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101.
102.
Christian J. Sanders Joseph M. Smoak A. Sathy Naidu Denise R. Araripe Lucian M. Sanders Sambasiva R. Patchineelam 《Environmental Earth Sciences》2010,60(6):1291-1301
The stability of a mangrove ecosystem in Cananeia, Brazil, is assessed based on investigations of the site-specific temporal
rise in relative sea level during the past 50 years, 100-year sediment accumulation rates (SAR) and sources of organic matter
(OM). Addressing this, three sediment cores were collected in a transect, intertidal mud flat, mangrove margin and well into
the forest. The net SAR, as estimated by the age–depth relationships of 210Pb and 137Cs, is between 2.5 and 3.9 mm year−1. These rates are comparable to the estimates based on the Pb and Zn contaminant markers corresponding to mining initiation
in the region in 1918. Further, the SARs are lower than the rate of regional relative sea level rise (4 mm year−1) as indicated by the past 50-year tide gauge record, but the rate is higher than the eustatic sea level rise (1.7 ± 0.3 mm year−1). The stratigraphies of TOC/TN, δ13C(OC), OP and δ15N indicate site-specific mangal vegetal litter, which is the predominant source of OM at all core sites, during the past century
and reflects a stable mangal system over that time span. 相似文献
103.
Christopher?F.?D'EliaEmail author Walter?R.?Boynton James?G.?Sanders 《Estuaries and Coasts》2003,26(2):171-185
The Patuxent River, Maryland, is a nutrient-overenriched tributary of the Chesapeake Bay. Nutrient inputs from sewage outfalls
and nonpoint sources (NPS) have grown substantially during the last four decades, and chlorophylla levels have increased markedly with concomitant reductions in water quality and dissolved oxygen concentrations. The Patuxent
has gained national attention because it was one of the first river basins in the U.S. for which basin-wide nutrient control
standards were developed. These included a reduction in NPS inputs and a limit on both nitrogen (N) and phosphorus (P) loadings
in sewage discharges intended to return the river to 1950s conditions. Full implementation of point source controls occurred
by 1994, but population growth and land-use changes continue to increase total nutrient loadings to the river. The present
paper provides the perspectives of scientists who participated in studies of the Patuxent River and its estuary over the last
three decades, and who interacted with policy makers as decisions were made to develop a dual nutrient control strategy. Although
nutrient control measures have not yet resulted in dramatic increases in water quality, we believe that without them, more
extensive declines in water quality would have occurred. Future reductions will have to come from more effective NPS controls
since future point source loading will be difficult to further reduce with present technology. Changing land use will present
a challenge to policy makers faced with sprawling population growth and accelerated deforestation. 相似文献
104.
Gerhardt?F.?RiedelEmail author James?G.?Sanders Denise?L.?Breitburg 《Estuaries and Coasts》2003,26(2):323-338
We examined individual and interactive effects of two stressors—nutrients (nitrogen [N] and phosphorus [P]) and trace elements
(a mix of arsenic [As], copper [Cu], and cadmium [Cd], and in a second experiment also zinc [Zn] and nickel [Ni])—on phytoplankton
of the mesohaline Patuxent River, a tributary of Chesapeake Bay. Experiments were conducted in twenty 1-m3 mesocosms. Four mesocosm runs used two levels of nutrient loadings (0.7–1.0 × ambient N loading and enriched to 1.3–1.6 ×
ambient N loading) crossed with two levels of trace elements (ambient and enriched approximately 2–5 × higher than ambient
concentrations) crossed with five progressive levels of ecosystem complexity. To examine seasonal patterns of responses to
stressors, data from these experiments were combined with results of a similar experiment conducted during 1996 (Breitburg
et al. 1999a). A second mesocosm experiment examined effects of individual and mixed trace elements, both alone and in combination
with nutrients, to further examine which nutrient-trace element interactions were important. Nutrients consistently increased
phytoplankton productivity and biomass. Most of the increased biomass was created by large centric diatoms, which increased
the mean cell size of the phytoplankton community. Trace element additions decreased phytoplankton productivity and biomass,
as well as the contribution of large centric diatoms to phytoplankton biomass. When both trace elements and nutrients were
added, trace elements reduced nutrient stimulation. Although the magnitude of the response to nutrient additions tended to
be somewhat greater in spring, the seasonal patterns of trace element effects, and nutrient-trace element interactions were
far more striking with significant responses restricted to spring mesocosm runs. The second experiment indicated that both
As and Cu were more inhibitory to phytoplankton in spring than in summer, but As was more inhibitory in the low nutrient treatments
and Cu was more inhibitory in the nutrient enrichment treatments. The potential for strong seasonal patterns and high temporal
variability in stressor effects and multiple stressor interactiosn will require close attention in the design and interpretation
of management-relevant research and monitoring and may indicate the need for seasonally varying management strategies. 相似文献
105.
Biogeochemical interactions between a suite of trace elements and nutrients were examined in a series of experimental mesocosm experiments to understand how multiple stressors affect estuarine environments and how these effects are modified by the complexity of the system used to examine them. Experimental treatment included additions of nutrients and trace elements separately and combined, along with a gradient in experimental system complexity. Eight mesocosm experiments were carried out from 1996 through 1998. Increased nutrients generally decreased dissolved trace element concentrations, in large part through an increase in phytoplankton biomass, but also by increasing the concentration of metals in the particles. Trace element additions increased dissolved nutrients by decreasing phytoplankton biomass. The presence of sediments reduced both dissolved trace element and nutrient concentrations. Other complexity treatments had weaker effects on both dissolved nutrients and trace elements. Many of the observed effects appeared to be seasonal, occurring only in spring, or their magnitude was greater in spring. This may be linked to a change from phosphorus to nitrogen limitation that often occurs in the Patuxent River estuary in the late spring or early summer period. 相似文献
106.
Evaluation of on-line DEMs for flood inundation modeling 总被引:1,自引:0,他引:1
Recent and highly accurate topographic data should be used for flood inundation modeling, but this is not always feasible given time and budget constraints so the utility of several on-line digital elevation models (DEMs) is examined with a set of steady and unsteady test problems. DEMs are used to parameterize a 2D hydrodynamic flood simulation algorithm and predictions are compared with published flood maps and observed flood conditions. DEMs based on airborne light detection and ranging (LiDAR) are preferred because of horizontal resolution, vertical accuracy (∼0.1 m) and the ability to separate bare-earth from built structures and vegetation. DEMs based on airborne interferometric synthetic aperture radar (IfSAR) have good horizontal resolution but gridded elevations reflect built structures and vegetation and therefore further processing may be required to permit flood modeling. IfSAR and shuttle radar topography mission (SRTM) DEMs suffer from radar speckle, or noise, so flood plains may appear with non-physical relief and predicted flood zones may include non-physical pools. DEMs based on national elevation data (NED) are remarkably smooth in comparison to IfSAR and SRTM but using NED, flood predictions overestimate flood extent in comparison to all other DEMs including LiDAR, the most accurate. This study highlights utility in SRTM as a global source of terrain data for flood modeling. 相似文献
107.
108.
Melnikov's method and averaging 总被引:3,自引:0,他引:3
Jan A. Sanders 《Celestial Mechanics and Dynamical Astronomy》1982,28(1-2):171-181
109.
A data base of 111 filter-collected marine atmospheric particulates is used to describe the distribution of lead over the North and South Atlantic, the Mediterranean Sea, the Red Sea, the Gulf of Aden and the northern and central Arabian Sea. The distribution of atmospheric Pb is assessed in terms of enrichment factor diagrams, and it is shown that over the marine regions studied in both the Northern and Southern Hemispheres the distribution of Pb in the atmosphere is controlled by the mixing of a background component, or components, with crustal material within certain concentration limits. For the Northern Hemisphere samples used in the investigation there is a reasonably well-defined Pb concentration minimum of ~ 0.6 ng m?3 of air; however, this will be severely decreased in more remote Northern Hemisphere marine regions. Geometric average Pb atmospheric concentrations vary from one marine region to another, ranging from ~ 0.98 ng m?3 of air for the South Atlantic westerlies to ~ 15 ng m?3 of air in the North Atlantic westerlies; although the latter reduces to ~ 7 ng m?3 of air when ‘polluted’ samples are excluded. Lead sea-surface deposition fluxes are calculated on the basis of two deposition velocities (0.25 and 1 cm s?1), the largest flux (220 ng Pb cm?2 yr?1) being found for the westerlies over the eastern margins of the North Atlantic. The distribution of lead over the North Atlantic is assessed in terms of the global lead budget and it is estimated that a maximum of ~ 24% of the total ‘natural’ lead injected annually into the World atmosphere, and ~ 3.5% of the anthropogenic lead injected annually into the Northern Hemisphere atmosphere, are deposited over the North Atlantic sea surface. 相似文献
110.
D.B. Sanders 《Astrophysics and Space Science》1999,266(1-2):331-348
We summarize the evidence from multiwavelength observations that the dominant power source in the majority of ultraluminous infrared galaxies (ULIGs) may be an active galactic nucleus (AGN). In the broader context of the debate, we also show that –- 1. ULIGs are indeed a key stage in the transformation of merging gas-rich disks into ellipticals,2. ULIGs are plausibly the precursors of quasi-stellar objects (QSOs), and 3. ULIGs do appear to be local templates of the high luminosity tail of major gas-rich mergers at z 1–4. 相似文献