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421.
  总被引:1,自引:0,他引:1  
  相似文献   
422.
423.
    
Benthic macrofaunal populations through their feeding, bioturbation, burrow construction and sediment irrigation activities have profound influences on organic matter inputs to marine sediments (biodeposition) and on the vertical distribution of deposited organic matter within the sediment. These effects in turn influence the rates and pathways of organic matter mineralisation, and element cycles. Similarly, bioturbation, burrow construction and burrow irrigation are major determinants of sediment-water column fluxes of oxygen and nutrients.

In this review, I discuss the influences of the different benthic macrofaunal feeding (functional) groups on mineralisation processes and sediment-water column fluxes of particulate and dissolved nutrients. How these effects influence diagenic processes, the balance between aerobic and anaerobic processes, and the redox status of the surficial sediments. Finally, I discuss some of the limitations of the predominantly laboratory techniques which have been used to study “macrofaunal effects” and how this hinders the inclusion of the effects in quantitative sediment biogeochemical models.  相似文献   
424.
    
Small‐scale, decentralized and community‐owned renewable energy is widely acknowledged to be a desirable feature of low carbon futures, but faces a range of challenges in the context of conventional, centralized energy systems. This paper draws on transition frameworks to investigate why the UK has been an inhospitable context for community‐owned renewables and assesses whether anything fundamental is changing in this regard. We give particular attention to whether political devolution, the creation of elected governments for Scotland, Wales and Northern Ireland, has affected the trajectory of community renewables. Our analysis notes that devolution has increased political attention to community renewables, including new policy targets and support schemes. However, these initiatives are arguably less important than the persistence of key features of socio‐technical regimes: market support systems for renewable energy and land‐use planning arrangements that systemically favour major projects and large corporations, and keep community renewables to the margins. There is scope for rolling out hybrid pathways to community renewables, via joint ownership or through community benefit funds, but this still positions community energy as an adjunct to energy pathways dominated by large, corporate generation facilities. Copyright © 2015 John Wiley & Sons, Ltd and ERP Environment  相似文献   
425.
  总被引:1,自引:0,他引:1  
In large samples of trees > or = 1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes of stature at maturity (SAM). We then compared the proportional representation of understory trees (1-2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae [Bombacacoidea]) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1-2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration.  相似文献   
426.
    
This study investigates the brief piping signals (\"stop signals\") of honey bee workers by exploring the context in which worker piping occurs and the identity and behavior of piping workers. Piping was stimulated reliably by promoting a colony's nectar foraging activity, demonstrating a causal connection between worker piping and nectar foraging. Comparison of the behavior of piping versus non-piping nectar foragers revealed many differences, e.g., piping nectar foragers spent more time in the hive, started to dance earlier, spent more time dancing, and spent less time on the dance floor. Most piping signals (approximately 99%) were produced by tremble dancers, yet not all (approximately 48%) tremble dancers piped, suggesting that the short piping signal and the tremble dance have related, but not identical, functions in the nectar foraging communication system. Our observations of the location and behavior of piping tremble dancers suggest that the brief piping signal may (1) retard recruitment to a low-quality food source, and (2) help to enhance the recruitment success of the tremble dance.  相似文献   
427.
428.
    
Second Caribbean Conference on Science, Hazards and Hazard Management; Kingston, Jamaica, 9-12 October 1996
Mitigating the Millennium: Seminar on Community Participation and Impact Measurement in Disaster Preparedness and Mitigation Programmes; Overseas Development Institute, London, 9 October 1996  相似文献   
429.
Evaluating the consequences and future of land protection requires broad temporal and spatial perspectives of ecological and cultural factors. We assessed the development of a system of protected areas comprising 37% of central Massachusetts in terms of changing rates and means of land protection. We compared protected areas to the surrounding matrix in terms of physical, biological, and historical features and used these results to raise issues concerning future planning. The rate, purpose, and means of land protection in the North Quabbin Region (168,312 ha) have been dynamic as a result of changes in cultural values and transformation of the landscape from predominantly agriculture to forest. Protected lands are managed by 25 federal and state agencies, private groups, and municipal departments and commissions and are physically and biologically typical of the regional landscape which results from (1) participation of diverse organizations with varied agendas; (2) predominance of large government acquisitions driven by landscape-scale criteria; and (3) absence of coordination among groups. The large area, relative homogeneity and largely undeveloped status of the North Quabbin Region suggest conservation goals distinct from those in the fragmented and extensively developed neighboring areas of the Connecticut River Valley and Cape Cod and Islands Region. Large tracts of forests, wetlands, and lakes in the North Quabbin Region provide (1) habitat for species requiring extensive, intact areas; (2) the opportunity to maintain broad-scale ecological processes; (3) connections to regional conservation areas; and (4) recreation. To realize the area's potential, a comprehensive plan must be based on a broad-scale perspective and historical understanding of the landscape.  相似文献   
430.
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