全文获取类型
收费全文 | 162篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 15篇 |
地球物理 | 44篇 |
地质学 | 44篇 |
海洋学 | 19篇 |
天文学 | 31篇 |
自然地理 | 16篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 10篇 |
2012年 | 3篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 7篇 |
2007年 | 11篇 |
2006年 | 12篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有172条查询结果,搜索用时 15 毫秒
11.
Robin Brett 《Geochimica et cosmochimica acta》1973,37(1):165-170
Several workers have proposed that lunar samples were magnetized by a field created by a lunar core of molten Fe. Low abundances of siderophile elements in lunar rocks are compatible with formation of a metallic lunar core. A molten Fe core requires that the bulk of the Moon was above, or close to, the melting point, a requirement which disagrees with most models of the lunar thermal regime.A core (or perhaps a layer or pockets) of molten Fe-Ni-S, at or close to the eutectic composition would act as a lunar dynamo, and be at a temperature (approx. 1000°C) consistent with some reasonable models of lunar thermal history. The existence of a Fe-Ni-S core would also partly explain the depletion in volatile elements in lunar basalts. Such a core, occupying up to 20 per cent of the Moon's radius requires a bulk S content for the moon of only 0.3 wt per cent. 相似文献
12.
Robin Brett 《Geochimica et cosmochimica acta》1973,37(12):2697-2703
The outer portion of the Moon including the Al-rich crust and the source regions of mare basalts was either accreted heterogeneously or was the product of widespread differentiation of an originally homogeneous source. A number of constraints make the heterogeneous accretion model unlikely; the differentiation model appears more plausible.If the differentiation model is correct, a series of cumulate rocks complimentary to the Al-rich crustal rocks must exist. The mare basalts may have been derived from such a complimentary cumulate for several reasons. For example, Philpottset al. (1973) on the basis of REE studies, suggest that Apollo 11 and 17 mare basalts were formed by partial melting of a cumulate rich in a phase(s) containing high Ti and heavy REE. The high Ti of Apollo 11 and 17 basalts is not readily explained in terms of partial melting of an undifferentiated mantle, but is consistent with partial melting of a pyroxene cumulate enriched in Fe, Ti oxides. The characteristic Fe-rich nature of mare basalts would be partly a consequence of melting of oxide cumulate minerals. It is postulated that the plagioclase-poor source region of mare basalts was enriched in an intercumulus residual liquid. During the partial melting that produced mare basalts, this material was largely incorporated into the melt, thus explaining the ancient model ages observed in most mare basalts. If the cumulate model is correct, then samples derived from the true (undifferentiated) lunar mantle have not been identified. 相似文献
13.
Isaac Larbi Emmanuel Obuobie Anne Verhoef Stefan Julich Karl-Henz Feger Aymar Yaovi Bossa 《水文科学杂志》2020,65(13):2196-2209
ABSTRACT The need for a detailed investigation of the Vea catchment water balance components cannot be overemphasized due to its accelerated land-cover dynamics and the associated impacts on the hydrological processes. This study assessed the possible consequences of land-use change scenarios (i.e. business as usual, BAU, and afforestation for the year 2025) compared to the 2016 baseline on the Vea catchment’s water balance components using the Soil and Water Assessment Tool (SWAT) model. The data used include daily climate and discharge, soil and land use/land cover maps. The results indicate that the mean annual water yield may increase by 9.1% under the BAU scenario but decrease by 2.7% under the afforestation scenario; actual evapotranspiration would decrease under BAU but increase under afforestation; and groundwater recharge may increase under both scenarios but would be more pronounced under the afforestation scenario. These outcomes highlight the significance of land-cover dynamics in water resource management and planning at the catchment. 相似文献
14.
15.
Qunying Luo William Bellotti Martin Williams Ian Cooper Brett Bryan 《Climatic change》2007,85(1-2):89-101
This study presents a model-based risk assessment of wheat production under projected climate change by 2080 in eight locations
of South Australia. The vulnerability of wheat production under future climate change was quantitatively evaluated via a risk
analysis in which the identification of critical yield thresholds applies. Research results show that risk (conditional probability
of not exceeding the critical yield thresholds) increased more or less across all locations under the most likely climate
change. Wheat production in drier areas such as Minnipa, Orroroo and Wanbi will not be economically viable under the most
likely climate change. Intensive studies on adaptation are now required. 相似文献
16.
17.
Landslides - In regions of infrequent but potentially damaging seismicity, modern earthquake inventories may be insufficient to provide inputs to seismic hazard analyses (i.e., fault locations and... 相似文献
18.
19.
Our understanding of planet formation depends in fundamental ways on what we learn by analyzing the composition, mineralogy, and petrology of meteorites. Yet, it is difficult to deduce the compositional and thermal gradients that existed in the solar nebula from the meteoritic record because, in most cases, we do not know where meteorites with different chemical and isotopic signatures originated. Here we developed a model that tracks the orbits of meteoroid-sized objects as they evolve from the ν6 secular resonance to Earth-crossing orbits. We apply this model to determining the number of meteorites accreted on the Earth immediately after a collisional disruption of a D∼200-km-diameter inner-main-belt asteroid in the Flora family region. We show that this event could produce fossil chondrite meteorites found in an ≈470 Myr old marine limestone quarry in southern Sweden, the L-chondrite meteorites with shock ages ≈470 Myr falling on the Earth today, as well as asteroid-sized fragments in the Flora family. To explain the measured short cosmic-ray exposure ages of fossil meteorites our model requires that the meteoroid-sized fragments were launched at speeds >500 m s−1 and/or the collisional lifetimes of these objects were much shorter immediately after the breakup event than they are today. 相似文献
20.
Matthew J. Cashman Allen C. Gellis Eric Boyd Mathias J. Collins Scott W. Anderson Brett D. McFarland Ashley M. Ryan 《地球表面变化过程与地形》2021,46(6):1145-1159
In this study, we captured how a river channel responds to a sediment pulse originating from a dam removal using multiple lines of evidence derived from streamflow gages along the Patapsco River, Maryland, USA. Gages captured characteristics of the sediment pulse, including travel times of its leading edge (~7.8 km yr−1) and peak (~2.6 km yr−1) and suggest both translation and increasing dispersion. The pulse also changed local hydraulics and energy conditions, increasing flow velocities and Froude number, due to bed fining, homogenization and/or slope adjustment. Immediately downstream of the dam, recovery to pre-pulse conditions occurred within the year, but farther downstream recovery was slower, with the tail of the sediment pulse working through the lower river by the end of the study 7 years later. The patterns and timing of channel change associated with the sediment pulse were not driven by large flow or suspended sediment-transporting events, with change mostly occurring during lower flows. This suggests pulse mobility was controlled by process-factors largely independent of high flow. In contrast, persistent changes occurred to out-of-channel flooding dynamics. Stage associated with flooding increased during the arrival of the sediment pulse, 1 to 2 years after dam removal, suggesting persistent sediment deposition at the channel margins and nearby floodplain. This resulted in National Weather Service-indicated flood stages being attained by 3–43% smaller discharges compared to earlier in the study period. This study captured a two-signal response from the sediment pulse: (1) short- to medium-term (weeks to months) translation and dispersion within the channel, resulting in aggradation and recovery of bed elevations and changing local hydraulics; and (2) dispersion and persistent longer-term (years) effects of sediment deposition on overbank surfaces. This study further demonstrated the utility of US Geological Survey gage data to quantify geomorphic change, increase temporal resolution, and provide insights into trajectories of change over varying spatial and temporal scales. 相似文献