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331.
An in situ high pressure powder diffraction study, using high-brilliance synchrotron radiation, on lead feldspar (PbAl2Si2O8) was performed. Two samples, with Q
od=0.68 and 0.76, were loaded in a diamond anvil cell and were compressed up to 11 GPa. Up to P=7.1 GPa the only phase present
is lead feldspar. In the range 7.1–9.4 GPa sudden changes in the position of the reflections suggest the transformation of
lead feldspar to a new phase (probably feldspar-like). The absence of split that would be compatible with triclinic symmetry
rules out the monoclinic-triclinic transition, that was reported for the structurally similar strontium feldspar. At P>9.4 GPa some new extra reflections not indexable in the feldspar cell are present as well. During decompression the lead
feldspar was the only phase present at P<6 GPa. Peak enlargement was observed with pressure, probably preliminary to amorphization. However almost complete amorphization
was observed only after fortuitous shock compression at ∼18 GPa; the crystallinity was recovered at room pressure after decompression.
The bulk modulus for lead feldspar was K=71.0(9) and 67.6(1.2) GPa for the two samples, in the range reported for feldspars.
The cell parameters show a compression pattern which is similar to that observed in anorthite, with Δa/a
0>Δc/c
0>Δb/b
0; comparison with the high temperature behaviour shows that for lead feldspar the strain tensor with pressure is more isotropic
and the deformation along a is less prominent. A turnover in the behaviour of the β angle with pressure suggests a change in the compression behaviour
at P∼2 GPa. Rietveld refinement of the Pb coordinates was performed in a series of spectra with pressure ranging from 0.6 to 6.5
GPa. The combined analysis of cell parameters and Pb coordinates with pressure showed that the compression of the structure
is mainly achieved by an approach of Pb atoms along a
*.
Received: 21 July 1998 / Revised, accepted: 13 October 1998 相似文献
332.
Neutron powder diffraction experiments in the temperature range 300–1770 K were performed at BENSC, Berlin, Germany, on synthetic
(Mg0.70Fe0.23) Al1.97O4. The cation partitioning over the crystallographic tetrahedral and octahedral sites was determined as a function of temperature
through joint Rietveld refinements and advanced minimization techniques. The thermal expansion coefficients of the lattice
parameter and inter-atomic bond lengths were also obtained from the full-profile structure refinements. The behaviour of the
polyhedral bond-lengths, especially the T−O distances, and of the cell constant upon heating, clearly indicate that the interdiffusion
of tetrahedral and octahedral Mg/Al cations starts at about 950 K. This result is straightforwardly supported by the direct
analysis of the neutron site scattering factors: Fe always retains tetrahedral coordination at all temperatures, and the cation
rearrangement is entirely due to Mg and Al diffusion.
Received: 18 November 1997 / Revised, accepted: 23 August 1998 相似文献
333.
334.
从用户和生产厂家的观点阐述如何评定金刚石微粉的质量。着重论述根据金刚石微粉的粒度、颗粒形状、锐利性、抗磨耗性和强度来评定金刚石微粉的质量 相似文献
335.
超细粉末材料粒度测试技术研究 总被引:1,自引:0,他引:1
随着科学技术的发展,越来越多的细粒级粉末产品成为社会需求。如何便捷、准确地获得这些超细粉料的粒度数据,也就成了工艺矿物学工作者的一个课题。粒度测试分析中存在一些仍未解决的问题,例如采用不同的测试方法得到不同的粒度数据、取样的代表性和制样的合理性等。对于超细粉料,除了上述普通物料粒度测试中存在的问题之外,还会出现一些新问题,例如团聚现象的普遍性及其给各种测试方法带来的技术难题。近年来中国颗粒学会、国家有色金属工业局和冶金工业局等单位在这些方面做了许多有益探索,但在一些难题面前仍然显得软弱无力,主要… 相似文献
336.
变粒岩的鉴定通常以显微镜鉴定技术为主,但在显微镜下区分颗粒细小的长石、石英及绿泥石、蒙脱石、云母等层状硅酸盐矿物十分困难,仅通过显微鉴定技术对变粒岩进行定名可能产生较大误差,这对地质填图和原岩恢复工作会造成一些偏差,导致得出错误的地质结论。随着X射线衍射分析技术的发展,该技术已广泛应用于矿物学和岩石学的研究,本研究将结合X射线粉晶衍射技术,对显微镜下难以区分的细小矿物进行鉴定。共选用23件变粒岩样品,利用X射线粉晶衍射分析和显微镜岩石薄片鉴定技术,对变粒岩矿物组分进行检测,用X射线粉晶衍射矿物半定量分析结果验证岩石薄片鉴定结果准确性。显微镜岩石薄片鉴定结果与X射线粉晶衍射物相分析结果对比显示,10件样品定名一致,其余13件样品详细定名有差异。通过分析产生差异的原因,可以认为显微镜岩石薄片鉴定优势在于能确定岩石结构和构造,以及常见矿物组分;X射线粉晶衍射法的优势在于能检测出显微镜下较难区分的细小石英和长石颗粒的相对含量,并能检测出颗粒较小的绿泥石、蒙脱石及云母等层状硅酸盐矿物,该方法对含量较少、颗粒较细的矿物检测效果较好。实验证明将显微岩石薄片鉴定技术和X射线粉晶衍射技术相结合,才能更准确对变粒岩进行定名,为地学研究提供更符合客观实际的技术数据和分析结论。 相似文献
337.
338.