全文获取类型
收费全文 | 587篇 |
免费 | 21篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 49篇 |
地球物理 | 121篇 |
地质学 | 218篇 |
海洋学 | 69篇 |
天文学 | 68篇 |
综合类 | 1篇 |
自然地理 | 75篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 7篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 26篇 |
2015年 | 16篇 |
2014年 | 21篇 |
2013年 | 46篇 |
2012年 | 24篇 |
2011年 | 43篇 |
2010年 | 33篇 |
2009年 | 30篇 |
2008年 | 36篇 |
2007年 | 30篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 26篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有612条查询结果,搜索用时 0 毫秒
31.
32.
33.
Elizabeth Griffin 《Astronomy& Geophysics》2001,42(2):2.25-2.26
Elizabeth Griffin argues for international action to rescue astronomical observations from decay and obsolescence. 相似文献
34.
In this paper we analyze some Viking infrared thermal mapping (IRTM) measurements of local Martian dust storms observed in the southern tropical region of the planet between Ls=225 and 262°. The derived opacities of these storms show that in the most opaque regions of the cloud, the optical thickness may be ≈6. Away from the individual clouds, the opacity is ≈2, which is still about four times the background level of dustiness in the Martian atmosphere. We find considerable structure in the derived opacity which will create corresponding variations in the atmospheric heating, which in turn may have an important feedback upon the local winds. 相似文献
35.
Constraining the process by which volcanoes become unstable is difficult. Several models have been proposed to explain the
driving forces which cause volcanic edifices to catastrophically collapse. These include models for destabilisation of volcanic
flanks by wedging due to dyke intrusion and the weakening of mechanical properties by pressurisation of pore fluids. It is
not known which, if any, of the models are relevant to particular sector collapse events. Recent developments in the palaeomagnetic
estimation of emplacement temperatures of volcaniclastic rocks have shown that even relatively low emplacement temperatures
can be recorded by volcaniclastics with high fidelity. We have carried out a palaeomagnetic study of emplacement temperatures
to investigate the role of igneous activity in the initiation of the 9,500 b.p. Murimotu sector collapse of Mt Ruapehu, New Zealand. This debris avalanche deposit has three fades which are stratigraphically
superimposed, and the lowermost fades contains three lithological assemblages representing different segments of the edifice
which were transported with little internal mixing within the flow. We have determined that some of the dacite-bearing assemblage
1, fades 1 was hot (∼350 °C) during transport and emplacement, whereas none of the other lithological assemblages of fades
contained hot material. Our interpretation is that a dacite dome was active on the ancient Ruapehu edifice immediately prior
to the Murimotu sector collapse. The partially cooled carapace of the dome and material shed from this part was incorporated
into the avalanche deposit, along with cold lavas and volcaniclastics. We have not found evidence for incorporation of material
at or close to magmatic temperatures, at least in the sampled locations. Our palaeomagnetic work allows us to develop a comprehensive,
new palaeomagnetic classification of volcaniclastics.
Published online: 25 January 2003
Editorial responsibility: D. Dingwell 相似文献
36.
Lisa L. Etherington Philip N. Hooge Elizabeth R. Hooge David F. Hill 《Estuaries and Coasts》2007,30(6):927-944
Alaska, U.S.A, is one of the few remaining locations in the world that has fjords that contain temperate idewater glaciers.
Studying such estuarine systems provides vital information on how deglaciation affects oceanographic onditions of fjords and
surrounding coastal waters. The oceanographic system of Glacier Bay, Alaska, is of particular interest ue to the rapid deglaciation
of the Bay and the resulting changes in the estuarine environment, the relatively high oncentrations of marine mammals, seabirds,
fishes, and invertebrates, and the Bay’s status as a national park, where ommercial fisheries are being phased out. We describe
the first comprehensive broad-scale analysis of physical and iological oceanographic conditions within Glacier Bay based on
CTD measurements at 24 stations from 1993 to 2002. easonal patterns of near-surface salinity, temperature, stratification,
turbidity, and euphotic depth suggest that freshwater nput was highest in summer, emphasizing the critical role of glacier
and snowmelt to this system. Strong and persistent tratification of surface waters driven by freshwater input occurred from
spring through fall. After accounting for seasonal nd spatial variation, several of the external physical factors (i.e., air
temperature, precipitation, day length) explained a large mount of variation in the physical properties of the surface waters.
Spatial patterns of phytoplankton biomass varied hroughout the year and were related to stratification levels, euphotic depth,
and day length. We observed hydrographic atterns indicative of strong competing forces influencing water column stability
within Glacier Bay: high levels of freshwater ischarge promoted stratification in the upper fjord, while strong tidal currents
over the Bay’s shallow entrance sill enhanced ertical mixing. Where these two processes met in the central deep basins there
were optimal conditions of intermediate tratification, higher light levels, and potential nutrient renewal. These conditions
were associated with high and sustained hlorophylla levels observed from spring through fall in these zones of the Bay and provide a framework for understanding he abundance
patterns of higher trophic levels within this estuarine system. 相似文献
37.
Elizabeth J. Botha Brigitte Leblon Bernie Zebarth James Watmough 《International Journal of Applied Earth Observation and Geoinformation》2007,9(4):360-374
Optimizing nitrogen (N) fertilization in crop production by in-season measurements of crop N status may improve fertilizer N use efficiency. Hyperspectral measurements may be used to assess crop N status by estimating leaf chlorophyll content. This study evaluated the ability of the PROSAIL canopy-level reflectance model to predict leaf chlorophyll content. Trials were conducted with two potato cultivars under different N fertility rates (0–300 kg N ha−1). Canopy reflectance, leaf area index (LAI) and leaf chlorophyll and N contents were measured. The PROSAIL model was able to predict leaf chlorophyll content with reasonable accuracy later in the growing season. The low estimation accuracy earlier in the growing season could be due to model sensitivity to non-homogenous canopy architecture and soil background interference before full canopy closure. Canopy chlorophyll content (leaf chlorophyll content × LAI) was predicted less accurately than leaf chlrophyll content due to the low estimation accuracy of LAI for values higher than 4.5. 相似文献
38.
This paper examines similarities and differences in the emergence of high-tech enterprise and the growth of associated industry in Cambridgeshire and Oxfordshire since the 1960s. These cases are viewed as instances of a generic phenomenon: the emergence and growth of the science-based ‘innovative milieu’. A conceptual scheme drawn from complexity studies is used to introduce explanatory coherence into the apparently scattered and disconnected factors relevant to the genesis of high-tech milieux. 相似文献
39.
Robert A. Berner Elizabeth K. Berner Robin S. Keir 《Earth and Planetary Science Letters》1976,30(2):169-178
The depth distribution of pteropod and planktonic foram tests, and fine-grained (<62 μm) aragonite, high-Mg calcite (12 mode mol.% MgCO3), and low-Mg calcite has been determined for surface sediments of an area of the eastern slope of the Bermuda pedestal. Over the range 1800–3000 m, fine-grained aragonite and fine-grained high-Mg calcite gradually disappear relative to fine-grained low-Mg calcite, and pteropods gradually disappear relative to planktonic forams. This is interpreted as preferential dissolution of aragonite (and high-Mg calcite) relative to low-Mg calcite over this depth range. Coarse aragonitic debris derived from shallow-water organisms living on the Bermuda platform does not show consistent disappearance over the same depth zone. Chemical analyses of bottom water samples taken at the same time as some of the sediment samples indicate that the degree of saturation with respect to aragonite ΩA over the zone of aragonite disappearance ranges from 0.55 to 0.85; i.e. major dissolution occurs only at ΩA values distinctly less than one. These results lend credence to the hypothesis that CaCO3 dissolution in the oceans, both as aragonite and as calcite, takes place mainly as a response to complex chemical kinetic phenomena and not as a result of the simple attainment of undersaturation (thermodynamic hypothesis) or the resuspension of bottom sediment (hydrodynamic hypothesis). 相似文献
40.
Elizabeth A. V. Mackie Jeremy M. Lloyd Melanie J. Leng Michael J. Bentley Carol Arrowsmith 《第四纪科学杂志》2007,22(6):579-591
Carbon isotopes (δ13C) and C/N ratios from bulk organic matter have recently been used as alternative proxies for relative sea‐level (RSL) reconstruction where there are problems associated with conventional biological indictors. A previous study on a single isolation basin (Upper Loch nan Eala) in northwest Scotland has shown a clear relationship between δ13C, C/N ratios and palaeosalinity from Younger Dryas and Holocene aged sediments. In this paper we present results of δ13C and C/N ratio analyses from other isolation basins in northwest Scotland over the Holocene and the Lateglacial period in order to validate this technique. The results from the Holocene sequences support the earlier findings that this technique can be used to identify RSL change from isolation basins over the Holocene in this region. The relationship between δ13C, C/N ratios and RSL change is not apparent in sediments of Lateglacial age. Other environmental variables such as atmospheric CO2 concentration, poor vegetation development and temperature influence δ13C values during this period. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献