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311.
Roberto Simonini Valentina Grandi Gloria Massamba-N'Siala Mirko Iotti Giuseppe Montanari & Daniela Prevedelli 《Marine Ecology》2009,30(2):241-254
In this paper we looked for the most suitable method for benthic ecological quality status (EcoQS) assessment of the North-western Adriatic Sea. Taking into account the historical and present information, we inter-compared our expectations in terms of EcoQS, with the Bentix, AMBI and M-AMBI classification metrics results, and investigated the sensitivity of these indices to the spatial, seasonal and inter-annual variability of benthic communities. The sampling sites were located at increasing distances with respect to the Po River mouth, along an (inverse) gradient of eutrophication. Moreover, a 2-year monthly monitoring plan (October 2004–September 2006) was carried out at the CEBEB site, located in a central position with respect to the investigated area. The results highlighted that the three indices differed in the sensitivity to spatial and temporal variability of the benthic communities. The strong seasonal and inter-annual changes in the benthic communities had a significant effect on the Bentix, whereas no relevant modifications were observed on the EcoQS assignation obtained using the M-AMBI and AMBI methods. The environmental quality ratios (EQR) values and EcoQS classification obtained by the Bentix and AMBI did not match expectations, as they were not inversely correlated with the site distances with respect to the Po mouth, whereas the M-AMBI clearly discriminated the most and the least eutrophicated sites. It thus appears that the M-AMBI could be considered to be the most valuable method for the ecological-status assessment of the North-western Adriatic Sea benthic ecosystem. 相似文献
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313.
Tomáš Bešta Jan Novák Dagmar Dreslerová Vlasta Jankovská Alexandra Bernardová Lenka Lisá Daniela Valentová 《Boreas: An International Journal of Quaternary Research》2015,44(3):563-574
Palaeolimnological reconstruction of the aquatic environment in Lake Komo?any, based on sedimentology, geochemistry, and diatom and macrofossil analyses in the littoral part of the basin, reflects the mid‐Holocene history of the profile from its origin c. 9100 cal. a BP to its final transformation into an alder carr c. 4100 cal. a BP. The existence of the littoral zone can be best explained by increased precipitation during the studied interval. A stable diatom community, diatom‐inferred total phosphorus (50–80 μg L?1) and pH (~7.6), along with stable concentrations of elements associated with changes in its watershed indicate a long‐lasting, balanced aquatic environment with no major shifts attributable to external factors, including climate change. From c. 4700 cal. BP, there started a transition to terrestrial conditions, caused by either natural infilling processes or decreased precipitation. Alternation of remarkable dry/wet phases was not detected, in contrast to numerous analogous central European and supraregional records. Potential human impact was revealed through increases of Corylus and Populus pollen in the Neolithic. These anthropogenic changes in the lake surroundings had no detectable influence on the lacustrine environment. The gathered data suggest undramatic, balanced mid‐Holocene environmental and climatic settings for this central European locality, in direct contrast to numerous analogous studies from the region emphasizing fluctuations and shifts found in the sediment record. 相似文献
314.
Acta Geotechnica - The complete loss of soil strength and stiffness, which occurs during soil liquefaction, marks a change of state of the soil that switches from solid to liquid. In particular,... 相似文献
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317.
Large-scale numerical simulation of groundwater flow and solute transport in discretely-fractured crystalline bedrock 总被引:1,自引:0,他引:1
A large-scale fluid flow and solute transport model was developed for the crystalline bedrock at Olkiluoto Island, Finland, which is considered as potential deep geological repository for spent nuclear fuel. Site characterization showed that the main flow pathways in the low-permeability crystalline bedrock on the island are 13 subhorizontal fracture zones. Compared to other sites investigated in the context of deep disposal of spent nuclear fuel, most deep boreholes drilled at Olkiluoto are not packed-off but are instead left open. These open boreholes intersect the main fracture zones and create hydraulic connections between them, thus modifying groundwater flow. The combined impact of fracture zones and open boreholes on groundwater flow is simulated at the scale of the island. The modeling approach couples a geomodel that represents the fracture zones and boreholes with a numerical model that simulates fluid flow and solute transport. The geometry of the fracture zones that are intersected by boreholes is complex, and the 3D geomodel was therefore constructed with a tetrahedral mesh. The geomodel was imported into the numerical model to simulate a pumping test conducted on Olkiluoto Island. The pumping test simulation demonstrates that fracture-borehole intersections must be accurately discretized, because they strongly control groundwater flow. The tetrahedral mesh provides an accurate representation of these intersections. The calibrated flow model was then used for illustrative scenarios of radionuclide migration to show the impact of fracture zones on solute transport once the boreholes were backfilled. These mass transport simulations constitute base cases for future predictive analyses and sensitivity studies, since they represent key processes to take into consideration for repository performance assessment. 相似文献
318.
Daniela Veronica Ghica 《Journal of Seismology》2011,15(3):487-506
Data recorded with the Bucovina Romanian Seismic Array (BURAR) seismic array between January 2005 and December 2008 were analyzed
to verify the monitoring capabilities of regional and distant seismicity. For this time interval, nearly 35,000 events detected
by BURAR and identified in seismic bulletins (Preliminary Determination of Epicenters and Romanian Earthquake Catalogue) were
investigated using parameters as backazimuth, epicentral distance and magnitude. A remarkably detection capability is emphasized
for teleseismic observations (Δ > 20°). BURAR onsets could be associated to almost 60% of all events in the teleseismic distance,
with a magnitude detection threshold of 4.5 (mb). When no threshold magnitude is applied, the full detection capability of
BURAR is in the same order as the performance of GERES array, which is one of the most sensitive stations in Central Europe.
For regional events, detection capability decreases to about 16% of all events within regional distance range. The site conditions
(crustal structure and high frequency cultural noise) as well as array dimension, affect the signal coherency and reduce the
array detection capability for regional events. For both teleseismic and regional distances, a monthly variation of BURAR
detection capabilities has been found; the number of events detected during the summer time is diminished by the specific
seasonal human activity and atmospheric conditions (thunderstorms). To prove the good detection capability of the BURAR for
teleseismic distances, a comparison with the observations of the Romanian Real Time Network in terms of magnitude and epicentral
distance was carried out. The higher signal detection capability of BURAR is due to the array techniques applied in data processing,
which enhance the signal-to-noise ratio. The monitoring performed by the BURAR seismic array provides a good azimuthal coverage
of the regional and distant seismicity, in a large range of epicentral distances. 相似文献
319.
Geosynthetic-reinforced and jet grout column-supported embankments on soft soils: Numerical analysis and parametric study 总被引:2,自引:0,他引:2
Using a computer code based on the finite element method, a study is conducted to analyse the time-dependent behaviour of a geosynthetic-reinforced and jet grout column-supported embankment on soft soils, as well as the influence of three factors: the embankment height, the elastic modulus of column and the column spacing. The cylindrical unit cell formulation is used. The numerical model incorporates the Biot consolidation theory with soil constitutive relations simulated by the p–q–θ critical state model. Special emphasis is given to the analysis of several parameters: settlement, excess pore pressure, effective stress, stress level, tension in the geosynthetic, soil arching effect and overall efficiency coefficient. 相似文献
320.
Miroslav Trnka Josef Eitzinger Daniela Semer��dov�� Petr Hlavinka Jan Balek Martin Dubrovsky Gerhard Kubu Petr ?t��p��nek Sabina Thaler Martin Mo?ny Zden��k ?alud 《Climatic change》2011,108(1-2):261-289
During the past few decades, the basic assumption of agroclimatic zoning, i.e., that agroclimatic conditions remain relatively stable, has been shattered by ongoing climate change. The first aim of this study was to develop a tool that would allow for effective analysis of various agroclimatic indicators and their dynamics under climate change conditions for a particular region. The results of this effort were summarized in the AgriClim software package, which provides users with a wide range of parameters essential for the evaluation of climate-related stress factors in agricultural crop production. The software was then tested over an area of 114,000 km2 in Central Europe. We have found that by 2020, the combination of increased air temperature and changes in the amount and distribution of precipitation will lead to a prolonged growing season and significant shifts in the agroclimatic zones in Central Europe; in particular, the areas that are currently most productive will be reduced and replaced by warmer but drier conditions in the same time the higher elevations will most likely experience improvement in their agroclimatic conditions. This positive effect might be short-lived, as by 2050, even these areas might experience much drier conditions than observed currently. Both the rate and the scale of the shift are amazing as by 2020 (assuming upper range of the climate change projections) only 20?C38% of agriculture land in the evaluated region will remain in the same agroclimatic and by 2050 it might be less than 2%. On the other hand farmers will be able to take advantage of an earlier start to the growing season, at least in the lowland areas, as the proportion of days suitable for sowing increases. As all of these changes might occur within less than four decades, these issues could pose serious adaptation challenges for farmers and governmental policies. The presented results also suggest that the rate of change might be so rapid that the concept of static agroclimatic zoning itself might lose relevance due to perpetual change. 相似文献