全文获取类型
收费全文 | 52篇 |
免费 | 20篇 |
国内免费 | 7篇 |
专业分类
大气科学 | 4篇 |
地球物理 | 24篇 |
地质学 | 31篇 |
海洋学 | 2篇 |
天文学 | 4篇 |
综合类 | 2篇 |
自然地理 | 12篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 4篇 |
2012年 | 1篇 |
2011年 | 5篇 |
2010年 | 1篇 |
2009年 | 6篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有79条查询结果,搜索用时 15 毫秒
71.
High-temperature oxide-melt calorimetry and Rietveld refinement of powder X-ray diffraction patterns were used to investigate the energetics and structure of the hematite–corundum solid solution and ternary phase FeAlO3 (with FeGaO3 structure). The mixing enthalpies in the solid solution can be described by a polynomial ΔHmix=WX hem(1?X hem) with W=116 ± 10 kJ mol?1. The excess mixing enthalpies are too positive to reproduce the experimental phase diagram, and excess entropies in the solid solution should be considered. The hematite–corundum solvus can be approximately reproduced by a symmetric, regular-like solution model with ΔG excess=(W H ?TW S )X hem X cor, where W H= 116 ± 10 kJ mol?1 and W S =32 ± 4 J mol?1 K?1. In this model, short-range order (SRO) of Fe/Al is neglected because SRO probably becomes important only at intermediate compositions close to Fe:Al=1:1 but these compositions cannot be synthesized. The volume of mixing is positive for Al-hematite but almost ideal for Fe-corundum. Moreover, the degree of deviation from Vegard's law for Al-hematite depends on the history of the samples. Introduction of Al into the hematite structure causes varying distortion of the hexagonal network of oxygen ions while the position of the metal ions remains intact. Distortion of the hexagonal network of oxygen ions attains a minimum at the composition (Fe0.95Al0.05)2O3. The enthalpy of formation of FeAlO3 from oxides at 298 K is 27.9 ± 1.8 kJ mol?1. Its estimated standard entropy (including configurational entropy due to disorder of Fe/Al) is 98.9 J mol?1 K?1, giving the standard free energy of formation at 298 K from oxides and elements as +19.1 ± 1.8 and ?1144.2 ± 2.0 kJ mol?1, respectively. The heat capacity of FeAlO3 is approximated as C p (T in K)= 175.8 ? 0.002472T ? (1.958 × 106)/T 2? 917.3/T 0.5+(7.546 × 10?6) T 2 between 298 and 1550 K, based on differential scanning calorimetric measurements. No ferrous iron was detected in FeAlO3 by Mössbauer spectroscopy. The ternary phase is entropy stabilized and is predicted to be stable above about 1730 ± 70 K, in good agreement with the experiment. Static lattice calculations show that the LiNbO3-, FeGaO3-, FeTiO3-, and disordered corundum-like FeAlO3 structures are less stable (in the order in which they are listed) than a mechanical mixture of corundum and hematite. At high temperatures, the FeGaO3-like structure is favored by its entropy, and its stability field appears on the phase diagram. 相似文献
72.
Thermodynamics of gas and steam-blast eruptions 总被引:1,自引:1,他引:0
L. G. Mastin 《Bulletin of Volcanology》1995,57(2):85-98
Eruptions of gas or steam and non-juvenile debris are common in volcanic and hydrothermal areas. From reports of non-juvenile eruptions or eruptive sequences world-wide, at least three types (or end-members) can be identified: (1) those involving rock and liquid water initially at boiling-point temperatures (boiling-point eruptions); (2) those powered by gas (primarily water vapor) at initial temperatures approaching magmatic (gas eruptions); and (3) those caused by rapid mixing of hot rock and ground- or surface water (mixing eruptions). For these eruption types, the mechanical energy released, final temperatures, liquid water contents and maximum theoretical velocities are compared by assuming that the erupting mixtures of rock and fluid thermally equilibrate, then decompress isentropically from initial, near-surface pressure (10 MPa) to atmospheric pressure. Maximum mechanical energy release is by far greatest for gas eruptions (1.3 MJ/kg of fluid-rock mixture)-about one-half that of an equivalent mass of gunpowder and one-fourth that of TNT. It is somewhat less for mixing eruptions (0.4 MJ/kg), and least for boiling-point eruptions (0.25 MJ/kg). The final water contents of crupted boiling-point mixtures are usually high, producing wet, sloppy deposits. Final erupted mixtures from gas eruptions are nearly always dry, whereas those from mixing eruptions vary from wet to dry. If all the enthalpy released in the eruptions were converted to kinetic energy, the final velocity (v
max) of these mixtures could range up to 670 m/s for boiling-point eruptions and 1820 m/s for gas eruptions (highest for high initial pressure and mass fractions of rock (m
r) near zero). For mixing eruptions, v
max ranges up to 1150 m/s. All observed eruption velocities are less than 400 m/s, largely because (1) most solid material is expelled when m
r is high, hence v
max is low; (2) observations are made of large blocks the velocities of which may be less than the average for the mixture; (3) heat from solid particles is not efficiently transferred to the fluid during the eruptions; and (4) maximum velocities are reduced by choked flow or friction in the conduit. 相似文献
73.
The adsorption performance of β‐ionone on four types of granular activated carbon (GAC) in water was investigated through batch experiments. The effect of initial β‐ionone concentrations and natural organic matter (NOM) adsorbed on GAC, adsorption kinetic and isothermal models were also studied. The results showed that four types of GAC all had good adsorption performance for β‐ionone, the equilibrium adsorption amount of the GAC employed was in the order of YK > GK > MZ‐A > MZ‐B. The adsorption amount increased with increasing initial concentrations. The presence of NOM could reduce adsorption of β‐ionone to a certain extent, and small molecular weight (MW) fractions (particularly <1000 Da) exhibited a remarkably competitive effect on the adsorption of β‐ionone. The experimental data showed good correlation with pseudo‐first‐order model. Furthermore, adsorption of β‐ionone on GAC fitted Freundlich, Langmuir, and Tempkin isotherms in the range of experimental concentrations, but followed Freundlich isothermal model most appropriate. The thermodynamic parameters were calculated by the results of the experiment, which showed adsorption of β‐ionone on GAC as being endothermic and spontaneous. 相似文献
74.
75.
76.
77.
The paper presents a review of constitutive modelling of unsaturated soils. After a brief historical perspective, a number of existing constitutive models are classified and discussed according to the type of stress variables adopted in their formulation. Afterwards, attention is given to recent developments in the proposal of coupled hydraulic-mechanical models and the possibility of casting them in a sound thermodynamical framework. Finally, a double structure model for expansive soils is described. The incorporation of microstructural considerations and its use as a platform for incorporating the influence of new variables are highlighted. 相似文献
78.
Fougerite is a new iron oxide, a mixed M(II)–M(III) hydroxide, a member of the green rust group. Its structure consists of a brucitic layer of Fe(III)–Fe(II)–Mg(II), where the excess of the positive charge due to Fe3+ is compensated in the interlayer by anions. The limits of composition are structurally and geochemically constrained, and the stabilities of the mineral and green rusts are obtained by a thermodynamic model of a regular solid solution, for different compensating anions and for any allowed composition of the brucitic layer. 相似文献
79.