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981.
Michael Wrle Frank Krumeich Fabian Bieri Hans‐Joachim Muhr Reinhard Nesper 《无机化学与普通化学杂志》2002,628(12):2778-2784
The walls of vanadium oxide nanotubes (VOx‐NTs) are built up by vanadate layers between which the structure‐directing template, either a primary amine or a diamine with long alkyl chain, is located. The feasibility of various exchange reactions under preservation of the tubular morphology indicates a high structural flexibility of the VOx‐NTs. The structure of the vanadate layers appears to be the same in all tubular vanadates, as revealed by the similarity of the diffraction patterns. Plate‐like crystals of a new crystalline phase, structurally closely related to the nanotubes, have now been prepared with ethylene diamine, applying a route that is analogous to the VOx‐NT synthesis. The single crystal X‐ray structure determination showed that this new phase has the composition (en)V7O16 and crystallizes with triclinic symmetry. The structure is composed of V7O16 layers between which ethylene diamine mo le cules are embedded. The V7O16 layers comprise two sheets of square VO5 pyramids and VO4 tetrahedra that connect these sheets. The available experimental data establish that this V7O16 layer also is the basic element of the VOx‐NT wall structure. The simulated X‐ray powder diffraction pattern calculated with a corresponding structural mode for VOx‐NTs agrees well with the observed one. 相似文献
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Synthesis and Crystal Structure of the Nitrido Complexes [(n‐Bu)4N]2[{(L)Cl4Re≡N}2PtCl2] (L = THF und H2O) and [(n‐Bu)4N]2[(H2O)Cl4Re≡N‐PtCl(μ‐Cl)]2 The threenuclear complex [(n‐Bu)4N]2[{(THF)Cl4Re≡N}2—PtCl2] ( 1a ) is obtained by the reaction of [(n‐Bu)4N][ReNCl4] with [PtCl2(C6H5CN)2] in THF/CH2Cl2. It forms red crystals with the composition 1a · 2 CH2Cl2 crystallizing in the tetragonal space group I41/a with a = 3186.7(2); c = 1311.2(1) pm and Z = 8. If the reaction of the educts is carried out without THF, however under exposure to air the compound [(n‐Bu)4N]2[{(H2O)Cl4Re≡N}2PtCl2] ( 1b ) is obtained as red trigonal crystals with the space group R3 and a = 3628.3(3), c = 1231.4(1) pm and Z = 9. In the centrosymmetric complex anions [{(L)Cl4Re≡N}2PtCl2]2— a linear PtCl2moiety is connected in a trans arrangement with two complex fragments [(L)Cl4Re≡N]— via asymmetric nitrido bridges Re≡dqN‐Pt. For PtII such results a square‐planar coordination PtCl2N2. The linear nitrido bridges are characterized by distances Re‐N = 169.5 pm and Pt‐N = 188.8 pm ( 1a ), respectively, Re‐N = 165.6 pm and Pt‐N = 194.1 pm ( 1b ). By the reaction of [(n‐Bu)4N][ReNCl4] with PtCl4 in CH2Cl2 platinum is reduced forming the heterometallic ReVI/PtII complex, [(n‐Bu)4N]2[(H2O)Cl4Re≡N‐PtCl(μ‐Cl)]2 ( 2 ). It crystallizes in the monoclinic space group C2/c with a = 2012.9(1); b = 1109.0(2); c = 2687.4(4) pm; β = 111.65(1)° and Z = 4. In the central unit ClPt(μ‐Cl)2PtCl of the anionic complex [(H2O)Cl4Re≡N‐PtCl(μ‐Cl)]22— with the symmetry C2 the coordination of the Pt atoms is completed by two nitrido bridges Re≡N‐Pt to nitrido complex fragments [(H2O)Cl4Re≡N] — forming a square‐planar arrangement for the Pt atoms. The distances in the linear nitrido bridges are Re‐N = 165.9 pm and Pt‐N = 190.1 pm. 相似文献
986.
Tyrosine-derived polycarbonates having carboxylic acid pendant groups were characterized by water contact angle and X-ray photoelectron spectroscopy (XPS). A pronounce decrease of receding angle as well as contact angle hysteresis as a function of acid composition strongly indicated that the acid groups are more accessible at the water/polymer interface after hydration. pH dependent contact angle confirmed an existence of carboxylic acid groups in the surface region. The receding angle transition appearing in the pH range of 4-6 was a consequence of hydrophilicity change due to interconverting from carboxylic acid (-COOH) to carboxylate ion (-COO−). The surface compositions of imidazole-labeled polymers as analyzed by XPS were consistent with the bulk stoichiometry of the polymers. Reactivity of acid groups towards chemical reaction at the surface was also investigated. The acid groups at the surface of polymers were capable of adsorbing a significant amount of calcium ion from simulated body fluid and being activated by a reaction with N-hydroxysuccinimide. 相似文献
987.
In the present study, a computational approach for the numerical simulation of ductile fracture within the framework of the finite element method is proposed. In the developed macroscopic formulation, the inelastic behavior in the bulk of the material is described by the finite elasto‐plastic material model proposed in [4]. The failure process is modeled by introducing discontinuities when a special local fracture criterion is satisfied. The discontinuities are incorporated via special triangular finite elements with embedded interfaces following the line of [2]. Finally, the numerical procedure is evaluated for a twodimensional representative test problem. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
988.
We consider a homogenized macro‐continuum with locally attached microstructure of granules and derive specific micromacro transitions by a consistent transfer of discrete micro‐variables to field variables on a continuous macrostructure. Displacements and rotational constraints are imposed on the granules on the defined boundary frame of the microstructure. The constraints for linear displacements and uniform tractions on the surface yield upper and lower bound characteristics for periodic boundary conditions with regard to the aggregate stiffness. Secondly, we perform two‐scale analyses where we link simulations on the macro‐ and the microscales. Therein, coupled boundary‐value problems are solved on both scales. The macroscopic homogeneous problem is solved by a finite element method where the material model is implemented using the directly evaluated micro‐macro transitions on the basis of the discrete microstructures. Finally, a model problem is investigated to clarify the proposed method. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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