全文获取类型
收费全文 | 171篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 15篇 |
地球物理 | 48篇 |
地质学 | 56篇 |
海洋学 | 29篇 |
天文学 | 14篇 |
自然地理 | 16篇 |
出版年
2024年 | 1篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 16篇 |
2012年 | 11篇 |
2011年 | 13篇 |
2010年 | 13篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1982年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有182条查询结果,搜索用时 0 毫秒
31.
Victoria Reyes-García Oriol Andrés-Conejero Álvaro Fernández-Llamazares Isabel Díaz-Reviriego José-Luis Molina 《社会与自然资源》2019,32(4):452-472
Society’s understanding of a conflict is mediated by information provided in mass media, for which researchers stress the importance of analyzing media portrays of stakeholders in a conflict. We analyze information from the Bolivian press regarding the construction of a road crossing the Isiboro-Sécure Indigenous Territory and National Park (TIPNIS). Using stakeholder’s and social network analyses, we explore stakeholder’s positions and alliances as represented in the media and contrast it with previous scholarly work. We found that some actors cited as central in scholar analyses of the conflict are largely absent in the media (e.g., private investors, conservationist sector) and that the media tend to present stakeholders as having more homogeneous positions than the academic literature does while also neglecting some important alliances in their account. The media also suggests that Indigenous communities are forging stronger alliances with urban sectors and civil society, alliances not stressed by researchers. 相似文献
32.
Leticia Gmez-Mendoza Ernesto Vega-Pea M. Isabel Ramírez Jos Luis Palacio-Prieto Leopoldo Galicia 《Applied geography (Sevenoaks, England)》2006,26(3-4):276-290
The objective of study was to explore short-term trends of processes that determine land-use change in Sierra Norte of Oaxaca (SNO), Mexico. Land use and land cover changes (LULCC) were estimated in a complex mosaic of vegetation in the SNO from 1980 to 2000, and projected them to 2020 through a Markovian model. SNO is highly vulnerable to climatic change according to a 2050 GCM scenario. However, 3% annual rate of tropical and temperate forest deforestation from agriculture and livestock encroachment, suggest the threat from land-use change is higher than that from climatic change for this study site. Productive land-use strategies are needed to reduce such high deforestation rates for tropical regions. Controlling deforestation would also reduce short-term effects of CO2 emissions to the atmosphere. Because of the necessity to evaluate anthropogenic ecosystem changes, it is imperative to separate short-term influences such as deforestation, from long-term influences such as climatic change. 相似文献
33.
Javier Alcántara-Carrió Silvia Albarracín Isabel Montoya Montes Germán Flor-Blanco Ángela Fontán Bouzas Jorge Rey Salgado 《Geo-Marine Letters》2013,33(2-3):209-216
The objective of this study is to document and interpret a recently discovered carbonate-cemented coastal barrier on the inner shelf of the Gulf of Valencia (western Mediterranean Sea). The coastal barrier was identified in a high-resolution digital bathymetric model based on a cartographic survey of the study area using a multibeam echosounder. Moreover, radiocarbon dating and petrographic analyses were performed on a rock sample recovered from the seabed. The data reveal the submerged coastal barrier to be approx. 1.7 km wide and 70 km long, and incised by channels of various dimensions. Aligned more or less parallel to the modern coastline, it is interpreted as corresponding to the shoreline of a former sea-level stillstand. The barrier and lagoon system became stranded above sea level in the course of a subsequent forced regression, which also caused the incision of the river courses. Age dating of the cemented rock suggests that the fossil coastal barrier most probably formed during the prolonged Tyrrhenian (Eemian) sea-level highstand, induration taking place by carbonate cementation at the contact between freshwater and seawater (beach-rock formation). The fact that the fossil barrier is today submerged below modern sea level is explained by the sustained subsidence affecting the region. 相似文献
34.
35.
36.
Isabel C. Romero Myrna Jacobson Jed A. Fuhrman Marilyn Fogel Douglas G. Capone 《Marine Ecology》2012,33(1):117-127
The bioavailability of nutrients is important in controlling ecological processes and nitrogen cycling in oligotrophic mangrove forests, yet the variation of diazotrophic community structure and activity with nutrient availability in sediments remains largely unexplored. To investigate for the first time how nutrients in sediments affect spatial and temporal patterns of diazotrophic community structure and activity, the sedimentary environment of Twin Cays, Belize, was examined with respect to the effects of long‐term fertilization [treatments: control (Ctrl), nitrogen (N), and phosphorus (P)] on N2 fixation rates and nifH gene community structure. We found that N2 fixation rates were significantly higher at the P‐treatment, intermediate at the Ctrl‐treatment and lower in the N‐treatment (P: 4.2 ± 0.5, Crtl: 0.8 ± 0.1, N: 0.4 ± 0.1 nmol·N·g?1·h?1; P < 0.001) with spatial (Ctrl‐ and P‐treatments) and temporal (only P‐treatment) variability positively correlated with live root abundance (r2 = 0.473, P < 0.001) and concentration (r2 = 0.458, P < 0.0001). The community structure of diazotrophs showed larger spatial and temporal variability in the fertilized treatments than in the Ctrl‐treatment, with the relative abundance of OTUs (nifH operational taxonomic units) at the fertilized treatments inversely related to live root abundance. Overall, long‐term fertilization (with either N or P) affects not only nutrient levels in mangrove sediments directly, but also spatial and temporal patterns of both community structure and activity and likely plant‐microbe interactions as well. Our findings suggest that the maintenance of natural nutrient conditions in mangrove sediments is important to ensure the stability of microbial functional groups like diazotrophs. 相似文献
37.
Giuliana Panieri Angelo Camerlenghi Isabel Cacho Cristina Sanchez Cervera Miquel Canals Sara Lafuerza Gemma Herrera 《Marine Geology》2012
The hypothesis that benthic foraminifera are useful proxies of local methane emissions from the seafloor has been verified on sediment core KS16 from the headwall of the Ana submarine landslide in the Eivissa Channel, Western Mediterranean Sea. The core MS312 from a nearby location with no known methane emissions is utilised as control. The core was analysed for biostratigraphy, benthic foraminiferal assemblages, Hyalinea balthica and Uvigerina peregrina carbon and oxygen stable isotope composition, and sedimentary structures. The upper part of the core records post-landslide deglacial and Holocene normal marine hemipelagic sediments with highly abundant benthic foraminifera species that are typical of outer neritic to upper bathyal environment. In this interval, the δ13C composition of benthic foraminifera indicates normal marine environment analogous to those found in the control core. Below the sedimentary hiatus caused by the emplacement of the slide, the foraminiferal assemblages are characterised by lower density and higher Shannon Index. Markedly negative δ13C shifts in benthic foraminifera are attributed to the release of methane through the seabed. The mean values of the 13C anomaly in U. peregrina are ? 0.951 ± 0.208 in the pre-landslide sediments, and ? 0.269 ± 0.152 in post-slide reworked sediments deposited immediately above the hiatus. The δ13C anomaly in Hyalinea balthica is ? 2.497 ± 0.080 and ? 2.153 ± 0.087, respectively. To discard the diagenetic effects on the δ13C anomaly, which could have been induced by Ca–Mg replacement and authigenic carbonate overgrowth on foraminifera tests, a benthic foraminifera subsample has been treated following an oxidative and reductive cleaning protocol. The cleaning has resulted, only in some cases, in a slight reduction of the anomaly by 0.95% for δ13C and < 0.80% for δ18O. Therefore, the first conclusion is that the diagenetic alteration is minor and it does not alter significantly the overall carbon isotopic anomaly in the core. Consequently, the pre-landslide sediments have been subject to pervasive methane emissions during a time interval of several thousand years. Methane emissions continued during and immediately after the occurrence of Ana Slide at about 61.5 ka. Subsequently, methane emissions decreased and definitely ceased during the last deglaciation and the Holocene. 相似文献
38.
Sauermilch Isabel Mateo Zenon Richard P. Boaga Jacopo 《Marine Geophysical Researches》2019,40(4):635-641
Marine Geophysical Research - Time–depth relationships (TDR) are required for correlating geological information from drill sites with seismic reflection profiles. Conventional... 相似文献
39.
Ludovic Puig Göran Pilbratt Astrid Heske Isabel Escudero Pierre-Elie Crouzet Bram de Vogeleer Kate Symonds Ralf Kohley Pierre Drossart Paul Eccleston Paul Hartogh Jeremy Leconte Giusi Micela Marc Ollivier Giovanna Tinetti Diego Turrini Bart Vandenbussche Paulina Wolkenberg 《Experimental Astronomy》2018,46(1):211-239
ARIEL, the Atmospheric Remote sensing Infrared Exoplanet Large survey, is one of the three M-class mission candidates competing for the M4 launch slot within the Cosmic Vision science programme of the European Space Agency (ESA). As such, ARIEL has been the subject of a Phase A study that involved European industry, research institutes and universities from ESA member states. This study is now completed and the M4 down-selection is expected to be concluded in November 2017. ARIEL is a concept for a dedicated mission to measure the chemical composition and structure of hundreds of exoplanet atmospheres using the technique of transit spectroscopy. ARIEL targets extend from gas giants (Jupiter or Neptune-like) to super-Earths in the very hot to warm zones of F to M-type host stars, opening up the way to large-scale, comparative planetology that would place our own Solar System in the context of other planetary systems in the Milky Way. A technical and programmatic review of the ARIEL mission was performed between February and May 2017, with the objective of assessing the readiness of the mission to progress to the Phase B1 study. No critical issues were identified and the mission was deemed technically feasible within the M4 programmatic boundary conditions. In this paper we give an overview of the final mission concept for ARIEL as of the end of the Phase A study, from scientific, technical and operational perspectives. 相似文献
40.