全文获取类型
收费全文 | 222篇 |
免费 | 6篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 12篇 |
地球物理 | 33篇 |
地质学 | 127篇 |
海洋学 | 7篇 |
天文学 | 34篇 |
自然地理 | 12篇 |
出版年
2019年 | 3篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 9篇 |
2012年 | 5篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 8篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 6篇 |
1999年 | 3篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1984年 | 5篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1964年 | 3篇 |
1957年 | 2篇 |
1955年 | 3篇 |
1951年 | 3篇 |
1948年 | 2篇 |
1934年 | 2篇 |
1933年 | 3篇 |
1932年 | 2篇 |
1928年 | 2篇 |
1927年 | 3篇 |
1926年 | 3篇 |
1925年 | 2篇 |
1915年 | 1篇 |
1914年 | 3篇 |
1913年 | 1篇 |
排序方式: 共有228条查询结果,搜索用时 843 毫秒
131.
132.
133.
Wilhelm Heinrich Paul Metz Werner Bayh 《Contributions to Mineralogy and Petrology》1986,93(2):215-221
Stoichiometric mixtures of tremolite and dolomite were heated to 50° C above equilibrium temperatures to form forsterite and calcite. The pressure of the CO2-H2O fluid was 5 Kb and \(X_{{\text{CO}}_{\text{2}} }\) varied from 0.1 to 0.6. The extent of the conversion was determined by the amount of CO2 produced. The resulting mixtures of unreacted tremolite and dolomite and of newly-formed forsterite and calcite were examined with a scanning electron microscope. All tremolite and dolomite grains showed obvious signs of dissolution. At fluid compositions with \(X_{{\text{CO}}_{\text{2}} }\) less than about 0.4, the forsterite and calcite crystals are randomly distributed throughout the charges, indicating that surfaces of the reactants are not a controlling factor with respect to the sites of nucleation of the products. A change is observed when \(X_{{\text{CO}}_{\text{2}} }\) is greater than about 0.4; the forsterite and calcite crystals now nucleate and grow at the surface of the dolomite grains, thus indicating a change in mechanism at medium CO2 concentrations. As the reaction progresses, the dolomite grains become more and more surrounded by forsterite and calcite, finally forming armoured relics of dolomite. Under experimental conditions this characteristic texture can only be formed if the CO2-concentration is greater than about 40 mole %. These findings make it possible to estimate the CO2-concentration from the texture of the dolomite+tremolite+forsterite+calcite assemblage. The results suggest a dissolution-precipitation mechanism for the reaction investigated. In a simplified form it consists of the following 4 steps:
- Dissolution of the reactants tremolite and dolomite.
- Diffusion of the dissolved constituents in the fluid.
- Heterogeneous nucleation of the product minerals.
- Growth of forsterite and calcite from the fluid.
134.
The orientational ordering transition R \(R\bar 3m - R\bar 3c\) in NaNO3 near 552 K has been investigated using x-ray diffraction techniques. NaNO3 is a model system for CaCO3 and other minerals with orientational disorder of triangular molecules in a simple NaCl-type matrix. The temperature evolution of the integrated intensities of the superlattice reflection \(\bar 1\) 23 and the fundamental reflection 110 are discussed in terms of Landau theory of two coupled order parameters. It is shown that the known phenomenological critical exponent (Poon and Salje 1988) and the anomalous thermal expansion at T > T tr (Reeder et al. 1988) can be understood as the result of a Z point instability which mainly describes the NO 3 - disorder, and a second order parameter linked with the spontaneous strain of this phase transition. 相似文献
135.
136.
137.
Wilhelm Johannes 《Contributions to Mineralogy and Petrology》1984,86(3):264-273
The beginning of melting in the system Qz-Or-Ab-An-H2 O was experimentally reversed in the pressure range
kbar using starting materials made up of mixtures of quartz and synthetic feldspars. With increasing pressure the melting
temperature decreases from 690° C at 2 kbar to 630° C at 17 kbar in the An-free alkalifeldspar granite system Qz-Or-Ab-H2O. In the granite system Qz-Or-Ab-An-H2O the increase of the solidus temperature with increasing An-content is only very small. In comparison to the alkalifeldspar
granite system the solidus temperature increases by 3° C (7° C) if albite is replaced by plagioclase An 20 (An 40). The difference
between the solidus temperatures of the alkalifeldspar granite system and of quartz — anorthite — sanidine assemblages (system
Qz-Or-An-H2O) is approximately 50° C.
With increasing water pressures plagioclase and plagioclase-alkalifeldspar assemblages become unstable and are replaced by
zoisite+kyanite+quartz and zoisite+muscovite-paragonitess +quartz, respectively. The pressure stability limits of these assemblages are found to lie between 6 and 16 kbar at 600°
C. At high water pressures (10–18 kbar) zoisite — muscovite — quartz assemblages are stable up to 700 and 720° C. The solidus
curve of this assemblage is 10–20° C above the beginning of melting of sanidine — zoisite — muscovite — quartz mixtures.
The amount of water necessary to produce sufficient amounts of melt to change a metamorphic rock into a magmatic looking one
is only small. In case of layered migmatites it is shown that 1 % of water (or even less) is sufficient to transform portions
of a gneiss into (magmatic looking) leucosomes. High grade metamorphic rocks were probably relatively dry, and anatectic magmas
of granitic or granodioritic composition are usually not saturated with water. 相似文献
138.
At the San Luis Potosí (SLP) volcanic field (Central Mexico), Quaternary basanites and tuff breccias have sampled a suite of ultramafic xenoliths, predominately spinel lherzolites, spinel-olivine websterites, spinel pyroxenites, and hornblende-rich pyroxenites. Spinel lherzolites from the La Ventura maars have protogranular to equigranular textures, those from the Santo Domingo maars are strongly sheared. Both spinel-lherzolite types show similar whole-rock major and trace-element abundances. They are fertile to slightly depleted with mineralogical and geochemical heterogeneities induced by partial melting processes. Pyroxenites with either magmatic or metamorphic textures are high-pressure cumulates. Hornblende-rich pyroxenites are genetically linked to the host basanites. Most of the protogranular spinel lherzolites contain veinlets of glass along grain boundaries. These glasses are chemically homogeneous and have trachybasaltic to trachyandesitic compositions. Mg- and Fe2+-partitioning between olivine and glass suggests chemical equilibrium between the melts represented by the glasses and the spinel-lherzolite mineral assemblage at about 1,000°C and 10 to 15 kbar. The melts are interpreted to be of upper mantle origin. They may have been formed by in-situ partial melting in the presence of volatiles or represent percolating melts chemically buffered by the spinel-lherzolite mineral assemblage at uppermost mantle conditions. Mineral chemistry in all rock types of the whole xenolith suite reveals distinct disequilibrium features reflecting partial re-equilibration stages towards lower temperatures estimated to be from 1,050°C to 850°C at 9 to 15 kbar. The presence of similar zoning and exsolution features mainly documented in pyroxenes along with similar maximum and minimum temperatures requires all sampled xenoliths to have undergone the same temperature regime within the upper mantle. The sheared spinel lherzolites from the Sto. Domingo field are interpreted as formerly protogranular material which was sheared during uplift and cooling. The estimated mantle temperatures are higher than those predicted by low heat-flow measurements at the SLP fild, indicating that surface heat flow has not equilibrated to elevated temperatures at depth. This strongly supports a young perturbation event beneath the SLP area and connects the onset of uplift and cooling of the SLP-mantle segment with the back-arc extensional regime of the Quaternary volcanic cycle of the Transmexican Volcanic Belt. 相似文献
139.
Alexander T. Basilevsky Gerhard Neukum Stephanie C. Werner Alexander Dumke Stephan van Gasselt Thomas Kneissl Wilhelm Zuschneid Daniela Rommel Lorenz Wendt Mary Chapman James W. Head Ronald Greeley 《Planetary and Space Science》2009,57(8-9):917-943
The Mangala Valles is a 900-km long outflow channel system in the highlands adjacent to the south-eastern flank of the Tharsis bulge. This work was intended to answer the following two questions unresolved in previous studies: (1) Was there only one source of water (Mangala Fossa at the valley head which is one of the Medusae Fossae troughs or graben) or were other sources also involved in the valley-carving water supply, and (2) Was there only one episode of flooding (maybe with phases) or were there several episodes significantly separated in time. The geologic analysis of HRSC image 0286 and mapping supported by analysis of MOC and THEMIS images show that Mangala Valles was carved by water released from several sources. The major source was Mangala Fossa, which probably formed in response to magmatic dike intrusion. The graben cracked the cryosphere and permitted the release of groundwater held under hydrostatic pressure. This major source was augmented by a few smaller-scale sources at localities in (1) two mapped heads of magmatic dikes, (2) heads of two clusters of sinuous channels, and (3) probably several large knob terrain locals. The analysis of results of crater counts at more than 60 localities showed that the first episode of formation of Mangala Valles occurred ~3.5 Ga ago and was followed by three more episodes, one occurred ~1 Ga ago, another one ~0.5 Ga ago, and the last one ~0.2 Ga ago. East of the mapped area there are extended and thick lava flows whose source may be the eastern continuation of the Mangala source graben. Crater counts in 10 localities on these lava flows correlate with those taken on the Mangala valley elements supporting the idea that the valley head graben was caused by dike intrusions. Our observations suggest that the waning stage of the latest flooding episode (~0.2 Ga ago) led to the formation at the valley head of meander-like features sharing some characteristics with meanders of terrestrial rivers. If this analogy is correct this could suggest a short episode of global warming in Late Amazonian time. 相似文献
140.
Assessing the strength of regional changes in near-surface climate associated with a global warming of 2°C 总被引:2,自引:1,他引:1
Wilhelm May 《Climatic change》2012,110(3-4):619-644
In this study, the strength of the regional changes in near-surface climate associated with a global warming of 2°C with respect to pre-industrial times is assessed, distinguishing between 26 different regions. Also, the strength of these regional climate changes is compared to the strength of the respective changes associated with a markedly stronger global warming of 4.5°C. The magnitude of the regional changes in climate is estimated by means of a normalized regional climate change index, which considers changes in the mean as well as changes in the interannual variability of both near-surface temperature and precipitation. The study is based on two sets of four ensemble simulations with the ECHAM5/MPI-OM coupled climate model, each starting from different initial conditions. In one set of simulations (1860–2200), the greenhouse gas concentrations and sulphate aerosol load have been prescribed according to observations until 2000 and according to the SRES A1B scenario after 2000. In the other set of simulations (2020–2200), the greenhouse gas concentrations and sulphate aerosol load have been prescribed in such a way that the simulated global warming does not exceed 2°C with respect to pre-industrial times. The study reveals the strongest changes in near-surface climate in the same regions for both scenarios, i.e., the Sahara, Northern Australia, Southern Australia and Amazonia. The regions with the weakest changes in near-surface climate, on the other hand, vary somewhat between the two scenarios except for Western North America and Southern South America, where both scenarios show rather weak changes. The comparison between the magnitude of the regional changes in near-surface climate for the two scenarios reveals relatively strong changes in the 2°C-stabilization scenario at high northern latitudes, i.e., Northeastern Europe, Alaska and Greenland, and in Amazonia. Relatively weak regional climate changes in this scenario, on the other hand, are found for Eastern Asia, Central America, Central South America and Southern South America. The ratios between the regional changes in the near-surface climate for the two scenarios vary considerably between different regions. This illustrates a limitation of obtaining regional changes in near-surface climate associated with a particular scenario by means of scaling the regional changes obtained from a widely used “standard” scenario with the ratio of the changes in the global mean temperature projected by these two scenarios. 相似文献