cement-based materials. 相似文献
966.
Laurence Latu-Romain Maelig Ollivier Arnaud Mantoux Geoffroy Auvert Odette Chaix-Pluchery Eirini Sarigiannidou Edwige Bano Bernard Pelissier Charbel Roukoss Herv�� Roussel Florian Dhalluin Bassem Salem Nikoletta Jegenyes Gabriel Ferro Didier Chaussende Thierry Baron 《Journal of nanoparticle research》2011,13(10):5425-5433
Si nanowires (NWs), with diameters of about 800 nm and lengths of about 10 ??m, previously synthesized by the VLS method with gold catalyst, were carburized at 1,100 °C under methane for conversion into SiC nanostructures. These experiments have shown that Si NWs have been transformed into SiC nanotubes (NTs) with approximately the same sizes. Nanotubes?? sidewall thickness varies from 20 to 150 nm depending on the NTs?? height. These SiC nanotubes are hexagonal in shape and polycrystalline. A model of growth based on the out-diffusion of Si through the SiC layer was proposed to explain the transformation from Si nanowires to SiC nanotubes. This model was completed with thermodynamic calculations on the Si?CH2?CCH4?CO2 system and with results from complementary experiment using propane precursor. Routes for obtaining crystalline SiC NTs using this reaction are proposed. 相似文献
967.
968.
Florence Déclaire Mabou Perrin Lanversin Foning Tebou David Ngnokam Dominique Harakat Laurence Voutquenne‐Nazabadioko 《Magnetic resonance in chemistry : MRC》2014,52(1-2):32-36
A new triterpenoid bidesmoside (leptocarposide) possessing an acyl group in their glycosidic moiety (1), together with the known luteolin‐8‐C‐glucoside (2) and 1‐O‐β‐d ‐glucopyranosyl‐(2S,3R,8E)‐2‐[(2′R)‐2‐hydroxypalmitoylamino]‐8‐octadecen‐1,3‐diol (3) was isolated from the n‐butanol‐soluble fraction of whole plant of Ludwigia leptocarpa (Nutt) Hara (Onagraceae). Structure of compound 1 has been assigned on the basis of spectroscopic data (1H and 13C NMR, 1H‐1H COSY, HSQC, HMBC, and ROESY), mass spectrometry, and by comparison with the literature. This compound was further screened for its potential antioxidant properties by using the radical scavenging assay model 2,2‐diphenyl‐1‐picrylhydrazyl and reveals non‐potent antioxidant activities, while compound 2 shows SC50 of 0,038 mM. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
969.
Marion Girod Michaël Mazarin Trang N. T. Phan Didier Gigmes Laurence Charles 《Journal of polymer science. Part A, Polymer chemistry》2009,47(13):3380-3390
Characterization of block size in poly(ethylene oxide)‐b‐poly(styrene) (PEO‐b‐PS) block copolymers could be achieved by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) after scission of the macromolecules into their constituent blocks. The performed hydrolytic cleavage was demonstrated to specifically occur on the targeted ester function in the junction group, yielding two homopolymers consisting of the constitutive initial blocks. This approach allows the use of well‐established MALDI protocols for a complete copolymer characterization while circumventing difficulties inherent to amphiphilic macromolecule ionization. Although the labile end‐group in PS homopolymer was modified by the MALDI process, PS block size could be determined from MS data since polymer chains were shown to remain intact during ionization. This methodology has been validated for a PEO‐b‐PS sample series, with two PEO of number average molecular weight (Mn) of 2000 and 5000 g mol?1 and Mn(PS) ranging from 4000 to 21,000 g mol?1. Weight average molecular weight (Mw), and thus polydispersity index, could also be reached for each segment and were consistent with values obtained by size exclusion chromatography. This approach is particularly valuable in the case of amphiphilic copolymers for which Mn values as determined by liquid state nuclear magnetic resonance might be affected by micelle formation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3380–3390, 2009 相似文献
970.