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71.
72.
The characteristics of confined epitaxial growth are investigated with the goal of determining the contributing effects of mask attributes (spacing, feature size) and growth conditions (V/III ratio, pressure, temperature) on the efficiency of the approach for dislocation density reduction of GaN. In addition to standard (secondary electron and atomic force) microscopy, electron channeling contrast imaging (ECCI) is employed to identify extended defects over large (tens of microns) areas. Using this method, it is illustrated that by confining the epitaxial growth, high quality GaN can be grown with dislocation densities approaching zero. 相似文献
73.
Matthias Westerhausen Sabine Weinrich Manfred Oßberger Norbert W. Mitzel 《无机化学与普通化学杂志》2003,629(4):575-577
The reaction of calcium‐bis[bis(trimethylsilyl)amide] with two equivalents triethylgallium yields nearly quantitatively the addition product. In the solid state the calcium atoms are coordinated by two nitrogen atoms and two ethyl groups, whereas in solution all ethyl substituents are magnetically equivalent even at low temperatures. The Ca‐C‐Ga two‐electron three‐center bonds show mean Ca‐N and Ca‐C distances of 243 and 268 pm, respectively. 相似文献
74.
75.
Lei Wang Rui-Min Xu Bo Yan 《International Journal of Infrared and Millimeter Waves》2007,28(12):1133-1141
An accurate small-signal modeling approach applied to GaAs-based pHEMT devices is presented. The procedure for extracting
equivalent-circuit model parameters is illustrated in detail. A genetic algorithm (GA) program is developed to optimize the
model parameters in order to improve the modeling accuracy. The validity of modeling approach is verified by comparing the
simulated and measured result of two pHEMTs and a fabricated ka-band power amplifier. The conclusion can be drawn that the
proposed modeling method is rather accurate and efficient. 相似文献
76.
The (111)B surface of GaAs has been investigated using scanning tunneling microscopy (STM) and a number of different reconstructions have been found at different surface stoichiometries. In accordance with electron diffraction studies, we find the series (2 × 2), (1 × 1)LT, (
) and (1 × 1)HT with increasing annealing temperature, corresponding to decreasing surface As concentration. The (1 × 1)LT is of particular interest, since it only occurs in a narrow temperature window between the two more established reconstructions, the (2 × 2) and the (
). We find the (1 × 1)LT to take the form of a mixture of the local structures of both the (2 × 2) and (
) phases, rather than having a distinct structure. This is behaviour consistent with a kinetically limited system, dominated by the supply of As adatoms to the surface, and may be an example of a continuous phase transition. Above the (1 × 1)LT transition, atomic resolution images of the (
) surface reveal only a three-fold symmetry of the hexagonal structural units, brought about by inequivalent surface bonding due to the 23.4° rotation of the surface unit cell relative to the substrate. This is responsible for the disorder found in the (
) reconstruction, since the structure may form in one of two domains. At lower surface As concentration, the (1 × 1)HT surface adopts a structure combining small domains of a
19.1° structure and random disorder. There is no apparent similarity between the (1 × 1)LT and (1 × 1)HT structures, which may be due to our measurements being conducted at room temperature and without an As flux to control the surface As concentration. 相似文献
77.
The gallides SrRh2Ga2, SrIr2Ga2, and Sr3Rh4Ga4 were obtained from the elements by induction melting and subsequent annealing. They were investigated by powder and single‐crystal X‐ray diffraction: CaRh2B2 type, Fddd, a = 573.2(1), b = 1051.3(1), c = 1343.7(2) pm, wR2 = 0.0218, 398 F2 values, 15 variables for SrRh2Ga2; a = 576.0(1), b = 1045.5(1), c = 1350.6(3) pm for SrIr2Ga2, and Na3Pt4Ge4 type, I$\bar{4}$ 3m, a = 777.4(2) pm, wR2 = 0.0234, 190 F2 values, 11 variables for Sr3Ir4Ga4. The gallides SrRh2Ga2 and Sr3Ir4Ga4 exhibit complex, covalently bonded three‐dimensional [Rh2Ga2] and [Ir4Ga4] networks with short Rh–Ga (241–246 pm) and Ir–Ga (243–259 pm) distances. The strontium atoms fill large cages within these networks. They are coordinated by 8 Rh + 10 Ga in SrRh2Ga2 and by 4 Ir + 8 Ga in Sr3Ir4Ga4. The structure of SrRh2Ga2 is discussed along with the monoclinic distortion variants HoNi2B2 and BaPt2Ga2 on the basis of a group‐subgroup scheme. 相似文献
78.
《Comptes Rendus Chimie》2017,20(2):190-196
Nanotube properties are strongly dependent on their structures. In this study, gallium nitride nanotubes (GaNNTs) are analyzed in armchair and zigzag conformations. The wurtzite GaN (0001) surface is used to model the nanotubes. Geometry optimization is performed at the PM7 semiempirical level, and subsequent single-point energy calculations are carried out via Hartree–Fock and B3LYP methods, using the 6-311G basis set. Semiempirical and ab initio methods are used to obtain strain energy, charge distribution, dipole moment, |HOMO-LUMO| gap energy, density of states and orbital contribution. The gap energy of the armchair structure is 3.82 eV, whereas that of the zigzag structure is 3.92 eV, in agreement with experimental data. 相似文献
79.
Oracio Serrano 《Journal of organometallic chemistry》2011,696(10):2217-2219
The nickel (0) compound Ni(COD)(GaAr′)2 (Ar′ = C6H3-2,6-(C6H3-2,6-i-Pr2)2), 1, was synthesized by the reaction of Ni(COD)2 (COD = 1,5-cyclooctadiene) with (GaAr′)2. Compound 1 reacted with ethylene at 25 °C and at 1 atm pressure to give the bimetallic cluster [Ni2(GaAr′)2(η1:η1-μ2-C2H4)], 2, through the incorporation of one molecule of ethylene and displacement of COD. The structure of 2 featured an unusual Ni2Ga2C2 core bicyclic structure in which the C2H4 moiety bridges the Ga···Ga edge of a Ga2Ni2 tetrahedron. The galliums each carry an η1-bonded Ar′ substituent which complexes the nickel atom by an η6-π interaction with one of its flanking Ar’ rings. 相似文献
80.
Dinorah Gambino Mariana FernándezDiego Santos Gustavo A. EtcheverríaOscar E. Piro Fernando R. PavanClarice Q.F. Leite Isabel TomazFernanda Marques 《Polyhedron》2011,30(7):1360-1366
In the search for gallium bioactive compounds five Ga(III) complexes, [GaIII(L-H)2](NO3), with tridentate salicylaldehyde semicarbazone derivatives as ligands (L) have been synthesized and characterized in the solid state and in solution by different techniques. The crystal structure of [GaIII(L4-H)2](NO3)·2H2O, where L4 is 3-ethoxysalicylaldehyde semicarbazone, was solved by X-ray diffraction methods. The gallium(III) ion is in a distorted octahedral environment, coordinated to two nearly planar and mutually perpendicular 3-ethoxysalicylaldehyde semicarbazonato anions acting as tridentate ligands through their phenol and carbonyl oxygen atoms and their azomethine nitrogen atom. Their biological potential has been explored by evaluating their activity on Mycobacterium tuberculosis, causative agent of tuberculosis, and their cytotoxicity on tumor cell lines. Three different human tumor cell lines were selected that show different degrees of resistance to metallodrugs: ovarian A2780 (low resistance), breast MCF7 (medium resistance) and prostate PC3 (high resistance) cells. Although the complexes have not shown activity on M. tuberculosis, complexation with gallium has led to the enhancement of the cytotoxic potencies of the organic compounds. Those complexes that contain a bromide substituent at the phenolate ring have shown the highest cytotoxicities. In particular, [GaIII(L2-H)2](NO3), where L2 is 5-bromosalicylaldehyde semicarbazone,·has shown a remarkable cytotoxicity on A2780 tumor cell line with an IC50 value of the same order than cisplatin (IC50 Ga-L2 = 2.4 ± 0.3 μM; IC50 cisplatin = 2.0 ± 0.1 μM, 72 h incubation at 37 °C). Interestingly, this complex has also shown moderate cytotoxicity against MCF7 and PC3 cells (IC50 MCF7 = 30 ± 6; IC50 PC3 = 18 ± 3 μM). Therefore, this gallium compound could be considered a promising wide spectrum potential anti-tumor agent. 相似文献