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51.
James F. Saunders Marylee Murphy Martyn Clark William M. Lewis 《Journal of the American Water Resources Association》2004,40(5):1339-1349
ABSTRACT: Historical flow records are used to estimate the regulatory low flows that serve a key function in setting discharge permit limits through the National Pollutant Discharge Elimination System, which provides a nationwide mechanism for protecting water quality. Use of historical records creates an implicit connection between water quality protection and climate variability. The longer the record, the more likely the low flow estimate will be based on a broad set of climate conditions, and thus provides adequate water quality protection in the future. Unfortunately, a long record often is not available at a specific location. This analysis examines the connection between climate variability and the variability of biologically based and hydrologically based low flow estimates at 176 sites from the Hydro‐Climatic Data Network, a collection of stream gages identified by the USGS as relatively free of anthropogenic influences. Results show that a record of 10 to 20 years is necessary for satisfactory estimates of regulatory low flows. Although it is possible to estimate a biologically based low flow from a record of less than 10 years, these estimates are highly uncertain and incorporate a bias that undermines water quality protection. 相似文献
52.
We draw on the economic, corporate governance, and family business literatures to explain why the effects of family on family firms makes this governance form theoretically distinct from those of public and private non‐family firms. Our thesis is that parental altruism, when combined with private ownership and owner‐management, influences the ability of the firm's owner‐manager to exercise self‐control, which, in turn, can expose some family firms to conflicts rooted in the agency threats of moral hazard, hold‐up, and adverse selection. We then discuss why some other family firms are able to minimize these dark side threats and thereby attain altruism's brighter side. Finally, we discuss how altruism's influence changes over time as ownership becomes dispersed among family members and across generations. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
53.
Quantifying and Evaluating Ecosystem Health: A Case Study from Moreton Bay, Australia 总被引:1,自引:0,他引:1
As part of the program monitoring the ecosystem health of Moreton Bay, Queensland, Australia, we developed a means for assessing
ecosystem health that allows quantitative evaluation and spatial representations of the assessments. The management objectives
for achieving ecosystem health were grouped into ecosystem objectives, water quality objectives, and human health objectives.
For the first two groups, aspects of the ecosystem (e.g., trophic status) were identified, and an indicator was chosen for
each aspect. Reference values for each indicator were derived from management objectives and compared with the mapped survey
values. Subregions for which the indicator statistic was equal to or better than the assigned reference value are referred
to as “compliant zones.” High-resolution surface maps were created from spatial predictions on a fine hexagonal grid for each
of the indicators. Eight reporting subregions were established based on the depth and predicted residence times of the water.
Within each reporting subregion, the proportion that was compliant was calculated. These results then were averaged to create
an integrated ecosystem health index. The ratings by a team of ecosystem experts and the calculated ecosystem health indices
had good correspondence, providing assurance that the approach was internally consistent, and that the management objectives
covered the relevant biologic issues for the region. This method of calculating and mapping ecosystem health, relating it
directly to management objectives, may have widespread applicability for ecosystem assessment. 相似文献
54.
Removal of selenate from water by zerovalent iron 总被引:1,自引:0,他引:1
Zerovalent iron (ZVI) has been widely used in the removal of environmental contaminants from water. In this study, ZVI was used to remove selenate [Se(VI)] at a level of 1000 microg L(-1) in the presence of varying concentrations of Cl-, SO(2-)4, NO(-)3, HCO(-)3, and PO(3-)4. Results showed that Se(VI) was rapidly removed during the corrosion of ZVI to iron oxyhydroxides (Fe(OH)). During the 16 h of the experiments, 100 and 56% of the added Se(VI) was removed in 10 mM Cl- and SO(2-)4 solutions under a closed contained system, respectively. Under an open condition, 100 and 93% of the added Se(VI) were removed in the Cl- and SO(2-)4 solutions, respectively. Analysis of Se species in ZVI-Fe(OH) revealed that selenite [Se(IV)] and nonextractable Se increased during the first 2 to 4 h of reaction, with a decrease of Se(VI) in the Cl- experiment and no detection of Se(VI) in the SO(2-)4 experiment. Two mechanisms can be attributed to the rapid removal of Se(VI) from the solutions. One is the reduction of Se(VI) to Se(IV), followed by rapid adsorption of Se(IV) to Fe(OH). The other is the adsorption of Se(VI) directly to Fe(OH), followed by its reduction to Se(IV). The results also show that there was little effect on Se(VI) removal in the presence of Cl- (5, 50, and 100 mM), NO(-)3 (1, 5, and 10 mM), SO(2-)4 (5 mM), HCO(-)3 (1 and 5 mM), or PO(3-)4 (1 mM) and only a slight effect in the presence of SO(2-)4 (50 and 100 mM), HCO(-)3 (10 mM), and PO(3-)4 (5 mM) during a 2-d experiment, whereas 10 mM PO(3-)4 significantly inhibited Se(VI) removal. This work suggests that ZVI may be an effective agent to remove Se from Se-contaminated agricultural drainage water. 相似文献
55.
William M. Adams Martin R. Perrow Angus Carpenter 《Journal of Environmental Planning and Management》2005,48(6):877-889
The restoration of river environments has been of growing importance to river management and planning in the UK. The extension of ecological restoration to floodplains as well as river channels is more complex, partly because of the range of stakeholders and the diversity of relevant management institutions. This paper draws on a qualitative survey of river managers in the UK to identify institutional factors relevant to the success or failure of floodplain restoration projects. 相似文献
56.
Yongsung Cho K. William. Easter Laura M.J. McCann Frances Homans 《Journal of the American Water Resources Association》2005,41(3):729-740
ABSTRACT: The concentrations of iron and sulfate in community water supplies are a concern for a number of areas in southwestern Minnesota. This study used the contingent valuation method to determine how much consumers would be willing to pay to improve their drinking water quality. On average, individuals were willing to pay US$5.25 per month (in 1995 U.S. dollars) to reduce the level of iron and US$4.33 per month to reduce the level of sulfate in their water to the USEPA's secondary standards for drinking water quality. Respondents with negative perceptions of their drinking water quality were willing to pay more to improve water quality. The aggregate annual willingness to pay (WTP) for all consumers in community water systems in southwestern Minnesota that were out of compliance with water quality standards were estimated to be US$2.4 million and US$2.0 million (in 1995 dollars) for reducing the levels of iron and sulfate, respectively. Yet the total WTP of consumers who use small community water systems may not be enough to pay the full cost of providing improved water in those systems. Economies of scale in water treatment and difficulties in financing improvements mean that technical innovation, government assistance, or institutional changes may be needed to improve water quality in these areas. 相似文献
57.
Simulation of vegetation dynamics and management strategies on south Texas, semi-arid rangeland 总被引:1,自引:0,他引:1
In this paper, we describe a model designed to simulate seasonal dynamics of warm and cool season grasses and forbs, as well as the dynamics of woody plant succession through five seral stages, in each of nine different plant communities on the Rob and Bessie Welder Wildlife Refuge. The Welder Wildlife Refuge (WWR) is located in the Gulf Coastal Prairies and Marshes ecoregion of Texas. The model utilizes and integrates data from a wide array of research projects that have occurred in south Texas and WWR. It is designed to investigate the effects of alternative livestock grazing programs and brush control practices, with particular emphasis on prescribed burning, the preferred treatment for brush on the WWR. We evaluated the model by simulating changes in the plant communities under historical (1974-2000) temperature, rainfall, livestock grazing rotation, and brush control regimes, and comparing simulation results to field data on herbaceous biomass and brush canopy cover collected on the WWR over the same period. We then used the model to simulate the effects of 13 alternative management schemes, under each of four weather regimes, over the next 25 years. We found that over the simulation period, years 1974-2000, the model does well in simulating the magnitude and seasonality of herbaceous biomass production and changes in percent brush canopy cover on the WWR. It also does well in simulating the effects of variations in cattle stocking rates, grazing rotation programs, and brush control regimes on plant communities, thus providing insight into the combined effects of temperature, precipitation, cattle stocking rates, grazing rotation programs, and brush control on the overall productivity and state of woody plant succession on the WWR. Simulation of alternative management schemes suggests that brush canopy removal differs little between summer and winter prescribed burn treatments when precipitation remains near the long-term average, but during periods of low precipitation canopy removal is greater under winter prescribed burning. The model provides a useful tool to assist refuge personnel with developing long-term brush management and livestock grazing strategies. 相似文献
58.
Using empirical models of species colonization under multiple threatening processes to identify complementary threat‐mitigation strategies
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Ayesha I.T. Tulloch Alessio Mortelliti Geoffrey M. Kay Daniel Florance David Lindenmayer 《Conservation biology》2016,30(4):867-882
Approaches to prioritize conservation actions are gaining popularity. However, limited empirical evidence exists on which species might benefit most from threat mitigation and on what combination of threats, if mitigated simultaneously, would result in the best outcomes for biodiversity. We devised a way to prioritize threat mitigation at a regional scale with empirical evidence based on predicted changes to population dynamics—information that is lacking in most threat‐management prioritization frameworks that rely on expert elicitation. We used dynamic occupancy models to investigate the effects of multiple threats (tree cover, grazing, and presence of an hyperaggressive competitor, the Noisy Miner (Manorina melanocephala) on bird‐population dynamics in an endangered woodland community in southeastern Australia. The 3 threatening processes had different effects on different species. We used predicted patch‐colonization probabilities to estimate the benefit to each species of removing one or more threats. We then determined the complementary set of threat‐mitigation strategies that maximized colonization of all species while ensuring that redundant actions with little benefit were avoided. The single action that resulted in the highest colonization was increasing tree cover, which increased patch colonization by 5% and 11% on average across all species and for declining species, respectively. Combining Noisy Miner control with increasing tree cover increased species colonization by 10% and 19% on average for all species and for declining species respectively, and was a higher priority than changing grazing regimes. Guidance for prioritizing threat mitigation is critical in the face of cumulative threatening processes. By incorporating population dynamics in prioritization of threat management, our approach helps ensure funding is not wasted on ineffective management programs that target the wrong threats or species. 相似文献
59.
60.
Céline Jézéquel Pablo A. Tedesco William Darwall Murilo S. Dias Renata G. Frederico Max Hidalgo Bernard Hugueny Javier Maldonado-Ocampo Koen Martens Hernan Ortega Gislene Torrente-Vilara Jansen Zuanon Thierry Oberdorff 《Conservation biology》2020,34(4):956-965
Conserving freshwater habitats and their biodiversity in the Amazon Basin is a growing challenge in the face of rapid anthropogenic changes. We used the most comprehensive fish-occurrence database available (2355 valid species; 21,248 sampling points) and 3 ecological criteria (irreplaceability, representativeness, and vulnerability) to identify biodiversity hotspots based on 6 conservation templates (3 proactive, 1 reactive, 1 representative, and 1 balanced) to provide a set of alternative planning solutions for freshwater fish protection in the Amazon Basin. We identified empirically for each template the 17% of sub-basins that should be conserved and performed a prioritization analysis by identifying current and future (2050) threats (i.e., degree of deforestation and habitat fragmentation by dams). Two of our 3 proactive templates had around 65% of their surface covered by protected areas; high levels of irreplaceability (60% of endemics) and representativeness (71% of the Amazonian fish fauna); and low current and future vulnerability. These 2 templates, then, seemed more robust for conservation prioritization. The future of the selected sub-basins in these 2 proactive templates is not immediately threatened by human activities, and these sub-basins host the largest part of Amazonian biodiversity. They could easily be conserved if no additional threats occur between now and 2050. 相似文献