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排序方式: 共有266条查询结果,搜索用时 15 毫秒
61.
Christina Simkanin Ian C. Davidson John F. Dower Glen Jamieson Thomas W. Therriault 《Marine Ecology》2012,33(4):499-511
Anthropogenic habitats such as marinas and docks are focal points for marine invasions, but relatively little is known about the infiltration of nearby natural habitats by these invaders. To address infiltration by four geographically widespread ascidian invaders, we used a two‐step approach: (i) a field survey with equitable sampling in adjacent artificial and natural habitats in British Columbia, Canada, and (ii) a literature review, to infer larger scale patterns across species’ introduced global ranges. Our field survey revealed differential distribution patterns among the four ascidians recorded, with infiltration of natural rocky habitats by two species, Botrylloides violaceus and Botryllus schlosseri. We did not record Didemnum vexillum or Styela clava in natural habitats, though they were both recorded on adjacent artificial structures. Globally, these ascidian species are predominantly found associated with anthropogenic habitats including floating docks, pilings and aquaculture installations, but they have infiltrated natural habitats in some areas of their introduced range. The factors contributing to infiltration of nearby natural benthic habitats remains unclear, but determining which mechanisms are important for encouraging or hindering the establishment and spread of nonindigenous species beyond artificial structures requires survey and experimental work beyond anthropogenic habitats. Such work will aid our understanding of marine introduction dynamics, invasiveness, and associated management implications. 相似文献
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Land use and marine spatial planning processes are increasingly supported by systematic assessment techniques, particularly by multi‐criteria spatial analysis methods. This has been facilitated by the growing release and uptake of web‐mapping tools, which contribute to transparent, consistent, and informed planning processes and decisions. This article reviews the usability, functionality, and applicability of contemporary planning web‐mapping tools to identify the state‐of‐the‐art and future prospects. The review reveals that interfaces are increasingly available and intuitively applicable by non‐specialized users. Basic map navigation and data querying functionality is being expanded to incorporate advanced map‐making and online data geoprocessing capabilities that enable deriving new data and insights. However, the majority of published planning web tools are one‐off solutions, and a disconnect between research and practice is rendering many of these inaccessible or obsolete. Despite the significant progress made in advancing their provision in the last decade, there is a need for developing transferable interfaces that are maintained beyond project end dates, for them to effectively and consistently support planning processes. 相似文献
64.
Guleid Artan Hussein Gadain Jodie L. Smith Kwabena Asante Christina J. Bandaragoda James P. Verdin 《Natural Hazards》2007,43(2):167-185
Floods are the most common and widespread climate-related hazard on Earth. Flood forecasting can reduce the death toll associated
with floods. Satellites offer effective and economical means for calculating areal rainfall estimates in sparsely gauged regions.
However, satellite-based rainfall estimates have had limited use in flood forecasting and hydrologic stream flow modeling
because the rainfall estimates were considered to be unreliable. In this study we present the calibration and validation results
from a spatially distributed hydrologic model driven by daily satellite-based estimates of rainfall for sub-basins of the
Nile and Mekong Rivers. The results demonstrate the usefulness of remotely sensed precipitation data for hydrologic modeling
when the hydrologic model is calibrated with such data. However, the remotely sensed rainfall estimates cannot be used confidently
with hydrologic models that are calibrated with rain gauge measured rainfall, unless the model is recalibrated.
G. Artan, J. L. Smith and K. Asante – work performed under USGS contract 03CRCN0001. 相似文献
65.
Justus E. E. van Beusekom Dirk Mengedoht Christina B. Augustin Mario Schilling Maarten Boersma 《International Journal of Earth Sciences》2009,98(2):251-260
From March 2002 to until April 2003 we investigated the seasonal nutrient and phytoplankton dynamics in the central Bornholm
Basin (Baltic Sea) within the framework of the German GLOBEC Project. We choose a nested approach consisting of vertical fluorescence
profiles, phytoplankton counts and nutrient analyses. The Fluoroprobe (MultiProbe, BBE Moldaenke) is capable of distinguishing
four algal groups (Cryptophyceae, Cyanophyceae, Chlorophyceae, Bacillariophyceae + Dinophyceae). Winter nutrient concentrations
were about 5 μM NO3 and 0.5 μM PO4 in the central Basin. The spring phytoplankton bloom was dominated by the diatom Skeletonema sp. and reached a maximum of about 270 μg C/l before the onset of the seasonal stratification. Protozooplankton was dominated
by the Mesodinium rubrum (a phototrophic ciliate = Myrionecta rubra) and reached a maximum biomass of about 200–300 μg C/l about 2 weeks after the demise of the diatom spring bloom. During summer,
the water column was stratified and a subsurface maximum developed near the thermocline consisting of Bacillariophyceae, Cryptophycea
and other phototrophic flagellates. Phytoplankton and protozooplankton biomass was generally low. Nutrient concentrations
point towards a nitrogen limitation during this period. The stratification period ended during September and surface nutrient
concentrations increased again. Protozooplankton reached a second maximum during September. With the Fluoroprobe small scale
structures in the plankton community could be detected like a subsurface Cryptophyceae maximum near the thermocline that however,
could not be confirmed by cell counts. The chlorophyll a estimate of the Fluoroprobe was in good agreement with the phytoplankton
biomass estimated from counts. We conclude that only by combining modern sensing technology with microscopy, the small-scale
dynamics and taxonomic spectrum of the plankton can be fully captured. 相似文献
66.
Christina A. Stringer 《The Australian geographer》2002,33(1):63-77
This paper explores the changing relationship of a region (Hawkes Bay, New Zealand), its industries and enterprises to Asia-Pacific industrial complexes. Land-based industries in Hawkes Bay provide examples of new connections and local adaptations of production to emerging agro-food and forestry complexes, centred upon East Asia. Integration into these complexes, which has only been possible in the context of the gradual relaxation of regulatory regimes that has occurred over the past two decades, has facilitated access to new markets. In some cases, integration is an outcome of East Asian ownership of New Zealand-based nodes along the commodity chain. In others, it is an outcome of New Zealand actors producing to meet 'site of consumption' demand. The paper concludes that new dynamics in the spheres of trade, production and investment are instituted by and feed into new geographic links and interactions, referred to in the paper as a rescaling of the region. 相似文献
67.
The Vaikijaur Cu–Au–(Mo) deposit is located in the ca. 1.88 Ga calc-alkaline Jokkmokk granitoid near the Archaean–Proterozoic
palaeoboundary within the Fennoscandian shield of northern Sweden. The Skellefte VMS district lies immediately to the south
and the northern Norrbotten Fe-oxide–Cu–Au deposits to the north. The Vaikijaur deposit occupies an area of 2×3 km within
the Jokkmokk granitoid and includes stockwork quartz-sulphide veinlets and disseminated chalcopyrite, pyrite, gold, molybdenite,
magnetite, and pyrrhotite. Porphyritic mafic dykes were emplaced along fractures in a ring dyke pattern. The Jokkmokk granitoid,
dykes, and the mineralized area are foliated, indicating that mineralization predated the main regional deformation. The mineralized
area is characterized by strong potassic alteration. Phyllic and propylitic alteration zones are also present. A pyrite-rich
inner core is surrounded by a concentric zone with pyrite, chalcopyrite, and gold. Molybdenite is distributed irregularly
throughout the chalcopyrite zone. Geophysical data indicate a strongly conductive central zone in the mineralized area bordered
by conductive and high magnetic zones. Five high precision Re–Os age determinations for three molybdenite occurrences from
outcrop and drill core samples constrain the age of porphyry-style Cu–Au–(Mo) mineralization to between 1889±10 and 1868±6 Ma.
A younger molybdenite is associated with a much later metamorphic event at about 1750 Ma. These data suggest that primary
porphyry-style mineralization was associated with calc-alkaline magmatism within the Archaean–Proterozoic boundary zone at
ca. 1.89–1.87 Ga. 相似文献
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69.
Christina Anagnostopoulou Konstantia Tolika 《Theoretical and Applied Climatology》2012,107(3-4):479-489
In the present study, both parametric (peak over threshold: mean residual life, dispersion index, threshold choice) and non-parametric (percentiles indices 95% and 99%) statistical techniques are employed, aiming at the identification of rainfall thresholds above which a precipitation event can be characterized as extreme. The analysis is based on 45?years (1960–2004) rain gauge daily records from 65 meteorological stations over the European region. According to two climatologically based criteria that were introduced in the study, it was found that a combined peak over threshold methodology has been shown to yield higher threshold values above which extreme precipitation events occur, in comparison to the 95th percentile indices. Overall, concerning northern Europe, it was found that in the majority of the stations, the threshold values vary from 20 to 30?mm, while the results concerning the Mediterranean region are less coherent and the selection of extreme precipitation thresholds differs from region to region. Stations over eastern Mediterranean appear to have thresholds higher than 30?mm, while stations located over the main cyclone trajectories and the cyclogenesis zone of Mediterranean are those with the higher extreme precipitation thresholds (higher than 45?mm). 相似文献
70.