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排序方式: 共有156条查询结果,搜索用时 15 毫秒
1.
Controlling geological and hydrogeological processes in an arsenic contaminated aquifer on the Red River flood plain,Vietnam 总被引:1,自引:0,他引:1
2.
The ecological aspect of meiofaunal communities in Can Gio mangrove forest, Ho Chi Minh city, Vietnam has not been investigated
before. The composition, distribution, density and biodiversity of meiofaunal communities were studied along an intertidal
transect at the Khe Nhan mudflat. Each time, three replicate samples were collected in four stations along a transect following
the water line from low tide level up to the mangrove forest edge. In total, 18 meiofaunal taxa were found with the dominant
taxa belonging to Nematoda, Copepoda, Sarcomastigophora and Polychaeta. The densities of meiofauna ranged from 1156 inds/10
cm2 to 2082 inds/10 cm2. The increase in densities from the mangrove forest edge towards the low water line was significant. Along the mudflat transect,
the biodiversity (expressed by different indices) was relatively high at different taxonomic levels but did not vary significantly
along the mudflat except for taxa richness. Eighty nematode genera belonging to 24 families with Comesomatidae having the
highest abundance 33.8 % were found.Theristus andNeochromadora decreased in densities from the lower water line towards the mangrove forest edge, whileParacomesoma andHopperia are typical and more abundant at the middle of the mudflat.Halalaimus increased from high on the mudflat to the low water line. 相似文献
3.
Simplified formulae for designing coastal forest against tsunami run-up: one-dimensional approach 总被引:2,自引:0,他引:2
In the present study, laboratory experiments were conducted to validate the applicability of a numerical model based on one-dimensional nonlinear long-wave equations. The model includes drag and inertia resistance of trees to tsunami flow and porosity between trees and a simplified forest in a wave channel. It was confirmed that the water surface elevation and flow velocity by the numerical simulations agree well with the experimental results for various forest conditions of width and tree density. Further, the numerical model was applied to prototype conditions of a coastal forest of Pandanus odoratissimus to investigate the effects of forest conditions (width and tree density) and incident tsunami conditions (period and height) on run-up height and potential tsunami force. The modeling results were represented in curve-fit equations with the aim of providing simplified formulae for designing coastal forest against tsunamis. The run-up height and potential tsunami forces calculated by the curve-fit formulae and the numerical model agreed within ± 10% error. 相似文献
4.
Nathalie van Vliet Ole Mertz Andreas Heinimann Tobias Langanke Unai Pascual Birgit Schmook Cristina Adams Dietrich Schmidt-Vogt Peter Messerli Stephen Leisz Jean-Christophe Castella Lars Jørgensen Torben Birch-Thomsen Cornelia Hett Thilde Bech-Bruun Amy Ickowitz Kim Chi Vu Kono Yasuyuki Jefferson Fox Christine Padoch Alan D. Ziegler 《Global Environmental Change》2012,22(2):418-429
This meta-analysis of land-cover transformations of the past 10–15 years in tropical forest-agriculture frontiers world-wide shows that swidden agriculture decreases in landscapes with access to local, national and international markets that encourage cattle production and cash cropping, including biofuels. Conservation policies and practices also accelerate changes in swidden by restricting forest clearing and encouraging commercial agriculture. However, swidden remains important in many frontier areas where farmers have unequal or insecure access to investment and market opportunities, or where multi-functionality of land uses has been preserved as a strategy to adapt to current ecological, economic and political circumstances. In some areas swidden remains important simply because intensification is not a viable choice, for example when population densities and/or food market demands are low. The transformation of swidden landscapes into more intensive land uses has generally increased household incomes, but has also led to negative effects on the social and human capital of local communities to varying degrees. From an environmental perspective, the transition from swidden to other land uses often contributes to permanent deforestation, loss of biodiversity, increased weed pressure, declines in soil fertility, and accelerated soil erosion. Our prognosis is that, despite the global trend towards land use intensification, in many areas swidden will remain part of rural landscapes as the safety component of diversified systems, particularly in response to risks and uncertainties associated with more intensive land use systems. 相似文献
5.
Summary The three-dimensional mesoscale cloud-resolving model ARPS (Advanced Regional Prediction System) was used to investigate the
dispersal of an inert seeding agent within a cumulonimbus (Cb) cloud developing from two different initial states. In this
paper, we stress the influence vortices in the cloud have on seeding agent dispersion. If a strong directional ambient wind
shear is present in the lowest layer, a vortex pair formed at the flanks of the simulated cloud. Following the velocity field,
a considerable amount of the injected seeding agent would be thrown out to the rear of the cloud, where both updrafts associated
with vortices and downdrafts occurred. After a short time the agent was present only in the cloud periphery. If the Cb cloud
developed under conditions where directional ambient wind shear did not exist, seeding agent dispersion would be quite different.
In this case, almost all the seeding agent was transported into the main updraft, while the residence time of the agent within
the cloud was longer due to the weaker cloud dynamics. Therefore, we must pay attention to whether or not the cloud contains
vortices when we make the decision where to seed. This is necessary in order to minimize the loss of seeding material. 相似文献
6.
In this paper, the ability of a material rate‐independent system to evolve toward another mechanical state from an equilibrium configuration, with no change in the control parameters, is investigated. From a mechanical point of view, this means that the system can spontaneously develop kinetic energy with no external disturbance from an equilibrium state, which corresponds to a particular case of bifurcation. The existence of both conjugate incremental strain and stress such that the second‐order work vanishes is established as a necessary and sufficient condition for the appearance of this bifurcation phenomenon. It is proved that this fundamental result is independent of the constitutive relation of the rate‐independent material considered. Then the case of homogeneous loading paths is investigated, and, as an illustration, the subsequent results are applied to interpret the well‐known liquefaction observed under isochoric triaxial loading conditions with loose granular materials. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
7.
Meiobenthos in estuary part of ha long bay (gulf of tonkin, south china sea, vietnam) 总被引:1,自引:0,他引:1
Olga Pavlyuk Yulia Trebukhova Nguyen Vu Thanh Nguyen Dinh Tu 《Ocean Science Journal》2008,43(3):153-160
The distribution of the taxonomical composition and the density of meiobenthos depending on some factors of environment has
been studied in bottom sediments of the northern estuary part of Ha Long Bay (Cua Luc estuary). The basic factor of influence
on meiobenthic community structure was the granulometric composition of sediment. The greatest taxonomic diversity is noted
in the silted sands, lowest — in the silty sediments. The density of meiobenthic community was higher in the silty sediments.
Slightly expressed correlation between the density of nematodes and the percentage of silty particles in the sediments is
detected (Spearman rank correlation coefficient was 0.49±0.21, p=0.035). The nematodes were dominant at all stations. In total,
representatives of 66 species of nematodes belonging to 17 families and 52 genera were identified. 相似文献
8.
Dieke Postma Søren Jessen Mai Thanh Duc Pham Hung Viet Flemming Larsen 《Geochimica et cosmochimica acta》2010,74(12):3367-508
Sediments from the Red River and from an adjacent floodplain aquifer were investigated with respect to the speciation of Fe and As in the solid phase, to trace the diagenetic changes in the river sediment upon burial into young aquifers, and the related mechanisms of arsenic release to the groundwater. Goethite with subordinate amounts of hematite were, using Mössbauer spectroscopy, identified as the iron oxide minerals present in both types of sediment. The release kinetics of Fe, As, Mn and PO4 from the sediment were investigated in leaching experiments with HCl and 10 mM ascorbic acid, both at pH 3. From the river sediments, most of the Fe and As was mobilized by reductive dissolution with ascorbic acid while HCl released very little Fe and As. This suggests As to be associated with an Fe-oxide phase. For oxidized aquifer sediment most Fe was mobilized by ascorbic acid but here not much As was released. However, the reduced aquifer sediments contained a large pool of Fe(II) and As that is readily leached by HCl, probably derived from an unidentified authigenic Fe(II)-containing mineral which incorporates As as well. Extraction with ascorbic acid indicates that the river sediments contain both As(V) and As(III), while the reduced aquifer sediment almost exclusively releases As(III). The difference in the amount of Fe(II) leached from river and oxidized aquifer sediments by ascorbic acid and HCl, was attributed to reductive dissolution of Fe(III). The reactivity of this pool of Fe(III) was quantified by a rate law and compared to that of synthetic iron oxides. In the river mud, Fe(III) had a reactivity close to that of ferrihydrite, while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite. Mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic Fe-oxides as a reference. Sediments were incubated, both unamended and with acetate added, and monitored for up to 2 months. The river mud showed the fastest release of both Fe and As, while the effect of acetate addition was minor. This suggests that the presence of reactive organic carbon is not rate limiting. In the case of the river and aquifer sediments, the release of Fe and As was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor. The reduced aquifer sediment apparently can sustain slower but prolonged microbially-driven release of As. The highly reactive pools of Fe(III) and As in the river mud could be due to reoxidation of As and Fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river. Deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of As onto the floodplain and into the underlying aquifers. 相似文献
9.
10.
T.T.A. Vu K.-G. Zink K. Mangelsdorf R. Sykes H. Wilkes B. Horsfield 《Organic Geochemistry》2009,40(9):963-977
The bulk properties and bitumen molecular compositions of a rank-series of 38 humic coals from the New Zealand Coal Band (Cretaceous–Cenozoic) have been analysed to investigate early maturation processes affecting coaly organic matter through diagenesis to moderate catagenesis (Rank(Sr) 0.0–11.8, Ro 0.23–0.81%). The samples comprise a relatively restricted range of vitrinite rich coal types formed largely from higher land plant material under relatively oxic conditions, but with a significant contribution from microbial biomass. With increasing rank, total organic carbon contents show a general increase, whereas moisture and asphaltene contents decrease. Bitumen yields also decrease through the stages of diagenesis and early catagenesis (Rank(Sr) < 9, Ro < 0.55%), indicating partial loss of initial bitumen during early maturation. Thermal generation of hydrocarbons begins slowly at Rank(Sr) 5–6 (Ro 0.40%) as indicated by the constant occurrence and gradual increase of isoprenoids (e.g., pristane and phytane) and hopanoids in their more mature αβ configuration. This early phase of catagenesis, not previously recognised in New Zealand coals, is followed at Rank(Sr) 9 (Ro 0.55%) by the main catagenesis phase characterised by a more rapid increase in the generation of hydrocarbons, including total n-alkanes, isoprenoids and αβ-hopanes. Changes in the maturity of New Zealand coals can be traced by the Carbon Preference Index and several hopane maturity parameters, including 22S/(22S + 22R), αβ/(αβ + βα) and ββ/(αβ + βα + ββ). 相似文献