全文获取类型
收费全文 | 301篇 |
免费 | 14篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 10篇 |
地球物理 | 57篇 |
地质学 | 132篇 |
海洋学 | 26篇 |
天文学 | 20篇 |
综合类 | 4篇 |
自然地理 | 60篇 |
出版年
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 11篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 26篇 |
2012年 | 9篇 |
2011年 | 16篇 |
2010年 | 17篇 |
2009年 | 19篇 |
2008年 | 14篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 4篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 4篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有318条查询结果,搜索用时 15 毫秒
131.
Phosphorus export dynamics and hydrobiogeochemical controls across gradients of scale,topography and human impact 下载免费PDF全文
Genevieve Ali Henry Wilson Jane Elliott Amber Penner Aminul Haque Cody Ross Maliheh Rabie 《水文研究》2017,31(18):3130-3145
Concentration‐discharge (c‐Q) plots are routinely used as an integrated signal of watershed response to infer solute sources and travel pathways. However, the interpretation of c‐Q data can be difficult unless these data are fitted using statistical models. Such models are frequently applied for geogenic solutes, but it is unclear to what extent they might aid in the investigation of nutrient export patterns, particularly for total dissolved phosphorus (TDP) which is a critical driver of downstream eutrophication problems. The goal of the present study was therefore to statistically model c‐Q relations (where c is TDP concentrations) in a set of contrasting watersheds in the Northern Great Plains—ranging in size from 0.2 to 1000+ km2—to assess the controls of landscape properties on TDP transport dynamics. Six statistical models were fitted to c‐Q data, notably (a) one linear model, (b) one model assuming that c‐Q relations are driven by the mixing of end‐member waters from different landscape locations (i.e., hydrograph separation), (c) one model relying on a biogeochemical stationarity hypothesis (i.e., power law), (d) one model hypothesizing that c‐Q relations change as a function of the solute subsurface contact time (i.e., hyperbolic model), and (e) two models assuming that solute fluxes are mostly dependent on reaction rates (i.e., chemical models). Model performance ranged from mediocre (R2 < 0.2) to very good (R2 > 0.9), but the hydrograph separation model seemed most universal. No watershed was found to exhibit chemostatic behaviour, but many showed signs of dilution or enrichment behaviour. A tendency toward a multi‐model fit and better model performance was observed for watersheds with moderate slope and higher effective drainage area. The relatively poor model performance obtained outside these conditions illustrates the likely importance of controls on TDP concentrations in the region that are independent of flow dynamics. 相似文献
132.
133.
Geochemistry of mafic dykes in the Antarctic Peninsula continental-margin batholith: a record of arc evolution 总被引:6,自引:0,他引:6
Jane H. Scarrow Philip T. Leat Christopher D. Wareham Ian L. Millar 《Contributions to Mineralogy and Petrology》1998,131(2-3):289-305
Mafic dykes of the Antarctic Peninsula continental-margin arc are compositionally diverse, comprising calc-alkaline (dominant),
shoshonite, tholeiite, and OIB-like varieties. Their compositions give information about different mafic magma sources tapped
during arc evolution. The compositional groups represent partial melts of at least five distinct mantle sources: a low-ɛNd
subduction-modified, garnet-bearing, lithospheric mantle (older calc-alkaline); a high-ɛNd subduction-modified, garnet-bearing,
lithospheric mantle (shoshonites); a high-ɛNd subduction-modified, spinel-bearing, asthenospheric mantle (younger calc-alkaline);
E-MORB-like spinel-bearing asthenosphere depleted by a previous melting event (tholeiites); and within-plate non-subduction
modified, garnet- and spinel-bearing, asthenosphere (OIB-like). Slab-derived fluids, subducted sediment, and arc crust also
contributed to the magmas. Consideration of previous work in the light of our new compositional and geochronological data
enables presentation of a summary of arc evolution. For most of the Cretaceous and Tertiary, the tectonic regime of the Antarctic
Peninsula arc was transtensional, and calc-alkaline magmas intruded. An oceanic spreading centre collided with the trench
during the Late Cretaceous and induced tectonic changes which caused tapping of different magma sources. A pulse of shoshonitic,
tholeiitic, and OIB-like mafic magmatism resulted. Three ridge-trench collisions are now recognized during the history of
the arc, in Mid–Late Jurassic, Late Cretaceous, and Early–Mid Tertiary times.
Received: 13 January 1997 / Accepted: 5 December 1997 相似文献
134.
135.
136.
Jane?A.?GilottiEmail author Allen?P.?Nutman Hannes?K.?Brueckner 《Contributions to Mineralogy and Petrology》2004,148(2):216-235
A variety of eclogites from an east-west transect across the North-East Greenland eclogite province have been studied to establish the timing of high pressure (HP) and ultrahigh-pressure (UHP) metamorphism in this northern segment of the Laurentian margin. Garnet + omphacite ± amphibole + whole rock Sm-Nd isochrons from a quartz eclogite, a garnet + omphacite + rutile eclogite and a partially melted zoisite eclogite in the western HP belt are 401±2, 402±9 and 414±18 Ma, respectively. Corresponding sensitive high-resolution ion microprobe (SHRIMP) 206Pb/238U ages of metamorphic zircon in the same samples are 401±7, 414±13, and 393 ±10 Ma. Metamorphic zircon domains were identified using morphology, cathodoluminescence (CL) imaging, U, Th, Th/U and trace element contents. Zircon from the quartz eclogite and the garnet + omphacite + rutile eclogite are typical of eclogite facies zircon with rounded to subhedral shapes, patchy to homogenous CL domains, low U, and very low Th and Th/U. The partially melted eclogite contains euhedral zircons with dark, sector-zoned, higher U, Th and Th/U inherited cores. Three cores give a Paleoproterozoic 207Pb/206Pb age of 1,962±27 Ma, interpreted as the age of the leucogabbroic protolith. CL images of the bright overgrowths show faint oscillatory zoning next to homogenous areas that indicate zircon growth in the presence of a HP melt and later recrystallization. Additional evidence that zircon grew during eclogite facies conditions is the lack of a Eu anomaly in the trace element data for all the samples. These results, combined with additional less precise Sm-Nd ages and our earlier work, point to a Devonian age of HP metamorphism in the western and central portions of the eclogite province. An UHP kyanite eclogite from the eastern part of the transect contains equant metamorphic zircon with homogeneous to patchy zoning in CL and HP inclusions of garnet, omphacite and kyanite. These zircons have slightly higher U, Th and Th/U values than the HP ones, no Eu anomaly, and are thus comparable to UHP zircons in the literature. The 206Pb/238U age of these zircons is 360±5 Ma, much younger than the HP eclogites. The same sample gives a Sm-Nd age of 342±6 Ma. Unlike the HP eclogites, the Sm-Nd age of the UHP rock is ca. 20 Ma younger than the U-Pb zircon age and most likely records slow cooling through the closure temperature, since peak temperatures were in excess of 900°C. Widespread HP metamorphism of both the Laurentian and Baltica continental margins marks the culmination of this continent–continent collision in the Devonian. Carboniferous UHP conditions, though localized in the east, suggest a prolonged collisional history rather than a short-lived Scandian orogeny. The traditional Silurian Scandian orogeny should thus be extended through the Devonian. 相似文献
137.
Thomas?P.?ChapinEmail author Jane?M.?Caffrey Hans?W.?Jannasch Luke?J.?Coletti John?C.?Haskins Kenneth?S.?Johnson 《Estuaries and Coasts》2004,27(5):882-894
Nitrate and water quality parameters (temperature, salinity, dissolved oxygen, turbidity, and depth) were measured continuously with in situ NO3 analyzers and water quality sondes at two sites in Elkhorn Slough in Central California. The Main Channel site near the mouth of Elkhorn Slough was sampled from February to September 2001. Azevedo Pond, a shallow tidal pond bordering agricultural fields further inland, was sampled from December 1999 to July 2001. Nitrate concentrations were recorded hourly while salinity, temperature, depth, oxygen, and turbidity were recorded every 30 min. Nitrate concentrations at the Main Channel site ranged from 5 to 65 μM. The propagation of an internal wave carrying water from ≈100 m depth up the Monterey Submarine Canyon and into the lower section of Elkhorn Slough on every rising tide was a major source of nitrate, accounting for 80–90% of the nitrogen load during the dry summer period. Nitrate concentrations in Azevedo Pond ranged from 0–20 μM during the dry summer months. Nitrate in Azevedo Pond increased to over 450 μM during a heavy winter precipitation event, and interannual variability driven by differences in precipitation was observed. At both sites, tidal cycling was the dominant forcing, often changing nitrate concentrations by 5-fold or more within a few hours. Water volume flux estimates were combined with observed nitrate concentrations to obtain nitrate fluxes. Nitrate flux calculations indicated a loss of 4 mmol NO3 m?2 d?1 for the entire Elkhorn Slough and 1 mmol NO3 m?2 d?1 at Azevedo Pond. These results suggested that the waters of Elkhorn Slough were not a major source of nitrate to Monterey Bay but actually a nitrate sink during the dry season. The limited winter data at the Main Channel site suggest that nitrate was exported from Elkhorn Slough during the wet season. Export of ammonium or dissolved organic nitrogen, which we did not monitor, may balance some or all of the NO3 flux. 相似文献
138.
Regional geochemical data from the 1:250,000 map series of Great Britain produced by the Institute of Geological Sciences are processed using a computer system developed for the National Geochemical Data Bank. The system, which can be used for the selective or complete retrieval of data and for statistical analysis and plotting, incorporates a procedure for determining accuracy and precision. Changes in accuracy are monitored by analysis of standards and the redetermination of sub-sets of samples using an instrumental neutron activation method. Samples are assigned random numbers in the field and are re-ordered sequentially prior to preparation and analysis in order to determine systematic errors occurring within batches of samples.Sampling, sub-sampling and analytical precision are monitored using analysis of variance methods on the results obtained on duplicate samples and analyses. The system for the efficient processing of this information is described and examples of the different types of error presented. 相似文献
139.
Ecological restoration, cultural preferences and the negotiation of ‘nativeness’ in Australia 总被引:1,自引:0,他引:1
The paper addresses cultural assumptions about ‘nativeness’ and ‘belonging’ to place as they are implicated in notions of ‘ecological restoration’. Given the centrality of complex notions of ‘indigeneity’ to the issue of what ecological ‘restoration’ means in Australia, this is a rich area for cultural and historical analysis. Case materials illustrate the negotiated and ambiguous nature of Australian ideas about what ‘belongs’ ecologically and culturally across the broad continent of this relatively young post-Settler nation. We seek to foreground these issues through consideration of what ‘restoring’ nature might mean in the context of debates about native plants, the re-introduction of an iconic species of ground dwelling bird, the removal of cane toads that are demonised as highly ‘alien’, and the multiple ways in which the dingo is regarded ambiguously as both native and a ‘pest’ that needs to be controlled and culled. By showing how ‘restoration’ can be understood and mobilised in a variety of ways – in terms of the ‘re-naturing’, ‘re-valuing’ and/or ‘repatriating’ of indigenous species, as well as impassioned rejection of ‘exotics’ – we emphasise the importance of social science for building a well-grounded sense of how environmental management priorities and approaches are informed by a wider set of cultural assumptions. 相似文献
140.
This report analyses a decade of geography scholarship student entry and achievement data (n = 10,205) to reveal patterns and trends of high‐achieving school students. The study is an exploratory analysis, the aim of which is to describe where the greatest scholarship success has occurred, as well as attendant demographic characteristics of New Zealand's most capable geography students and their schools. Emerging from the regions is a localised story of students from an extremely narrow number of schools achieving disproportionate scholarship success. This raises questions in the wider geography teaching community about the possibility of a broader constituency achieving scholarship awards. 相似文献