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131.
John Selden Burke W. Judson Kenworthy Lisa L. Wood 《Estuarine, Coastal and Shelf Science》2009,81(4):533-543
Estimates of abundance and size of three commercially exploited grunt species indicate ontogenetic changes in habitat utilization concentrate their juveniles within the lagoon of the Bay of La Parguera, Puerto Rico. Eleven biotopes, defined by four benthic structures (reef, mangrove, vegetation beds and unconsolidated sediments) and three geographic zones (inner lagoon, outer lagoon and bank shelf) were sampled randomly by visual surveys. French, bluestriped and white grunt (Haemulon flavolineatum, Haemulon sciurus and Haemulon plumeri) were common in the bay and appeared to exhibit similar life history patterns of cross-shelf migration and habitat selection. Recently settled grunts were dispersed over vegetated and unconsolidated soft-bottom sediments of the bay. The juvenile stage occurred in highest densities in shallow lagoon biotopes among the submerged prop-roots of mangrove stands and on inshore reefs. Length data indicates that grunts migrate offshore to adult habitat via increasingly deep reefs. Indices of biotope nursery function based on standing stock estimates of juveniles identified three biotopes, all within the inner lagoon as essential habitat for juveniles of 5–10 cm length interval. This concentration of juveniles within biotopes of the lagoon could represent a bottleneck to recruitment for grunt stocks. Evidence that quantity and quality of lagoon nurseries may limit recruitment indicates that these areas represent a key component of a marine protected area designed to restore fisheries within the bay. 相似文献
132.
133.
Shifts in resource availability and resulting land use changes are important research themes for coupled human and natural systems and human dimensions of global environmental change. This study examines the relationship between groundwater depletion and agricultural land use change within a single county in the High Plains, where agro-economic systems and populations are dependent on access to reliable groundwater supplies. Results indicate a significant relationship between high proportionate decreases in groundwater and land being removed from irrigation. This case study strengthens the links among local, regional, and global environmental change, and contributes to a greater understanding of the High Plains in the context of regional sustainability and vulnerability concerns. 相似文献
134.
Lisa A. Crause Warrick A. Lawson Arne A. Henden 《Monthly notices of the Royal Astronomical Society》2007,375(1):301-306
Decline onset times were measured in long-term visual light curves for five R Coronae Borealis (RCB) variable stars. These included RY Sgr and V854 Cen, the two RCB stars previously reported to have a relationship between dust formation events and pulsational variations. Analysis of the decline epochs showed that all decline onsets for a given star obey a linear ephemeris tied to the object's dominant radial pulsation period. Thus, in addition to confirming the pulsation–decline correlation for RY Sgr and V854 Cen, this same behaviour was demonstrated in UW Cen, R CrB and S Aps for the first time. This general result firmly establishes the connection between radial pulsation and mass loss in the RCB stars. The dominant pulsation period of ≈40 d for all of these objects therefore represents the characteristic time-scale on which these stars produce dust. 相似文献
135.
Sediment microphytobenthos, such as diatoms and photosynthetic bacteria, are functionally important components of food webs
and are key mediators of nutrient dynamics in marine wetlands. The medium to long-term recovery of benthic microproducers
in restored habitats designed to improve degraded coastal wetland sites is largely unknown. Using taxon-specific photopigments,
we describe the composition of microphytobenthic communities in a large restoration site in southern California and differences
in the temporal recovery of biomass (chlorophylla), composition, and taxonomic diversity between vegetatedSpartina foliosa salt marsh and unvegetated mudflat. Visually distinct, spatially discreet, microphytobenthic patches appeared after no more
than 7 mo within the restoration site and were distinguished by significant differences in biomass, taxonomic diversity, and
the relative abundance of cyanobacteria versus diatoms. Sediment chlorophylla concentrations within the restored site were similar to concentrations in nearby natural habitat 0.2–2.2 yr following marsh
creation, suggesting rapid colonization by microproducers. RestoredSpartina marsh very rapidly (between 0.2 and 1.2 yr) acquired microphytobenthic communities of similar composition and diversity to
those in naturalSpartina habitat, but restored mudflats took at least 1.6 to 2.2 yr to resemble natural mudflats. These results suggest relatively
rapid recovery of microphytobenthic communities at the level of major taxonomic groups. Sediment features, such as pore water
salinity andSpartina density, explained little variation in microphytobenthic taxonomic composition. The data imply that provision of structural
heterogeneity in wetland construction (such as pools and vascular plants) might speed development of microproducer communities,
but no direct seeding of sediment microfloras may be necessary. 相似文献
136.
Water and poverty in the United States 总被引:1,自引:0,他引:1
Contrary to reports of 100% access to safe water and sanitation in international surveys, the United States (US) has a complex landscape of low-income water problems. This paper begins with a critical international perspective on water and poverty in the US. It shows that the US had a declining role in international water programs during the late-20th century, which contributed to limited international awareness of low-income water programs in the US, and limited US awareness of low-income water issues. To address the first problem, we provide an overview of low-income water programs in the US with an emphasis on those that serve small communities. We then examine census data on inadequate water systems in Colorado, which indicate that severe plumbing deficiencies persist despite these public water programs. Inadequate plumbing rates are lower than income poverty rates, however, which indicate partially successful strategies for achieving low-income water services. Analysis of local data in urban, rural, and mountainous areas of the state shows that poverty and water problems are correlated in complex ways, which has implications for all nations striving for universal access to safe water and sanitation. 相似文献
137.
138.
Moore M Lefkovitz L Hall M Hillman R Mitchell D Burnett J 《Marine pollution bulletin》2005,50(2):156-166
Effluent upgrades for metropolitan Boston have included toxicant reduction, primary and secondary treatment and outfall extension. Between 1992 and 2003 winter flounder at five stations were surveyed annually for liver and muscle burden and chronic hepatic sub-lethal impacts of polynuclear and halogenated aromatic hydrocarbons, and metals. Trends in flounder availability and fin condition were also examined. In 1988 12% of the adult winter flounder in Boston Harbor exhibited hepatic neoplasms and up to 80% had hepatic hydropic vacuolation (HV). Tumor prevalence fell to 0-2% and HV to <50% by 1996. Since then tumors have been absent, while a steady prevalence of HV has persisted, consistent with lower hydrocarbon loading and tissue levels. Contaminants and HV also fell with distance from the Boston outfall. After the outfall extension was activated in 2000, there has been no significant change in flounder liver health at the new outfall site. 相似文献
139.
Suzanna Randall Gilles Fontaine Elizabeth Green Dave Kilkenny Lisa Crause Oliver Cordes Simon O’Toole Lázló Kiss Bi-Qing For Pierre-Olivier Quirion 《Astrophysics and Space Science》2004,291(3-4):465-471
We report on the outcome of the first major multi-site campaign on a long-period variable subdwarf B star. The target PG 1627+017 was observed for a total of 334 h during April/May/June 2003 from the lynchpin observatory at Mt. Bigelow, Arizona, with important contributions coming from co-observations at SAAO, Calar Alto and Siding Spring. Preliminary analysis indicates the presence of 8–10 probable periods in the range ~4500 to ~8900 s with relative amplitudes between 0.1 and 0.5%;. The range over which the periods are found is in qualitative agreement with theoretical predictions and the number of periods found shows potential for an in-depth asteroseismological analysis. Multi-colour observations show that the relative amplitudes of pulsation are larger in the U-band than in the R, which again is in agreement with theory. However, more multi-colour observations are needed to be able to make statements at the quantitative level. 相似文献
140.
The Canadian Centre for Climate Modelling and Analysis atmospheric general circulation model (AGCM4) is used to study the
role of shallow convection in the hydrologic and energy cycles of the atmosphere. Sensitivity tests with AGCM4 show a marked
effect of the parameterization of shallow convection in the model. In particular, including the parameterization of shallow
convection produces considerably enhanced vertical mixing and decreased stratiform cloud amounts in the lower subtropical
atmosphere over the oceans. The differences in simulated stratiform cloud amounts are associated with a change in the globally
averaged outgoing shortwave radiative flux at the top of the atmosphere of about 11 W m−2. Additionally, precipitation rates are considerably reduced for stratiform clouds and enhanced for convective clouds in the
subtropics, if the parameterization of shallow convection is included in the model. Additional tests show that the simulated
responses in cloud amounts and precipitation to the treatment of shallow convection are robust. Additional simulations with
modified closures for deep convection and other changes to the treatment of convection in the model still lead to similar
responses of the model results. 相似文献