全文获取类型
收费全文 | 125篇 |
免费 | 5篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 15篇 |
地球物理 | 43篇 |
地质学 | 37篇 |
海洋学 | 16篇 |
天文学 | 11篇 |
综合类 | 2篇 |
自然地理 | 9篇 |
出版年
2023年 | 1篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 10篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 7篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 8篇 |
2010年 | 5篇 |
2009年 | 11篇 |
2008年 | 6篇 |
2007年 | 11篇 |
2006年 | 3篇 |
2005年 | 7篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 7篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1983年 | 2篇 |
排序方式: 共有135条查询结果,搜索用时 46 毫秒
71.
Lake-outlets are transitional areas recognized as highly productive ecosystems in terms of density and biomass of aquatic insects. Life cycle, secondary production, trophic guilds and environmental constraints of caddisfly assemblages were investigated on a natural lake-outlet stream (Nant y Fall) in Patagonia, Argentina. We investigated the site monthly from May 2007 to April 2008 by recording environmental data and sampling caddis larvae using a Surber sampler at riffle areas (n = 36). Mastigoptila longicornuta, Smicridea annulicornis, Smicridea frequens, Brachysetodes quadrifidus and Parasericostoma ovale displayed well synchronized univoltine life cycles, while Neoatopsyche brevispina, Neopsilochorema tricarinatum, showed an asynchronous development pattern, although most of them had an extended recruitment, similar to those reported for non lake-outlet streams in the area. Annual secondary production per species varied from 8.22 (B. quadrifidus) to 3568.83 mg m−2 y−1 (P. ovale), with overall caddisfly production amounting to 4.8 g m−2 y−1. Shredder/collector-filterer ratio was 3.3/1 suggesting that the system was detrital based. Redundancy analysis indicated that seasonally dynamic variables such as discharge, benthic particulate organic matter and temperature were the main predictors of seasonal caddisfly assemblage variation. We propose that the variety of food resources and the significant spatial heterogeneity at lake-outlet streams contribute to sustain a rich caddisfly community. 相似文献
72.
Leonardo Strazzere Daniel A. Gregori Leonardo Benedini Paulo Marcos Mercedes V. Barros Mauro C. Geraldes Cecilia Pavon Pivetta 《地学前缘(英文版)》2019,10(1):299-314
The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Formation. The basal part of this unit, which was deposited in high-gradient topographic relief, is composed of conglomerates and sandstones with thin layers of reworked tuffs. The lithofacies associations of the basal part indicate that the depositional mechanisms were mantled and gravitational flows.The middle part of the unit consists of fine sandstones, limestones, and black siltstones that were deposited in low-energy fluvial and lacustrine environments. The outcrops are located along the NEe SW direction and the major thickest units represented by limestones and siltstones, occur near the southeastern border of this NEeS W depocenter. Since the rhyolitic and trachytic lava flows and tuffs of the Marifil Volcanic Complex are interbedded with the sedimentary sequences of the Puesto Piris Formation,both units are coeval. Zircon Ue Pb age was obtained for a trachytic lava flow(193.4 ±3.1 Ma) suggesting that sedimentation and volcanism are Sinemurian. This extensional episode was recorded in the eastern,western, and southwestern sectors of the North Patagonian Massif, and is possibly associated with the Gondwana supercontinent breakup. 相似文献
73.
This paper investigates the effects of supplemental viscous damping on the seismic response of one‐storey, asymmetric‐plan systems responding in the inelastic range of behaviour. It was found that addition of the supplemental damping reduces not only deformation demand but also ductility and hysteretic energy dissipation demands on lateral load resisting elements during earthquake loading. However, the level of reduction strongly depends on the plan‐wise distribution of supplemental damping. Nearly optimal reduction in demands on the outermost flexible‐side element, an element generally considered to be the most critical element, was realized when damping was distributed unevenly in the system plan such that the damping eccentricity was equal in magnitude but opposite in algebraic sign to the structural eccentricity of the system. These results are similar to those noted previously for linear elastic systems, indicating that supplemental damping is also effective for systems expected to respond in the inelastic range. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
74.
Cecilia E. Enriquez Georgy I. Shapiro Alejandro J. Souza Andrei G. Zatsepin 《Ocean Dynamics》2005,55(5-6):476-489
A three dimensional structure of mesoscale circulation in the Black Sea is simulated using the Proudman Oceanographic Laboratory
Coastal Ocean Modelling System. A number of sensitivity tests reveal the response of the model to changes in the horizontal
resolution, time steps, and diffusion coefficients. Three numerical grids are examined with x-fine (3.2 km), fine (6.7 km) and coarse (25 km) resolution. It is found that the coarse grid significantly overestimates
the energy of the currents and is not adequate even for the study of basin-scale circulation. The x-fine grid, on the other hand, does not give significant advantages compared to the fine grid, and the latter is used for
the bulk of simulations. The most adequate parameters are chosen from the sensitivity study and used to model both the basin-scale
circulation and day-to-day variability of mesoscale currents for the months of May and June of 2000. The model is forced with
actual wind data every 6 h and monthly climatic data for evaporation, precipitation, heat fluxes and river run-off. The results
of the fine grid model are compared favourably against the satellite imagery. The model adequately reproduces the general
circulation and many mesoscale features including cyclonic and anticyclonic eddies, jets and filaments in different parts
of the Black Sea. The model gives a realistic geographical distribution and parameters of mesoscale currents, such as size,
shape and evolution of the eddies. 相似文献
75.
Institutional change and natural resource use in coastal Vietnam 总被引:1,自引:0,他引:1
Cecilia Luttrell 《GeoJournal》2001,55(2-4):529-540
Vietnam is currently undergoing a rapid economic and social transition involving the dismantling of the co-operative system
and the official embracing of a market economy. The paper uses an institutional approach to examine adaptation to such changes
in two coastal communes in mangrove forest areas. Having provided the historical and policy context of reforms which have
taken place in Vietnam in the area of resource management, the paper goes on to discuss changes currently taking place in
access to resources. The complexity of property rights regimes are then examined in the light of such changes, with particular
focus on the effects of privatisation and the increased effects of integration with external markets. Using livelihood diversification
as a key concept for understanding local adaptation to such changes, the paper concludes with discussion of the socially differentiated
impacts of the process and the implications for future livelihoods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
76.
Sahel Mahdavi Bahram Salehi Cecilia Moloney Weimin Huang Brian Brisco 《International Journal of Digital Earth》2018,11(7):703-729
Speckle degrades the radiometric quality of a Synthetic Aperture Radar (SAR) image. Previous methods for speckle reduction have used a fixed-size window for filtering the entire image. This, however, may not be effective for the entire image, as land covers of different sizes require different filtering windows. In this paper, a novel method is proposed by which each pixel in the image is filtered with a window appropriate for the size of object within it. The real in-phase and the imaginary quadrature components of the SAR images determine the best window size and the pixels in the intensity image are filtered using their own optimal windows. The proposed method is presented for both single- and multi-polarized SAR images, and the results of several common filters that were modified are presented. This approach is applied to two RADARSAT-2 images: one over San Francisco, California, USA and the other over St. John’s, Newfoundland and Labrador, Canada, producing results that were similar to, or outperformed, comparable filters while retaining details and suppressing speckle effectively. While the method was successful for single-look intensity data, it offers great potential for multi-look and amplitude data as well. 相似文献
77.
Cecilia Martinez-Rosales Juan Jos Marizcurrena Andrs Iriarte Natalia Fullana Hctor Musto Susana Castro-Sowinski 《极地研究(英文版)》2015,(1)
We report the isolation of a cold-adapted bacterium belonging to the genus Janthinobacterium (named AU11), from a water sample collected in Lake Uruguay (King George Island, South Shetlands). AU11 (gro... 相似文献
78.
Macrobenthic surf zone communities of temperate sandy beaches: spatial and temporal patterns 下载免费PDF全文
The spatial and temporal patterns within the surf zone epibenthic assemblages were studied in a coastal fringe of Argentina to determine whether assemblage compositions, abundance, species richness and diversity vary spatially and temporarily. Sampling was conducted seasonally in two sandy beaches over 2 years with a benthic sledge used to collect the fauna in the upper centimeters of soft bottom sediments and the epifauna on the sediment surface. Physical variables were measured in the same coastal sites where biological sampling was conducted. A total of 58 morphospecies were collected. Peracarid crustaceans were the most abundant group. The mysid Pseudobranchiomysis arenae (new genus–new species) (29.73 ± 17.79 ind. per sample) and the isopod Leptoserolis bonaerensis (51.54 ± 22.35 ind. per sample) were the most abundant and common species and were present regularly throughout the sampling period. Differences in the surf zone community composition were found between the beaches; these differences could be related to variation in physical parameters such as sand grain size and wave climate, indicating the possible influence of the morphodynamic state of the beaches on the epibenthic assemblages. A seasonal abundance trend was detected, reflecting the changes in abundance of the two dominant species; the richness pattern was not easily detectable due to the sporadic appearance of non‐resident species in the surf zone, probably due to different causes, including dispersion by entry of water from surrounding areas, littoral currents and storms. The surf zone studied presents a complex and dynamic epibenthic community that appears to be influenced by the morphodynamic state of the beach and the dynamic of non‐resident species. 相似文献
79.
80.
Fernanda Montes de Oca Luciana Motta María Sofía Plastani Cecilia Laprida Andrea Lami Julieta Massaferro 《Journal of Paleolimnology》2018,59(2):175-187
Remote lakes of northern Patagonia are ideal sites for examining climate- and non-climate-driven changes in aquatic ecosystems because there is little evidence of human influence and there is no detailed information on recent environmental trends in the region (i.e. the last 200 years). Subfossil chironomids (Diptera: Chironomidae) are useful paleoindicators due to their specific response to numerous environmental factors. Here, we analyze the chironomid subfossil assemblages from two remote lakes located in different environmental settings in Nahuel Huapi National Park of northern Patagonia, Argentina. Chironomids combined with sedimentary pigments (chlorophyll derivatives and total carotenoids) and organic matter provided information on the environmental history of the lakes for the last ca. 200 years. The 210Pb chronology and tephra layers are used to establish the chronology of changes in the chironomid assemblages associated to different environmental factors that impacted the area during the period covered by the study. The deposition of volcanic ash affected the abundance and composition of chironomid assemblage throughout the record of both lakes. However, changing climate conditions and human activities are also responsible for chironomid changes in the last 50 years. 相似文献