全文获取类型
收费全文 | 161篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 21篇 |
地球物理 | 43篇 |
地质学 | 36篇 |
海洋学 | 19篇 |
天文学 | 40篇 |
自然地理 | 6篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 10篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 14篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 11篇 |
2009年 | 5篇 |
2008年 | 7篇 |
2007年 | 11篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1983年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有171条查询结果,搜索用时 31 毫秒
51.
Geslaine Rafaela Lemos Gonçalves Luana Ferraz da Silveira Palomares Aline Nonato Sousa Gilson Stanski Gustavo Sancinetti Rogerio Caetano da Costa Antonio Leão Castilho 《Marine Ecology》2020,41(4):e12606
The Brazilian coast is home to two species of Majoid crabs: Libinia ferreirae and Libinia spinosa, with similar habits, as they live in symbiosis with the jellyfish Lychnorhiza lucerna during their juvenile stage and dwell on the bottom of the ocean near the coast when adults. This study investigated the spatial and temporal distribution of L. ferreirae and L. spinosa during different ontogenic phases on the south and south-eastern coast of Brazil, between latitudes 22º and 27ºS. Our results showed that both species have different distributions during their development in the three studied regions. Libinia ferreirae were more abundant associated with jellyfish, and L. spinosa were more abundant in the free-living phase. Environmental factors, especially temperature and salinity, for associated and free-living crabs, respectively, are the main factors that need to be supported for the establishment of these specimens. We were able to identify that the presence or absence of hosts (given the ecological interactions between the species) is determinant in finding the associated crabs. Geographical variations (morphology of the regions, marine currents and the strength of the tide) are linked directly to the movement of the jellyfish hosts to the coast, influencing the abundance of L. fereirae and L. spinosa populations and affecting their distribution patterns. We can infer that both species are connected with other populations because of the association with the jellyfish, crabs could be passively transported along the south and south-eastern coast of Brazil, maintaining the connection between metapopulations. 相似文献
52.
Gustavo M. Martins Andr F. Amaral Francisco M. Wallenstein Ana I. Neto 《Marine environmental research》2009,67(4-5):237-245
It is widely recognised that coastal-defence structures generally affect the structure of the assemblages they support, yet their impact on adjacent systems has been largely ignored. Breakwaters modify the nearby physical environment (e.g. wave action) suggesting a local impact on biological parameters. In the present study, an ACI (After-Control-Impact) design was used to test the general hypothesis that the artificial sheltering of an exposed coast has a strong effect on the structure and functioning of adjacent systems. The effects of a reduction in hydrodynamics were clear for a number of taxa and included the replacement of barnacles, limpets and frondose algae by an increasing cover of ephemeral algae. These effects were evident both at early and late successional stages. Results suggest that the artificial sheltering of naturally exposed coasts can have a strong impact promoting a shift from consumer- to producer-dominated communities, which has important ecological and energetic consequences for the ecosystem. 相似文献
53.
54.
The effects of nutrient availability and litter quality on litter decomposition were measured in two oligotrophic phosphorus
(P)-limited Florida Everglades esturies, United States. The two estuaries differ, in that one (Shark River estuary) is directly
connected to the Gulf of Mexico and receives marine P, while the other (Taylor Slough estuary) does not receive marine P because
Florida Bay separates it from the Gulf of Mexico. Decomposition of three macrophytes.Cladium jamaicense, Eleochaaris spp., andJuncus roemerianus, was studied using a litter bag technique over 18 mo. Litter was exposed to three treatments: soil surface+macroinvertebrates
(=macro), soil surface without macroinvertebrates (=wet), and above the soil and water (=aerial). The third treatment replicated
the decomposition of standing dead leaves. Decomposition rates showed that litter exposed to the wet and macro treatments
decomposed significantly faster than the aerial treatment, where atmospheric deposition was the only source of nutrients.
Macroinvertebrates had no influence on litter decompostion rates.C. jamaicense decomposed faster at sites, with higher P, andEleocharis spp. decomposed significantly faster at sites with higher nitrogen (N). Initial tissue C:N and C:P molar ratios revealed
that the nutrient quality of litter of bothEleocharis spp. andJ. roemerianus was higher thanC. jamaicense, but onlyEleocharis spp. decomposed faster thanC. jamaicense. C. jamaicense litter tended to immobilize P, whileEleocharis spp. litter showed net remineralization of N and P. A comparison with other estuarine and wetland systems revealed the dependence
of litter decomposition on nutrient availability and litter quality. The results from this experiment suggest that Everglades
restoration may have an important effect on key ecosystem processes in the estuarine ecotone of this landscape. 相似文献
55.
The kinematics and structure of NGC 1313 are discussed on the basis of interferometric observations. Several uniformly rotating components, a total mass of 2×1010 solar masses, and deviations from pure circular movement of an amplitude of almost 20 km s–1 are found. 相似文献
56.
Marcelo Zeri Jos�� Francisco Oliveira-J��nior Gustavo Bastos Lyra 《Meteorology and Atmospheric Physics》2011,113(3-4):139-152
Time series of pollutants and weather variables measured at four sites in the city of Rio de Janeiro, Brazil, between 2002 and 2004, were used to characterize temporal and spatial relationships of air pollution. Concentrations of particulate matter (PM10), sulfur dioxide (SO2) and carbon monoxide (CO) were compared to national and international standards. The annual median concentration of PM10 was higher than the standard set by the World Health Organization (WHO) on all sites and the 24?h means exceeded the standards on several occasions on two sites. SO2 and CO did not exceed the limits, but the daily maximum of CO in one of the stations was 27% higher on weekends compared to weekdays, due to increased activity in a nearby Convention Center. Air temperature and vapor pressure deficit have both presented the highest correlations with pollutant??s concentrations. The concentrations of SO2 and CO were not correlated between sites, suggesting that local sources are more important to those pollutants compared to PM10. The time series of pollutants and air temperature were decomposed in time and frequency by wavelet analysis. The results revealed that the common variability of air temperature and PM10 is dominated by temporal scales of 1?C8?days, time scales that are associated with the passage of weather events, such as cold fronts. 相似文献
57.
Seagrass beds have higher biomass, abundance, diversity and productivity of benthic organisms than unvegetated sediments. However, to date most studies have analysed only the macrofaunal component and ignored the abundant meiofauna present in seagrass meadows. This study was designed to test if meiobenthic communities, especially the free-living nematodes, differed between seagrass beds and unvegetated sediments. Sediment samples from beds of the eelgrass Zostera capricorni and nearby unvegetated sediments were collected in three estuaries along the coast of New South Wales, Australia. Results showed that sediments below the seagrass were finer, with a higher content of organic material and were less oxygenated than sediments without seagrass. Univariate measures of the fauna (i.e. abundance, diversity and taxa richness of total meiofauna and nematode assemblages) did not differ between vegetated and unvegetated sediments. However multivariate analysis of meiofaunal higher taxa showed significant differences between the two habitats, largely due to the presence and absence of certain taxa. Amphipods, tanaidacea, ostracods, hydrozoans and isopods occurred mainly in unvegetated sediments, while kinorhyncs, polychaetes, gastrotrichs and turbellarians were more abundant in vegetated sediments. Regarding the nematode assemblages, 32.4% of the species were restricted to Z. capricorni and 25% only occurred in unvegetated sediments, this suggests that each habitat is characterized by a particular suite of species. Epistrate feeding nematodes were more abundant in seagrass beds, and it is suggested that they graze on the microphytobenthos which accumulates underneath the seagrass. Most of the genera that characterized these estuarine unvegetated sediments are also commonly found on exposed sandy beaches. This may be explained by the fact that Australian estuaries have very little input of freshwater and experience marine conditions for most of the year. This study demonstrates that the seagrass and unvegetated sediments have discrete meiofaunal communities, with little overlap in species composition. 相似文献
58.
Saint-Hilaire Pascal von Praun Christoph Stolte Etzard Alonso Gustavo Benz Arnold O. Gross Thomas 《Solar physics》2002,210(1-2):143-164
The RHESSI Experimental Data Center (HEDC) at ETH Zürich aims to facilitate the use of RHESSI data. It explores new ways to
speed up browsing and selecting events such as solar flares. HEDC provides pre-processed data for on-line use and allows basic
data processing remotely over the Internet. In this article, we describe the functionality and contents of HEDC, as well as
first experiences by users. HEDC can be accessed at http://www.hedc.ethz.ch. Additional graphical material and color versions of most figures are available on the CD-ROM accompanying this volume.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022413302246 相似文献
59.
Hugo Ninanya Nilson Guiguer Eurípedes A. VargasJr Gustavo Nascimento Edmar Araujo Caroline L. Cazarin 《Hydrogeology Journal》2018,26(7):2257-2282
This work presents analysis of groundwater flow conditions and groundwater control measures for Vazante underground mine located in the state of Minas Gerais, Brazil. According to field observations, groundwater flow processes in this mine are highly influenced by the presence of karst features located in the near-surface terrain next to Santa Catarina River. The karstic features, such as caves, sinkholes, dolines and conduits, have direct contact with the aquifer and tend to increase water flow into the mine. These effects are more acute in areas under the influence of groundwater-level drawdown by pumping. Numerical analyses of this condition were carried out using the computer program FEFLOW. This program represents karstic features as one-dimensional discrete flow conduits inside a three-dimensional finite element structure representing the geologic medium following a combined discrete-continuum approach for representing the karst system. These features create preferential flow paths between the river and mine; their incorporation into the model is able to more realistically represent the hydrogeological environment of the mine surroundings. In order to mitigate the water-inflow problems, impermeabilization of the river through construction of a reinforced concrete channel was incorporated in the developed hydrogeological model. Different scenarios for channelization lengths for the most critical zones along the river were studied. Obtained results were able to compare effectiveness of different river channelization scenarios. It was also possible to determine whether the use of these impermeabilization measures would be able to reduce, in large part, the elevated costs of pumping inside the mine. 相似文献
60.
Steven A.C. van Benthem Raúl W. Valenzuela Gustavo J. Ponce 《Geofísica Internacional》2013,52(4):385-402
Upper mantle shear wave anisotropy under stations in southern Mexico was measured using records of SKS phases. Fast polarization directions where the Cocos plate subducts subhorizontally are oriented in the direction of the relative motion between the Cocos and North American plates, and are trench-perpendicular. This pattern is interpreted as subslab entrained flow, and is similar to that observed at the Cascadia subduction zone. Earlier studies have pointed out that both regions have in common the young age of the subducting lithosphere. Changes in the orientation of the fast axes are observed where the subducting plates change dip and/or are torn, and are thus indicative of 3-D flow around the slab edges. They are consistent with slab rollback, as previously shown by other authors. Some stations located away from the plate boundaries have their fast directions controlled by the absolute motion of the North American plate. The fast axis for station ZAIG, located in the Mesa Central, is oriented WNW-ESE and is different from all the other measurements in this study. 相似文献