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901.
Ramos LA Ulic SE Romano RM Erben MF Lehmann CW Bernhardt E Beckers H Willner H Della Védova CO 《Inorganic chemistry》2010,49(23):11142-11157
Fluorocarbonyl thio- and isothiocyanate, FC(O)SCN and FC(O)NCS, were fully characterized by IR (gas, Ar and N(2) matrixes), Raman (liquid and solid), UV (gas), and (13)C NMR (liquid) spectroscopy, as well as single-crystal X-ray diffraction. Their vibrational and conformational properties were analyzed using matrix isolation techniques guided by quantum chemical calculation at the ab initio [MP2 and CCSD(T)], density functional theory B3LYP, and CBS-QB3 levels of theory. A complete assignment of the fundamental modes of FC(O)SCN was performed. In both the gas and liquid states, FC(O)SCN and FC(O)NCS were found to exist as two conformers (C(s) symmetry), in which the carbonyl double bond (C═O) adopts a synperiplanar (syn) and an antiperiplanar (anti) orientation with respect to either the SCN or NCS group. For FC(O)SCN, the conformational enthalpy difference, ΔH° = H°(anti) - H°(syn), was determined by matrix IR experiments to be 0.9 ± 0.2 kcal mol(-1). The conformational equilibria were evaluated by fast-cooling gaseous samples highly diluted in argon at different temperatures as cryogenic matrixes. The conformational properties of both molecules were analyzed in terms of the hyperconjugative electronic effect applying the natural bond orbital method. The kinetics of the thermal conversion of the high-energy anti into the syn FC(O)NCS conformer was studied in Ar and N(2) matrixes at cryogenic temperatures. The reversed syn → anti photoisomerization was observed using UV-vis light. Rearrangement of FC(O)SCN into FC(O)NCS was observed in the neat liquid and in solution. Under 193 nm (ArF excimer laser) irradiation, FC(O)NCS isolated in cryogenic Ar matrixes forms FC(O)SCN. At low temperature, single crystals of the two constitutional isomers were obtained using a miniature zone melting procedure. According to X-ray diffraction, they exclusively crystallize in their syn forms (C(s) symmetry) in the orthorhombic crystal system. 相似文献
902.
Ferreira FC Oliveira BG Ventura E do Monte SA Braga CF Araújo RC Ramos MN 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,64(1):156-160
The optimised geometries of heterocyclic hydrogen-bonded complexes, C2H4O...HX and C3H6O...HX, where X=F or Cl, were determined at DFT/B3LYP/6-311++G(d,p) computational level. Structural, electronic and vibrational properties of these complexes are used in order to compare the strained ring, which confer the great reactivity of these heterocyclic rings with monoprotic acids, forming a primary hydrogen bond. A secondary hydrogen bond between the hydrogen atoms of the CH2 groups and the halide species also takes place, thus causing a nonlinearity (characterized by the theta angle), in the primary hydrogen bond. 相似文献
903.
Ramos JM Viana RM Téllez S CA Pereira WC Izolani AO da Silva MI 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,65(2):433-438
To elucidate tentative assignments of metal-ligand modes of thiosemicarbazide complexes, a structural study and a assignment of the normal vibrations of 2-methylthiosemicarbazide copper(II) nitrate, [Cu(2MeTSC)(2)(NO(3))(2)] have been done through the ab initio DFT: pBP86/DN** procedure, and through the normal coordinate analysis (NCA). In the vibrational calculations, the elongated CuONO(2) bonds of the nitrate groups were considered in the CS and CN tautomers of the complex. DFT calculations had revealed that the infrared spectra can be well interpreted through the CN tautomer, failing in the prediction of the -NO(2) group wavenumbers. A little difference stabilization energy for the tautomers were found: for the CN tautomer was E=-3487,36376a.u., and for the CS tautomer, E=-3473,93598a.u. The observed combination bands at 1763.0 and at 1754.0 cm(-1) are an indicative that the -NO(3)(-) groups acts as monodentate ligands. Calculations had confirmed the experimental assignment of the infrared spectrum. 相似文献
904.
We give a positive answer to M. Traizet's open question about the existence of complete embedded minimal surfaces with Scherk-ends
without planar geodesics. In the singly periodic case, these examples get close to an extension of Traizet's result concerning
asymmetric complete minimal submanifolds of
with finite total curvature.
Dedicated to Hermann Karcher on the Occasion of his 65th Birthday
Martín's research is partially supported by MCYT-FEDER grant number BMF2001-3489. 相似文献
905.
Laver M Forgan EM Brown SP Charalambous D Fort D Bowell C Ramos S Lycett RJ Christen DK Kohlbrecher J Dewhurst CD Cubitt R 《Physical review letters》2006,96(16):167002
We report an extensive investigation of magnetic vortex lattice (VL) structures in single crystals of pure niobium with the magnetic field applied parallel to a fourfold symmetry axis, so as to induce frustration between the cubic crystal symmetry and hexagonal VL coordination expected in an isotropic situation. We observe new VL structures and phase transitions; all the VL phases observed (including those with an exactly square unit cell) spontaneously break some crystal symmetry. One phase even has the lowest possible symmetry of a two-dimensional Bravais lattice. This is quite unlike the situation in high-Tc or borocarbide superconductors, where VL structures orient along particular directions of high crystal symmetry. The causes of this behavior are discussed. 相似文献
906.
Rivadulla F Otero-Leal M Espinosa A de Andrés A Ramos C Rivas J Goodenough JB 《Physical review letters》2006,96(1):016402
From Raman spectroscopy, magnetization, and thermal expansion on the system La(2/3)(Ca(1-x)Sr(x))(1/3)MnO3, we have been able to provide a quantitative basis for the heterogeneous electronic model for manganites exhibiting colossal magnetoresistance (CMR). We construct a mean-field model that accounts quantitatively for the measured deviation of T(C)(x) from the T(C) predicted by de Gennes double-exchange in the adiabatic approximation and predicts the occurrence of a first-order transition for a strong coupling regime, in accordance with the experiments. The existence of a temperature interval T(C) < T < T*, where CMR may be found, is discussed in connection with the occurrence of an idealized Griffiths phase. 相似文献
907.
Alanine-scanning mutagenesis of protein-protein interfacial residues is a very important process for rational drug design. In this study, we have used the improved MM-PBSA approach that combining molecular mechanics and continuum solvent permits one to calculate the free energy differences through alanine mutation. To identify the binding determinants of the complex formed between the IgG1 (immunoglobulin-binding protein G) and protein G, we have extended the experimental alanine scanning mutagenesis study to both proteins of this complex and, therefore, to all interfacial residues of this binding complex. As a result, we present new residues that can be characterized as warm spots and, therefore, are important for complex formation. We have further increased the understanding of the functionality of this improved computational alanine-scanning mutagenesis approach testing its sensitivity to a protein-protein complex with an interface made up of residues mainly polar. In this study, we also have improved the method for the detection of an important amino acid residue that frequently constitutes a hot spot--tryptophan. 相似文献
908.
T. F. A. Alves A. C. A. Ramos G. A. Farias R. N. Costa Filho N. S. Almeida 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(3):92-9
The effect of Dresselhauss spin-orbit coupling on transport and thermodynamic properties
of a non-interacting two-dimensional electron gas (2DEG) is investigated. The Hamiltonian
used also includes a tilted magnetic field and a Rashba spin-orbit interaction. The
Dresselhauss spin-orbit interaction, likewise the Rashba spin-orbit interaction,
introduces a beating pattern in the conductivity tensor and in the magnetization along the
field direction. A method to estimate the contribution of the Rashba and Dresselhauss
interactions to the beating pattern is given using the periodicity of the beating
patterns. 相似文献
909.
910.