全文获取类型
收费全文 | 227篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 29篇 |
地球物理 | 75篇 |
地质学 | 67篇 |
海洋学 | 14篇 |
天文学 | 41篇 |
自然地理 | 19篇 |
出版年
2023年 | 1篇 |
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2017年 | 17篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 13篇 |
2013年 | 15篇 |
2012年 | 2篇 |
2011年 | 3篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 6篇 |
2006年 | 10篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 9篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1971年 | 4篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1962年 | 1篇 |
1959年 | 1篇 |
1946年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有251条查询结果,搜索用时 15 毫秒
111.
Middle Paleozoic to Middle Jurassic terrane assemblies in the Klamaths and Sierran Foothills consist of mafic–ultramafic complexes + fine‐grained terrigenous strata derived from previously accreted continental‐margin belts. Sutured oceanic terranes reflect c. 230 Myr of margin‐parallel slip involving chiefly transtension and transpression. Quartzofeldspathic clastic rocks and blueschists ± eclogites are very rare. Little devolatilization occurred at magmagenic depths; hence, coeval hydrothermal ore deposits and granitoids are uncommon. In contrast, nearly head‐on Cretaceous subduction of the Farallon plate generated the massive Klamath–Sierra Nevada volcanic–plutonic arc, reflecting dewatering of the eastward descending oceanic lithosphere in the magmagenic zone. Immature Great Valley forearc and Franciscan trench deposits shed from the arc record c. 70 Myr. of rapid crustal growth. Au‐bearing solutions rising from magmagenic depths, exsolved from plutons, and expelled from heated wall rocks were mobilized attending arc construction. Precipitation of gold‐bearing quartz veins occurred where H2O + CO2‐bearing fluids encountered major geochemical discontinuities in the wall rocks. 相似文献
112.
Contamination patterns and molluscan and polychaete assemblages in two Persian (Arabian) Gulf oilfields 下载免费PDF全文
Paolo G. Albano Nadezhda Filippova Jan Steger Hannah Schmidbaur Adam Tomašových Michael Stachowitsch Martin Zuschin 《Marine Ecology》2016,37(4):907-919
This study examined two shallow‐water, offshore oil facilities and their surroundings in the Umm Al Dalkh and Zakum oilfields [United Arab Emirates, Persian (Arabian) Gulf]. The focus was on sediment contamination levels and the detection of disturbance based on two representative invertebrate components of the benthos: molluscs and polychaetes. We tested the hypothesis that significant disturbance to the community has occurred, by examining whether distance from the platform or variation in contaminants explains among‐site variation in the composition of benthic communities. Moreover, we also tested the hypothesis that organic enrichment because of oil input has modified the feeding guild structure by examining whether the relative abundances of filter‐feeders, deposit‐feeders and omnivores are correlated with distance from the platform or with contamination by hydrocarbons. The contamination levels and their spatial distribution in the sediments differed significantly between the two fields, as did their mollusc and polychaete communities. The within‐field variability, however, was much lower: no clear structuring of contamination values and species composition and abundance was detectable in relation to distance from the oil platform. Contamination levels were low, often below detection levels or international guideline values. Variation in contaminant concentrations did not explain variation in taxonomic composition and abundance. The relative abundance of the above‐mentioned feeding guilds did not correlate with either distance from the platform or with contaminant concentrations. These patterns may reflect the long time that has elapsed since drilling (15–20 years), which appears to have allowed contaminants to disperse and degrade and assemblages to recover from the impact, if indeed such a disturbance ever occurred. In contrast to low values of barium and total petroleum hydrocarbons, associated with well drilling, some metals were at their highest concentrations beneath the central platforms. This suggests that production‐related activities (including platform cleaning and maintenance) are currently a more relevant contamination source. 相似文献
113.
114.
Glacier‐fed river thermal regimes vary markedly in space and time; however, knowledge is limited on the fundamental processes controlling alpine stream temperature dynamics. To address the research gap, this study quantified heat exchanges at the water surface and bed of the Taillon glacier‐fed stream, French Pyrénées. Hydro‐meteorological observations were recorded at 15‐min intervals across two summer melt seasons (2010 and 2011), and energy balance components were measured or estimated based on site‐specific data. Averaged over both seasons, net radiation was the largest heat source (~80% of total flux); sensible heat (~13%) and friction (~3%) were also sources, while heat exchange across the channel–streambed interface was negligible (<1%). Latent heat displayed distinct interannual variability and contributed 5% in 2010 compared with 0.03% in 2011. At the sub‐seasonal scale, latent heat shifted from source to sink, possibly linked to the retreating valley snowline that changed temperature and humidity gradients. These findings represent the first, multiyear study of the heat exchange processes operating in a glacier‐fed stream, providing fundamental process understanding; the research highlights the direct control antecedent (winter) conditions that have on energy exchange and stream temperature during summer months. In particular, the timing and volume of snowfall/snowmelt can drive thermal dynamics by the following: (1) altering the length of the stream network exposed to the atmosphere and (2) controlling the volume and timing of cold water advection downstream. Finally, this study highlights the need to develop long‐term hydro‐meteorological monitoring stations to improve the understanding of these highly dynamic, climatically sensitive systems. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
115.
116.
117.
118.
Nigel Harris Alison Hunt Ian Parkinson Andrew Tindle Magisuren Yondon Samantha Hammond 《Contributions to Mineralogy and Petrology》2010,160(1):67-81
Garnet-bearing mantle xenoliths have been recovered from Quaternary alkali basalts, both within and peripheral to the Hangay
dome of central Mongolia. Microfabric analysis and thermobaromery, combining empirical thermobarometers and the self-consistent
dataset of THERMOCALC, indicate that garnet websterites from the Shavaryn-Tsaram volcanic centre at the dome core were formed
in the spinel-lherzolite upper mantle at pressures of 17–18 kbars and temperatures of 1,070–1,090°C, whereas garnet lherzolites
were derived from greater depths (18–20 kbars). Garnet lherzolites from the Baga Togo Uul vents near the dome edge were formed
at 18–22 kbars under significantly cooler conditions (960–1,000°C). These xenoliths reveal reaction coronas of (1) orthopyroxene,
clinopyroxene, plagioclase and spinel mantling garnets; (2) spongy rims of olivine replacing orthopyroxene and (3) low-Na,
low-Al clinopyroxene replacing primary clinopyroxene. Trace-element abundances indicate that clinopyroxene from these coronas
is in chemical equilibrium with the host magma. The thermobarometric and textural data suggest that lherzolite xenoliths from
both sites were derived from depths of 60–70 km and entrained in magma at 1,200–1,300°C. The average rate of ascent, as determined
by olivine zoning, lies in the range 0.2–0.3 m s−1. The contrast in thermal profiles of the upper mantle between the two sites is consistent with a mantle plume beneath the
Hangay dome with elevated thermal conditions beneath the core of the dome being comparable to estimates of the Pleistocene
geotherm beneath the Baikal rift. 相似文献
119.
Matthew G. Hannah 《GeoJournal》2010,75(4):397-406
Ewald’s recent genealogy of constructions of risk in Western societies argues that the 1980s saw an important paradigm shift
to the “precautionary principle”. Critical scholars have taken up this idea as a lens through which to interpret the Bush
administration’s ‘war on terror’. I argue that 11 September 2001 actually brought about qualitative changes to this paradigm.
Bush’s pre-emptive doctrine is driven, and perhaps even more importantly, continually justified to the US population, by what
might be called the “trans-precautionary principle”, a move from “decisionism” to “actionism”, and a new radicalization of
the way fear is produced and managed. Donald Rumsfeld’s famous typology of different articulations of knowledge and ignorance
offers an excellent analytical window onto the connections between ignorance, fear and geopolitical action in this new regime.
In the latter part of the essay, his four modes of knowledge/ignorance are arrayed, for heuristic purposes, in an abstract
spatial grid organized along dimensions of the specificity and possession of knowledge. This allows a ‘mapping’ of some of
the Bush administration’s more controversial strategies in the ‘war on terror’, as a set of different pathways through Rumsfeld
Space. 相似文献
120.