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51.
Allison Schein Simon C. Courtenay Cindy S. Crane Kevin L. Teather Michael R. van den Heuvel 《Estuaries and Coasts》2012,35(3):799-810
Artificial fertilizers are contributing to the replacement of eelgrass (Zostera marina) by sea lettuce (Ulva lactuca) in estuaries of Prince Edward Island (PEI), Canada. In this study, we found that the nearshore fish community differed between
areas dominated by these two vegetations within an estuary in every month sampled (April–August). Adult northern pipefish
(Syngnathus fuscus), threespine stickleback (Gasterosteus aculeatus), blackspotted stickleback (Gasterosteus wheatlandi), and Atlantic silverside (Menidia menidia) were most strongly associated with eelgrass, while mummichog (Fundulus heteroclitus), ninespine stickleback (Pungitius pungitius), and American eel (Anguilla rostrata) were often more numerous in sea lettuce. Sea lettuce stations tended to have more young-of-the-year mummichog, fourspine
stickleback (Apeltes quadracus), and Gasterosteus sp. than eelgrass stations but fewer young-of-the-year northern pipefish and Atlantic silverside. Fish richness and abundance
were significantly lower in the sea lettuce than eelgrass habitat during August when benthic hypoxia occurred. We conclude
that the loss of eelgrass from PEI estuaries will result in significant declines in fish biodiversity. 相似文献
52.
The Corsica River, located on Maryland’s eastern shore, has been the site of restoration efforts targeting sediment and nutrient
load reductions. Previous work has indicated that agricultural activities supply most of these materials; however, their dynamics
and fate are largely unknown. To address these needs, bottom sediments have been collected and analyzed for their chemical
and textural properties. Long-term (decadal) accumulation rates are determined with 210Pb (half-life 22.3 years), verified with 137Cs, and range from 0.18 to 0.84 g/cm2/year in the subtidal region and 0.3–1.89 g/cm2/year in the marshes. These estimates are compared with likely sediment sources to determine the direction of exchange with
the adjacent estuary (Chester River), which is a subtributary of Chesapeake Bay, with the Chester River likely supplying 0.94 × 103 t/year of sediment to the Corsica, ∼16% of the total sediment input. The radiochemical data are used to interpret profiles
of grain size and nitrogen and to provide improved estimates of nitrogen burial. Comparison of the Corsica River to similar
systems highlights the importance of marshes in trapping sediment and nutrient inputs from the watershed. 相似文献
53.
A unique feature of migration in China is its two-track system, one consisting of permanent migration and temporary migration. This article examines whether and how hukou reforms and the maturation of migration streams since the 1980s have changed the two-track system. Using data on interprovincial migration from the 1990 and 2000 censuses, our empirical analysis focuses on the differentials between permanent migrants and temporary migrants and their changes over time. We document the size, migration reasons, and selectivity of migrants, and we evaluate the determinants of the dichotomy between permanent migrants and temporary migrants via logistic regression models. Our findings show that between 1990 and 2000 the gaps between interprovincial permanent migrants and temporary migrants did not narrow but in most aspects had widened. There is little evidence that hukou reforms have lowered the barriers to urban citizenship. At the same time, a larger spectrum of the rural population has joined the temporary migration streams. The net result is a persistence of the two-track migration system, where permanent migrants increasingly assume the position of social and economic elites and temporary migrants are the disadvantaged and disenfranchised. 相似文献
54.
Jianhong Xue Cindy LeeStuart G. Wakeham Robert A. Armstrong 《Organic Geochemistry》2011,42(4):356-367
Principal components analysis (PCA) is a multivariate data analysis tool that can be used to recombine the variables of a large multivariate dataset in such a way that the first few variables of the reconstructed dataset account for the majority of the variance in the data. Application of PCA in marine geochemistry has become quite common in recent years. In this study, we illustrate the use of PCA through examples that arose while investigating the geochemistry of sinking particles during the MedFlux project. The examples presented do not simply repeat the analyses of the original study, but instead extend them in the context of simultaneous application of PCA and cluster analysis. Our results show that constructing a one dimensional (1D) “degradation index” using only the first principal component (PC) is in most cases oversimplified, and that constructing 2D or 3D “degradation trajectories” with the first 2 or 3 PCs is more informative. Use of the first three PCs is indicated when the variance explained by the third PC is comparable in magnitude to that explained by the second PC in the reconstructed dataset. We also discuss the use of scree plots and cluster analysis in helping decide whether the third PC is needed to capture the essential information in the dataset. 相似文献
55.
Pallav Ray Chidong Zhang Mitchell W. Moncrieff Jim Dudhia Julie M. Caron L. Ruby Leung Cindy Bruyere 《Climate Dynamics》2011,36(1-2):161-184
Tropical channel models, defined as models that are global in the zonal direction but bounded in the meridional direction, are particularly useful for simulating the Madden-Julian oscillation (MJO) and understanding its physical and dynamical basis. Influences from the extratropics through the lateral boundaries have been found to be essential to the reproduction of the initiation of certain MJO events. This led to a hypothesis that multi-year simulations using a tropical channel model would reproduce reasonable MJO statistics under the influence of prescribed lateral boundary conditions derived from global reanalyses. Interestingly, the MJO statistics in such a multi-year simulation by a high-resolution tropical channel model are not better than those from global climate models. The error in the atmospheric mean state is found to be a possible reason for the poor MJO statistics in the simulation. Nevertheless, even with a large error in the mean state, the multi-year simulation captures two MJO events previously found to be initiated by extratropical influences. However, the model does not reproduce a third event, whose initiation is not directly influenced by the extratropics. This implies that in the absence of dynamical interactions between the MJO and the lateral boundary conditions, the error in the mean state could be sufficient to prevent the MJO initiation. To explore this third MJO event further, a series of sensitivity tests are conducted. These tests show that the simulation of this event is neither critically influenced by the cumulus parameterization employed, nor the initial conditions when the model is integrated 2?weeks prior to the MJO initiation. The model captures this event when the MJO signal is already present in the initial conditions. The use of high-resolution sea surface temperature does not improve the simulation of the third MJO event. A higher-resolution nested domain covering the Indo-Pacific warm pool region and including a cloud-system resolving domain over the Indonesian Maritime Continent has little effect on the MJO initiation over the Indian Ocean. In <2?weeks the error in the simulation is comparable to the climate error. The role of the simulated MJO on the mean state is also explored. Implications and limitations of these results are discussed. 相似文献
56.
Bias corrections of global models for regional climate simulations of high-impact weather 总被引:1,自引:1,他引:0
Cindy L. Bruyère James M. Done Greg J. Holland Sherrie Fredrick 《Climate Dynamics》2014,43(7-8):1847-1856
All global circulation models (GCMs) suffer from some form of bias, which when used as boundary conditions for regional climate models may impact the simulations, perhaps severely. Here we present a bias correction method that corrects the mean error in the GCM, but retains the six-hourly weather, longer-period climate-variability and climate change from the GCM. We utilize six different bias correction experiments; each correcting different bias components. The impact of the full bias correction and the individual components are examined in relation to tropical cyclones, precipitation and temperature. We show that correcting of all boundary data provides the greatest improvement. 相似文献
57.
Cindy Lebeaupin Brossier Karine Béranger Charles Deltel Philippe Drobinski 《Ocean Modelling》2011,36(1-2):1-25
The Mediterranean basin features a semi-enclosed sea, where interactions and feedbacks between the atmosphere and the Sea at various temporal and spatial scales play a predominant role in the regional climate. This study analyzes the Mediterranean Sea response in sensitivity experiments conducted by driving the NEMO-MED12 oceanic model in perpetual mode with various atmospheric forcings, all produced by the WRF non-hydrostatic mesoscale atmospheric model, but differing by their resolutions: two horizontal resolutions (20 km at basin scale and 6.7 km in the North-Western [NWE] area) and two temporal resolutions (daily and three-hourly). The atmospheric fields available from August 1998 to July 1999 are in good agreement with estimates derived from satellite data. The heat budget of the Mediterranean Sea represents an heat loss of 5 W/m2 and the annual freshwater budget is ?1.04 m, in agreement with climatologies. An increase in the spatial resolution in the NWE area modifies the modeled circulation from ?10% to +15% for the SST, from ?30% to +50% for the SSS, from ?10% to +30% for the MLD and from ?10% to +30% for the EKE in surface. The increase in the wind speed with a better chanelling by the land orography enhances in particular the oceanic convection process in the NWE area. On the other hand, the increase in the temporal resolution reduces the convection process, because of the diurnal restratification of the oceanic upper layer. It also reduces the surface parameters high-frequency variability, whereas it increases the EKE values in surface, due to the rapid response to the wind. 相似文献
58.
Cindy R. Tam Victoria M. Kaspi Bryan M. Gaensler Eric V. Gotthelf 《Astrophysics and Space Science》2007,308(1-4):519-523
The population of clearly identified anomalous X-ray pulsars has recently grown to seven, however, one candidate anomalous
X-ray pulsar (AXP) still eludes re-confirmation. Here, we present a set of seven Chandra ACIS-S observations of the transient
pulsar AX J1845.0-0258, obtained during 2003. Our observations reveal a faint X-ray point source within the ASCA error circle
of AX J1845.0-0258’s discovery, which we designate CXOU J184454.6-025653 and tentatively identify as the quiescent AXP. Its
spectrum is well described by an absorbed single-component blackbody (kT∼2.0 keV) or power law (Γ∼1.0) that is steady in flux on timescales of at least months, but fainter than AX J1845.0-0258 was during its 1993 period
of X-ray enhancement by at least a factor of 13. Compared to the outburst spectrum of AX J1845.0-0258, CXOU J184454.6-025653
is considerably harder: if truly the counterpart, then its spectral behavior is contrary to that seen in the established transient
AXP XTE J1810-197, which softened from kT∼0.67 keV to ∼0.18 keV in quiescence. This unexpected result prompts us to examine the possibility that we have observed an
unrelated source, and we discuss the implications for AXPs, and magnetars in general.
相似文献
59.
Oysters from the north-west coast of Canada contain high levels of cadmium, a toxic metal, in amounts that exceed food safety guidelines for international markets. A first required step to determine the sources of cadmium is to identify possible spatial and temporal trends in the accumulation of cadmium by the oyster. To meet this objective, rather than sample wild and cultured oysters of unknown age and origin, an oyster “grow-out” experiment was initiated. Cultured oyster seed was suspended in the water column up to a depth of 7 m and the oyster seed allowed to mature a period of 3 years until market size. Oysters were sampled bimonthly and at time of sampling, temperature, chlorophyll-a, turbidity and salinity were measured. Oyster total shell length, dry tissue weights, cadmium concentrations (μg g−1) and burdens (μg of cadmium oyster−1) were determined. Oyster cadmium concentrations and burdens were then interpreted with respect to the spatial and temporal sampling design as well as to the measured physio-chemical and biotic variables. When expressed as a concentration, there was a marked seasonality with concentrations being greater in winter as compared in summer; however no spatial trend was evident. When expressed as a burden which corrects for differences in tissue mass, there was no seasonality, however cadmium oyster burdens increased from south to north. Comparison of cadmium accumulation rates oyster−1 among sites indicated three locations, Webster Island, on the west side of Vancouver Island, and two within Desolation Sound, Teakerne Arm and Redonda Bay, where point sources of cadmium which are not present at all other sampling locations may be contributing to overall oyster cadmium burdens. Of the four physio-chemical factors measured only temperature and turbidity weakly correlated with tissue cadmium concentrations (r2 = −0.13; p < 0.05). By expressing oyster cadmium both as concentration and burden, regional and temporal patterns were demonstrated, which may have been missed if just concentration was determined. 相似文献
60.
The near-sea surface meteorological conditions associated with the Mediterranean heavy precipitation events constitute, on
a short time scale, a strong forcing on the ocean mixed layer. This study addresses the question of the optimal time frequency
of the atmospheric forcing to drive an ocean model in order to make it able to capture the fine scale ocean mixed layer response
to severe meteorological conditions. The coupling time frequency should allow the ocean model to reproduce the formation of
internal low-salty boundary layers due to sudden input of intense precipitation, as well as the cooling and deepening of the
ocean mixed layer through large latent heat fluxes and stress under the intense low-level jet associated with these events.
In this study, the one-dimensional ocean model is driven by 2.4-km atmospheric simulated fields on a case of Mediterranean
heavy precipitation, varying the time resolution of the atmospheric forcing. The results show that using a finer temporal
resolution than 1 h for the atmospheric forcing is not necessary, but a coarser temporal resolution (3 or 6 h) modifies the
event course and intensity perceived by the ocean. Consequently, when using a too coarse temporal resolution forcing, typically
6 h, the ocean model fails to reproduce the ocean mixed layer fine scale response under the heavy rainfall pulses and the
strong wind gusts. 相似文献