全文获取类型
收费全文 | 259篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 30篇 |
地球物理 | 39篇 |
地质学 | 136篇 |
海洋学 | 10篇 |
天文学 | 22篇 |
综合类 | 6篇 |
自然地理 | 12篇 |
出版年
2022年 | 4篇 |
2021年 | 2篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 5篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1986年 | 2篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1969年 | 2篇 |
1965年 | 2篇 |
1964年 | 2篇 |
1957年 | 3篇 |
1956年 | 4篇 |
1955年 | 2篇 |
1953年 | 2篇 |
1951年 | 3篇 |
1948年 | 5篇 |
1936年 | 1篇 |
1934年 | 1篇 |
1930年 | 1篇 |
1928年 | 2篇 |
1916年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有266条查询结果,搜索用时 375 毫秒
261.
Michael?C.?JollandsEmail author Hugh?St.?C.?O’Neill J?rg?Hermann 《Contributions to Mineralogy and Petrology》2014,168(3):1055
The diffusion, substitution mechanism and solubility limits of Zr and Hf in synthetic forsterite (Mg2SiO4) and San Carlos olivine (Mg0.9Fe0.1)2SiO4 have been investigated between 1,200 and 1,500 °C as a function of the chemical potentials of the components in the system MgO(FeO)–SiO2–ZrO2(HfO2). The effect of oxygen fugacity and crystallographic orientation were also investigated. The solubilities of Zr in forsterite are highest and diffusion fastest when the coexisting three-phase source assemblage includes ZrSiO4 (zircon) or HfSiO4 (hafnon), and lower and slower, respectively, when the source assemblage includes MgO (periclase). This indicates that Zr and Hf substitute on the octahedral sites in olivine, charge balanced by magnesium vacancies. Diffusion is anisotropic, with rates along the crystal axes increasing in the order a < b < c. The generalized diffusion relationship as a function of chemical activity (as \(a_{{{\text{SiO}}_{2} }}\)), orientation and temperature is: \(logD_{\text{Zr}} = \frac{1}{4}loga_{{{\text{SiO}}_{2} }} + logD_{0} - \left( {\frac{{368 \pm 17\;{\text{kJ}}\;{\text{mol}}^{ - 1} }}{{2.303\;{\text{RT}}}}} \right)\) where the values of log D 0 are ?3.8(±0.5), ?3.4(±0.5) and ?3.1(±0.5) along the a, b and c axes, respectively. Most experiments were conducted in air (fO2 = 10?0.68 bars), but one at fO2 = 10?11.2 bars at 1,400 °C shows no resolvable effect of oxygen fugacity on Zr diffusion. Hf is slightly more soluble in olivine than Zr, but diffuses slightly slower. Diffusivities of Zr in experiments in San Carlos olivine at 1,400 °C, fO2 = 10?6.6 bars are similar to those in forsterite at the same conditions, showing that the controls on diffusivities are adequately captured by the simple system (nominally iron-free) experiments. Diffusivities are in good agreement with those measured by Spandler and O’Neill (Contrib Miner Petrol 159:791–818, 2010) in San Carlos olivine using silicate melt as the source at 1,300 °C, and fall within the range of most measurements of Fe–Mg inter-diffusion in olivine at this temperature. Forsterite–melt partitioning experiments in the CaO–MgO–Al2O3–SiO2–ZrO2/HfO2 show that the interface concentrations from the diffusion experiments represent true equilibrium solubilities. Another test of internal consistency is that the ratios of the interface concentrations between experiments buffered by Mg2SiO4 + Mg2Si2O6 + ZrSiO4 or Mg2SiO4 + ZrSiO4 + ZrO2 (high silica activity) to those buffered by Mg2SiO4 + MgO + ZrO2 (low silica activity) agree well with the ratios calculated from thermodynamic data. This study highlights the importance of buffering chemical potentials in diffusion experiments to provide constraints on the interface diffusant concentrations and hence validate the assumption of interface equilibrium. 相似文献
262.
Thomas Schneider von Deimling Hermann Held Andrey Ganopolski Stefan Rahmstorf 《Climate Dynamics》2006,27(2-3):149-163
The concentration of greenhouse gases (GHGs) in the atmosphere continues to rise, hence estimating the climate system’s sensitivity to changes in GHG concentration is of vital importance. Uncertainty in climate sensitivity is a main source of uncertainty in projections of future climate change. Here we present a new approach for constraining this key uncertainty by combining ensemble simulations of the last glacial maximum (LGM) with paleo-data. For this purpose we used a climate model of intermediate complexity to perform a large set of equilibrium runs for (1) pre-industrial boundary conditions, (2) doubled CO2 concentrations, and (3) a complete set of glacial forcings (including dust and vegetation changes). Using proxy-data from the LGM at low and high latitudes we constrain the set of realistic model versions and thus climate sensitivity. We show that irrespective of uncertainties in model parameters and feedback strengths, in our model a close link exists between the simulated warming due to a doubling of CO2, and the cooling obtained for the LGM. Our results agree with recent studies that annual mean data-constraints from present day climate prove to not rule out climate sensitivities above the widely assumed sensitivity range of 1.5–4.5°C (Houghton et al. 2001). Based on our inferred close relationship between past and future temperature evolution, our study suggests that paleo-climatic data can help to reduce uncertainty in future climate projections. Our inferred uncertainty range for climate sensitivity, constrained by paleo-data, is 1.2–4.3°C and thus almost identical to the IPCC estimate. When additionally accounting for potential structural uncertainties inferred from other models the upper limit increases by about 1°C. 相似文献
263.
Elevated groundwater salinity associated with produced water, leaching from landfills or secondary salinity can degrade arable soils and potable water resources. Direct-push electrical conductivity (EC) profiling enables rapid, relatively inexpensive, high-resolution in-situ measurements of subsurface salinity, without requiring core collection or installation of groundwater wells. However, because the direct-push tool measures the bulk EC of both solid and liquid phases (ECa), incorporation of ECa data into regional or historical groundwater data sets requires the prediction of pore water EC (ECw) or chloride (Cl?) concentrations from measured ECa. Statistical linear regression and physically based models for predicting ECw and Cl? from ECa profiles were tested on a brine plume in central Saskatchewan, Canada. A linear relationship between ECa/ECw and porosity was more accurate for predicting ECw and Cl? concentrations than a power-law relationship (Archie’s Law). Despite clay contents of up to 96%, the addition of terms to account for electrical conductance in the solid phase did not improve model predictions. In the absence of porosity data, statistical linear regression models adequately predicted ECw and Cl? concentrations from direct-push ECa profiles (ECw = 5.48 ECa + 0.78, R 2 = 0.87; Cl? = 1,978 ECa – 1,398, R 2 = 0.73). These statistical models can be used to predict ECw in the absence of lithologic data and will be particularly useful for initial site assessments. The more accurate linear physically based model can be used to predict ECw and Cl? as porosity data become available and the site-specific ECw–Cl? relationship is determined. 相似文献
264.
Hermann Harder 《Chemical Geology》1974,14(4):241-253
The synthesis of illite mixed-layer minerals at surface conditions is possible through precipitation of Al hydroxides from Si-, Mg- and K-containing solutions. It has been shown that amorphous hydroxides of Al, Fe, etc. are capable of coprecipitating silica even from very dilute solutions. By aging of these X-ray amorphous hydroxide—silica precipitates under certain conditions, clay minerals can be synthesized at low temperatures. The presence of Mg particularly favors the formation of three-layer clay minerals. Mg-rich Al hydroxide—silica precipitates permit formation of tri- and di-octahedral smectite, illite and chlorite. The formation of three-layer clay minerals is only possible when the precipitates contain at least 6% MgO. The precipitates stay amorphous if the Mg content is lower. The adsorption of Mg and K on the hydroxide—silica precipitate controls the illite or montmorillonite portion in the mixture of the three-layer silicates. There is a competition for K and Mg adsorption on the hydroxide—silica precipitates. Higher K concentration inhibits the three-layer mineral formation through the lowering of the Mg content in the precipitates. Illite mineral formation is favored under certain K/Mg ratios. Higher NaCl contents do not favor the three-layer mineral formation.The enrichment of Mg and K in the precipitates is not as large as the enrichment of Si in the hydroxides. This means that the illite mineral formation is only possible from solutions with a high-salt content like seawater. 相似文献
265.
OH-bearing planar defects in olivine produced by the breakdown of Ti-rich humite minerals from Dabie Shan (China) 总被引:2,自引:0,他引:2
Jörg Hermann John D. Fitz Gerald Nadia Malaspina Andrew J. Berry Marco Scambelluri 《Contributions to Mineralogy and Petrology》2007,153(4):417-428
The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies
conditions in garnet-pyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier
transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxyl-stretching region.
Two intense peaks were observed at 3,564 and 3,394 cm−1, identical in energy to peaks in Ti-clinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed
the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic
of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive
spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite
planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect
beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation
in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in
subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable
in hotter parts of the oceanic mantle such as where basaltic magmas are generated. 相似文献
266.
One of the largest brown coal producing districts in the world is the Miocene of Niederlausitz Lignite area in the southeastern part of Germany. Production is in a range of 320 million t/yr. The resources of the first (shallowest) Miocene seam have nearly been exhausted and it is now mainly the second seam which is being mined. A fourth is being explored. The third Miocene and the Oligocene seam, Calau, are unminable. All brown coal is mined in open pits. The rank of brown coal of the second Miocene seam ranges from fuel coal to coking coal. Its heat value (dry) from 22.2 to 23.5 MJ, its ash content (dry) from 6% to 13%, its moisture from 57% to 59%, and its seam thickness from 10 to 12 m. Due to the close relationship between swamp facies and the main coal quality parameters, the coal quality can be directly determined from the drill log.The Oligocene and Miocene brown coal formation was synchronous with the alpine orogenesis and the seafloor spreading of the North Atlantic Ocean, which both caused north and east oriented migrations of the labile basement of central Europe. Periods of compression alternated with longer periods of isostatic subsidence and sedimentation. Additionally, the trends of thickness and facies of sediments were controlled by a block system in the basement of the brown coal district of Niederlausitz, uplifting, subsiding, collapsing, rotating or spreading.The second Lower Miocene seam is situated at sea level in the north of the Niederlausitz area and rises to the south to +150 to +180 m above sea level, due to considerable widespread subsidence and uplifting since the Lower Miocene. Horizontal tectonic movements were caused by the collapse of asymmetric grabens with slight tendency to rotation. Regional shear movements led to block faulting followed by volcanism. Counter-clockwise rotation of the basement blocks is assumed, a hypothesis supported by recent tension measurements and seismic observations. Ice cover in the Pleistocene caused wide destruction zones, narrow and deep channels and intensively folded or imbricated seam structures. Some gravity-induced plastic structures were also formed. 相似文献