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271.
This paper describes a study conducted by the National Laboratory for Civil Engineering of Portugal (LNEC), in cooperation with the Defense University Center at the Spanish Naval Academy and “La Sapienza,” University of Rome, to assess the health and safety conditions of the Noble Hall floor in the São Carlos National Theater (Lisbon, Portugal). In a multidisciplinary approach, extensive fieldwork was carried out. The survey included the location and characterization of beams in the various areas of the floor by using two ground penetrating radar (GPR) systems equipped with two different ground- or air-coupled antennas, local inspection openings to visually assess the geometry, timber species and conservation state of structural members, and an assessment of the conservation state of the timber beam ends using drilling equipment. All the tests performed and the results obtained are presented. The potential of using non-destructive tests for the inspection of timber cultural heritage structures, particularly GPR, is discussed, and some practical recommendations are made. 相似文献
272.
Cruz Palacín Gonzalo Giribet Susanna Carner Luis Dantart Xavier Turon 《Journal of Sea Research》1998,39(3-4)
Numerous studies of interactions between urchins and algae in temperate areas have shown an important structuring effect of sea urchin populations. These studies focused almost wholly on the effect of high urchin densities on laminarian forests. In contrast, algal communities below 5–6 m depth in the northwestern Mediterranean are characterised by low sea urchin densities (<5 ind m−2) and the absence of laminarian forests. No previous research has addressed sea urchin/algal interactions in this type of community. To determine the effect of the most abundant echinoid species, Paracentrotus lividus, on well-established algal communities in this area, we performed a removal–reintroduction experiment in rocky patches located between 13 and 16 m depth in the northwestern Mediterranean, where sea urchin densities ranged between 0.9 and 3.4 ind m−2. After 6 months, the cover of non-crustose algae was significantly higher in the plots from which sea urchins had been removed than in control plots (84 vs 67% cover). These removal plots reverted to their original state upon reintroduction of sea urchins. The non-crustose algae consisted of turfing and frondose forms, with the former representing some 70% of the non-crustose algal cover. Change in the cover of turfing algae was responsible for the significant increase in algal development in the sea urchin removal plots. The response of frondose algae to the treatment varied between algal species. It is concluded that grazing by P. lividus exerts a significant effect on habitat structure, even in communities with low sea urchin densities, such as those found in vast areas of the Mediterranean sublittoral. 相似文献
273.
Francisco Guerra‐Martínez Arturo García‐Romero Andrea Cruz‐Mendoza Laura Osorio‐Olvera 《Singapore journal of tropical geography》2019,40(3):387-409
This study evaluates the dynamics and identifies the indirect biophysical and socio‐economic factors related to the recovery, degradation and deforestation of the tropical dry forest (TDF) cover in the municipality of Tehuantepec, Oaxaca, Mexico. Annual rates and transition matrices were determined to identify indirect factors; the cartographic information of 25 variables with shift points were overlaid and Generalized Linear Models (GLM) were applied. The change process with the greatest impact in TDF during the study period (1993–2011) was degradation, with 10468 ha degraded (12 per cent of the initial tropical cover); recovery of coverage was the second most important change process, with 4808 ha (5.5 per cent); and deforestation was the change process with the lowest impact, with a loss of 2800 ha (3.23 per cent). The net balance was negative, with a decrease (through land degradation and deforestation) of 8460 ha (9.75 per cent). The recovery of coverage was mainly associated with biophysical factors such as land suitability and accessibility to natural vegetation. On the other hand, deforestation and degradation of coverage were associated with both biophysical and socioeconomic factors such as land suitability, accessibility to natural vegetation, migration, marginalization, population pressure, economy, education and health. The findings of this study determined the spatial distribution of forest recovery, deforestation and degradation processes at a regional level, allowing for future researchers to focus their efforts at local and landscape levels. Also, the work allows for an approximation of the factors associated with the change processes studied, hence supporting the allocation of resources for the establishment of management, conservation, development and restoration strategies of tropical dry forests at the regional level. 相似文献
274.
Peter Kolapo Moshood Onifade Akinseye Praise Oluwatomisin Martha Amwaama Khadija Said Omar Abdulsalam Jibril Ismail Lawal Abiodun Emman Aladejare Adeyemi 《Geotechnical and Geological Engineering》2022,40(4):1637-1661
Geotechnical and Geological Engineering - Historically, the idea of designing and installing rockbolts in rockmasses can be traced back to the construction of the Snowy Mountain hydroelectric... 相似文献
275.
276.
277.
Russell Main Moses Azong Cho Renaud Mathieu Martha M. O’Kennedy Abel Ramoelo Susan Koch 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):751-761
Quantifying photosynthetic activity at the regional scale can provide important information to resource managers, planners and global ecosystem modelling efforts. With increasing availability of both hyperspectral and narrow band multispectral remote sensing data, new users are faced with a plethora of options when choosing an optical index to relate to their chosen or canopy parameter. The literature base regarding optical indices (particularly chlorophyll indices) is wide ranging and extensive, however it is without much consensus regarding robust indices. The wider spectral community could benefit from studies that apply a variety of published indices to differing sets of species data. The consistency and robustness of 73 published chlorophyll spectral indices have been assessed, using leaf level hyperspectral data collected from three crop species and a variety of savanna tree species. Linear regression between total leaf chlorophyll content and bootstrapping were used to determine the leafpredictive capabilities of the various indices. The indices were then ranked based on the prediction error (the average root mean square error (RMSE)) derived from the bootstrapping process involving 1000 iterative resampling with replacement. The results show two red-edge derivative based indices (red-edge position via linear extrapolation index and the modified red-edge inflection point index) as the most consistent and robust, and that the majority of the top performing indices (in spite of species variability) were simple ratio or normalised difference indices that are based on off-chlorophyll absorption centre wavebands (690–730 nm). 相似文献
278.
Marta Rodrigues Anabela Oliveira Martha Guerreiro André Bustorff Fortunato José Menaia Luís Mesquita David Alexandra Cravo 《Ocean Dynamics》2011,61(6):841-856
This study aims at understanding the fecal contamination behavior in a small coastal stream (Aljezur, Portugal), which has
significant economic and ecological values. Like in most small coastal systems, circulation and water renewal in the Aljezur
stream exhibit a strong variability due to their dependence on tides, waves, intermittent river flows, and a highly variable
morphology. Hence, the problem was approached through a combination of field surveys and the development and application of
a hard-coupled three-dimensional hydrodynamic and fecal contamination model. Salinity and temperature results have shown that
mixing and transport in the stream are very sensitive to the river flow and wind forcing. The model is able to represent the
main patterns and trends observed in Escherichia coli and fecal enterococcus concentrations along the stream, for different environmental and contamination conditions, suggesting
die-off rates on the order of 0.50–0.55 day−1. Die-off rate and the representation of the sediment-associated processes were identified as the major remaining sources
of uncertainty in the model. Results show that, owing to the processes that occur along the stream, fecal bacteria reach the
beaches water in numbers that comply with the European Bathing Waters Directive, even during the summer periods when the upstream
concentrations are larger. In particular, results suggest a direct relation between the tidal propagation upstream and the
reduction of the fecal bacteria concentrations along the stream that can be relevant for the development of a strategy for
the management of the system’s water safety. 相似文献
279.
Groundwater salinization in the Azores archipelago (Portugal) 总被引:1,自引:1,他引:0
J. Virgílio Cruz Rui Coutinho Dina Pacheco Raquel Cymbron Paulo Antunes Pedro Freire Sandra Mendes 《Environmental Earth Sciences》2011,62(6):1273-1285
Groundwater salinization in coastal regions causes severe constraints to water supply and economic losses to society worldwide. In the Azores archipelago, groundwater abstraction in wells drilled in coastal aquifers is very important for water supply, and quality problems have been reported. Therefore, a groundwater chemistry dataset from wells was compiled to study groundwater salinization in these aquifers. Waters are mainly of the Na–Cl type, presenting a slightly acidic to slightly alkaline character, with a pH between 5.63 and 8.50 (median 7.40). Electrical conductivity measurements range from 127 to 9,670 μS/cm (median 862), suggesting highly variable mineralization, with higher values observed on Santa Maria, São Miguel, Pico, Graciosa, and São Jorge islands. The major-ion composition reflects the contribution of seawater to the groundwater compositional evolution, which is essentially explained by seawater intrusion into wells. In many samples, exchange reactions of Na+ + K+ for Ca2+ + Mg2+ are associated with salinization. The seawater fraction in groundwater composition reaches a maximum of 22.5%. These results are extremely challenging to water managers in the Azores because failure to comply with national water quality regulations and with European Union groundwater directive requirements often occurs. 相似文献
280.
Gustavo Indalecio Cancelo Juan Cruz Estrada Guillermo Fernandez Moroni Ken Treptow Ted Zmuda H. Thomas Diehl 《Experimental Astronomy》2012,34(1):13-29
Scientific CCDs designed in thick high resistivity silicon (Si) are excellent detectors for astronomy, high energy and nuclear physics, and instrumentation. Many applications can benefit from CCDs ultra low noise readout systems. The present work shows how sub electron noise CCD images can be achieved using digital signal processing techniques. These techniques allow 0.4 electrons of noise at readout bandwidths of up to 10?Kpixels per second while keeping the full CCD spatial resolution and signal dynamic range. 相似文献