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951.
952.
Paolo Allia Marco Co?sson Paola Tiberto Franco Vinai Oana Bretcanu 《Journal of magnetism and magnetic materials》2010,322(9-12):1286-1289
Slow fluctuations of the electrical resistance R have been systematically observed in three glass-ceramics containing aggregates of magnetite nanoparticles, in measurements where R was studied as a function of time at the magnetic remanence. These fluctuations are shown to be an intrinsic (i.e., not instrumental or spurious) feature of these materials. The associated electrical noise has been obtained by performing a numerical FFT transform of different segments of the R(t) curves after proper baseline subtraction. In this way, the spectral density has been investigated in the very low-frequency region (1×10?3<f<0.2 Hz), usually not covered in standard noise measurements. The spectral density shows a 1/fα behaviour (with α?1.6) in all cases. The results are discussed in terms of the existing models about conductance fluctuations in half-metallic oxides in the hopping regime. It is suggested that electron trapping–detrapping mechanisms (thought to be the source of electrical noise) play a relevant role in the hopping processes between adjacent nanoparticle aggregates of magnetite, which dominate the material's resistivity. 相似文献
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955.
Federico Coppola Paola Cimino Umberto Raucci Maria Gabriella Chiariello Alessio Petrone Nadia Rega 《Chemical science》2021,12(23):8058
We present electronic structure methods to unveil the non-radiative pathways of photoinduced charge transfer (CT) reactions that play a main role in photophysics and light harvesting technologies. A prototypical π-stacked molecular complex consisting of an electron donor (1-chloronaphthalene, 1ClN) and an electron acceptor (tetracyanoethylene, TCNE) was investigated in dichloromethane solution for this purpose. The characterization of TCNE:π:1ClN in both its equilibrium ground and photoinduced low-lying CT electronic states was performed by using a reliable and accurate theoretical–computational methodology exploiting ab initio molecular dynamics simulations. The structural and vibrational time evolution of key vibrational modes is found to be in excellent agreement with femtosecond stimulated Raman spectroscopy experiments [R. A. Mathies et al., J. Phys. Chem. A, 2018, 122, 14, 3594], unveiling a correlation between vibrational fingerprints and electronic properties. The evaluation of nonadiabatic coupling matrix elements along generalized normal modes has made possible the interpretation on the molecular scale of the activation of nonradiative relaxation pathways towards the ground electronic state. In particular, two low frequency vibrational modes such as the out of plane bending and dimer breathing and the TCNE central C C stretching play a prominent role in relaxation phenomena from the electronic CT state to the ground state one.We present electronic structure methods to unveil the non-radiative pathways of photoinduced charge transfer (CT) reactions that play a main role in photophysics and light harvesting technologies. 相似文献
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957.
Mattea Carmen Castrovilli Paola Bolognesi Antonella Cartoni Daniele Catone Patrick O’Keeffe Anna Rita Casavola Stefano Turchini Nicola Zema Lorenzo Avaldi 《Journal of the American Society for Mass Spectrometry》2014,25(3):351-367
In the present work, we studied the photoinduced ion chemistry of the halogenated pyrimidines, a class of prototype radiosensitizing molecules, in the energy region 9–15 eV. The work was stimulated by previous studies on inner shell site-selective fragmentation of the pyrimidine molecule, which have shown that the fragmentation is governed by the population/formation of specific ionic states with a hole in valence orbitals, which in turn correlate to accessible dissociation limits. The combined experimental and theoretical study of the appearance energies of the main fragments provides information on the geometric structure of the products and on the role played by the specific halogen atom and the site of halogenation in the dissociation process. This information can be used to gain new insights on the elementary mechanisms that could possibly explain the enhanced radiation damage to the DNA bases or to the medium in which the bases are embedded, thereby contributing to their radiosensitizing effect. Figure
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958.
Ventrella Andrea Verrone Raffaella Cosma Pinalysa Fini Paola Longobardi Francesco Lippolis Vincenzo Pascale Michelangelo Catucci Lucia 《Journal of solution chemistry》2014,43(8):1436-1447
Journal of Solution Chemistry - The interaction of ochratoxin A (OTA) with heptakis-2,6-di-O-methyl-β-cyclodextrin (DIMEB) in aqueous solutions at two different pHs (3.5 and 9.5) was studied... 相似文献
959.
Anna Barattucci Paola Bonaccorsi Teresa Papalia Nadia Manganaro Giuseppe Gattuso 《Tetrahedron letters》2014
meso-(R,S)-Dithia[3.3]-paracyclophane S,S′-dioxide is formed with complete stereoselection by the thermolysis of 3,3′-[1,4-phenylene-bis(methylenesulfinyl)]-dipropanoate—that generates in situ two transient sulfenic acid functions—in the presence of p-diethynylbenzene. By employing an improved procedure that we have recently optimized, the title compound has been prepared in a 70% yield as a single diastereoisomer. A density functional B3LYP/6-311+G(d,p) study demonstrates that the final syn-addition cyclization step takes place under kinetic control, through a five-membered transition state that defines the stereochemistry of the resulting cyclophane. 相似文献
960.
Aura Tintaru Christophe Chendo Qi Wang Stéphane Viel Gilles Quéléver Ling Peng Paola Posocco Sabrina Pricl Laurence Charles 《Analytica chimica acta》2014
Tandem mass spectrometry and ion mobility spectrometry experiments were performed on multiply charged molecules formed upon conjugation of a poly(amidoamine) (PAMAM) dendrimer with a poly(ethylene oxide) (PEO) linear polymer to evidence any conformational modification as a function of their charge state (2+ to 4+) and of the adducted cation (H+vs Li+). Experimental findings were rationalized by molecular dynamics simulations. The G0 PAMAM head-group could accommodate up to three protons, with protonated terminal amine group enclosed in a pseudo 18-crown-6 ring formed by the PEO segment. This particular conformation enabled a hydrogen bond network which allowed long-range proton transfer to occur during collisionally activated dissociation. In contrast, lithium adduction was found to mainly occur onto oxygen atoms of the polyether, each Li+ cation being coordinated by a 12-crown-4 pseudo structure. As a result, for the studied polymeric segment (Mn = 1500 g mol−1), PEO-PAMAM hybrid molecules exhibited a more expanded shape when adducted to lithium as compared to proton. 相似文献