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111.
112.
Antonino Corsaro Ugo Chiacchio Giancarlo Perrini Pierluigi Caramella Giovanni Purrello 《Journal of heterocyclic chemistry》1985,22(3):797-799
Cycloadditions of nitrile oxides to N-mono and unsubstituted β-aminocinnamonitriles are remarkably affected by the hydrogen acceptor ability of the solvent. Addition to C ? N bond predominates in non and weak hydrogen bond acceptor solvents because of the assistance of favourable hydrogen bonding effects. In strong hydrogen bond acceptor solvents the assistance is fully relieved and the regular addition to C ? C bond becomes prevalent. 相似文献
113.
Experimental study on the retention of silica particles in gravitational field-flow fractionation effects of the mobile phase composition 总被引:3,自引:0,他引:3
Pierluigi Reschiglian Dora Melucci Giancarlo Torsi 《Journal of chromatography. A》1996,740(2):245-252
Effects of mobile phase composition can play an effective role in modulating the retention of particles in gravitational field-flow fractionation (GFFF), the simplest and cheapest among field-flow fractionation (FFF) techniques. In the framework of an optimized procedure for the GFFF characterization of particulate systems, an experimental approach to the effects of the mobile phase composition on the retention of silica particles retention is presented. The role of the ionic strength and the presence of surfactant are emphasized, with special regards to the shape of the particles. Moreover, the first experimental evidence of potential-barrier GFFF is reported. 相似文献
114.
115.
Claudio Bianchini Andrea Meli Annabella Orlandini Giancarlo Scapacci 《Journal of organometallic chemistry》1981,215(3):C59-C62
The reaction of the zwitterion Et3PCS2, with iron (II) tetrafluoroborate in the presence of 1,2-bis(diethylphosphino) ethane (depe) and NaBPh4 gave the unusual complex [(depe)2Fe(S2CPEt3)] (BPh4)2 (I), whose structure has been determined by X-ray analysis. A dithioformatoiron(II) complex was made by treating I with NaBH4. 相似文献
116.
Alessandro Dondoni Tiziano DallOcco Giancarlo Fantin Marco Fogagnolo Alessandro Medici 《Tetrahedron letters》1984,25(33):3633-3636
N-Ethoxycarbonylthiazolium chloride generated from 1,3-thiazole and ethyl chloroformate, treated with lithium carbanions of esters, Grignard reagents, silyl enol ethers and esters, undergo nucleophilic addition at C2 affording the corresponding 2-substituted N-ethoxycarbonylthiazolines. 相似文献
117.
118.
Renato Dogliotti Angelo Luvison Giancarlo Pirani 《Optical and Quantum Electronics》1979,11(6):541-550
The problem of pulse shaping and sensitivity to timing errors in optical fibre data communication is considered. The performance of the overall transmission system is the average probability of error, which is computed for intersymbol interference, thermal noise, and shot noise in avalanche photodiodes. An analysis of the immunity to small sampling errors of various Nyquist pulses indicates useful design criteria. 相似文献
119.
Giulio Ceccarelli Giancarlo Berti Giorgio Lippi Bruno Macchia 《Magnetic resonance in chemistry : MRC》1970,2(4):379-388
NMR spectra of several styrene, stilbene and stilbazole oxides have been determined, and chemical shifts and coupling constants have been correlated with cis-and trans-configurations. Assignments have been made for all protons, and double resonance technique and 13C? H coupling constants have been used in some particular cases. An explanation is proposed for the observation that chemical shifts of oxirane protons are higher for cis than for trans isomers. 相似文献
120.
The bis- and tris-pyrylium and thiopyrylium cations 1-4 were prepared in gram scale by heterocyclization of the corresponding bis- and tris-1,5-pentanediones 6 and 8. Their reaction with CD3ONa in CD3OD was studied by 1H NMR at -40 degrees C and at +25 degrees C. At low temperature, kinetically controlled mixtures of 2H and/or 4H adducts were detected, whereas at room temperature the mixtures equilibrated to yield, in all of the cases, the more stable 2H adducts exclusively. A spectrophotometric study of the reactions with sodium methoxide in methanol was carried out at 25.0 degrees C with the aim of determining the stepwise equilibrium constants for the addition of MeO- at the alpha position of the heteroaromatic rings. The obtained equilibrium constants allowed the evaluation of the electronic effects of chalcogenopyrylium and 2H-chalcogenopyran subunits as substituents. Despite the different sensitivity to electronic effects, pyrylium and thiopyrylium rings have a similar electron-withdrawing effect with a sigma(+)p approximately 0.8 and a sigma(+)m approximately 0.5. Apart from the expected importance of the inductive effect due to the positive charge, the difference between these two values remarks the importance of the resonance contribution. In contrast both the neutral 2H-pyranyl and thiopyranyl rings have a negligible effect as substituents, independently of the position, para or meta, they occupy. 相似文献