全文获取类型
收费全文 | 286篇 |
免费 | 13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 | 56篇 |
地质学 | 116篇 |
海洋学 | 27篇 |
天文学 | 20篇 |
综合类 | 4篇 |
自然地理 | 60篇 |
出版年
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 13篇 |
2013年 | 26篇 |
2012年 | 9篇 |
2011年 | 15篇 |
2010年 | 15篇 |
2009年 | 18篇 |
2008年 | 13篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 5篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 8篇 |
2000年 | 2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 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971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302条查询结果,搜索用时 324 毫秒
41.
This survey provides baseline information on sediment characteristics, porewater, adsorbed and plant tissue nutrients from intertidal coastal seagrass meadows in the central region of the Great Barrier Reef World Heritage Area. Data collected from 11 locations, representative of intertidal coastal seagrass beds across the region, indicated that the chemical environment was typical of other tropical intertidal areas. Results using two different extraction methods highlight the need for caution when choosing an adsorbed phosphate extraction technique, as sediment type affects the analytical outcome. Comparison with published values indicates that the range of nutrient parameters measured is equivalent to those measured across tropical systems globally. However, the nutrient values in seagrass leaves and their molar ratios for Halophila ovalis and Halodule uninervis were much higher than the values from the literature from this and other regions, obtained using the same techniques, suggesting that these species act as nutrient sponges, in contrast with Zostera capricorni. The limited historical data from this region suggest that the nitrogen and phosphorus content of seagrass leaves has increased since the 1970s concomitant with changing land use practice. 相似文献
42.
Jane M. Reed Francesc Mesquita-Joanes Huw I. Griffiths 《Journal of Paleolimnology》2012,47(2):251-275
Diatoms (Bacillariophyceae; single-celled algae) and ostracods (Ostracoda; shelled microcrustacea) are known for their sensitivity
to salinity. In palaeolimnology, the potential has yet to be tested for quantifying past salinity, lake level, and by inference,
climate change, by application of multiple-indicator transfer functions. We used weighted averaging techniques to derive diatom
(n = 91; r
2
= 0.92) and ostracod (n = 53; r
2
= 0.83) conductivity transfer functions from modern diatom, ostracod and water chemistry data collected in lakes of central,
western and northern Turkey. Diatoms were better represented across the full gradient than ostracods, at intermediate levels
of conductivity in particular, but both transfer functions were statistically robust. Because transfer functions are not infallible,
we further tested the strength and simplicity of salinity response and the potential for identifying characteristic associations
of diatom and ostracod taxa in different parts of the salinity gradient, to improve palaeoclimate reconstruction. We identified
a subset of 51 samples that contained both diatoms and ostracods, collected at the same time from the same habitat. We used
Two-Way Indicator Species Analysis of a combined diatom-ostracod data set, transformed to achieve numerical equivalence, to
explore distributions in more detail. A clear ecological threshold was apparent at ~3 g l−1 salinity, rather than at 5 g l−1, the boundary used by some workers, equating to the oligosaline-mesosaline boundary. Other salinity boundaries were poorly
defined, indicating lack of a simple, well-defined salinity response. We did, however, define characteristic associations
of taxa, to facilitate the distinction to be drawn between a hydrologically open, fresh lake and an oligosaline lake, in palaeoenvironmental
reconstruction. Over the rest of the salinity gradient, we highlighted the potential for the multi-proxy approach to strengthen
ostracod-based reconstruction in particular, to overcome the problem of broad apparent tolerance ranges in common halophilic
taxa such as Limnocythere inopinata, which often dominate in low-diversity fossil assemblages. The combination of multi-proxy quantitative reconstruction, complemented
by qualitative understanding of ecological responses generated by the analysis, remains a powerful tool in Quaternary palaeoclimate
research. 相似文献
43.
Joëlle Gergis Ailie Jane Eyre Gallant Karl Braganza David John Karoly Kathryn Allen Louise Cullen Rosanne D’Arrigo Ian Goodwin Pauline Grierson Shayne McGregor 《Climatic change》2012,111(3-4):923-944
This study presents the first multi-proxy reconstruction of rainfall variability from the mid-latitude region of south-eastern Australia (SEA). A skilful rainfall reconstruction for the 1783–1988 period was possible using twelve annually-resolved palaeoclimate records from the Australasian region. An innovative Monte Carlo calibration and verification technique is introduced to provide the robust uncertainty estimates needed for reliable climate reconstructions. Our ensemble median reconstruction captures 33% of inter-annual and 72% of decadal variations in instrumental SEA rainfall observations. We investigate the stability of regional SEA rainfall with large-scale circulation associated with El Niño–Southern Oscillation (ENSO) and the Inter-decadal Pacific Oscillation (IPO) over the past 206 years. We find evidence for a robust relationship with high SEA rainfall, ENSO and the IPO over the 1840–1988 period. These relationships break down in the late 18th–early 19th century, coinciding with a known period of equatorial Pacific Sea Surface Temperature (SST) cooling during one of the most severe periods of the Little Ice Age. In comparison to a markedly wetter late 18th/early 19th century containing 75% of sustained wet years, 70% of all reconstructed sustained dry years in SEA occur during the 20th century. In the context of the rainfall estimates introduced here, there is a 97.1% probability that the decadal rainfall anomaly recorded during the 1998–2008 ‘Big Dry’ is the worst experienced since the first European settlement of Australia. 相似文献
44.
John M. Kennish Colleen Montoya Jane Whitsett John S. French 《Marine environmental research》1985,17(2-4)
Hydrocarbons are being introduced into the marine environment from a variety of sources including combustion processes, crude oil spills, fuel oil spills, and controlled disposal such as processed ballast water. Even in the relatively clean waters of Alaska hydrocarbons are being released at an alarming rate. The purpose of this study was to determine the optimum conditions for the metabolism of a representative hydrocarbon by Coho Salmon Oncorhynchus kisutch liver microsomes. The product of cyclohexane metabolism in the salmon microsomal system was identified by gas chromatography-mass spectrometry as cyclohexanol. Conditions of the microsome incubation were varied systematically to determine the optimum temperature, pH, and ionic strength for cyclohexanol production. Cyclohexanol was quantified by capillary column gas chromatography. Maximum cyclohexanol formation was achieved at 20°C, a pH of 8·0–8·5 and an ionic strength of 0·026. A linear rate of cyclohexanol formation is seen from 0–60 min of incubation and there is an apparent decrease in the rate from 60–90 min. Poor stability of the microsomal preparation from the species studied was also identified and several stability studies have been undertaken using cyclohexane metabolism as a monitor. 相似文献
45.
Annika Nolte Malte Eley Matthias Schöniger David Gwapedza Jane Tanner Sukhmani Kaur Mantel Konstantin Scheihing 《水文研究》2021,35(6):e14264
To increase the resilience of regional water supply systems in South Africa in the face of anticipated climatic changes and a constant increase in water demand, water supply sources require diversification. Many water-stressed metropolitan regions in South Africa depend largely on surface water to cover their water demand. While climatic and river discharge data is widely available in these regions, information on groundwater resources – which could support supply source diversification – is scarce. Groundwater recharge is a key parameter that is used to estimate groundwater amounts that can be sustainably exploited at a sub-watershed level. Therefore, the objective of this study was to develop a reliable hydrological modelling routine that enables the assessment of regional spatio-temporal variations of groundwater recharge to discern the most promising areas for groundwater development. Accordingly, we present a semi-distributed hydrological modelling approach that incorporates water balance routines coupled with baseflow modelling techniques to yield spatio-temporal variations of groundwater recharge on a regional level. The approach is demonstrated for the actively managed catchment areas of the Amathole Water Supply System situated in a semi-arid part of the Eastern Cape of South Africa. In the investigated study area, annual groundwater recharge exhibits a high spatio-temporal heterogeneity and is estimated to vary between ~0.5% and 8% of annual rainfall. Despite some uncertainties induced by limited data availability, calibration and validation of the model were found to be satisfactory and yielded model results similar to (point) data of annual groundwater recharge reported in earlier studies. Our approach is therefore found to derive crucial information for efficiently targeting more detailed groundwater exploration studies and could work as a blueprint for orientating groundwater potential exploration in similar environments. 相似文献
46.
47.
48.
The American horseshoe crab, Limulus polyphemus, is found along the Atlantic and Gulf of Mexico coasts in genetically isolated populations. Eggs are laid in shoreline beaches that expose developing embryos to combinations of environmental stressors. Whether populations of L. polyphemus differ in multi-stressor tolerance had never been tested. We assessed the multi-stressor tolerance of L. polyphemus embryos from a population in Delaware Bay (DE) and determined whether these differed from the multi-stressor tolerance of embryos from a more southerly Florida Gulf Coast (FGC) population. We monitored the field sediment temperatures and determined multi-stressor tolerance of DE embryos, then compared these to published data for FGC embryos. For multi-stressor tolerance, we assessed development success of embryos in 2-week exposures to 36 full-factorial combinations of temperature (20, 25, 30, 35 °C), salinity (5, 15, and 34 ppt), and ambient O2 (5, 13, and 21% O2), followed by 2 weeks in recovery conditions. Sediment temperatures in the DE site ranged from 9.5 to 46 °C, with extended periods exceeding 35 °C. Development success was similar between the DE and FGC populations in 14 of 26 multi-stressor combinations. The DE embryos were generally more successful in conditions that included high temperature or moderate hyposalinity, whereas the FGC embryos were generally more successful in conditions that included extreme hyposalinity. This suggests that although multi-stressor tolerances are generally similar between the two populations, specific differences exist that correlate more with differences in nest microenvironment than latitude. 相似文献
49.
Ty V. Wamsley Mary A. Cialone Jane M. Smith Bruce A. Ebersole Alison S. Grzegorzewski 《Natural Hazards》2009,51(1):207-224
The purpose of this investigation was to examine storm surge and wave reduction benefits of different environmental restoration
features (marsh restoration and barrier island changes), as well as the impact of future wetland degradation on local surge
and wave conditions. Storm surge simulations of two representative hurricanes were performed using the ADCIRC storm surge
model with the inclusion of radiation stress gradients from the STWAVE nearshore wave model. Coupled model simulations were
made for a number of landscape configurations that involved both restored and degraded wetland features. The impact of barrier
island condition on hurricane surge and waves was also evaluated. Effects of landscape features were represented by changes
in elevation and frictional resistance. Restoration and degradation of marsh resulted in decreases (for restoration cases)
and increases (for degradation cases) in both surge and waves. The magnitude of change was correlated with the magnitude of
the horizontal extent and elevation changes in the marsh. In general, the wave change patterns are consistent with the water
level changes. Deflation of the Chandeleur Islands (barrier island chain) resulted in slightly increased surge. Results suggest
that coastal marsh does have surge and wave reduction potential. Results also indicate that the impact of the landscape features
is amplified in areas where there are levee “pockets.” Barrier islands and coastal ridges reduce wave heights, even if in
a degraded condition and thus can reduce wave energy in wetland areas, protecting them from erosion. 相似文献
50.
全球重要农业文化遗产(GIAHS)经济评估概念框架:以中国稻鱼共生系统为例(英文) 总被引:2,自引:1,他引:1
Sonja BERWECK Parviz KOOHAFKAN Mary Jane Ramos dela CRUZ 闵庆文 焦雯珺 孙业红 刘某承 《资源与生态学报(英文版)》2013,4(3):202-211
全球重要农业文化遗产(GIAHS)项目是2002年由联合国粮农组织(FAO)发起,旨在建立全球重要农业文化遗产及其有关的景观、生物多样性、知识和文化保护体系,并在世界范围内得到认可与保护,使之成为可持续管理的基础。农业文化遗产地往往被认为比非遗产地更具经济价值,但目前还没有经济学分析来证明这一点,也没有任何针对农业文化遗产地的复杂的经济性能标准来长期监测其经济功能。本研究的目的在于建立一个经济评价方法,可用于遗产地与非遗产地之间比较。为此,本文选择了成本效益分析(CBA)方法。鉴于数据可得性的限制,经济分析的框架应该包括分析的方向、假设和数据要求,由此指导未来对GIAHS的经济评价。本研究选择中国青田稻鱼共生系统作为案例,根据数据可得性并针对不同活动(旅游,国内和国际市场的销售产品)以及相似系统间比较进行计算。 相似文献