全文获取类型
收费全文 | 194篇 |
免费 | 18篇 |
国内免费 | 44篇 |
专业分类
大气科学 | 11篇 |
地球物理 | 56篇 |
地质学 | 88篇 |
海洋学 | 65篇 |
综合类 | 5篇 |
自然地理 | 31篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 10篇 |
2012年 | 6篇 |
2011年 | 11篇 |
2010年 | 8篇 |
2009年 | 26篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有256条查询结果,搜索用时 31 毫秒
51.
Maja A. Lazzaretti Kurt W. Hanselmann Helmut Brandl Daniel Span Reinhard Bachofen 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):285-299
P, Fe, Mn, and S species were analyzed in water samples from the sediment-water interface collected at four seasonally different times during the course of a year at two sampling sites in the southern basin of Lake Lugano (Lago di Lugano). The results reveal the strong influence of the biogeochemical processes in the sediment on the chemical composition of the lake water above. Consumption of oxygen and nitrate under oxic to microoxic conditions in the water column as well as sequential release of reduced manganese and iron under anoxic conditions was observed as a direct or indirect consequence of microbially mediated degradation of organic matter. The seasonal pattern observed for the release and the retainment of dissolved reduced iron and manganese correlates well with the one for dissolved phosphate. Iron, manganese and phosphorus cycling are coupled tightly in these sediments. Both sediment types act as sinks for hydrogen sulfide and sulfate. An inner-sedimentary sulfur cycle is proposed to couple iron, manganese and phosphorus cycling with the degradation of organic matter. Nutrient cycling at the sediment-water interface might thus be driven by a microbially regulated electron pumping mechanism. The results contribute to a better understanding of the role of sediment processes in the lake's internal phosphorus cycle and its seasonal dynamics. 相似文献
52.
Melanie J. Leng Bernd Wagner N. John Anderson Ole Bennike Ewan Woodley Simon J. Kemp 《第四纪科学杂志》2012,27(6):575-584
Here we present Holocene organic carbon, nitrogen, sulphur, carbon isotope ratio and macrofossil data from a small freshwater lake near Sisimiut in south‐west Greenland. The lake was formed c. 11 cal ka BP following retreat of the ice sheet margin and is located above the marine limit in this area. The elemental and isotope data suggest a complex deglaciation history of interactions between the lake and its catchment, reflecting glacial retreat and post‐glacial hydrological flushing probably due to periodic melting of local remnant glacial ice and firn areas between 11 and 8.5 cal ka BP. After 8.5 cal ka BP, soil development and associated vegetation processes began to exert a greater control on terrestrial–aquatic carbon cycling. By 5.5 cal ka BP, in the early Neoglacial cooling, the sediment record indicates a change in catchment–lake interactions with consistent δ13C while C/N exhibits greater variability. The period after 5.5 cal ka BP is also characterized by higher organic C accumulation in the lake. These changes (total organic carbon, C/N, δ13C) are most likely the result of increasing contribution (and burial) of terrestrial organic matter as a result of enhanced soil instability, as indicated by an increase in Cenococcum remains, but also Sphagnum and Empetrum. The impact of glacial retreat and relatively subdued mid‐ to late Holocene climate variation at the coast is in marked contrast to the greater environmental variability seen in inland lakes closer to the present‐day ice sheet margin. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
53.
A heavy rainfall case related to Mesoscale Convective Systems (MCSs) over
the Korean Peninsula was selected to investigate the impact of radar data
assimilation on a heavy rainfall forecast. The Weather Research and
Forecasting (WRF) three-dimensional variational (3DVAR) data assimilation
system with tuning of the length scale of the background error covariance
and observation error parameters was used to assimilate radar radial
velocity and reflectivity data. The radar data used in the assimilation
experiments were preprocessed using quality-control procedures and
interpolated/thinned into Cartesian coordinates by the SPRINT/CEDRIC
packages. Sensitivity experiments were carried out in order to determine the
optimal values of the assimilation window length and the update frequency
used for the rapid update cycle and incremental analysis update experiments.
The assimilation of radar data has a positive influence on the heavy
rainfall forecast. Quantitative features of the heavy rainfall case, such as
the maximum rainfall amount and Root Mean Squared Differences (RMSDs) of
zonal/meridional wind components, were improved by tuning of the length
scale and observation error parameters. Qualitative features of the case,
such as the maximum rainfall position and time series of hourly rainfall,
were enhanced by an incremental analysis update technique. The positive
effects of the radar data assimilation and the tuning of the length scale
and observation error parameters were clearly shown by the 3DVAR increment. 相似文献
54.
55.
In this study, we determined pH, phosphorus content and the number of P-dis- solving/decomposing bacteria in relation to the depth in the sediment of Guanting reservoir in Beijing. The pH value was slightly increased from 8.0 in the surface to 8.5 in the bottle (69 cm in depth) of sediment. The highest P content, 1269 mg/kg, was detected in the 35 cm layer, followed by the 5 cm (993 mg/kg) and 69 cm (580 mg/kg) layers. The number of inorganic P-dissolving bacteria varied from 6(102 to 8(104 and the organic P-discomposing bacteria were from 1.9(103 to 6.3(104 per gram sediment in different depths, which were counted under 28℃ and 20℃ ( pH7.5 and 8.5. The number of P-dissolving/discomposing bacteria was directly correlated to the P content in each layer of sediments. The analysis of P-dissolving/decomposing ability of bacteria showed that some of these bacteria were also capable of accumulating P intracellularly. The intracellular P-accumulation was more efficient at lower temperature; in contrast, the activity of P-dissolving/decomposing was stronger at higher temperature. So the content of dissolved P in water body, or quality of water, could be affected by the change of temperature via the regulation of bacterial activity. On the basis of 16S rDNA sequencing, the 13 efficient P-dis- solving/decomposing bacteria were identified as Bacillus spp., Bacterium sp., Microbacterium sp., Paenibacillus sp. and Pseudomonas sp. 相似文献
56.
This study tests the hypothesis that Fourier-transform infrared spectroscopy (FTIRS) of lake sediments can be used to infer
past changes in tree-line position and total organic carbon (TOC) content of lake water. A training set of 100 lakes from
northern Sweden spanning a broad altitudinal and TOC gradient from 0.7 to 14.9 mg/l was used to assess whether vegetation
zones and TOC can be modelled from FTIR spectra of surface sediments (0–1 cm) using principal component analysis (PCA) and
partial least squares (PLS) regression. Preliminary results show that FTIRS of lake sediments can be used to reconstruct past
changes in tree line and the TOC content of lake water, which is hardly surprising since FTIRS registers the properties of
organic and minerogenic material derived from the water mass and the drainage area. The FTIRS model for TOC gives a root mean
squared error (RMSECV) of calibration of 1.4 mg/l (10% of the gradient) assessed by internal cross-validation (CV) yielding
an Rcv2 of 0.64. This should be compared with a near-infrared spectroscopy (NIRS) and diatom transfer function for TOC from the same
set of lakes, which have a Rcv2 of 0.61 and 0.31, and RMSECV of 1.6 and 2.3 mg/l, respectively. The FTIRS-TOC model was applied to a Holocene sediment core
from a tree-line lake and the results show similar trends as inferences from NIRS and pollen from the same core. Overall,
the results indicate that changes in FTIR spectra from lake sediments reflect differences in catchment vegetation and TOC,
and that FTIRS-models based on surface-sediment samples can be applied to sediment cores for retrospective analysis. 相似文献
57.
Seunghun KANG Saikat Ghosh Baoshan XING 《中国地球化学学报》2006,25(B08):263-264
Soils are the largest carbon reservoir in the terrestrial system. Soils contain about three times more carbon than vegetation and twice as much as that present in the atmosphere. Soil organic matter (SOM) is very complex in composition and structure, formed of heterogeneous substances and generally associated with minerals in soils. SOM is classified as labile and stable fractions on the basis of residence time, determined not only by the chemical composition of SOM, but also by types of protection or bonds within soils. The stable carbon fraction is protected either physically or chemically. To understand the process of SOM stabilization, physicochemical properties of organic-mineral complexes were determined by Fourier transformed infrared (FTIR) with attenuated total reflectance (ATR) and diffuse reflectance (DRIFT), atomic force microscopy (AFM), and nuclear magnetic spectroscopy (NMR). Humic acids and carboxylic acids with relatively short carbon chains were used as sorbates, and goethite, kaolinite, and montmorillonite as adsorbents. Humic acid was fractionated during adsorption on the minerals, which was highly influenced by the characteristics of minerals. For instance, long-chain aliphatic carbon was likely to be adsorbed onto the surface of kaolinite and montmorillonite, while goethite surface attracted carboxylic functional groups of humic acid. 相似文献
58.
对成矿溶液性质的认识是成矿理论和成矿预测的基础。本文用云南腾冲热泉水、勐野并钾盐卤水、青岛海洋水、贵州赤天化含油气水、贵阳雨水以及从贵阳森林公园腐殖土中提取的含腐植酸的水溶液,和自配的pH=1.0的含氯酸性水,对西南地区不同岩性的四种矿源岩样进行了加温浸泡溶解实验。另外还利用表生风化淋滤模拟实验装置对该四种矿源岩样进行了三种不同大气雨水的风化淋滤模拟实验。实验结果表明酸雨和酸性水最容易形成高含量的成矿溶液;含腐植酸的水有时对多种金属也能形成较高含量的合矿溶液。但现代雨水、腾冲火山热泉水、勐野井钾盐卤水、青岛海洋水、贵州赤天化含油气水等近中性和偏碱性的表生水对Fe、Mn、Cu、Pb、Zn、等常量金属元素几乎不能形成高含量的合矿溶液;当溶液中存在强络合剂时,可能对某些贵金属和稀有、分散元素的搬运和成矿具有较重要意义。 相似文献
59.
土壤圈在全球变化中的意义与研究内容 总被引:17,自引:0,他引:17
土壤圈是地圈系统的重要组成部分,它处于地圈系统,即气圈、水圈、生物圈与岩石圈的交界面,是最活跃、最富生命力的圈层。土壤圈的物质循环是全球变化中物质循环的重要内容,因此,研究土壤圈及其物质循环的结构与功能,对全球变化,特别对全球土壤变化有密切关系。土壤圈在全球土壤变化中的研究内容包括:土壤圈与地圈各圈层的物质循环;水土资源的时空变化;土壤肥力变化与农业持续发展,区域治理与环境建设等,这些都是全球土壤变化,特别是中国全球变化的主题,应引起高度重视。 相似文献
60.
Tobias Schaller H. Christoph Moor Bernhard Wehrli 《Aquatic Sciences - Research Across Boundaries》1997,59(4):326-344
In Baldeggersee, the distributions of solid phase Fe, Mn, V, Cr, As and Mo were determined in different sediment strata, deposited
under various deep-water oxygen conditions. Iron concentrations are correlated with water depth when an anoxic sediment is
in contact with an oxic water column. Benthic redox gradients trigger iron transport towards the deepest site (geochemical
focusing) and loss of iron from the shallower parts through the outflow. Fe cycling in the lake is inhibited by oxygen penetration
into the sediment. Vanadium and arsenic can be used as tracers for the internal Fe cycle. Their distribution patterns are
highly correlated with iron. In case of a stable oxycline in the deep water, Mo is enriched in the sediment and correlates
with Mn. The horizontal distribution patterns of Fe, V, As and the correlation of Fe and Mn with trace metals are promising
proxy indicators for the reconstruction of deep-water oxygen conditions during deposition. 相似文献