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排序方式: 共有223条查询结果,搜索用时 15 毫秒
221.
K. Vermonden R. S. E. W. Leuven G. van der Velde A. J. Hendriks M. M. van Katwijk J. G. M. Roelofs E. C. H. E. T. Lucassen O. Pedersen K. Sand-Jensen 《Aquatic Sciences - Research Across Boundaries》2010,72(3):379-389
Biodiversity in urban areas is affected by a multitude of stressors. In addition to physico-chemical stress factors, the native
regional species pool can be greatly reduced in highly urbanized landscapes due to area loss and fragmentation. In this study,
we investigated how macrophyte composition and diversity in urban water systems are limited by the regional species pool and
local environmental conditions. Canonical correspondence analysis of the macrophyte species composition revealed that urban
and semi-natural water systems differed and differences could be related to local abiotic variables such as pH and iron concentrations.
Macrophytes in the semi-natural area were typical for slightly acid and oligotrophic conditions. In urban water systems, exotic
species characteristic of eutrophic conditions were present. In the semi-natural areas, the number of macrophyte species exceeded
the number of species expected from species–area relationships of artificial water bodies in rural areas. In urban areas,
the number of macrophyte species was similar to artificial water systems in rural areas. Macrophyte species present in the
study areas also were generally found within 20–30 km distance to the study area. Macrophyte species composition in urban
water systems and semi-natural water systems appeared to be influenced by the regional species pool within approximately 30 km
of the locations. Nevertheless, site limitation ultimately determined the local macrophyte species composition and diversity
in urban water systems and in semi-natural water systems. 相似文献
222.
S.L. Jaccard E.D. Galbraith D.M. Sigman G.H. Haug R. Francois T.F. Pedersen P. Dulski H.R. Thierstein 《Earth and Planetary Science Letters》2009,277(1-2):156-165
Measurements of benthic foraminiferal cadmium:calcium (Cd/Ca) have indicated that the glacial–interglacial change in deep North Pacific phosphate (PO4) concentration was minimal, which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redox-sensitive trace metal records from Ocean Drilling Program (ODP) Site 882 (NW subarctic Pacific, water depth 3244 m) to make inferences about changes in deep North Pacific oxygenation – and thus respired carbon storage – over the past 150,000 yr. These observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep-water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water mass was depleted in oxygen during glacial maxima, though it was not anoxic. We reconcile our results with the existing benthic foraminiferal Cd/Ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed, rather than remineralized. This change would have corresponded to an increase in the deep Pacific storage of respired carbon, which would have lowered atmospheric carbon dioxide (CO2) by sequestering CO2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea. The magnitude of change in preformed nutrients suggested by the North Pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pCO2. 相似文献
223.
Cristina?PulidoEmail author Kaj?Sand-Jensen Esther?C.?H.?E.?T.?Lucassen Jan?G.?M.?Roelofs Klaus?P.?Brodersen Ole?Pedersen 《Aquatic Sciences - Research Across Boundaries》2012,74(2):351-360
Isoetids, as indicators of near-pristine softwater lakes, have a high priority in national and international (European Water
Directive Framework) assessments of ecological lake quality. Our main goal was to identify the most important environmental
factors that influence the composition of plant communities and specifically determine the presence and abundance of the isoetid
Lobelia dortmanna in NW European softwater lakes. Geographical position and composition of surface water, porewater, sediment and plant communities
were examined in 39 lakes in four regions (The Netherlands, Denmark, West Norway and East Norway) distributed over a 1,200-km
long distance. We confirmed that lake location was accompanied by significant changes in environmental variables between NW
European lakes. Lake location was the single most important determinant of vegetation composition and it had significant individual
contributions independent of the coupling to environmental variables. This influence of location was supported by a significant
decline of community similarity with geographical distance between pairs of lakes at regional, inter-regional and international
scales. Combining the geographical position with environmental variables for surface water, porewater and sediment significantly
improved prediction of vegetation composition. Specifically, the combination of latitude, surface water alkalinity, porewater
phosphate and redox potential offered the highest correlation (BIO ENV correlation 0.66) to vegetation composition. This complex
analysis can also account for high sediment variability in the littoral zone of individual lakes, by using site-specific physico-chemical
sediment factors, and offer better predictions of vegetation composition when lake water chemistry is relatively homogeneous
among lakes within regions. 相似文献