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941.
Allylation and vinylation of aryl radicals generated from aryl diazonium salts provides rapid and efficient access to chlorinated and brominated derivatives of styrene and allylbenzene. Allyl chlorides were found to be better substrates than bromides due to decreased halogen transfer. Donor- and acceptor-substituted diazonium salts are well tolerated. The products represent important precursors for numerous further transformations. 相似文献
942.
Heinrich Lang Petra Zoufalá Sami Klaib Amaya del Villar Gerd Rheinwald 《Journal of organometallic chemistry》2007,692(19):4168-4176
Heterobimetallic {cis-[Pt](μ-σ,π-CCPh)2}[Cu(NCMe)]BF4 (3a: [Pt] = (bipy)Pt, bipy = 2,2′-bipyridine; 3b: [Pt] = (bipy′)Pt, bipy′ = 4,4′-dimethyl-2,2′-bipyridine) is accessible by the reaction of cis-[Pt](CCPh)2 (1a: [Pt] = (bipy)Pt, 1b: [Pt] = (bipy′)Pt]) with [Cu(NCMe)4]BF4 (2). Substitution of NCMe by PPh3 (4) can be realized by the reaction of 3a with 4, whereby [{cis-[Pt](μ-σ,π-CCPh)2}Cu(PPh3)]BF4 (5) is formed. On prolonged stirring of 3 and 5, respectively, NCMe and PPh3 are eliminated and tetrametallic {[{cis-[Pt](η2-CCPh)2}Cu]2}(BF4)2 (6) is produced. Addition of an excess of NCMe to 6 gives heterobimetallic 3a.When instead of NCMe or PPh3 chelating molecules such as bipy (7) are reacted with 3a then the heterobimetallic π-tweezer molecule [{cis-[Pt](μ-σ,π-CCPh)2}Cu(bipy)]BF4 (8) is formed. Treatment of 8 with another equivalent of 7 produced [Cu(bipy2)]BF4 (9) along with [Pt](CCPh)2. However, when 3b is reacted with 1b in a 1:1 molar ratio then 10 and 11 of general composition [{[Pt](CCPh)2}2Cu]BF4 are formed. These species are isomers and only differ in the binding of the PhCC units to copper(I). A possible mechanism for the formation of 10 and 11 is presented.The solid state structures of 6, 10 and 11 are reported. In 11 the [{cis-[Pt](μ-σ,π-CCPh)2}2Cu]+ building block is set-up by two nearly orthogonal positioned bis(alkynyl) platinum units which are connected by a Cu(I) ion, whereby the four carbon-carbon triple bonds are unsymmetrical coordinated to Cu(I). In trimetallic 10 two cis-[Pt](CCPh)2 units are bridged by a copper(I) center, however, only one of the two PhCC ligands of individual cis-[Pt](CCPh)2 fragments is η2-coordinated to Cu(I) giving rise to the formation of a [(η2-CCPh)2Cu]+ moiety with a linear alkyne-copper-alkyne arrangement (alkyne = midpoint of the CC triple bond). In 6 two almost parallel oriented [Pt](CCPh)2 planes are linked by two copper(I) ions, whereby two individual PhCC units, one associated with each Pt building block, are symmetrically π-coordinated to Cu. 相似文献
943.
Först M Niehusmann J Plötzing T Bolten J Wahlbrink T Moormann C Kurz H 《Optics letters》2007,32(14):2046-2048
We demonstrate high-speed all-optical switching via vertical excitation of an electron-hole plasma in an oxygen-ion implanted silicon-on-insulator microring resonator. Based on the plasma dispersion effect the spectral response of the device is rapidly modulated by photoinjection and subsequent recombination of charge carriers at artificially introduced fast recombination centers. At an implantation dose of 1 x 10(12) cm(-2) the carrier lifetime is reduced to 55 ps, which facilitates optical switching of signal light in the 1.55 mum wavelength range at modulation speeds larger than 5 Gbits/s. 相似文献
944.
Kiriazis A Rüffer T Jäntti S Lang H Yli-Kauhaluoma J 《Journal of combinatorial chemistry》2007,9(2):263-266
As part of our continuing studies of polymer-supported pericyclic reactions for preparing biologically interesting heterocyclic compounds, we have introduced a traceless solid-phase synthesis of hexahydrocinnolines. We developed a method in which mild reaction conditions can be used for the hetero-Diels-Alder reactions on a polymeric support. The dienoic 3-vinyl-2-cyclohexenol attached to a Wang resin through an ether linkage undergoes [4 + 2] cycloaddition reaction with several azadienophiles. The highly stereoselective Diels-Alder reaction showed preferential formation of a single cycloadduct resulting from an anti attack of the dienophile on the polymer-bound diene. Trifluoroacetic acid-mediated cleavage of the polymer-bound cycloadducts yields fused nonaromatic hexahydrocinnolines in moderate yields in three steps. 相似文献
945.
Talian I Orinák A Preisler J Heile A Onofrejová L Kaniansky D Arlinghaus HF 《Journal of separation science》2007,30(16):2570-2582
A comparison is made between two high resolution, surface-based, mass spectrometric methods: time-of-flight secondary ion mass spectrometry (TOF-SIMS) and matrix-assisted laser desorption/ionisation mass spectrometry (MALDI TOF-MS) in indication of abietic and gibberellic acids molecular profiles on different chromatographic thin layers. The analytes were applied to silica gel chromatographic thin layers with SIMS on-line interfacing channel, monolithic silica gel ultra-thin layers, and thin layers specifically designed for direct Raman spectroscopic analysis. Two MALDI matrices were used in this research: ferulic acid and 2,5-dihydroxybenzoic acid. The silica gel SIMS-interfacing channel strongly supported formation of numerous different MALDI MS fragments with abietic and gibberellic acids, and ferulic acid matrix. The most intense fragments belonged to [M-OH](+) and [M](+) ions from ferulic acid. Intense conjugates were detected with gibberellic acid. The MALDI MS spectrum from the monolithic silica gel surface showed very low analyte signal intensity and it was not possible to obtain MALDI spectra from a Raman spectroscopy treated chromatographic layer. The MALDI TOF MS gibberellic acid fragmentation profile was shielded by the matrix used and was accompanied by poor analyte identification. The most useful TOF-SIMS analytical signal response was obtained from analytes separated on monolithic silica gel and a SIMS-interfacing modified silica gel surface. New horizons with nanostructured surfaces call for high resolution MS methods (which cannot readily be miniaturised like many optical and electrochemical methods) to be integrated in chip and nanoscale detection systems. 相似文献
946.
We compute the next-to-next-to-leading-order (NNLO) QCD corrections to the thrust distribution in electron-positron annihilation. The corrections turn out to be sizable, enhancing the previously known next-to-leading-order prediction by about 15%. Inclusion of the NNLO corrections significantly reduces the theoretical renormalization scale uncertainty on the prediction of the thrust distribution. 相似文献
947.
4,5‐Dihydro‐1,2,3‐oxadiazole: A Very Elusive Key Intermediate in Various Important Chemical Transformations 下载免费PDF全文
Prof. Dr. Klaus Banert Neeraj Singh Benjamin Fiedler Prof. Dr. Joachim Friedrich Marcus Korb Prof. Dr. Heinrich Lang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(43):15092-15099
4,5‐Dihydro‐1,2,3‐oxadiazoles are postulated to be key intermediates in the industrial synthesis of ketones from alkenes, in the alkylation of DNA in vivo, and in the decomposition of N‐nitrosoureas; they are also a subject of great interest for theoretical chemists. In the presented report, the formation of 4,5‐dihydro‐1,2,3‐oxadiazole and the subsequent decay into secondary products have been studied by NMR monitoring analysis. The elusive properties evading characterization have now been confirmed by 1H, 13C, and 15N NMR spectroscopy, and relevant 2D experiments at very low temperatures. Our experiments with suitably substituted N‐nitrosoureas using thallium(I) alkoxides as bases under apolar conditions answer important questions on the existence and the secondary products of 4,5‐dihydro‐1,2,3‐oxadiazole. 相似文献
948.
M.Sc. Amelie L. Bartuschat Karina Wicht Prof. Dr. Markus R. Heinrich 《Angewandte Chemie (International ed. in English)》2015,54(35):10294-10298
Tertiary amides, which usually occur as cis/trans mixtures, can be effectively shifted to the cis conformation by placing a positive charge in close proximity to the amide carbonyl. This effect was used to prepare cis‐configured prolyl amides and to facilitate a strongly rotamer‐dependent radical cyclization. 相似文献
949.
Ultrafast Charge‐Transfer Reactions of Indoline Dyes with Anchoring Alkyl Chains of Varying Length in Mesoporous ZnO Solar Cells 下载免费PDF全文
Dr. Egmont Rohwer Iulia Minda Gabriele Tauscher Christoph Richter Dr. Hidetoshi Miura Prof. Dr. Derck Schlettwein Prof. Dr. Heinrich Schwoerer 《Chemphyschem》2015,16(5):943-948
Dye‐sensitized solar cells based on a mesoporous ZnO substrate were sensitized with the indoline derivatives DN91, DN216 and DN285. The chromophore is the same for each of these dyes. They differ from each other in the length of an alkyl chain, which provides a second anchor to the ZnO surface and prolongs cell lifetime. Ultrafast transient absorption measurements reveal a correlation between the length of the alkyl chain and the fastest electron‐injection process. The depopulation of the excited state and the associated emergence of the oxidized molecules are dominant spectral features in the transient absorption of the dyes with shorter alkyl chains. A slower picosecond‐scale decay proceeds at constant rate for all three derivatives and is assigned to electron transfer into the trap states of ZnO. All assignments are in good agreement with a higher quantum efficiency of charge injection leading to higher short‐circuit currents Jsc for dyes with shorter alkyl chains. 相似文献
950.
David Amschl Jörg Neddens Daniel Havas Stefanie Flunkert Roland Rabl Heinrich Römer Edward Rockenstein Eliezer Masliah Manfred Windisch Birgit Hutter-Paier 《BMC neuroscience》2013,14(1):1-14