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101.
本文应用平均Hamiltonian理论讨论了异核偶极相互作用引起的场相关化学位移,对照二阶微拢论的结果,发现计入了"A"项的额外影响。说明在讨论非久期项效应时,一级平均Hamiltonian比只用二阶微扰论的结果更精确。文中,应用平均Hamiltonian理论还讨论了同核偶极相互作用产生的场相关化学位移。 相似文献
102.
根据自旋回波成像脉冲序列中像点信号强度与重复时间TR及回波时间TE的关系,结合岩石孔隙流体核磁共振她豫的多指数特性,利用T1加权和T2加权微成像提取岩样扎隙结构的信息,以此区分大孔和微孔.1实验方法自旋回波单片核磁共振成像脉冲序列如图1所示问.图中,GX为X方向的梯度场,用于信号的频率编码,实现X方向的空间定位;GY为Y方向的梯度场,用于信号的相位编码,实现Y方向的空间定位;GZ为Z方向的梯度场,结合形状脉冲,用于确定选片的位置及片厚,实现Z方向的空间定位.RF是射频脉冲发射通道,由90°宽带脉冲和180℃窄带形状… 相似文献
103.
用23Na和27Al固体核磁共振研究Na+在γ-Al2O3上的吸附状态 总被引:1,自引:0,他引:1
The adsorption of Na~+ on γ-alumina surface at four coverages of Na_2CO_3 (5%, 10%, 15%, and 20% wt/wt) was characterized by solid-state ~(23)Na and ~(27)Al NMR spectroscopy. The experimental results suggest that two distinct adsorbed species are present on alumina surface: surface species and surface salts. At lower coverages of Na_2CO_3 (5% and 10%), a surface species is predominant, in which the Na~+ cations are associated with the oxygen atoms of γ-alumina. With increasing the loading level to 15%, a second adsorbed species begins to appear which is attributed to the surface salt, Na_2CO_3, deposited on the solid surface. Further adsorption of Na_2CO_3 leads to an increase in the amount of surface salt while the amount of surface species remains unchanged. ~1H-~(27)Al CP/MAS experiments give the evidence that some Na~+ cations in the form of surface species are coordinated with the Br~(‥)onsted acid sites of γ-alumina. This may be the main driving force that improves appreciably the catalytic efficiency of Na_2CO_3/γ-Al_2O_3 catalyst. 相似文献
104.
In this paper a study of the spin lattice relaxation times of dioxane(DO) adsorbed on various charcoals is presented. Results show that the magnetziation of DO decays biexponentially (Table 1) as observed in the case of adsorbed hydrocarbons~[6]. The fast relaxing molecules are considered to be those adsorbed in micropores with radii less than 1.0 nm whose motion is restricted and slowed down, thus they form a solid like phase. However, the slow relaxing ones are those condensed in the micropores, they are free to move and form the liquid like phase. Molecules condensed in the interior of the micropores exchange rapidly with those situated in the vicinity of the pore wall according to Eq.(2).Comparison of data in Table 1 may lead to a conclusion that charcoal with greater density of surface acidic groups and greater percentage of pore capacity with radius<1.0 nm (V_(10)/V_(30)) has a greater percentage of solid like phase (P_f). Although V_(10)/V_(30) of density of surface acidic groups. It is apparent that surface acidic groups in micropores play an important role in the formation of solid like phase of DO on charcoals. It seems that DO form hydrogen bond with the surface acidic groups. It is this hydrogen bond and the hinderance effect of pores restrict the DO from moving freely, which results in the formation of the so called solid like phase. It can be found from small (0.10 ml/gC). This implies that DO vapour may first condense in the micropores having more acidic groups and higher activation energy, and then fill in other pores step by step as the adsorption process proceeds. 相似文献
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107.
低磁场条件下天然气核磁共振特性的实验研究 总被引:13,自引:3,他引:10
研究天然气在低磁场条件下的核磁共振弛豫特性及含烃因子的变化对天然气的勘探和开发工作具有重要意义,由于受核磁共振仪器耐温、耐压条件的限制,这方面的研究工作非常少,国内还是空白. 本文在一套自行研制的耐高温、耐高压的低磁场(磁场强度0.056T )核磁共振设备上,对我国大庆油田深层天然气的核磁共振特性进行了实验研究,获得了天然气的T1弛豫时间、含烃因子随温度和压力变化的函数关系. 本文的研究内容对我国正在开展的核磁共振测井工作具有重要的参考价值. 相似文献
108.
Five neutral macromolecular polyester gadolinium (Ⅲ) complexes with pendant hydrophobic alkyland aromatic functional groups were prepared. The longitudinal relaxation rates of these complexes weremeasured. One of these Gd (Ⅲ) complexes was chosen for the acute toxicity test and T_1-weighted imagingmeasurement. Preliminary results showed that. compared with Gd-DTPA. the neutral macromoleculargadolinium (Ⅲ) complexes provide higher T_1 relaxivity enhancement and longer function duration. 相似文献
109.
聚合物-锂改性蒙脱石复合材料离子迁移 总被引:1,自引:0,他引:1
以聚合物(PEO,PEO-PMMA)和锂改性蒙脱石作为主要原料,采用聚合物粉末直接熔融嵌入的方法,制备聚合物-蒙脱石复合材料.利用NMR、AC阻抗等分析方法探讨了复合材料中聚合物链对 Li+离子迁移的影响.结果表明,聚合物(PEO)嵌入蒙脱石层间,层间聚合物链的无序度增大,有利于Li+离子迁移.PMMA引入对PEO链的改性,进一步加大聚合物链的无序度,更易于层间Li+离子迁移;复合材料的常温离子电导率接近10-2S·cm-1,且具有良好的温度稳定性. 相似文献
110.