全文获取类型
收费全文 | 247篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 1篇 |
地球物理 | 120篇 |
地质学 | 56篇 |
海洋学 | 42篇 |
天文学 | 12篇 |
自然地理 | 7篇 |
出版年
2014年 | 1篇 |
2012年 | 10篇 |
2011年 | 15篇 |
2008年 | 21篇 |
2007年 | 11篇 |
2006年 | 25篇 |
2005年 | 23篇 |
2004年 | 13篇 |
2003年 | 15篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 19篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1984年 | 2篇 |
排序方式: 共有249条查询结果,搜索用时 250 毫秒
221.
222.
The behavior of dissolved cadmium (Cd) in the Danube estuary was investigated through field sampling and mixing experiments using Danube River water and Black Sea water. The experiments were performed by mixing these two end-member waters in various proportions, with the addition of stable or radioactive Cd to the freshwater Danube end-member prior to the mixing. The release of Cd that resulted in maximum concentrations under field conditions was well simulated by mixing experiments. The experimental results were modeled assuming that the release of Cd was the sum of the contribution of physical effects resulting from dilution effects and the contribution of chemical effects resulting from dissolved Cd-complex formation (and isotopic exchange when concerned). In the absence of dissolved Cd-complexing ligands, the release of Cd due to the dilution of the particulate phase during mixing could explain part of the maximum concentrations observed in field conditions. Kinetic effects were established by comparing the theoretical and measured contribution of chemical effects resulting from dissolved Cd-complex formation. The non-equilibrium state observed during the mixing experiment suggested the presence of particulate labile Cd that was not easily mobilized. All these features supported the hypothesis that Cd released in estuaries is controlled both by the dilution of the particulate phase and by kinetic competitive complexation between particulate ligands (covering a large spectrum of nature and strength) and dissolved ligands. 相似文献
223.
在霍利黑德对新一代水位测量系统、气泡式和浮子式验潮仪进行比测的情况(英国普劳德曼海洋研究所J.M.Vssie等)1引言普劳德曼海洋研究所(POL)与其它许多海洋研究所一样,对精确测量海平面的工作很感兴趣。本报告中描述的现场经验是以与美国国家海洋测量局... 相似文献
224.
García-Luque E DelValls TA Casado-Martínez C Forja JM Gómez-Parra A 《Marine environmental research》2004,58(2-5):671-674
We describe the effect of heavy metals Zn, Cd, Pb and Cu on the induction of methallothioneins on the clam Scrobicularia plana along a salinity gradient simulated under laboratory conditions. The clams were exposed to constant heavy metal concentrations in a dynamic estuary simulator during a 15-day assay to investigate possible induction of metal-binding proteins in them. The concentration of heavy metals in water was analysed. Clams were analysed for methallothionein concentrations. The speciation of Zn, Cd, Pb and Cu along the salinity gradient was modelled. Zn showed the highest concentrations and its prevalent species was the free ion. Intersite differences have been observed in methallothionein concentration and related to the salinity gradient. It seems that synthesis of methallothioneins is the result of physiological forces acting in concert with the changes in the chemical speciation of metals, owing to the trace metals uptake is controlled by means of an interaction of physiology and physicochemistry. 相似文献
225.
Kinetic and toxicological characteristics of acetylcholinesterase from the gills of oysters (Crassostrea rhizophorae) and other aquatic species 总被引:1,自引:0,他引:1
The aim of this work was to characterize the cholinesterases from gills of Crassostrea rhizophorae in order to use them as biomarkers. Gills were homogenized and then centrifuged (9,000 x g, 4 degrees C, 30 min). S9 and Triton X-100 S9 treated (TX S9) fractions were employed as enzyme source. Km(ap) and Vmax were estimated, using acetylthiocholine iodide as substrate. Inhibition assays were performed with iso-OMPA and eserine. The Km(ap) for S9 and TX S9 fractions were 0.05 and 0.06 mM, whereas the Vmax were 1.92 and 5.84 nmol/min/mg protein. respectively. No inhibition was detected when the samples were incubated with iso-OMPA, suggesting the presence of acetylcholinesterases (AChE) in oyster gill homogenates. Sensitivity to eserine inhibition of AChE in the gills of oysters is intermediate when compared with other aquatic species. 相似文献
226.
Intertidal sediments and bivalves Scrobicularia plana from Bilbao estuary (Spain) were repeatedly sampled during and after the 1989-90 drought. The organic content (OC) and the concentration of most of the 10 metals analysed in sediments were extremely variable (e.g. Cd ranged from 4 to 112 micrograms g-1, ppm dry wt), and they were strongly related to an index applied to estimate the magnitude of the drought (namely the deficit flow of the main river). After OC normalisation, the correlation versus deficit was lost for some elements (Cr, Fe, Ni) but not for others (Cd, Co, Cu, Pb, Zn). This leads to the conclusion that both a natural and a man-induced process account for the observed rise and fall of the contamination pattern: the reduced river flow raised the metal-binding capacity of sediments, and restrictions in the water supply increased the corrosion of sewers and their leaching of some elements. The concentration of trace metals in local bivalves (Cd reached 100 and 458 ppm dry wt, respectively, for whole tissues and digestive gland) mirrored the sediment contamination dynamics, but at a slower pace. The means by which S. plana is able to tolerate such high Cd tissue levels remain unknown. These results constitute some prime field evidence of drought effects that should be born in mind when pollution and risk from climate change are assessed in estuaries. 相似文献
227.
Subsurface heterogeneity in hydraulic properties and processes is a fundamental challenge in hydrogeology. We have developed an improved method of borehole dilution testing for hydrostratigraphic characterization, in which distributed temperature sensing (DTS) is used to monitor advective heat movement. DTS offers many advantages over conventional technologies including response times in the order of seconds rather than minutes, the ability to profile temperature synoptically in a well without disturbing the fluid column, sensitivity to a wider range of flow rates than conventional spinner and heat pulse flow meters, and the ease of interpretation. Open-well thermal dilution tests in two multiaquifer wells near Madison, Wisconsin, provided detailed information on the borehole flow regimes, including flow rates and the locations of inflows from both fractures and porous media. The results led to an enhanced understanding of flow in a hydrostratigraphic unit previously conceptualized as homogenous and isotropic. 相似文献
228.
Lewis SE Brodie JE McCulloch MT Mallela J Jupiter SD Williams HS Lough JM Matson EG 《Marine pollution bulletin》2012,65(4-9):306-319
Coral cores were collected along an environmental and water quality gradient through the Whitsunday Island group, Great Barrier Reef (Australia), for trace element and stable isotope analysis. The primary aim of the study was to examine if this gradient could be detected in coral records and, if so, whether the gradient has changed over time with changing land use in the adjacent river catchments. Y/Ca was the trace element ratio which varied spatially across the gradient, with concentrations progressively decreasing away from the river mouths. The Ba/Ca and Y/Ca ratios were the only indicators of change in the gradient through time, increasing shortly after European settlement. The Mn/Ca ratio responded to local disturbance related to the construction of tourism infrastructure. Nitrogen isotope ratios showed no apparent trend over time. This study highlights the importance of site selection when using coral records to record regional environmental signals. 相似文献
229.
Lidbury I Johnson V Hall-Spencer JM Munn CB Cunliffe M 《Marine pollution bulletin》2012,64(5):1063-1066
The impacts of ocean acidification on coastal biofilms are poorly understood. Carbon dioxide vent areas provide an opportunity to make predictions about the impacts of ocean acidification. We compared biofilms that colonised glass slides in areas exposed to ambient and elevated levels of pCO(2) along a coastal pH gradient, with biofilms grown at ambient and reduced light levels. Biofilm production was highest under ambient light levels, but under both light regimes biofilm production was enhanced in seawater with high pCO(2). Uronic acids are a component of biofilms and increased significantly with high pCO(2). Bacteria and Eukarya denaturing gradient gel electrophoresis profile analysis showed clear differences in the structures of ambient and reduced light biofilm communities, and biofilms grown at high pCO(2) compared with ambient conditions. This study characterises biofilm response to natural seabed CO(2) seeps and provides a baseline understanding of how coastal ecosystems may respond to increased pCO(2) levels. 相似文献
230.
Rare earth elements (REE) were analyzed in surface sediments from the Guadiana Estuary (SW Iberian Pyrite Belt). NASC (North American Shale Composite) normalized REE patterns show clearly convex curvatures in middle-REE (MREE) with respect to light- and heavy-REE, indicating acid-mixing processes between fluvial waters affected by acid mine drainage (AMD) and seawater. However, REE distributions in the mouth (closer to the coastal area) show slightly LREE-enriched and flat patterns, indicating saline-mixing processes typical of the coastal zone. NASC-normalized ratios (La/Gd and La/Yb) do not discriminate between both mixing processes in the estuary. Instead, a new parameter (E(MREE)) has been applied to measure the curvature in the MREE segment. The values of E(MREE)>0 are indicative of acid signatures and their spatial distribution reveal the existence of two decantation zones from flocculation processes related to drought periods and flood events. Studying REE fractionation through the E(MREE) may serve as a good proxy for AMD-pollution in estuarine environments in relation to the traditional methods. 相似文献