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71.
Volodymyr Babizhetskyy Dr. Kurt Hiebl Hansjürgen Mattausch Arndt Simon 《无机化学与普通化学杂志》2010,636(7):1229-1235
New ternary rare earth metal boride carbides with compositions close to RE10B9C10 (RE = Gd, Tb) were prepared from the elements by melting around 1800 K followed by annealing in silica tubes at 1270 K for one month. The crystal structure of the terbium compound was solved by single‐crystal X‐ray diffraction. It crystallizes in a new structure type in the monoclinic space group P21/c, a = 7.937(1), b = 23.786(2), c = 11.172(1) Å, β = 133.74(1)°, Z = 4, R1 = 0.045 (wR2 = 0.11) for 5713 reflections with Io > 2σ(Io). In the structure BC2 units and single carbon atoms are attached to a zigzag boron chain forming the unprecedented B18C18 branching unit with a B–B distance of 2.42(2) Å between these units. In addition isolated carbon atoms occupy the centres of elongated octahedra formed by rare earth metal atoms. Disorder in the terbium position together with anomalous displacement ellipsoids for carbon atoms except of those in the BC2 fragments can be rationalized in terms of a slight deviation in stoichiometry, Tb10B9+xC10–x (x ≈? 0.2). The terbium compound is ferromagnetic below TC ≈? 45 K. Due to the presence of moderately narrow domain walls the magneto‐crystalline energy is small. 相似文献
72.
Alexey Lipatov Alexander Gribanov Andriy Grytsiv Peter Rogl Yurii Seropegin 《Journal of solid state chemistry》2010,183(4):829-6521
Phase relations have been established in the ternary system Ce-Rh-Si for the isothermal section at 800 °C based on X-ray powder diffraction and EPMA on about 80 alloys, which were prepared by arc melting under argon or by powder reaction sintering. From the 25 ternary compounds observed at 800 °C 13 phases have been reported earlier. Based on XPD Rietveld refinements the crystal structures for 9 new ternary phases were assigned to known structure types. Structural chemistry of these compounds follows the characteristics already outlined for their prototype structures: τ7—Ce3RhSi3, (Ba3Al2Ge2-type), τ8—Ce2Rh3−xSi3+x (Ce2Rh1.35Ge4.65-type), τ10—Ce3Rh4−xSi4+x (U3Ni4Si4-type), τ11—CeRh6Si4 (LiCo6P4-type), τ13—Ce6Rh30Si19.3 (U6Co30Si19-type), τ18—Ce4Rh4Si3 (Sm4Pd4Si3-type), τ21—CeRh2Si (CeIr2Si-type), τ22—Ce2Rh3+xSi1−x (Y2Rh3Ge-type) and τ24—Ce8(Rh1−xSix)24Si (Ce8Pd24Sb-type). For τ25—Ce4(Rh1−xSix)12Si a novel bcc structure was proposed from Rietveld analysis. Detailed crystal structure data were derived for τ3—CeRhSi2 (CeNiSi2-type) and τ6—Ce2Rh3Si5 (U2Co3Si5-type) by X-ray single crystal experiments, confirming the structure types. The crystal structures of τ4—Ce22Rh22Si56, τ5—Ce20Rh27Si53 and τ23—Ce33.3Rh58.2−55.2Si8.5−11.5 are unknown. High temperature compounds with compositions Ce10Rh51Si33 (U10Co51Si33-type) and CeRhSi (LaIrSi-type) have been observed in as-cast alloys but these phases do not participate in the phase equilibria at 800 °C. 相似文献
73.
Alexander Gribanov Andriy Grytsiv Yurii Seropegin 《Journal of solid state chemistry》2010,183(6):1278-1289
Two series of intermetallic alloys, RT2Si and RTSi2, have been synthesized from stoichiometric compositions. The crystal structures of EuPt1+xSi2−x (CeNiSi2-type), CeIr2Si (new structure type), YbPd2Si and YbPt2Si (both YPd2Si-type) have been elucidated from X-ray single crystal CCD data, which were confirmed by XPD experiments. The crystal structures of LaRh2Si and LaIr2Si (CeIr2Si-type), {La,Ce,Pr,Nd}AgSi2 (all TbFeSi2-type), and EuPt2Si (inverse CeNiSi2-type) were characterized by XPD data. RT2Si/RTSi2 compounds were neither detected in as-cast alloys Sc25Pt50Si25, Eu25Os25Si50 and Eu25Rh25Si50 nor after annealing at 900 °C. Instead, X-ray single crystal data prompted Eu2Os3Si5 (Sc2Fe3Si5-type) and EuRh2+xSi2−x (x=0.04, ThCr2Si2-type) as well as a new structure type for Sc2Pt3Si2 (own type). 相似文献
74.
It is shown that in LC of polymers, the interaction parameter in ternary mobile phases can be described by a plane, which is determined by the dependencies in binary mobile phases. Instead of a critical adsorption point, critical conditions are observed along a straight line of composition between the two critical points in binary mobile phases. Consequently, a separation of block copolymers under critical conditions for one block by an adsorption mechanism for the other block can be achieved in ternary mobile phases of different compositions, which allows an adjustment of the retention of the adsorbing block. 相似文献
75.
用离子交换法将具有K egg in结构11-钨锌三元杂多化合物K8[M ZnW11(H2O)O39](M=Co2+、N i2+、Cu2+、Cd2+)嵌入到Zn2A l类水滑石中,得到层状化合物:Zn2A l-[M ZnW11(H2O)O39](M=Co2+、N i2+、Cu2+、Cd2+),并用XRD、IR、UV对其进行了表征。结果表明,杂多阴离子进入水滑石层间后,仍保留了其K egg in结构。利用层状化合物催化合成乙酸正丁酯考察其催化活性,结果表明,层状化合物在酯化反应中显示优良的催化性能。 相似文献
76.
In this paper, a rigorous theoretical analysis has been made to study the dispersion relation of EM waves in periodic ternary one-dimensional photonic crystal having two different structures. In one case we have chosen glass-plasma and ZnS in one unit cell and in other case we have considered glass-plasma and MgF2 in one unit cell. Using Kronig-Penney model the dispersion relation for proposed structures has been obtained and numerical results are presented in the form of dispersion curves. The dependence of photonic band gap (PBG) characteristics on plasma frequency, plasma width and the width of dielectric media are discussed in the light of frequency gap and cutoffs of binary one-dimensional plasma photonic crystal. An attempt has been made to show how the PBG characteristic of a particular structure changes when the dielectric materials of its unit cell is changed by the other dielectric material. It is found that the structure having glass-plasma-ZnS in unit cell is more useful for broad band filtering and other plasma functioning devices compared to the structure having glass-plasma-MgF2 in one unit cell. 相似文献
77.
Structural, elastic, electronic and thermal properties of the MAX phase Nb2SiC are studied by means of a pseudo-potential plane-wave method based on the density functional theory. The optimized zero pressure geometrical parameters are in good agreement with the available theoretical data. The effect of high pressure, up to 40 GPa, on the lattice constants shows that the contractions along the c-axis were higher than those along the a-axis. The elastic constants Cij and elastic wave velocities are calculated for monocrystal Nb2SiC. Numerical estimations of the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature for ideal polycrystalline Nb2SiC aggregates are performed in the framework of the Voigt-Reuss-Hill approximation. The band structure shows that Nb2SiC is an electrical conductor. The analysis of the atomic site projected densities and the charge density distribution shows that the bonding is of covalent-ionic nature with the presence of metallic character. The density of states at Fermi level is dictated by the niobium d states; Si element has a little effect. Thermal effects on some macroscopic properties of Nb2SiC are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the primitive cell volume, volume expansion coefficient, bulk modulus, heat capacity and Debye temperature with pressure and temperature in the ranges of 0-40 GPa and 0-2000 K are obtained successfully. 相似文献
78.
Zadjia Atik 《Journal of Molecular Liquids》2011,163(2):89-92
The volumetric properties were evaluated from density data for the binary mixtures of (fluorobenzene + tert-butylmethyl ether), (α,α,α-trifluorotoluene + tert-butylmethyl ether), (tert-butylmethyl ether + ethanol), and the ternary mixtures of (fluorobenzene + tert-butylmethyl ether + ethanol) and (α,α,α-trifluorotoluene + tert-butylmethyl ether + ethanol). The observed densities were obtained by means of a vibrating-tube densimeter at the temperature 298.15 K and the pressure 101 kPa.The excess molar volumes of the ternary mixtures were estimated from binary solution data using several empirical equations with mean standard deviation less than 0.03 cm3·mol-1. Stable chemical cross-associations among the molecules forming the mixtures were revealed. 相似文献
79.
M. ElMassalami D. da S. OliveiraH. Takeya 《Journal of magnetism and magnetic materials》2011,323(16):2133-2136
Based on extensive Mossbauer effect (ME) and magnetization measurements, the orthorhombic AlFe2B2 was characterized as a ferromagnet (FM) because this character is evident as an onset of a FM transition at Tc=320 K and characteristic magnetizations isotherms below Tc. At liquid helium temperatures, the magnetization saturates to μsat≈1μB per Fe atom; a value which is half the one reported for the iron metal indicating a relatively more filled 3d band. The ME analysis revealed a hyperfine field H(0) of 88(2) kOe, an isomer shift (relative to Fe) of 0.50(2) mm/s, and a quadrupole parameter of 0.02 mm/s: all parameters extrapolated to zero Kelvin. The itinerant character of the magnetic moment will be discussed. 相似文献
80.
冗余函数和自反函数是特殊的布尔函数,本文阐述了冗余函数和自反函数的定义,提出了冗余函数和自反函数的性质,讨论了冗余函数和自反函数的图形检测方法.并用实例说明之.通过计算机编程操作.可以得到用于多变量冗余函数和自反函数检测的快速算法. 相似文献