全文获取类型
收费全文 | 249篇 |
免费 | 18篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 30篇 |
地球物理 | 84篇 |
地质学 | 66篇 |
海洋学 | 37篇 |
天文学 | 34篇 |
综合类 | 1篇 |
自然地理 | 17篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 16篇 |
2016年 | 18篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 21篇 |
2012年 | 11篇 |
2011年 | 22篇 |
2010年 | 8篇 |
2009年 | 22篇 |
2008年 | 11篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 3篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有275条查询结果,搜索用时 15 毫秒
271.
Rodrigo Augusto Bellezoni Cristiano Kenji Iwai Vagner Roberto Elis Wanderley da Silva Paganini Jorge Hamada 《Environmental Earth Sciences》2014,71(5):2429-2439
In Brazil, the large quantities of solid waste produced are out of step with public policies, technological developments, and government budgets for the division. In small municipalities, the common lack of technological knowledge and financial conditions for suitable waste disposal has resulted in a large number of illegal dumps. Therefore, small sanitary landfill facilities are working with simplified operations focusing on cost reduction and meeting the economic and technological standards of the city without endangering the environment or public health. Currently, this activity is regulated at a federal level although there is some uncertainty regarding the risk of soil and aquifer contamination as theses facilities do not employ liners. Thus, this work evaluates a small landfill to identify changes in soil and groundwater using geotechnical parameters, monitoring wells, and geophysical tests performed by electrical profiling. It is verified that based on current conditions, no contaminants have migrated via underground water aquifers, and overall no significant changes have occurred in the soil. It is concluded that, despite its simplicity, the method investigated is a viable alternative for the final disposal of municipal solid waste from small cities, especially in developing countries. 相似文献
272.
Amado LL da Rosa CE Leite AM Moraes L Pires WV Pinho GL Martins CM Robaldo RB Nery LE Monserrat JM Bianchini A Martinez PE Geracitano LA 《Marine pollution bulletin》2006,52(2):199-206
Biomarkers of exposure and effect of pollutants were analyzed in croakers Micropogonias furnieri (Teleostei: Sciaenidae) captured in winter and summer in a polluted and in a non-polluted site at the Patos Lagoon estuary (Southern Brazil). Catalase and glutathione S-transferase activities (exposure biomarkers) and lipid peroxidation (effect biomarker) were analyzed in liver samples. Other two effect biomarkers were also studied: blood cells DNA damage (through comet assay and micronucleus test) and respiratory burst measurements. In a broad view, results point to an important seasonal variation of the biochemical biomarkers analyzed. However, data obtained clearly indicate that croakers collected in winter at the polluted site were subjected to a level of clastogenic agents sufficient to generate irreversible genetic damages (mutations) and impair the fish immune system. 相似文献
273.
Yoon Seok Choi Jintae Lee Monica Prezzi Rodrigo Salgado 《Geotechnical and Geological Engineering》2017,35(4):1587-1604
Although the loads applied on piles are usually a combination of both vertical and lateral loads, very limited experimental research has been done on the response of pile groups subjected to combined loads. Due to pile–soil–pile interaction in pile groups, the response of a pile group may differ substantially from that of a single pile. This difference depends on soil state and pile spacing. This paper presents results of experiments designed to investigate pile interaction effects on the response of pile groups subjected to both axial and lateral loads. The experiments were load tests performed on model pile groups (2 × 2 pile groups) in calibration chamber sand samples. The model piles were driven into the sand samples prepared with different relative densities using a sand pluviator. The combined load tests were performed on the model pile groups subjected to different axial load levels, i.e., 0 (pure lateral loading), 25, 50, and 75% of the ultimate axial load capacity of the pile groups, defined as the load corresponding to a settlement of 10% of the model pile diameter. The combined load test results showed that the bending moment and lateral deflection at the head of the piles increased substantially for tests performed in the presence of axial loads, suggesting that the presence of axial loads on groups of piles driven in sand is detrimental to their lateral capacity. 相似文献
274.
Topological redundancy and ‘small‐world’ patterns in a food web in a subtropical ecosystem of Brazil
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hugo Bornatowski Rodrigo Barreto Andrés F. Navia Alberto Ferreira de Amorim 《Marine Ecology》2017,38(2)
According to graph theory, the frequency distribution of trophic interactions within a food web has deep structural implications, as it can highlight the presence of patterns associated with the web and indicate whether the properties of the web are independent of its size. A hypothesis is that ‘small‐world’ food webs are sensitive to the loss of species with the highest values. Therefore, the present work aimed to evaluate the degree to which a subtropical food web in Southern Brazil displays small‐world patterns and their resistance. As part of the assessment, we evaluated the topological redundancy values of species in the food web and then we simulated the exclusion of these species (such as sharks and sea birds), and also the exclusion of high centrality species (such as squids Loligo sp., portunid swimming crabs and the cutlassfish Trichiurus lepturus). The food web showed a ‘broad‐scale’ distribution of connections by node, and a small‐world pattern. As expected, a simplification of the network was observed after elimination of some species with high centrality. However, the food web was resistant to the loss of species with low topological redundancy, probably because these species occupy a high trophic level and do not participate in lots of routes within the food web. We highlight however, the importance of the application of multiple analyses to evaluate the importance of components in food webs, and fisheries management plans should consider both species of high centrality values and species with low topological redundancy. 相似文献
275.
Arthur Ayres Neto Vanessa Alves da Costa Clara Pinto Ferreira Maia Porto Thais Cristina Vargas Garrido Jean-Pierre Hermand 《Marine Georesources & Geotechnology》2020,38(4):437-449
AbstractMarine mining is the ocean’s new exploration frontier, and polymetallic crusts (PMCs) and ferromanganese nodules are considered a strategic resource for the future. Acoustic geophysical methods are a valuable tool for oceanic research and have been employed for several decades in the exploration of marine resources and environmental evaluations. The main objective of this work was to investigate the correlation between the chemical composition of PMCs from three different areas along the Brazilian continental margin and their physico-acoustic attributes (P-wave velocity, density and acoustic impedance). The results show that the geoacoustic properties of PMCs are correlated to their chemical composition. Measurements showed positive and negative trends between acoustic impedance and studied elements (Fe, Mn, Co, Cu, Zn, W and Ni) according to the direction of measurement, indicting high anisotropy levels. Our study sheds initial light on the correlation between acoustic properties and metal content of PMCs. The study facilitates assessments of the acoustic responses of PMCs allowing more efficient prospection and exploitation compared to ship-board geophysical techniques that are too qualitative to identify PMCs. The results can contribute to determining the best procedures and techniques for more efficient future exploration of this resource. 相似文献