全文获取类型
收费全文 | 622篇 |
免费 | 19篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 57篇 |
大气科学 | 34篇 |
地球物理 | 141篇 |
地质学 | 184篇 |
海洋学 | 44篇 |
天文学 | 144篇 |
综合类 | 4篇 |
自然地理 | 42篇 |
出版年
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 21篇 |
2017年 | 23篇 |
2016年 | 20篇 |
2015年 | 12篇 |
2014年 | 24篇 |
2013年 | 30篇 |
2012年 | 26篇 |
2011年 | 33篇 |
2010年 | 26篇 |
2009年 | 37篇 |
2008年 | 23篇 |
2007年 | 27篇 |
2006年 | 35篇 |
2005年 | 21篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 17篇 |
2001年 | 19篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1970年 | 5篇 |
排序方式: 共有650条查询结果,搜索用时 15 毫秒
641.
642.
643.
644.
645.
It has recently been suggested that tidal and radiogenic heating of Europa has led to formation and maintenance of a liquid water ocean overlain by a thin ice crust (S. W. Squyres, R. T. Reynolds, P. M. Cassen, and S. J. Peale (1983). Nature301, 225–226). The present work examines the environmental consequences of such a model with regard to the possible existence on Europa of regions that could satisfy the basic requirements for the survival of known organisms. Appropriate temperatures and long-term environmental stability are implied by the ocean model. The presence of necessary biogenic elements is assumed based on the expected origin of the ocean. The availability of biologically useful energy is assumed to be the principal limiting factor for life on Europa. Possible electrical, thermal, and chemical energy sources are discussed. Calculated resurfacing rates for the active crust model are used to estimate the quantity of photosynthetically active radiation that might reach the proposed ocean through crustal fractures. The amount of biomass that this energy could support, based on Antartic microorganism analogs, is estimated and discussed. Although these calculations cannot determine whether life forms exist or could exist on Europa, they do suggest that there may be regions on Europa, very limited on both space and time, with physical conditions that are within the range of adaptation of life on Earth. 相似文献
646.
正Recent scholars’work in Vol 58 Issue 1(2015)and Cheng and Li’s paper in Vol 58 Issue 7(2015)in Science China Earth Sciences propose development of"Watershed science"by"Bridging new advances in hydrological science with good management of river basins".An analysis of the language and key concepts used in the abstracts,titles and keywords of this set of 8 papers and an editorial reveals that‘Watershed’,‘River’,‘Science’and‘System’are the main 相似文献
647.
Ray Macdonald Bogus?aw Bagiński Fiorenzo Ronga Piotr Dzier?anowski Michele Lustrino Andrea Marzoli Leone Melluso 《Mineralogy and Petrology》2012,104(3-4):163-175
Matrix glass and melt inclusions in phenocrysts from pantellerite lavas of the Boseti volcanic complex, Ethiopia, record extreme fractionation of peralkaline silicic magma, with Al2O3 contents as low as 2.3?wt.%, FeO* contents up to 17?wt.% and SiO2 contents ~65?wt.%. The new data, and published data for natural and experimental glasses, suggest that the effective minimum composition for peralkaline silicic magmas has ~5?wt.% Al2O3, 13?wt.% FeO* and 66?±?2?wt.% SiO2. The dominant fractionating assemblage is alkali feldspar?+?fayalite?+?hedenbergite?+?oxides?±?quartz. Feldspar – melt relationships indicate that the feldspar is close to the minimum on the albite-orthoclase solid solution loop through the entire crystallization history. There is petrographic, mineralogical and geochemical evidence that magma mixing may have been a common process in the Boseti rhyolites. 相似文献
648.
Variability in dissolved organic matter fluorescence and reduced sulfur concentration in coastal marine and estuarine environments 总被引:1,自引:0,他引:1
Sarah G.S. DePalmaW. Ray Arnold James C. McGeerD. George Dixon D. Scott Smith 《Applied Geochemistry》2011,26(3):394-404
Fluorescence characterization of dissolved organic matter (DOM) and measurements of Cr-reducible sulfide (CRS) are presented for 72 coastal marine and estuarine water samples obtained from the USA and Canada. Each sample is identified according to source: terrigenous, autochthonous, wastewater or mixed. Fluorescence data are resolved into contributions from humic, fulvic, tyrosine and tryptophan-like fluorophores. Humic and fulvic-like fluorophores correlate well with dissolved organic C (DOC) (r2 = 0.73 and 0.71, respectively) but tyrosine and tryptophan-like fluorophores show no correlation with DOC. Quality factors are identified by normalization of fluorescence contributions to DOC. Humic and fulvic components show no statistical differences between sources but the amino acid-like fluorescence quality factors show significant variations between source, with highest values for autochthonous sources (0.07 ± 0.01 arbitrary fluorescence units per mg of C) versus low values (0.015 ± 0.005) for terrigenous source waters. CRS concentrations are highly variable from 0.07 ± 0.01 to 7703 ± 98 nM and do no correlate with DOC except when terrigenous source waters (n = 13) are separated out from the total sample set (r2 = 0.55). There is an open question in the literature; does DOC source matter in terms of protective effects towards metal toxicity? Here is shown that DOC molecular-level quality does vary and that this variation is mostly in terms of the contributions of amino acids to total fluorescence. 相似文献
649.
Ray Kostaschuk Dan Shugar Jim Best Dan Parsons Stuart Lane Rich Hardy Oscar Orfeo 《地球表面变化过程与地形》2009,34(12):1605-1611
Field data from the Rio Paraná, Argentina, are used to examine patterns of suspended sediment transport over a sand dune. Measurements of three‐dimensional velocity are made with an acoustic Doppler current profiler whilst suspended sediment concentration and particle size have been quantified using a laser in situ sediment scattering transmissometer. Suspended sediment concentration and streamwise and vertical sediment flux are highest close to the bed, with an upward vertical flux over the stoss side of the dune and downward flux over the lee side. Suspended sediment concentrations are higher over the crest compared with the trough and suspended sediment is coarsest near the bed. About 17% of the suspended‐load transported over the crest is deposited in the lee side before it reaches the trough. Most of this deposited sand is coarser sediment that originates close to the bed over the crest, a result consistent with simulations based on the model of Mohrig and Smith (Water Resources Research 1996; 32: 3207–3217) for the excursion lengths of sediment dispersed in the lee side of a dune. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
650.
C. J. Davis H. E. Matthews T. P. Ray W. R. F. Dent J. S. Richer 《Monthly notices of the Royal Astronomical Society》1999,309(1):141-152
Wide-field mapping of Serpens in submillimetre continuum emission and CO J =2–1 line emission is here complemented by optical imaging in [S ii ] λλ 6716, 6731 line emission. Analysis of the 450- and 850-μm continuum data shows at least 10 separate sources, along with fainter diffuse background emission and filaments extending to the south and east of the core. These filaments describe 'cavity-like' structures that may have been shaped by the numerous outflows in the region. The dust opacity index, β , derived for the identifiable compact sources is of the order of 1.0±0.2, with dust temperatures in excess of 20 K. This value of β is somewhat lower than for typical class I YSOs; we suggest that the Serpens sources may be 'warm', late class 0 or early class I objects.
With the combined CO and optical data we also examine, on large scales, the outflows driven by the embedded sources in Serpens. In addition to a number of new Herbig–Haro flows (here denoted HH 455–460), a number of high-velocity CO lobes are observed; these extend radially outwards from the cluster of submillimetre sources in the core. A close association between the optical and molecular flows is also identified. The data suggest that many of the submillimetre sources power outflows. Collectively, the outflows traced in CO support the widely recognized correlation between source bolometric luminosity and outflow power, and imply a dynamical age for the whole protostellar cluster of ∼3×104 yr. Notably, this is roughly equal to the proposed duration of the 'class 0' stage in protostellar evolution. 相似文献
With the combined CO and optical data we also examine, on large scales, the outflows driven by the embedded sources in Serpens. In addition to a number of new Herbig–Haro flows (here denoted HH 455–460), a number of high-velocity CO lobes are observed; these extend radially outwards from the cluster of submillimetre sources in the core. A close association between the optical and molecular flows is also identified. The data suggest that many of the submillimetre sources power outflows. Collectively, the outflows traced in CO support the widely recognized correlation between source bolometric luminosity and outflow power, and imply a dynamical age for the whole protostellar cluster of ∼3×10