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991.
Influence of pit removal methods on river network position 总被引:1,自引:1,他引:0
Digital elevation models often contain depressions that result in areas described as having no drainage, referred to as sinks or pits. These depressions disrupt the drainage surface, which disrupt routing of flow over the surface. Most of the attributes that can be extracted from a digital elevation model rely on flow‐routing algorithms to calculate the upslope contributing area. There is little information on the influence of the various algorithms on the position and on the connectivity of the extracted networks. The aim of this study was to assess the effects of pit removal methods, data sources and flow‐routing algorithms on the position of river networks. The results show that all factors and methods have an impact on the position of the extracted networks. The pit removal method combining filling and carving extracted river networks closer to the reference, as well the elevation models with higher resolution. Single‐flow direction methods provided more accurate positioning of river network, in this test area where the drainage is generally well defined. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
992.
Christiane Hudon Antonella Cattaneo Anne-Marie Tourville Poirier Philippe Brodeur Pierre Dumont Yves Mailhot Jean-Pierre Amyot Simon-Pierre Despatie Yves de Lafontaine 《Aquatic Sciences - Research Across Boundaries》2012,74(3):495-511
Submerged aquatic vegetation (SAV) constitutes a major component of fish habitat, providing support for epiphytes and invertebrates as well as shelter from predators. The effects of wetland epuration from a mesotrophic to a nearly oligotrophic state were examined over a 15?km long reach of the St. Lawrence River under the direct influence of major farmland tributaries. We hypothesized that the nutrient-enriched zone would support a higher biomass of SAV, epiphytes, macroinvertebrates and fish than the nitrogen-deficient epurated zone located downstream of the wetland. Predictions included that the enriched habitat would support a richer fish assemblage, with higher biomass and growth of juvenile yellow perch than found in the epurated zone. Results supported these hypotheses, demonstrating the chain of effects of nutrient reduction on the biomass of SAV (fourfold drop), invertebrate prey (ninefold), small (threefold) and large (1.5-fold) fish between the two zones. In addition to the reduction in SAV biomass, the replacement of filamentous chlorophytes by benthic mats of filamentous cyanobacteria in the epurated zone resulted in a less complex 3-D habitat structure and a low invertebrate availability for fish. Oligotrophication by wetland epuration exerted negative effects on fish habitat quality, food quantity and availability, with an impairment of juvenile perch growth and recruitment. A generalized model of the changes in habitat carrying capacity occurring with epuration (oligotrophication) or eutrophication is presented, with examples of other aquatic systems in which strong linkages between trophic status, SAV, invertebrates and fish productivity were also demonstrated. 相似文献
993.
Hydrogeological characterization of groundwater storage and drainage in an alpine karst aquifer (the Kanin massif,Julian Alps) 总被引:1,自引:0,他引:1 下载免费PDF全文
Janez Turk Arnauld Malard Pierre‐Yves Jeannin Metka Petrič Franci Gabrovšek Nataša Ravbar Jonathan Vouillamoz Tadej Slabe Valentin Sordet 《水文研究》2015,29(8):1986-1998
The Kanin massif is an important trans‐boundary aquifer, which stretches between Slovenia and Italy. The groundwater is only partially exploited, mainly for water supply, but the aquifer exhibits great potential for future exploitation. Since no consistent regional overview of the hydrogeological functioning of the Kanin massif was available, the decision was made to perform a study of this area, using a pragmatic approach based on 3D geological and hydrogeological modelling. The so‐called KARSYS approach was applied, with the aim of characterizing the groundwater reserves within this karst massif and of locating the main drainage axes that carry groundwater from the recharge areas to the respective springs. Delineation of the catchment areas of the corresponding springs was carried out, and some new explanations were obtained, especially with regard to the Mo?nica spring, which is located in Slovenia and forms a potential source of drinking water. It was found that this spring's catchment area extends as far as the Italian ski resort of Sella Nevea. The conceptual model also provides a possible explanation about the underground drainage towards the Boka spring and waterfall, which has been a challenge for decades. This new explanation is based on the existence of a perched groundwater body that feeds the Boka spring via a system of conduits. Despite some limitations, the results, which consist of a visualization of the underground drainage and groundwater storage within the Kanin massif, can be used as a basis for planning the sustainable management of karst waters in the studied area. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
994.
Point velocity and suspended sediment concentration measurements are used to calculate the total sediment discharge in sand-bed rivers.Calculations with the Series Expansion of the Modified Einstein Point Procedure(SEMEPP) depend on grain diameter d_s and settling velocity ω,flow depth h,shear velocity u*,and sampling depth h_p.This procedure extends the applicability of the Modified Einstein Procedure(MEP) by using point sediment concentration and velocity measurements.This procedure is tested using the laboratory data from Coleman,and field measurements from the Enoree,Middle Rio Grande and Mississippi Rivers.Based on 801 point measurements over 124 verticals at flow depths ranging from 0.17 m to 33.5 m and sediment concentrations less than 0.1 kg L~(-1),the accuracy of the calculations depends on u*/ω and h_p/d_s.Point measurement techniques like SEMEPP are well-suited when u*/ω 5 where at least 60%of the total sediment load is measured when 90%of the flow depth is sampled.The determination of sediment discharge from point measurements is most accurate in deep rivers when h_p/d_s 10.000.and u*/ω10.Point measurements are not well-suited for shallow rivers and laboratory flumes where h 0.5 m and when u*/ω 2. 相似文献
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Jennifer S. Le Blond Claire J. Horwell Peter J. Baxter Sabina A. K. Michnowicz Maura Tomatis Bice Fubini Pierre Delmelle Christina Dunster Herman Patia 《Bulletin of Volcanology》2010,72(9):1077-1092
The continuous ash and gas emissions from the Tavurvur cone in Rabaul caldera, Papua New Guinea, during 2007–08, raised concerns
regarding how exposure would affect the respiratory health of nearby populations and impact on the environment. As part of
a formal evaluation of the effects of volcanic emissions on public health, we investigated the potential health hazard of
the ash using a suite of selected mineralogical analyses and in vitro toxicity screening tests. The trachy-andesitic ash comprised 2.1–6.7 vol.% respirable (sub-4 μm diameter) particles. The crystalline silica content was 1.9–5.0 wt.% cristobalite (in the bulk sample) with trace amounts
of quartz and/or tridymite. Scanning electron microscopy showed that the ash particles were angular with sparse, fibre-like particles (∼3–60 μm max. diameter) observed in some samples, which we confirmed to be CaSO4 (gypsum, at <6 wt.% in the bulk samples) and not asbestiform fibres. The ash specific surface area was low (0.1–2.7 m2 g−1). The leached solution from one of the ash samples was slightly acidic (pH 5.6), but did not contain high levels of toxic
metals (such as F, Cu, Zn, Mn, As, Ni and Cd) when compared to previously tested volcanic ash leachates. Ash samples generated
potentially-harmful hydroxyl radicals through an iron-mediated catalytic reaction, in the range of 0.15–2.47 μmol m−2 (after 30 min of reaction). However, measurement of particle oxidative capacity (potential oxidative stress reaction using
ascorbic acid) and silica-like injury to red blood cells (erythrolysis assay, i.e. measurement of cell death) nevertheless revealed low biological reactivity.
The findings suggest that acute exposure to the ash would have a limited potential to exacerbate pre-existing conditions such as asthma or chronic bronchitis, and the potential for chronic exposure leading to silicosis was
low. 相似文献
999.
Trap Pierre Roger Françoise Cenki-Tok Bénédicte Paquette Jean-Louis 《International Journal of Earth Sciences》2017,106(2):453-476
International Journal of Earth Sciences - Unravelling the detailed pressure–temperature–time-deformation (P–T–t-D) evolution of magmatic and metamorphic rocks provides... 相似文献
1000.
Luigi Folco Pierre Rochette Jrme Gattacceca Natale Perchiazzi 《Meteoritics & planetary science》2006,41(3):343-353
Abstract— We report on the effectiveness of using magnetic measurements in the search for meteorites on the Antarctic ice sheet, which is thus far the Earth's most productive terrain. Magnetic susceptibility measurements carried out with a pocket meter (SM30) during the 2003/04 PNRA meteorite collection expedition to northern Victoria Land (Antarctica) proved to be a rapid, sensitive, non‐destructive means for the in situ identification, pairing, and classification of meteorites. In blue ice fields characterized by the presence of moraines and glacial drifts (e.g., Miller Butte, Roberts Butte, and Frontier Mountain), magnetic susceptibility measurements allowed discrimination of meteorites from abundant terrestrial stones that look like meteorites thanks to the relatively high magnetic susceptibility of the former with respect to terrestrial rocks. Comparative measurements helped identify 16 paired fragments found at Johannessen Nunataks, thereby reducing unnecessary duplication of laboratory analyses and statistical bias. Following classifications schemes developed by us in this and previous works, magnetic susceptibility measurements also helped classify stony meteorites directly in the field, thereby providing a means for selecting samples with higher research priority. A magnetic gradiometer capable of detecting perturbations in the Earth's magnetic field induced by the presence of meteorites was an efficient tool for locating meteorites buried in snow along the downwind margin of the Frontier Mountain blue ice field. Based on these results, we believe that magnetic sensors should constitute an additional payload for robotic search for meteorites on the Antarctic ice sheet and, by extension, on the surface of Mars where meteorite accumulations are predicted by theoretical works. Lastly, magnetic susceptibility data was successfully used to crosscheck the later petrographic classification of the 123 recovered meteorites, allowing the detection of misclassified or peculiar specimens. 相似文献