全文获取类型
收费全文 | 150篇 |
免费 | 12篇 |
专业分类
大气科学 | 8篇 |
地球物理 | 29篇 |
地质学 | 46篇 |
海洋学 | 37篇 |
天文学 | 28篇 |
综合类 | 1篇 |
自然地理 | 13篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 2篇 |
2011年 | 14篇 |
2010年 | 7篇 |
2009年 | 11篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 1篇 |
2002年 | 7篇 |
2001年 | 1篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有162条查询结果,搜索用时 140 毫秒
21.
22.
Adriana Beltrn-Przekurat Roger A. Pielke Sr. Debra P.C. Peters Keirith A. Snyder Albert Rango 《Journal of Arid Environments》2008,72(10):1897-1910
Our goal was to evaluate effects of broad-scale changes in vegetation from grasslands to shrublands over the past 150 years on near-surface atmosphere over the Jornada Experimental Range in the northern Chihuahuan Desert, using a regional climate model. Simulations were conducted using 1858 and 1998 vegetation maps, and data collected in the field. Overall, the vegetation shift led to small changes in sensible heat (SH) and an increase in latent heat (LH). The impacts of shrub encroachment depended on shrubland type: conversion from grass to mesquite cools the near-surface atmosphere and from grass to creosotebush warms it. Higher albedo of mesquite relative to grasses reduced available energy, which was dissipated mainly as LH due to the deeper root system in mesquite. In creosotebush-dominated areas, a decrease in albedo, an increase in roughness length and displacement height contributed to the SH increase and warmer temperatures. Sensitivity simulations showed that an increase in soil moisture content enhanced shrub LH and a reduction in mesquite cover enhanced the temperature differences. The observed shift in vegetation led to complex interactions between land and surface fluxes, demonstrating that vegetation itself is a weather and climate variable as it significantly influences temperature and humidity. 相似文献
23.
24.
Posidonia oceanica meadows can be severely damaged by dredge-fill operations. We report on the construction of gas pipelines that occurred between 1981 and 1993 in SW Sicily, Italy. A large portion of the meadow was mechanically removed, and the excavated trench was filled with a mosaic of substrates, ranging from sand to consolidated rock debris. Meadow loss and recovery were quantified over 7 years after the end of operations. We recorded an overall loss of 81.20 ha of meadow. Substrate strongly affected recovery as the percent cover by P. oceanica consistently increased on calcareous rubble, reaching values of 44.37 ± 3.05% in shallow sites after 7 years, whereas no significant increase occurred on other substrates. As in the Mediterranean Sea exploitation of coastal areas continues to grow with consequent impacts on P. oceanica meadows, this case study illustrates how artificial rubble-like materials could be employed to support the restoration of damaged meadows. 相似文献
25.
Emily?LeydenEmail author John?Tibby Adriana?García Atun?Zawadzki 《Journal of Paleolimnology》2011,46(4):637-647
Bombah Broadwater is a shallow coastal lake within the Ramsar-listed Myall Lakes system on the mid-north coast of New South
Wales, Australia. Increased nutrient and sediment loads resulting from catchment modification are thought to have instigated
the loss of aquatic plants in the lake, causing it to “switch” from a clear, macrophyte dominated system (similar to the conditions
in present day Myall Lake) to a turbid, phytoplankton dominated system. To assess this hypothesis, charophytes, foraminifera
and aquatic fauna remains from an 800 year sediment record were examined. The sediment chronology was established using 14C, 210Pb and 137Cs radiometric dating and sediment composition. Interestingly, a clear increase in charophytes since European arrival conflicted
with the hypothesised aquatic plant loss. Hence, it appears Bombah Broadwater has not undergone a change in stable state since
European arrival. An additional and unexpected finding in the patterns of the foraminifera and testate amoeba suggest that
Bombah Broadwater has freshened substantially since European arrival. This freshening may have resulted from increased catchment
run off as a result of the clearance of catchment vegetation. Since catchment vegetation clearance is widespread in Australia,
this finding raises the possibility that post-settlement freshening of coastal lakes may be a common occurrence. 相似文献
26.
John S. Armstrong-Altrin Ramasamy Nagarajan Jayagopal Madhavaraju Leticia Rosalez-Hoz Yong Il Lee Vysetti Balaram Adriana Cruz-Martínez Gladis Avila-Ramírez 《Comptes Rendus Geoscience》2013,345(4):185-202
This study focuses on the Jurassic (Huayacocotla and Pimienta Formations) and Upper Cretaceous (Méndez Formation) shales from the Molango Region, Hidalgo, Mexico. In this article, we discuss the mineralogy, major, and trace element geochemistry of the Mesozoic shales of Mexico. The goal of this study is to constrain the provenance of the shales, which belong to two different periods of the Mesozoic Era and to understand the weathering conditions and tectonic environments of the source region. 相似文献
27.
28.
Reinaldo L. Bozelli Adriano Caliman Rafael D. Guariento Luciana S. Carneiro Jayme M. Santangelo Marcos P. Figueiredo-Barros Joo J.F. Leal Adriana M. Rocha Letícia B. Quesado Paloma M. Lopes Vinicius F. Farjalla Claudio C. Marinho Fabio Roland Francisco A. Esteves 《Limnologica》2009,39(4):306-313
Human activities are exposing freshwater ecosystems to a wide range of stressors, whose direct and indirect effects can be alleviated or exacerbated through interactive effects with dynamic environmental drivers. This study used long-term data from two Neotropical lacustrine freshwater systems (Batata Lake, an Amazonian floodplain lake and Imboassica lagoon, an Atlantic coastal lagoon) subjected to different kinds of environmental fluctuations (i.e., flood pulse and sandbar opening) and anthropogenic impacts (i.e., siltation and eutrophication). Our objective was to determine whether the effects of human perturbations are contingent on modifications of important biotic and abiotic characteristics through environmental variability. For both ecosystems, environmental variability consistently interacted with anthropogenic perturbations to alter most of the variables analyzed, such as nutrient dynamics, chlorophyll-a concentration, zooplankton and benthic invertebrate species richness, and temporal community stability, which indicates that interactive effects between environmental variability and anthropogenic perturbations may impact a myriad of ecosystem properties. Furthermore, the nature of these interactive effects was highly dependent on the variable considered and on the ecosystem analyzed. For example, at Imboassica lagoon, sandbar openings interacted synergistically with trophic state to increase the phosphorus concentration in the water column. At Batata Lake, flooding generally alleviated the negative effects of siltation on species richness by both diluting inorganic suspended material concentration and by promoting local recruitment from the regional species pool. Such results indicate that our ability to understand and predict the outcome of anthropogenic impacts on inland aquatic systems can be hampered if we consider human stressors as “static” phenomena disconnected from dynamic interactions with major local environmental drivers. 相似文献
29.
Wagner José Barreto Dilson Norio Ishikawa Ieda Spacino Scarminio João de Souza Costa Paulo dos Santos Nora Miriam de Fatima Soares Romilaine Mansano Nicolau Adriana Celeste Esteves Gonçalves Sonia Regina Giancoli Barreto 《洁净——土壤、空气、水》2008,36(4):353-359
The conservation of large water resources is essential for the preservation of human life. The quantification and, more importantly, the speciation of chemical substances that indicate the presence of anthropogenic contamination in water resources are of great importance. This paper presents the results of analysis for the determination of organic, inorganic and total phosphorus, pseudo‐sulfur, and iron and manganese, in five fractions, in water sediments collected from the Capivara Hydroelectric Power Plant, Brazil. A study on the seasonal variation of these parameters was conducted, with data having been collected in the winter and in the summer, at two sites along the dam, 5 km apart, close to the city of Primeiro de Maio. Phosphorous was found in sediments and adjacent soil in the organic form (OP), and was used as an indicator of anthropogenic influence on the reservoir banks. Speciation of potentially toxic Mn showed that it is present in the exchangeable fraction of the 0–5 cm depth layer (sediment/water interface), making its transfer to the water column possible. Results from this study showed that domestic and industrial effluent treatment measures are needed for the preservation of the quality of aquatic environments. 相似文献
30.