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51.
Fisher CR MacDonald IR Sassen R Young CM Macko SA Hourdez S Carney RS Joye S McMullin E 《Die Naturwissenschaften》2000,87(4):184-187
During a research cruise in July 1997 in the Gulf of Mexico we discovered a gas hydrate approximately 1 m thick and over
2 m in diameter which had recently breached the sea floor at a depth of 540 m. The hydrate surface visible from the submarine
was considerably greater than that of any other reported hydrate. Two distinct color bands of hydrate were present in the
same mound, and the entire exposed surface of the hydrate was infested (2500 individuals/m2) with 2 to 4 cm-long worms, since described as a new species, Hesiocaeca
methanicola, in the polychaete family Hesionidae (Desbruyères and Toulmond 1998). H.
methanicola tissue stable isotope values are consistent with a chemoautotrophic food source. No evidence of chemoautotrophic symbionts
was detected, but geochemical data support the presence of abundant free living bacteria on the hydrate. The activities of
the polychaetes, grazing on the hydrate bacteria and supplying oxygen to their habitats, appears to contribute to the dissolution
of hydrates in surface sediments.
Received: 16 August 1999 / Accepted in revised form: 19 January 2000 相似文献
52.
MacDonald LH 《Environmental management》2000,26(3):299-315
Since any proposed activity could contribute to a wide range of potential CEs at different spatial and temporal scales, a
tiered or nested approach should be followed to assess CEs. The difficulty of assessing and predicting CEs also suggests that
in many cases the most efficient approach is to focus on minimizing on-site impacts. Under some circumstances adaptive management
can also be a viable alternative to detailed CE assessments. Regular monitoring and feedback is critical to the successful
management and regulation of CEs. 相似文献
53.
54.
PROBLEM: Most pedestrian fatalities occur at night. Although researchers have long understood that drivers have difficulty seeing pedestrians at night and that reflective clothing can dramatically enhance pedestrian conspicuity, the extent to which pedestrians understand these facts is unclear. This experiment quantified pedestrians' estimates of the ability of an approaching driver to recognize the presence of roadside pedestrians. METHOD: Ten younger and 10 older participants walked in place on the far shoulder of a closed-road circuit and pressed a button when they were confident that the approaching driver could first recognize that a pedestrian was present. RESULTS: Pedestrians overestimated their visibility and dramatically underestimated the benefit of conspicuity treatments. CONCLUSIONS: These results suggest that pedestrians fail to understand the magnitude of the nighttime conspicuity problem and the value of conspicuity treatments. Pedestrians may therefore unknowingly place themselves in danger at night. IMPACT: These results underscore the need to educate pedestrians about the dangers of interacting with traffic at night and about treatments that increase their safety. 相似文献
55.
Restoration of waterbird diversity and abundance is a key objective of river system management in Australia. Therefore, understanding the effects of climatic and hydrological variables on waterbird population dynamics is fundamental for successful river restoration programs. We investigated the population dynamics of waterbirds (total abundance) and seven functional waterbird groups in the floodplains of lower Murrumbidgee River. We found a general declining abundance trend from 1983 to 2007, except for the deep water foragers. We modelled the relative contribution of the climatic and hydrological factors to waterbird population decrease using the generalized additive model (GAM) framework after identifying the negative binomial distribution. Most of the seven functional groups were positively related to both annual rainfall and water usage, defined as the total water volume intercepted by the river reach, and the models indicated that rainfall was slightly more important. Temperature also played a role in waterbird abundance: the maximum summer temperature negatively influenced the abundance of dabbling ducks, shoreline foragers and fish eaters, while the minimum winter temperature positively affected the abundance of dabbling ducks and shoreline foragers. Overall, our results support the practice of providing environmental water for sustaining waterbird populations. However, environmental water provision is likely to be most effective when timed to coincide with antecedent rainfall. 相似文献
56.
Darren P. Croft Mathew Edenbrow Safi K. Darden Indar W. Ramnarine Cock van Oosterhout Joanne Cable 《Behavioral ecology and sociobiology》2011,65(12):2219-2227
Understanding how individuals modify their social interactions in response to infectious disease is of central importance
for our comprehension of how disease dynamics operate in real-world populations. Whilst a significant amount of theoretical
work has modelled disease transmission using network models, we have comparatively little understanding of how infectious
disease impacts on the social behaviour of individuals and how these effects scale up to the level of the population. We experimentally
manipulated the parasite load of female guppies (Poecilia reticulata) and introduced fish either infected with the ectoparasites Gyrodactylus spp. (experimental) or uninfected (control) into replicated semi-natural populations of eight size-matched female guppies.
We quantified the behaviour and social associations of both the introduced fish and the population fish. We found that infected
experimental fish spent less time associating with the population fish than the uninfected control fish. Using information
on which fish initiated shoal fission (splitting) events, our results demonstrate that the population fish actively avoided
infected experimental fish. We also found that the presence of an infected individual resulted in a continued decline in social
network clustering up to at least 24 h after the introduction of the infected fish, whereas in the control treatment, the
clustering coefficient showed an increase at this time point. These results demonstrate that the presence of a disease has
implications for both the social associations of infected individuals and for the social network structure of the population,
which we predict will have consequences for infectious disease transmission. 相似文献
57.
Until the turn of the century the inshore waters of North Carolina harbored populations of sea turtles large enough to support a commercial fishery. Based on a 4- to-5-year record of sighting reports by the public, interviews of recreational fishermen, and records kept by commercial fishermen the waters continue to provide important developmental habitats for loggerhead, green, and Kemp's ridley sea turtles. Leathertback and hawksbill sea turtles infrequently entered the inshore waters. Reports from the public and commercial fishermen indicated that sea turtles were present offshore North Carolina all year and were present in inshore waters April through December. Sea turtles were encountered most frequently in the Atlantic Ocean, but seasonal encounters in some inshore waters, such as Core and Pamlico Sounds, often were greater. In early May large numbers of leatherbacks were sighted in the ocean and moved northward along the beach. Reported sightings of leatherbacks declined markedly by late June. Based on incidental captures by commercial fishermen loggerhead turtles were the most numerous species in Pamlico and Core Sounds (80%), followed by green (15%) and Kemp's ridley sea turtles (5%). Most captured turtles were immature, and all were released alive. The abundance of immature sea turtles in North Carolina inshore waters serves to emphasize that southeast U.S. estuaries are important habitats for these threatened and endangered species. This recognition supported the decision of the U.S. National Marine Fisheries Service to extend the requirement for turtle excluder devices in shrimp trawls to inshore areas during the entire year, full implementation of these requirements was achieved by December 1994. 相似文献
58.
A procedure of extended sensitivity analysis for simulation models is developed which is applicable to the situation in which input uncertainties are specified in a multiplicative (rather than an additive) way. This type of specification usually occurs when error estimates are large relative to the parameter values. The input parameter errors are assumed to have log-normal distributions and the basis for this assumption is explained along with the advantages it provides. The new procedure, multiplicative sensitivity analysis, is developed for the purposes of internal model validation and identification of priorities for specific experimental and theoretical studies needed for a particular system being modelled. The applicability of the procedure in the very early stages of a research program is its main advantage and further expands the rôle of simulation models. 相似文献
59.
John MacDonald 《Journal of environmental psychology》1983,3(3):287-291
60.
Oysters live permanently immobilised by cementation of the left valve to a hard substrate. The contact zone between oysters
and natural substrata has been analysed using SEM imaging, electron dispersive X-ray microanalysis, electron backscatter diffraction
and Raman spectroscopy and reveals the influence of both biogenic and non-biogenic processes in oyster cementation. Original
adhesion is brought about by secretion of an organic component that acts as a nucleating surface onto which crystals precipitate.
These crystals have a random orientation and are composed of high Mg calcite. This suggests that the crystals nucleating on
the glue substrate are outwith the biological control experienced by the shell biomineralisation process and are formed by
inorganic precipitation from seawater. It is proposed that oysters do not control or secrete crystalline cement. Instead,
they adhere by secretion of an organic film onto which crystals precipitate from seawater. 相似文献