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Single crystals of the new compounds TM2Cu3Ga8 (TM=V, Mo, W) were synthesised from the elements. Structure determinations of the isotypic compounds (cI104, space group , Z=8; Mo2Cu3Ga8: a=11.9171(10) Å, 613 refl., 23 param., R1(F)=0.022, wR2(F2)=0.047; W2Cu3Ga8: 11.9248(8) Å, 346 refl., 23 param., R1(F)=0.048, wR2(F2)=0.086; V2Cu3Ga8: 11.7861(14) Å, 374 refl., 24 param., R1(F)=0.033, wR2(F2)=0.081) showed a new cubic structure type which can be classified as an ordered defect variant of a bcc packing with a′=4a: [(TM)2(Cu)3(□)3][Ga8]. The coordination polyhedra of the transition metals consist of Ga8-cubes with 3 sides capped by Cu leading to coordination number 11. The arrangement of the TMGa8Cu3-polyhedra is in a way they form itself a 3-fold capped cube. All compositions were confirmed by EDX measurements. 相似文献
104.
Synthesis and crystal structure of MgB12 总被引:1,自引:0,他引:1
Volker Adasch Thilo Ludwig Natascha Vojteer Harald Hillebrecht 《Journal of solid state chemistry》2006,179(9):2916-2926
Single crystals of MgB12 were synthesized from the elements in a Mg/Cu melt at 1600 °C. MgB12 crystallizes orthorhombic in space group Pnma with , and . The crystal structure (Z=30, 5796 reflections, 510 variables, R1(F)=0.049, wR2(I)=0.134) consists of a three dimensional net of B12 icosahedra and B21 units in a ratio 2:1. The B21 units are observed for the first time in a solid compound. Mg is on positions with partial occupation. The summation reveals the composition MgB12.35 or Mg0.97B12 , respectively. This is in good agreement with the value of MgB11.25 as expected by electronic reasons to stabilize the boron polyhedra and . 相似文献
105.
Antonio Currao Steffen Wengert Reinhard Nesper Jan Curda H. Hillebrecht 《无机化学与普通化学杂志》1996,622(3):501-508
Ca14Si19 is an overlooked binary phase in the Ca/Si system with a novel type of twodimensional silicon framework (R3 c, a = 867.85(6), c = 6852.8(8) pm, Z = 6). The basic building units are 3,3,3-barrelanes Si11 which are linked by Si3 bridges to form a twodimensional silicon framework leaving space for interstitial calcium atoms. The thickness of the silicon layers is about 800 pm. The compound is a semiconductor with a band gap of about EG = 0.1 eV and a diamagnetic moment of χmole = ?9 · 10?4 cm3mol?1. According to the relatively high linking of silicon atoms the reaction with air and moisture is fairly slow. 相似文献
106.
William N. Anderson JR. E. James Harner George E. Trapp 《Linear and Multilinear Algebra》2013,61(3-4):295-299
There is an isomorphism between the matrices over the Boolean algebra of subsets of a k-element set and the k-tuples of Boolean binary (i.e. zero-one) matrices. This isomorphism allows many problems concerning nonbinary Boolean matrices to the referred to the binary ease. However, there are some features of the general (i.e. nonbinary) case that have not been mentioned, although they differ somewhat from the binary case. We exhibit characterizations of the linear operators that preserve several invariants of matrices over finite Boolean algebras to illustrate the differences and similarities of the general vs. the binary cases. We employ a canonical form that is useful in applying the isomorphism. 相似文献
107.
Barbara Albert Prof. Dr. Harald Hillebrecht Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(46):8640-8668
Many of the fundamental questions regarding the solid‐state chemistry of boron are still unsolved, more than 200 years after its discovery. Recently, theoretical work on the existence and stability of known and new modifications of the element combined with high‐pressure and high‐temperature experiments have revealed new aspects. A lot has also happened over the last few years in the field of reactions between boron and main group elements. Binary compounds such as B6O, MgB2, LiB1?x, Na3B20, and CaB6 have caused much excitement, but the electron‐precise, colorless boride carbides Li2B12C2, LiB13C2, and MgB12C2 as well as the graphite analogue BeB2C2 also deserve special attention. Physical properties such as hardness, superconductivity, neutron scattering length, and thermoelectricity have also made boron‐rich compounds attractive to materials research and for applications. The greatest challenges to boron chemistry, however, are still the synthesis of monophasic products in macroscopic quantities and in the form of single crystals, the unequivocal identification and determination of crystal structures, and a thorough understanding of their electronic situation. Linked polyhedra are the dominating structural elements of the boron‐rich compounds of the main group elements. In many cases, their structures can be derived from those that have been assigned to modifications of the element. Again, even these require a critical revision and discussion. 相似文献
108.
109.
This paper is concerned with the construction and analysis ofcompact finite difference approximations to the model linearsource problem (pu')' + qu = f where the functions p,q, and f can have jump discontinuities at a finite number ofpoints. Explicit formulae that give O(h2) O(h3) and O(h4) accuracyare derived, and a procedure for computing three-point schemesof any prescribed order of accuracy is presented. A rigoroustruncation and discretization error analysis is offered. Numericalresults are also given. 相似文献
110.