全文获取类型
收费全文 | 3325篇 |
免费 | 68篇 |
国内免费 | 33篇 |
专业分类
安全科学 | 120篇 |
废物处理 | 102篇 |
环保管理 | 615篇 |
综合类 | 528篇 |
基础理论 | 868篇 |
环境理论 | 9篇 |
污染及防治 | 797篇 |
评价与监测 | 192篇 |
社会与环境 | 148篇 |
灾害及防治 | 47篇 |
出版年
2023年 | 13篇 |
2022年 | 17篇 |
2021年 | 39篇 |
2020年 | 20篇 |
2019年 | 32篇 |
2018年 | 79篇 |
2017年 | 76篇 |
2016年 | 83篇 |
2015年 | 86篇 |
2014年 | 95篇 |
2013年 | 243篇 |
2012年 | 157篇 |
2011年 | 202篇 |
2010年 | 149篇 |
2009年 | 163篇 |
2008年 | 174篇 |
2007年 | 206篇 |
2006年 | 206篇 |
2005年 | 150篇 |
2004年 | 107篇 |
2003年 | 102篇 |
2002年 | 116篇 |
2001年 | 65篇 |
2000年 | 59篇 |
1999年 | 49篇 |
1998年 | 51篇 |
1997年 | 60篇 |
1996年 | 46篇 |
1995年 | 55篇 |
1994年 | 51篇 |
1993年 | 29篇 |
1992年 | 31篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 17篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1965年 | 11篇 |
1959年 | 8篇 |
1957年 | 11篇 |
排序方式: 共有3426条查询结果,搜索用时 968 毫秒
641.
Increasing difficulties associated with balancing consumptive demands for water and achieving ecological benefits in aquatic ecosystems provide opportunities for new ecosystem-scale ecological response models to assist managers. Using an Australian estuary as a case study, we developed a novel approach to create a data-derived state-and-transition model. The model identifies suites of co-occurring birds, fish, benthic invertebrates and aquatic macrophytes (as ‘states’) and the changing physico-chemical conditions that are associated with each (‘transitions’). The approach first used cluster analysis to identify sets of co-occurring biota. Differences in the physico-chemical data associated with each state were identified using classification trees, with the biotic distinctness of the resultant statistical model tested using analysis of similarities. The predictive capacity of the model was tested using new cases. Two models were created using different time-steps (annual and quarterly) and then combined to capture both longer-term trends and more-recent declines in ecological condition. We identified eight ecosystem states that were differentiated by a mix of water-quantity and water-quality variables. Each ecosystem state represented a distinct biotic assemblage under well-defined physico-chemical conditions. Two ‘basins of attraction’ were identified, with four tidally-influenced states, and another four independent of tidal influence. Within each basin, states described a continuum of relative health, manifest through declining taxonomic diversity and abundances. The main threshold determining relative health was whether freshwater flows had occurred in the region during the previous 339 days. Canonical analyses of principal coordinates tested the predictive capacity of the model and demonstrated that the variance in the environmental data set was well captured (87%) with 52% of the variance in the biological data set also captured. The latter increased to >80% when long- and short-term biological data were analysed separately, indicating that the model described the available data for the Coorong well. This approach thus created a data-derived, multivariate model, where neither states nor transitions were determined a priori. The approach did not over-fit the data, was robust to patchy or missing data, the choice of initial clustering technique and random errors in the biological data set, and was well-received by local natural resource managers. However, the model did not capture causal relationships and requires additional testing, particularly during future episodes of ecological recovery. The approach shows significant promise for simplifying management definitions of ecological condition and, via scenario analyses, can be used to assist in manager decision-making of large, complex aquatic ecosystems in the future. 相似文献
642.
In multiply invaded ecosystems, introduced species should interact with each other as well as with native species. Invader-invader interactions may affect the success of further invaders by altering attributes of recipient communities and propagule pressure. The invasional meltdown hypothesis (IMH) posits that positive interactions among invaders initiate positive population-level feedback that intensifies impacts and promotes secondary invasions. IMH remains controversial: few studies show feedback between invaders that amplifies their effects, and none yet demonstrate facilitation of entry and spread of secondary invaders. Our results show that supercolonies of an alien ant, promoted by mutualism with introduced honeydew-secreting scale insects, permitted invasion by an exotic land snail on Christmas Island, Indian Ocean. Modeling of land snail spread over 750 sites across 135 km2 over seven years showed that the probability of land snail invasion was facilitated 253-fold in ant supercolonies but impeded in intact forest where predaceous native land crabs remained abundant. Land snail occurrence at neighboring sites, a measure of propagule pressure, also promoted land snail spread. Site comparisons and experiments revealed that ant supercolonies, by killing land crabs but not land snails, disrupted biotic resistance and provided enemy-free space. Predation pressure on land snails was lower (28.6%), survival 115 times longer, and abundance 20-fold greater in supercolonies than in intact forest. Whole-ecosystem suppression of supercolonies reversed the probability of land snail invasion by allowing recolonization of land crabs; land snails were much less likely (0.79%) to invade sites where supercolonies were suppressed than where they remained intact. Our results provide strong empirical evidence for IMH by demonstrating that mutualism between invaders reconfigures key interactions in the recipient community. This facilitates entry of secondary invaders and elevates propagule pressure, propagating their spread at the whole-ecosystem level. We show that identification and management of key facilitative interactions in invaded ecosystems can be used to reverse impacts and restore resistance to further invasions. 相似文献
643.
The even-aged northern hardwood forests of the Upper Great Lakes Region are undergoing an ecological transition during which structural and biotic complexity is increasing. Early-successional aspen (Populus spp.) and birch (Betula papyrifera) are senescing at an accelerating rate and are being replaced by middle-successional species including northern red oak (Quercus rubra), red maple (Acer rubrum), and white pine (Pinus strobus). Canopy structural complexity may increase due to forest age, canopy disturbances, and changing species diversity. More structurally complex canopies may enhance carbon (C) sequestration in old forests. We hypothesize that these biotic and structural alterations will result in increased structural complexity of the maturing canopy with implications for forest C uptake. At the University of Michigan Biological Station (UMBS), we combined a decade of observations of net primary productivity (NPP), leaf area index (LAI), site index, canopy tree-species diversity, and stand age with canopy structure measurements made with portable canopy lidar (PCL) in 30 forested plots. We then evaluated the relative impact of stand characteristics on productivity through succession using data collected over a nine-year period. We found that effects of canopy structural complexity on wood NPP (NPPw) were similar in magnitude to the effects of total leaf area and site quality. Furthermore, our results suggest that the effect of stand age on NPPw is mediated primarily through its effect on canopy structural complexity. Stand-level diversity of canopy-tree species was not significantly related to either canopy structure or NPPw. We conclude that increasing canopy structural complexity provides a mechanism for the potential maintenance of productivity in aging forests. 相似文献
644.
The present study addresses the effect of maternal diet on hatching success and condition of embryos and larvae of Antarctic
krill Euphausia superba. Lipid and fatty acid content and composition were determined in field and laboratory samples. Developmental stages analyzed
in embryos included: multiple-cell, gastrula, and limb-bud stages. Larval stages analyzed included: nauplius I, nauplius II,
and metanauplius. Laboratory-reared embryos were spawned by gravid females incubated under three feeding groups: (1) phytoplankton
mixture, (2) phytoplankton mixture and minced clam, and (3) phytoplankton mixture, minced clam, and commercial larval food.
Hatching success was highest in group 3 (100%), lowest in group 1 (0%), and highly variable in field samples (0–48%). Lipid
decreased slightly in embryos during embryonic development, while large decreases in lipid were found during nauplius development.
High levels of 18:2(n-6), 20:4(n-6), and 22:6(n-3) observed with group 3 samples coincided with high hatching success in krill
embryos. The ratio of 22:6(n-3)/20:5(n-3) also correlated to hatching success of embryos. The fatty acid profile of embryos
in group 3 was similar to that of the field-collected embryos, reflecting the contribution of the commercial larval food in
the maternal diet. In our study, the maternal diet was found to influence the fatty acid composition of embryos and in turn
affects the hatching success of krill. Specific polyunsaturated fatty acids appeared to play important roles in embryogenesis
in krill. 相似文献
645.
Sponges constitute an abundant and functionally important component of coral reef systems. Given their demonstrated resistance to environmental stress, it might be expected that the role of sponges in reef systems under modern regimes of frequent and severe disturbance may become even more substantial. Disturbances have recently reshaped the community structure of many Caribbean coral reefs shifting them towards a state of persistent low coral cover and often a dominance of macroalgae. Using competition and growth rates recorded from Glover's Atoll in Belize, we parameterise a mathematical model used to simulate the three-way competition between sponges, macroalgae and coral. We use the model to determine the range of parameters in which each of the three species might be expected to dominate. Emergent properties arise from our simple model of this complex system, and these include a special case in which heightened competitive ability of macroalgae versus coral may counter-intuitively prove to be advantageous to the persistence of corals. Importantly, we show that even under scenarios whereby sponges fail to invade the system, inclusion of this third antagonist can qualitatively affect the likelihood of alternative stable states - generally in favour of macroalgal dominance. The interplay between multi-species competition and predation is complex, but our efforts highlight a key process that has, until now, remained unexplored: the extent to which sponges dissipate algal grazing pressure by providing generalist fish with an alternative food source. We highlight the necessity of identifying the extent by which this process takes place in tropical systems in order to improve projections of alternative stable states for Caribbean coral reefs. 相似文献
646.
Effects of urbanization and urban stream restoration on the physical and biological structure of stream ecosystems 总被引:1,自引:0,他引:1
Violin CR Cada P Sudduth EB Hassett BA Penrose DL Bernhardt ES 《Ecological applications》2011,21(6):1932-1949
Streams, as low-lying points in the landscape, are strongly influenced by the stormwaters, pollutants, and warming that characterize catchment urbanization. River restoration projects are an increasingly popular method for mitigating urban insults. Despite the growing frequency and high expense of urban stream restoration projects, very few projects have been evaluated to determine whether they can successfully enhance habitat structure or support the stream biota characteristic of reference sites. We compared the physical and biological structure of four urban degraded, four urban restored, and four forested streams in the Piedmont region of North Carolina to quantify the ability of reach-scale stream restoration to restore physical and biological structure to urban streams and to examine the assumption that providing habitat is sufficient for biological recovery. To be successful at mitigating urban impacts, the habitat structure and biological communities found in restored streams should be more similar to forested reference sites than to their urban degraded counterparts. For every measured reach- and patch-scale attribute, we found that restored streams were indistinguishable from their degraded urban stream counterparts. Forested streams were shallower, had greater habitat complexity and median sediment size, and contained less-tolerant communities with higher sensitive taxa richness than streams in either urban category. Because heavy machinery is used to regrade and reconfigure restored channels, restored streams had less canopy cover than either forested or urban streams. Channel habitat complexity and watershed impervious surface cover (ISC) were the best predictors of sensitive taxa richness and biotic index at the reach and catchment scale, respectively. Macroinvertebrate communities in restored channels were compositionally similar to the communities in urban degraded channels, and both were dissimilar to communities in forested streams. The macroinvertebrate communities of both restored and urban degraded streams were correlated with environmental variables characteristic of degraded urban systems. Our study suggests that reach-scale restoration is not successfully mitigating for the factors causing physical and biological degradation. 相似文献
647.
648.
This paper describes the application of coastal hydro-informatic modelling (using the TELEMAC Modelling System) to address
management issues arising from projected hydrodynamical and morphological changes within a shallow, sandy estuarine environment.
The model incorporates the complex interaction of ocean, terrestrial and atmospheric processes. The case study of the Dyfi
Estuary, on the west coast of Wales, is highlighted here. As sea levels have risen locally and are predicted to rise further,
a National Nature Reserve (Borth Bog), which has been reclaimed from tidal waters by embankments, will be at increasing risk
from flooding episodes due to overtopping of these embankments at high tide. Present and predicted future tidal-fluvial scenarios
have been modelled in the Dyfi Estuary in order to estimate the potential for flooding. In addition, areas of greatest velocity
change and potential for sediment erosion/accretion have been identified. A further process that has been investigated is
how salt marsh migration is affected by sea-level rise. This case study exemplifies some fundamental and complex physical
processes inherent to estuaries, and shows how different management options can be assessed, before their implementation,
through a modelling approach. 相似文献
649.
Benefits of Bt cotton counterbalanced by secondary pests? Perceptions of ecological change in China 总被引:1,自引:0,他引:1
Jennifer H. Zhao Peter Ho Hossein Azadi 《Environmental monitoring and assessment》2011,173(1-4):985-994
In the past, scientific research has predicted a decrease in the effectiveness of Bt cotton due to the rise of secondary and other sucking pests. It is suspected that once the primary pest is brought under control, secondary pests have a chance to emerge due to the lower pesticide applications in Bt cotton cultivars. Studies on this phenomenon are scarce. This article furnishes empirical evidence that farmers in China perceive a substantial increase in secondary pests after the introduction of Bt cotton. The research is based on a survey of 1,000 randomly selected farm households in five provinces in China. We found that the reduction in pesticide use in Bt cotton cultivars is significantly lower than that reported in research elsewhere. This is consistent with the hypothesis suggested by recent studies that more pesticide sprayings are needed over time to control emerging secondary pests, such as aphids, spider mites, and lygus bugs. Apart from farmers?? perceptions of secondary pests, we also assessed their basic knowledge of Bt cotton and their perceptions of Bt cotton in terms of its strengths and shortcomings (e.g., effectiveness, productivity, price, and pesticide use) in comparison with non-transgenic cotton. 相似文献
650.
Seabloom EW Benfield CD Borer ET Stanley AG Kaye TN Dunwiddie PW 《Ecological applications》2011,21(6):2129-2142
Successful conservation management requires an understanding of how species respond to intervention. Native and exotic species may respond differently to management interventions due to differences arising directly from their origin (i.e., provenance) or indirectly due to biased representations of different life history types (e.g., annual vs. perennial life span) or phylogenetic lineages among provenance (i.e., native or exotic origin) groups. Thus, selection of a successful management regime requires knowledge of the life history and provenance-bias in the local flora and an understanding of the interplay between species characteristics across existing environmental gradients in the landscape. Here we tested whether provenance, phylogeny, and life span interact to determine species distributions along natural gradients of soil chemistry (e.g., soil nitrogen and phosphorus) in 10 upland prairie sites along a 600-km latitudinal transect running from southern Vancouver Island in British Columbia, Canada, to the Willamette Valley in Oregon, USA. We found that soil nitrate, phosphorus, and pH exerted strong control over community composition. However, species distributions along environmental gradients were unrelated to provenance, life span, or phylogenetic groupings. We then used a greenhouse experiment to more precisely measure the response of common grass species to nitrogen and phosphorus supply. As with the field data, species responses to nutrient additions did not vary as a function of provenance, life span, or phylogeny. Native and exotic species differed strongly in the relationship between greenhouse-measured tolerance of low nutrients and field abundance. Native species with the greatest ability to maintain biomass production at low nutrient supply rates were most abundant in field surveys, as predicted by resource competition theory. In contrast, there was no relationship between exotic-species biomass at low nutrient levels and field abundance. The implications of these findings for management of invasive species are substantial in that they overturn a general belief that reduction of nutrient supplies favors native species. The idiosyncratic nature of species response to nutrients in this study suggests that manipulation of nutrient supplies is unlikely to alter the overall balance between native and exotic species, although it may well be useful to control specific exotic species. 相似文献