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991.
SiHx (x = 1, 2, 3) ions impact on Si(0 0 1)(1 × 1):H and Si(0 0 1)(2 × 1):H surfaces has been studied by classical molecular dynamic simulations, considering an energetic range for the impinging species from 5 to 15 eV. Despite the initial full H coverage a high sticking coefficient has been obtained for all the species under investigation. A considerable fraction of adsorption events causes H removal from the surface while for other simulations a soft landing mechanism of the ions has been observed. Few representative minima for SiH2/Si(0 0 1)(2 × 1):H were re-converged by ab initio calculations in order to check the reliability of our results. 相似文献
992.
Stuart R. Batten 《Journal of solid state chemistry》2005,178(8):2475-2479
This article discusses the challenges that face the crystal engineer in the deliberate design of new network structures. These include control over ligand and metal coordination geometry, selection of network topology from a number of possibilities which all have the same connectivity, and control of methods of increasing packing efficiency, including interpenetration (both number of nets (including only one) and topology of interpenetration). These variables can lead to polymorphism and related phenomena, the bane of crystal engineers. Templation by counterions, guest molecules and/or solvents can also lead to unpredictable results. 相似文献
993.
Cellular instabilities of expanding hydrogen/propane spherical flames at elevated pressures: theory and experiment 总被引:1,自引:0,他引:1
An experimental and theoretical investigation of the onset of cellular instabilities on spherically expanding flames in mixtures of hydrogen and propane in air at elevated pressures was conducted. Critical conditions for the onset of instability were measured and mapped out over a range of pressures and mixture compositions. An asymptotic theory of hydrodynamic and diffusional-thermal cell development on flames in mixtures comprised of two scarce fuels burning in air was also formulated. Predicted values of Peclet number, defined as the flame radius at the onset of instability normalized by the flame thickness, were shown to compare favorably with the experimentally measured values. 相似文献
994.
N. Ozawa 《Surface science》2006,600(18):3550-3554
We investigate the quantum mechanical behavior of adsorbed hydrogen (H, D, T) on Cu(1 0 0) and (1 1 0) surfaces. We construct potential energy surfaces (PESs) for the motion of the hydrogen H atom on Cu(1 0 0) and (1 1 0) surfaces within the framework of density functional theory. The potential energy takes a minimum value on the hollow site of Cu(1 0 0) and on the short bridge site of Cu(1 1 0). Moreover, we calculate the quantum states of hydrogen atom motion on these calculated PESs. The ground state wave function of the hydrogen atom motion is strongly localized around the hollow site on the Cu(1 0 0) surface. On the other hand, the ground state wave function of the hydrogen atom motion on Cu(1 1 0) is distributed from the short bridge site to two neighboring pseudo-threefold sites. We finally show isotope effects on the quantum states of the motion of hydrogen on both surfaces. 相似文献
995.
The acid catalyzed hydrolytic cleavage of the oxazine rings in the readily available tetraoxazine derivatives of resorcinarenes results in tetraaminoresorcinarenes. A similar process applied to C2-symmetrical bisoxazine resorcinarene tetratosylates affords C2v-symmetrical resorcinarenediamines. The mild acylation of these resorcinareneamines with BOC-anhydride or para-nitrophenyl ester proceeds selectively at the nitrogen atoms without affecting the hydroxyl groups. Most of the resulting resorcinareneamides are thus obtained in preparative yields and can be easily purified by simple crystallizations. In the crystalline state the compounds obtained are found to bind chloride anions through hydrogen bonds and electrostatic interactions and to display a chiral arrangement of hydrogen bonded functional groups at the wide rim of the macrocycle. 相似文献
996.
The crystal structures of [pipH]2[WS4] ( 1 ) and the new compounds [pipH]3[WS4](HS) ( 2 ) and [pipH]4[WS4][WOS3] ( 3 ) (pip = piperidine) were determined. Hydrogen bonds between the piperidinium cations and the thiotungstate anions play a dominant structural role. Their strength and number correlates with the degree of distortion found for the tetrahedral anions. Unshared hydrogen bonds have a considerably stronger effect than bifurcated ones; the effect of trifurcated hydrogen bonds is extremely weak. HS? and [WOS3]2? are considerably stronger H bond acceptors than the [WS4]2? anion. 相似文献
997.
T. J. Greytak D. Kleppner D. G. Fried T. C. Killian L. Willmann D. Landhuis S. C. Moss 《Physica B: Condensed Matter》2000,280(1-4):20-26
The addition of atomic hydrogen to the set of gases in which Bose–Einstein condensation can be observed expands the range of parameters over which this remarkable phenomenon can be studied. Hydrogen, with the lowest atomic mass, has the highest transition temperature, 50 μK in our experiments. The very weak interaction between the atoms results in a high ratio of the condensate to normal gas densities, even at modest condensate fractions. Using cryogenic rather than laser precooling generates large condensates. Finally, two-photon spectroscopy is introduced as a versatile probe of the phase transition: condensation in real space is manifested by the appearance of a high-density component in the gas, condensation in momentum space is readily apparent in the momentum distribution, and the phase transition line can be delineated by following the evolution of the density of the normal component. 相似文献
998.
The synthesis and structures of five new compounds are reported. [Mg(6‐Oq)2(phen)2] ( 1 ), [Na(phen)3][(6‐HOq)(6‐Oq)] ( 2 ), 1/∞[Cu(3‐Opy)(3‐HOpy)2(PPh3)]∞ ( 3 ), 1/∞[Cu2{μ‐(6‐Oq)}(PPh3)2]∞ ( 4 ) and [Cu2(pht)2(μ‐dppm)2] ( 5 ) (6‐HOq = 6‐hydroxyquinoline; phen = 1,10‐phenanthroline, 3‐HOpy = 3‐hydroxypyridine; Hpht = phthalimide; dppm = bis‐(diphenylphosphino)methane) were prepared by deprotonation of N‐heterocyclic aromatic compounds with metal alkoxides. 1 – 5 represent useful starting materials for investigating the supramolecular cordination chemistry of organic anhydrides. 相似文献
999.
1000.
Ab initio and density functional calculations were used to analyze the interaction between a molecule of cyanic acid (HOCN) and up to 4 molecules of water at the B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) computational levels. The cooperative effect (CE) is increased with the increasing size of the studied clusters. Red shifts of the H–O stretching frequency for complexes involving HOCN as an H-donor were predicted. The strength of the hydrogen bonds in terms of molecular structures could be deduced from a comparison of HOCN–H2O with HCNO–H2O, HONC–H2O and HNCO–H2O HB clusters. The atom in molecules (AIM) method was used to analyze the cooperative effects on topological parameters. 相似文献