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321.
Surface water samples were collected from 55 sites in the Great Lakes Basin and analyzed for the presence of perchlorate using HPLC/MS/MS with an isotopically enriched internal standard. Sites included areas impacted by heavy industry, urbanization, agriculture and atmospheric deposition. Perchlorate was detected at several of the sites at concentrations close to the method detection limit (0.2 microg/l). Despite these low concentrations, its presence was confirmed by sample concentration and determination of the isotopic ratio of perchlorate. The presence of perchlorate at two of the sites was related to a fireworks display which had occurred prior to sampling. The other detections of perchlorate were in rivers/creeks draining watersheds which had high density livestock and crop farming activity. We suspect the two are related. To our knowledge, these are the first reported concentrations of perchlorate in Canadian surface waters. 相似文献
322.
Experiments were conducted in the autumn and winter of 1992/93 to examine habitat use by juvenile (age 0+) Atlantic cod, Gadus morhua L., before, during and following exposure to a passive or actively foraging predator (age 3+ cod). Experiments presented groups of juvenile cod (n=5 fish/group) with one of two combinations of three substrates; (1) gravel, sand, and a patch of artificial kelp (kelp), or (2) cobble, sand, and kelp. Cobble is known to provide juvenile cod with a refuge from predation. Kelp was used to test the hypothesis that juvenile cod associate with fleshy macroalgae in nature because of the safety it provides from predators. There was little difference in habitat use by juvenile cod before, during or following exposure to a passive predator. Under these conditions, juvenile cod appeared to prefer finer grained mineral substrates and avoided the kelp. The extent of the juvenile response to a passive predator was to avoid the predator's location in the experimental tank. In contrast, juvenile cod showed a significant shift in habitat use when exposed to an actively foraging predator, hiding in cobble or, when cobble was not available, in kelp. Use of both these habitats resulted in a significant reduction in predation risk to the juvenile cod. Our results suggest that: (1) an association with kelp provides safety from predation to juvenile cod, and (2) juvenile cod are capable for assessing the risk a predator represents and adjust their response accordingly. 相似文献
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325.
To extend coupled human–environment systems research and include the ecological effects of land-use and land-cover change and policy scenarios, we present an analysis of the effects of forest patch size and shape and landscape pattern on carbon storage estimated by BIOME-BGC. We evaluate the effects of including within-patch and landscape-scale heterogeneity in air temperature on carbon estimates using two modelling experiments. In the first, we combine fieldwork, spatial analysis, and BIOME-BGC at a 15-m resolution to estimate carbon storage in the highly fragmented and human-dominated landscape of Southeastern Michigan, USA. In the second, we perform the same analysis on 12 hypothetical landscapes that differ only in their degree of fragmentation. For each experiment we conduct four air-temperature treatments, three guided by field-based data and one empirically informed by local National Weather Service station data. The three field data sets were measured (1) exterior to a forest patch, (2) from the patch edge inward to 60 m on east-, south-, and west-facing aspects, separately, and (3) interior to that forest patch. Our field-data analysis revealed a decrease in maximum air temperature from the forest patch edge to a depth of 80 m. Within-patch air-temperature values were significantly different (α = 0.01) among transects (c.v. = 13.28) and for all measurement locations (c.v. = 30.58). Results from the first experiment showed that the interior treatment underestimated carbon storage by ~8000 Mg C and the exterior treatment overestimated carbon storage by 30,000 Mg C within Dundee Township, Southeastern Michigan, when compared to a treatment that included within-patch heterogeneity. In the second experiment we found a logarithmic increase in carbon storage with increasing fragmentation (r2 = 0.91). While a number of other processes (e.g. altered disturbance frequency or severity) remain to be included in future experiments, this combined field and modelling study clearly demonstrated that the inclusion of within-patch and landscape heterogeneity, and landscape fragmentation, each have a strong effect on forest carbon cycling and storage as simulated by a widely used ecosystem process model. 相似文献
326.
John M. Quinn Paul M. Brown Wendy Boyce Sarah Mackay Andrew Taylor Tony Fenton 《Journal of the American Water Resources Association》2001,37(6):1509-1515
ABSTRACT: Riparian zones perform a variety of biophysical functions that can be managed to reduce the effects of land use on instream habitat and water quality. However, the functions and human uses of riparian zones vary with biophysical factors such as landform, vegetation, and position along the stream continuum. These variations mean that “one size fits all” approaches to riparian management can be ineffective for reducing land use impacts. Thus riparian management planning at the watershed scale requires a framework that can consider spatial differences in riparian functions and human uses We describe a pilot riparian zone classification developed to provide such a framework for riparian management in two diverse river systems in the Waikato region of New Zealand. Ten classes of riparian zones were identified that differed sufficiently in their biophysical features to require different management. Generic “first steps” and “best practical” riparian management recommendations and associated costs were developed for each riparian class. The classification aims to not only improve our understanding of the effectiveness of riparian zone management as a watershed management tool among water managers and land owners, but to also provide a basis for deciding on management actions. 相似文献
327.
Oded Berger-Tal Shomen Mukherjee Burt P. Kotler Joel S. Brown 《Behavioral ecology and sociobiology》2009,63(12):1821-1827
Theory states that an optimal forager should exploit a patch so long as its harvest rate of resources from the patch exceeds
its energetic, predation, and missed opportunity costs for foraging. However, for many foragers, predation is not the only
source of danger they face while foraging. Foragers also face the risk of injuring themselves. To test whether risk of injury
gives rise to a foraging cost, we offered red foxes pairs of depletable resource patches in which they experienced diminishing
returns. The resource patches were identical in all respects, save for the risk of injury. In response, the foxes exploited
the safe patches more intensively. They foraged for a longer time and also removed more food (i.e., had lower giving up densities)
in the safe patches compared to the risky patches. Although they never sustained injury, video footage revealed that the foxes
used greater care while foraging from the risky patches and removed food at a slower rate. Furthermore, an increase in their
hunger state led foxes to allocate more time to foraging from the risky patches, thereby exposing themselves to higher risks.
Our results suggest that foxes treat risk of injury as a foraging cost and use time allocation and daring—the willingness
to risk injury—as tools for managing their risk of injury while foraging. This is the first study, to our knowledge, which
explicitly tests and shows that risk of injury is indeed a foraging cost. While nearly all foragers may face an injury cost
of foraging, we suggest that this cost will be largest and most important for predators. 相似文献
328.
Brown RW Gonzales C Hooper MJ Bayat AC Fornerette AM McBride TJ Longoria T Mielke HW 《Environmental geochemistry and health》2008,30(6):541-547
Residential lead (Pb) contamination, resulting from decades-long use of leaded gasoline and lead-based paint, is likely to
be present in soils in most urban areas. A screening level sampling effort demonstrated that Lubbock, Texas, USA, like other
cities of its age and size, has areas of elevated soil Pb. This effort was based on soil sampling performed on residential,
commercial and thoroughfare properties. The focus of this study was to investigate that component of soil contamination due
to combustion of leaded gasoline. Soils were collected from the 1–2 cm surface layer from street-side property borders, well
away from buildings that might lead to soil contamination from leaded paint chips. All samples were analyzed for Pb after
a 1 M HNO3 mild extraction to determine the amount of bioavailable Pb. Two of three transects through the city demonstrated significant
trends of decreasing Pb concentrations with distance from the city center, paralleling a decrease in developed property age.
Peak soil Pb concentrations outside city development was 4.9 ± 0.6 mg/kg while the median concentration for the city was 35.4 mg/kg.
Peak soil Pb concentrations in the city center ranged from 90.0 to 174.0 mg/kg and decreased exponentially to 6.0–9.0 mg/kg
at the furthest terminus of the residential transects. 相似文献
329.
Summary. Analysis of individuals of 17 troidine species demonstrated the presence of aristolochic acids in these butterflies in varying
concentrations. Although aristolochic acids do not occur in Aristolochia galeata leaves, they were present in Battus polydamas larvae reared on these leaves, and thus may be synthesized by the larvae from chemical precursors in the plant.
Received 17 August 1999; accepted 20 January 2000 相似文献
330.
Although prey may not have commercial value, their economic value can be ascertained in a predator-prey model if the predator has a harvest value. The economic optimal (recovery) path of the predator and prey are carefully described when growth is quadratic in the predator (prey) and linear in prey (predator). Parameter values, in part, resembling Pacific halibut are used to provide numerical illustrations. 相似文献