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771.
Consistent effects of nitrogen fertilization on soil bacterial communities in contrasting systems 总被引:11,自引:0,他引:11
Ecosystems worldwide are receiving increasing amounts of reactive nitrogen (N) through anthropogenic activities. Although the effects of increased N inputs on plant communities have been reasonably well studied, few comparable studies have examined impacts on whole soil bacterial communities, though they play critical roles in ecosystem functioning. We sampled soils from two long-term ecological research (LTER) experimental N gradients, both of which have been amended with NH4NO3; a grassland at Cedar Creek (27 years of N additions) and an agricultural field at Kellogg Biological Station (8 years of N additions). By examining shifts in bacterial communities across these contrasting ecosystem types, we could test competing hypotheses about the direct and indirect factors that might drive bacterial responses to elevated N inputs. Bacterial community structure was highly responsive to N additions. We observed predictable and consistent changes in the structure of the bacterial communities across both ecosystem types. Our results suggest that bacterial communities across these gradients are more structured by N and/or soil carbon availability than by shifts in the plant community or soil pH associated with the elevated nitrogen inputs. In contrast to the pronounced shifts in bacterial community composition and in direct contrast to the patterns often observed in plant communities, increases in N availability did not have consistent effects on the richness and diversity of soil bacterial communities. 相似文献
772.
Michael P. Harris Francis Daunt Mark Newell Richard A. Phillips Sarah Wanless 《Marine Biology》2010,157(4):827-836
Most seabirds die outside the breeding season, but understanding the key factors involved is hampered by limited knowledge
of nonbreeding distributions. We used miniature geolocating loggers to examine the movements between breeding seasons of Atlantic
puffins Fratercula arctica from a major North Sea colony where numbers have declined in recent years, apparently due to increased overwinter mortality.
The most intensively used region was the northwestern North Sea but most puffins also made excursions into the east Atlantic
in the early winter. Ringing recoveries previously indicated that adults from British east coast colonies remained within
the North Sea and hence were spatially segregated from those breeding on the west throughout the year. Updated analyses of
ringing recoveries support results from geolocators suggesting that usage of Atlantic waters is a recent phenomenon. We propose
that the increased adult mortality is related to changes in distribution during the nonbreeding period and reflects worsening
conditions in the North Sea. 相似文献
773.
Monica Gagliano Mark I. McCormick James A. Moore Martial Depczynski 《Marine Biology》2010,157(8):1849-1856
Ocean acidification is one of the key threats facing coral reef ecosystems, but there are few estimates of spatial and temporal
variability in pH among reef habitats. The present study documents levels of spatial variability in pH among coral reef habitats
(9 to 10), among locations separated by 100’s km of latitude and between east (Great Barrier Reef, GBR) and west (Ningaloo
Reef) coasts of Australia. Differences were found in pH between inshore and offshore waters along Ningaloo Reef (means 8.45,
8.53, respectively). Replicate assessments here ranged from 8.22 to 8.64. On the GBR, the range of values over all habitats
and replicates was 0.39 pH units (7.98 to 8.37). There were minor but significant differences of 0.05 pH units between 5 consecutive
days for habitats on average. Highest pH was recorded in filamentous algal beds maintained by the damselfish Dischistodus perspicillatus. Lowest pH was found in water extracted from sand-dwelling goby holes. While there were marked changes in pH over a 48-h
sampling period among 4 habitats at Lizard Island (GBR), there was little evidence of a diel trend. Understanding how pH varies
at scales that are relevant to organisms that live on shallow coral reefs is crucial for the design and interpretation of
experiments that test the effects on organisms of the changes in water chemistry predicted to affect oceans in the future. 相似文献
774.
Mark J. Brush 《Ecological modelling》2010,221(7):965-968
The development and application of ecosystem models in estuarine and coastal systems has grown exponentially over the past four decades. Models have become ensconced as major tools for both heuristic study of ecosystem structure and function as well as for informing management decisions, particularly with respect to cultural eutrophication. In recent years an ever-expanding toolbox of modeling approaches is being offered to complement traditional methods. This expansion of modeling in estuarine and coastal science was exemplified by four sessions devoted to modeling at the 2007 biennial conference of the Estuarine Research Federation in Providence, RI. We felt the time was right to propose a special session of Ecological Modelling to synthesize talks from these sessions to present the state of the art in coastal and estuarine modeling. The collection of papers contained in this special issue presents a diversity of traditional and novel modeling approaches, methods for assessing model validity and predictability, and the utility of models in management applications. We believe that together these papers provide an excellent overview of current approaches to modeling estuarine hydrodynamics, water quality, and ecosystem/food web dynamics, applications of complex and relatively simple modeling approaches, applications in both deep and shallow coastal systems, goals relevant for both heuristic and management applications, and perspectives based on traditional mechanistic model development as well as more recent alternative approaches. 相似文献
775.
Populations of bivalve filter feeders are distributed throughout the oligohaline waters of the Chesapeake Bay system and, to a lesser extent, in tidal fresh waters as well. Previous studies indicate these bivalves significantly diminish phytoplankton concentrations in one major tributary, the Potomac River, and observed chlorophyll concentrations suggest bivalve influence on phytoplankton in other oligohaline reaches. We incorporated a model of these bivalves into an existing eutrophication model of the system. The model indicated that bivalves may reduce phytoplankton concentrations in oligohaline and tidal fresh waters throughout the system but the most significant effects were noted in the Potomac and Patuxent tributaries. Bivalve impacts were related to hydraulic residence time. The greatest phytoplankton reductions occurred in the regions with the longest residence time. Model carbon and nutrient budgets indicated bivalves removed 14% to 40% of the carbon load, 11% to 23% of the nitrogen load, and 37% to 84% of the phosphorus load to the regions where their impact on computed chlorophyll was greatest. 相似文献
776.
Updated evaluation of exergy and emergy driving the geobiosphere: A review and refinement of the emergy baseline 总被引:2,自引:0,他引:2
Crucial to the method of emergy synthesis are the main driving emergy flows of the geobiosphere to which all other flows are referenced. They form the baseline for the construction of tables of Unit Emergy Values (UEVs) to be used in emergy evaluations. We provide here an updated calculation of the geobiosphere emergy baseline and UEVs for tidal and geothermal flows. First, we recalculate the flows using more recent values that have resulted from satellite measurements and generally better measurement techniques. Second, we have recalculated these global flows according to their available energy content (exergy) in order to be consistent with Odum's (1996) definition of emergy. Finally, we have reinterpreted the interaction of geothermal energy with biosphere processes thus changing the relationship between geothermal energy and the emergy baseline. In this analysis we also acknowledge the significant uncertainties related to most estimates of global data. In all, these modifications to the methodology have resulted in changes in the transformities for tidal momentum and geothermal energy and a minor change in the emergy baseline from 15.8E24 seJ/J to 15.2E24 seJ/J. As in all fields of science basic constants and standards are not really constant but change according to new knowledge. This is especially true of earth and ecological sciences where a large uncertainty is also to be found. As a consequence, while these are the most updated values today, they may change as better understanding is gained and uncertainties are reduced. 相似文献
777.
Phillip Cassey Golo Maurer Camille Duval John G. Ewen Mark E. Hauber 《Behavioral ecology and sociobiology》2010,64(10):1711-1720
Studies of avian eggshell coloration have been a long-standing research focus in behavioral evolutionary ecology. Museum collections
have provided a widely used resource because they allow efficient sampling across broad temporal, geographical, and taxonomic
ranges, even for species that are rare and for which sampling in the wild is ethically or practically unwarranted. We used
reflectance spectrophotometry across the avian visual spectrum to compare eggshell color of specimens of the song thrush (Turdus philomelos) in two museums (Natural History Museum, UK and Auckland Museum, New Zealand) with each other and with eggshells collected
fresh in New Zealand. These data enabled us to test the effects of source and storage in different museums, as well as time
since collection, across four metrics of eggshell coloration: blue-green and ultraviolet chroma, overall brightness, and the
spectral coefficient of variation. Variation within an egg, within a clutch, and among clutches, was similar between the two
museum datasets but different from those of fresh eggs. We found significant differences in all four metrics between the collections,
and that fresh eggshells reflected stronger in the blue-green wavelength than in museum eggs. This difference is most likely
due to different preservation techniques and storage histories. Furthermore, an effect of time since collection was only apparent
in the blue-green chroma and was higher in more recent museum eggshell samples. Our results support the use of historic museum
samples in intraspecific studies of shell coloration providing that efforts are made to compare specimens, which were collected
during similar periods. 相似文献
778.
Mark D. E. Fellowes Steve G. Compton James M. Cook 《Behavioral ecology and sociobiology》1999,46(2):95-102
The populations of many species are structured such that mating is not random and occurs between members of local patches.
When patches are founded by a single female and all matings occur between siblings, brothers may compete with each other for
matings with their sisters. This local mate competition (LMC) selects for a female-biased sex ratio, especially in species
where females have control over offspring sex, as in the parasitic Hymenoptera. Two factors are predicted to decrease the
degree of female bias: (1) an increase in the number of foundress females in the patch and (2) an increase in the fraction
of individuals mating after dispersal from the natal patch. Pollinating fig wasps are well known as classic examples of species
where all matings occur in the local patch. We studied non-pollinating fig wasps, which are more diverse than the pollinating
fig wasps and also provide natural experimental groups of species with different male morphologies that are linked to different
mating structures. In this group of wasps, species with wingless males mate in the local patch (i.e. the fig fruit) while
winged male species mate after dispersal. Species with both kinds of male have a mixture of local and non-local mating. Data
from 44 species show that sex ratios (defined as the proportion of males) are in accordance with theoretical predictions:
wingless male species<wing-dimorphic male species<winged male species. These results are also supported by a formal comparative
analysis that controls for phylogeny. The foundress number is difficult to estimate directly for non-pollinating fig wasps
but a robust indirect method leads to the prediction that foundress number, and hence sex ratio, should increase with the
proportion of patches occupied in a crop. This result is supported strongly across 19 species with wingless males, but not
across 8 species with winged males. The mean sex ratios for species with winged males are not significantly different from
0.5, and the absence of the correlation observed across species with wingless males may reflect weak selection to adjust the
sex ratio in species whose population mating structure tends not to be subdivided. The same relationship is also predicted
to occur within species if individual females adjust their sex ratios facultatively. This final prediction was not supported
by data from a wingless male species, a male wing-dimorphic species or a winged male species.
Received: 27 July 1998 / Received in revised form: 11 January 1999 / Accepted: 16 January 1999 相似文献
779.
Size assessment in simulated territorial encounters between male green frogs (Rana clamitans) 总被引:2,自引:0,他引:2
Mark A. Bee Stephen A. Perrill Patrick C. Owen 《Behavioral ecology and sociobiology》1999,45(3-4):177-184
We examined the ability of male green frogs to assess the size of an opponent based on the dominant frequency of their advertisement
call, which is negatively correlated with size, using synthetic stimuli to simulate intruders of different sizes. In one field
playback experiment, we broadcast a pair of stimuli representing a small and a large male; in a second experiment, we broadcast
calls of a medium and a large male. In both experiments, males produced calls with significantly lower dominant frequencies
in response to each stimulus. Contrast analyses revealed that males lowered the dominant frequency of their calls more in
response to the large-male stimulus than in responses to the small- and medium-male stimuli. In the second experiment, males
also responded to the large-male stimulus by calling at higher rates. There were no differences in mean note duration or the
number of moves made toward or around the playback speaker in response to any stimulus. Thus, the frequency of an opponent's
calls elicits a differential modification of calling behavior, primarily in the form of differential dominant frequency alteration,
suggesting that males use dominant frequency to assess the size of opponents during aggressive encounters.
Received: 17 April 1998 / Accepted after revision: 7 October 1998 相似文献
780.
Summary. The ability to perceive and respond to phytochemicals that reliably indicate poor suitability of a potential host plant confers
a selective advantage to ovipositing female swallowtail butterflies. Papilio glaucus females are generalists that nonetheless do not oviposit on red bay (Persea borbonia: Lauraceae). Red bay is toxic to P. glaucus neonates but is commonly found in habitats alongside their principal host plant, Magnolia virginiana, in central Florida. The hypothesis that deterrent compounds present in the leaves of red bay mediate its rejection by P. glaucus was evaluated in our study. Florida populations of P. glaucus did not oviposit on host leaves sprayed with the methanol extract of red bay foliage, although they accepted solvent-treated
and untreated tulip tree leaves in 3 choice bioassays. Additionally, tulip tree leaves sprayed with methanolic extracts of
red bay also deterred oviposition by P. glaucus females from Ohio, Kentucky and Pennsylvania, although these populations do
not naturally encounter red bay. Clearly, deterrent compounds found within this non-host are the basis of its rejection by
populations of P. glaucus and such recognition is fundamental to the species, not just a reflection of local adaptations.
Received 2 April 1999; accepted 11 June 1999. 相似文献