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81.
Neutron diffraction has been used to study the structure of a glass and melt of composition 75SiO2-15Na2O-10CaO. RMC modeling of the neutron and X-ray diffraction data for the glass allowed the determination of the Na and Ca environment. The structure has been investigated at 300K, just below the glass transition at 823 K and in the melt at 1273 K. The short range order does not present important modifications with temperature while significant reorganization appears at the medium range order. These latter changes can be associated with the Si and O pairs and indicate the relaxation of the silicate network. This indicates that the glass formation involved structural rearrangement during cooling. 相似文献
82.
Mattias Edén 《Journal of Non》2011,357(6):1595-1602
We present a strategy, referred to as “split network” analysis, for assessing the average network polymerization (rF) and mean number of bridging oxygen (BO) atoms (N?BOF) for each individual network former F in multi-component oxide-based glasses, primarily targeting those involving Al, B, P and Si. This requires a priori knowledge about the parameters {rF, N?BOF} of all network builders, but one, whose values are deduced by the split network procedure. We illustrate split-network concepts for establishing composition/structure/bioactivity correlations in Na-Ca-Si-P-O glasses. The cooperating influences on the bioactivity from the average polymerization degree of the silicate network and the amounts of orthophosphate and sodium ions are discussed. 相似文献
83.
The preceding part [M. Edén, J. Non.-Cryst. Solids, 357, (2011) 1595-1602] introduced the “split network” strategy for estimating the network polymerization degree (rA) and mean number of bridging oxygen (BO) atoms for a network former A, given that these parameters are known for all other network builders in the multi-component oxide glass. However, as the detailed ordering of BO and non-bridging oxygen (NBO) species is often difficult to assess experimentally, we summarize some “rules of thumb” for predicting the coordination number and tendency to accept NBO ions for Al3+, B3+, Si4+ and P5+ cations: they are helpful in scenarios devoid of experimental data. Using the parameters r and , we present expressions for the BO/NBO distributions among tetrahedrally coordinated cations, as predicted from the binary and random models. Multinuclear 11B, 27Al and 29Si solid-state NMR is exploited to derive the split network representations of a set of Na-Ca-(Al)-(B)-Si-O glasses. These results are subsequently used to gain structural insight into two commercial glass-wool fibers that constitute alumino-borosilicate networks modified by Na+, K+, Ca2+ and Mg2+ ions. 相似文献
84.
The structure factors of Mg2SiO4 glass have been measured using high energy x-ray diffraction up to pressures of 30.2 GPa, and the equation of state measured up to 12.8 GPa. The average Mg-O coordination numbers were extracted from the experimental pair distribution functions assuming two cases (i) there is no change in Si-O coordination number with pressure and (ii) the average Si-O coordination number increases the same as for pure SiO2 glass. Both analyses give similar results and show a gradual increase in the average Mg-O coordination number from 5.0 at ambient pressure to ~ 6.6(6) at 30.2 GPa. There is good qualitative agreement between the experimental structure and equation of state data for the glass compared to several recent molecular dynamics simulations carried out on liquid Mg2SiO4. 相似文献
85.
运用拉曼光谱技术研究了Na2O(K2O)—CaO(MgO)—SiO2,Na2O(K2O)—Al2O3—SiO2,Na2O(K2O)—B2O3—SiO2,Na2O(K2O)—PbO—SiO2和PbO—BaO—SiO2五个系统的玻璃。结果表明,阳离子对玻璃近程结构的改造会引起拉曼特征的变化。部分样品是根据古玻璃平均成分在实验室烧制的,这项研究对于运用激光拉曼光谱区分不同系统的古代硅酸盐玻璃有重要意义。 相似文献
86.
87.
E. Arroyabe 《Journal of solid state chemistry》2009,182(12):3254-3261
In the course of an excursion into the system K2O-CaO-SiO2, single crystalline material of the previously unknown compound K2Ca6Si4O15 has been obtained. Single crystal X-ray diffraction experiments revealed that the new phase is monoclinic (space group P12/c1) with the following basic crystallographic data: a=7.3782(8) Å, b=5.5677(5) Å, c=17.2466(17) Å, β=90.005(8)°, Z=2. According to Liebau's nomenclature, the compound can be classified as a mixed anion silicate containing insular [SiO4]-groups as well as [Si2O7]-dimers in the ratio 2:1, i.e. the crystallochemical formula can be written as K2Ca6[SiO4]2[Si2O7]. The silicate anions are linked by K- and Ca-ions distributed among five different non-tetrahedral M-positions and coordinated by six to eight nearest oxygen neighbors. Alternatively, the structure can be described as a heteropolyhedral framework built up by kröhnkite-type [M(SiO4)2O2]-chains in which the MO6 octahedra are corner-linked to bridging SiO4 tetrahedra. The chains (running parallel to [0 1 0]) are located in 4.6 Å wide layers parallel to (1 0 0). Neighboring sheets are shifted relative to each other by an amount of +δ or −δ along [0 0 1]. In the derived two layer …ABABAB… stacking sequence, chains belonging to adjacent sheets are linked by corner sharing of common oxygen atoms. The resulting network contains tunnels in which the more irregularly coordinated K- and Ca-ions are incorporated for charge compensation. A comparison between the present compound and structurally related mixed tetrahedral-octahedral frameworks is given. The characterization has been completed by Raman and FTIR-spectroscopy. An allocation of the bands to certain vibrational species has been aided by density functional theory (DFT) calculations. 相似文献
88.
硅酸盐熔体是典型的近程有序,远程无序的准稳定态分数维体系,文章采用X射线小角散射(SAXS)、低波数拉曼光谱(LWRS)及高温拉曼光谱(HTRS)实时、原位分析等技术,对高温熔融法和溶胶凝胶法合成的CaO-Al2O3-SiO2和Na2O-Al2O3-SiO2系列低维非晶硅酸盐试样进行了团粒结构粒度及其类声子振动频率的定量测定,获得了低温硅酸盐凝胶、高温硅酸盐熔体及其淬火玻璃相均具有纳米级(几个纳米至几十纳米)自相似团粒结构和类声子振动模的重要结论,进而建立了测定高温熔体介观团粒结构粒度的HTRS测定法,结果表明硅酸盐熔体的团粒结构粒度在高温下均会比其室温玻璃相的团粒尺度小,且高温熔体的网络结构基元也向桥氧数减少之基元转变。这些结论为探索自然界岩浆的地球化学特征、岩浆的结晶和演化以及低维硅酸盐材料结构性能的改进提供重要理论依据及信息。 相似文献
89.
90.
Divalent europium-activated strontium orthosilicate Sr2SiO4:Eu2+ and Mg0.1Sr1.9SiO4:Eu2+ phosphors were synthesized through the solid-state reaction technique. Their luminescent properties under ultraviolet excitation were investigated. The X-ray diffraction (XRD) results show that these phosphors are of α′-Sr2SiO4 phase with a trace of β-Sr2SiO4. Doping of Eu2+ ion into the crystal lattice results in the lattice constant being expended, while Mg2+ makes the lattice constant shrinking. A solid solution with the same crystal structure is formed when Eu2+ or Mg2+ substitutes part of Sr2+ ions and occupies the same lattice sites. The Sr2SiO4:Eu2+ phosphors show two emission spectra peaked at 535 and 473 nm originated from the 5d-4f transition of Eu2+ ion doped in two different Sr2+ sites in the host lattice. By substitution of 0.1 mol of Sr2+ with Mg2+, these two emission bands are tuned to be in the blue and yellow region (459 and 564 nm for Mg0.1Sr1.88SiO4:Eu0.02), respectively. The tuning effect is discussed. With a combination of the blue and yellow emission bands the phosphors show white color, indicating that these phosphors may become promising phosphor candidates for white light-emitting diodes (LEDs). 相似文献