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排序方式: 共有549条查询结果,搜索用时 31 毫秒
241.
Haijun Yang Christoph Kleinn Lutz Fehrmann Shouzheng Tang Steen Magnussen 《Environmental and Ecological Statistics》2011,18(2):223-237
Adaptive cluster sampling (ACS) is a sampling technique for sampling rare and geographically clustered populations. Aiming
to enhance the practicability of ACS while maintaining some of its major characteristics, an adaptive sample plot design is
introduced in this study which facilitates field work compared to “standard” ACS. The plot design is based on a conditional
plot expansion: a larger plot (by a pre-defined plot size factor) is installed at a sample point instead of the smaller initial
plot if a pre-defined condition is fulfilled. This study provides insight to the statistical performance of the proposed adaptive
plot design. A design-unbiased estimator is presented and used on six artificial and one real tree position maps to estimate
density (number of objects per ha). The performance in terms of coefficient of variation is compared to the non-adaptive alternative
without a conditional expansion of plot size. The adaptive plot design was superior in all cases but the improvement depends
on (1) the structure of the sampled population, (2) the plot size factor and (3) the critical value (the minimum number of
objects triggering an expansion). For some spatial arrangements the improvement is relatively small. The adaptive design may
be particularly attractive for sampling in rare and compactly clustered populations with an appropriately chosen plot size
factor. 相似文献
242.
A marine spatial planning (MSP) initiative—if to be successful—has to be rooted in a thorough understanding of the tradition
and structures of the governance system in the area targeted for the initiative. After decades of a mainly sectoral approach
towards maritime affairs, governments began to recognised the need for a governance framework that applies a more integrated
approach to maritime policy. The new Integrated Maritime Policy of the European Union is only one example for such a changed
way of policy and decision making. The assembly of a governance baseline can help to identify the crucial hindering and success
factors for the implementation of MSP. A governance baseline has two parts. Part One focuses upon the past and current performance
of the governance system as it has responded—or failed to respond—to changes in the condition of ecosystems in a specific
locale. Part Two of a baseline outlines a strategic approach to the design of a new program and records the goals, objectives
and strategies of MSP implementation. Focus on both governance processes and their outcomes is essential and forms the core
justification for documenting governance responses to ecosystem change. 相似文献
243.
Erik Bonsdorff 《Ambio》2021,50(4):753
Eutrophication, i.e. nutrient over-enrichment, has been a topic for academic and societal debate for the past five decades both on land and in aquatic systems fed by nutrients as diffuse loading from agricultural lands and as wastewater from industrial and municipal point-sources. The use of nutrients (primarily nitrogen and phosphorus) in excess became a problem with the onset of large-scale production and use of artificial fertilizers after World War II, and the effects on the aquatic environment became obvious some two to three decades later. In this Perspective, four seminal papers on eutrophication are discussed in light of the current knowledge of the problem, including future perspectives and outlooks in the light of global climate change and the demand for science-based holistic ecosystem-level policies and management options. 相似文献
244.
The Roles of Optimism in Conservation Biology 总被引:1,自引:0,他引:1
Erik Beever 《Conservation biology》2000,14(3):907-909
245.
Erik Degerman Johan Hammar Per Nyberg Gunnar Svardson 《Ambio-人类环境杂志》2001,30(8):522-528
瑞典四大湖(维纳恩、韦特恩、梅拉伦和哈马伦湖)的鱼类资源极其丰富,分布有红点鲑、鲑、鳟、白鲑、河鲈、梭鲈,、白斑狗鱼和鳗鲡等经济物种.研究表明,筑坝、航运、富营养化和过度开发等所产生的物理、化学和生物因素会对湖中的经济物种产生影响,导致湖中原有物种资源的种类组成发生变化.由于近年来的人类活动的影响,上述湖泊中原有鱼类组成中的优势种群发生了变化,一些物种消失了,一些新的物种在湖中出现,其原因主要是富营养化、鳗鲡和龙虾丰度的改变以及过度捕捞.过度捕捞在某种情况下是大湖的渔业生产引起的--在一个捕食者和竞食者同时存在的环境中,如果食物资源非常充足,鲑科鱼类以及梭鲈等鱼类在生活史上会倾向于在性成熟状态下生长,但在常规可捕规格的选择性调控下,这些物种会因产卵群体太小而导致资源量急刷下降. 相似文献
246.
In recent years, resilience engineering has been given considerable attention among safety researchers and analysts. The area represents a new way of thinking about safety. Whereas conventional risk management approaches are based on hindsight knowledge, failure reporting and risk assessments calculating historical data-based probabilities, resilience engineering looks for ways to enhance the ability of organisations to be resilient in the sense that they recognise, adapt to and absorb variations, changes, disturbances, disruptions and surprises. The implications of this shift in thinking are many. We focus in this paper on the understanding of the risk concept and how risk can be assessed and treated. The traditional ways of looking at risk are not suitable for use in resilience engineering, but other risk perspectives exist. A main purpose of this paper is to draw attention to such perspectives, in particular one category of perspectives where probability is replaced by uncertainty in the definition of risk. We argue that the basic ideas of resilience engineering can be supported by such risk perspectives. 相似文献
247.
Peer Hull Kristensen 《Safety Science》2011,49(7):964-973
Contrary to a widely held view, rather than seeing the certification of Occupational Health and Safety (OHS) as a barrier to increasing employee participation, this article views new ways of structuring participation as a necessary step towards making improvements in OHS management systems. The article first considers how work organization has changed and then in a similar way traces how bargaining has shifted from being distributive to become integrative to create a fundamental change in the negotiation regime. Finally, by analyzing an OHS-certified firm in greater depth, the article shows how solutions for improvements in OHS management and notable bottom-up formulations of OHS benchmarks may help us discover how the organizational form of firms with high-performance work organization can be developed through new participatory structures. 相似文献
248.
Regnery Julia Friesen Anton Geduhn Anke Göckener Bernd Kotthoff Matthias Parrhysius Pia Petersohn Eleonora Reifferscheid Georg Schmolz Erik Schulz Robert S. Schwarzbauer Jan Brinke Marvin 《Environmental Chemistry Letters》2019,17(1):215-240
Environmental Chemistry Letters - Anticoagulant rodenticides are used worldwide to control commensal rodents for hygienic and public health reasons. As anticoagulants act on all vertebrates, risk... 相似文献
249.
Wei He Ze-Lin Bai Wen-Xiu Liu Xiang-Zhen Kong Bin Yang Chen Yang Sven Erik Jørgensen Fu-Liu Xu 《Environmental science and pollution research international》2016,23(11):10335-10348
Surface sediment from large and eutrophic Lake Chaohu was investigated to determine the occurrence, spatial distribution, sources, and risks of polychlorinated biphenyls (PCBs) and heavy metals in one of the five biggest freshwater lakes in China. Total concentration of PCBs (Σ34PCBs) in Lake Chaohu was 672 pg g?1 dry weight (dw), with a range of 7 to 3999 pg g?1 dw, which was lower than other water bodies worldwide. The majority of heavy metals were detected at all sampling locations, except for Sr, B, and In. Concentrations of Al, Fe, Ca, Mn, Sr, Co, Zn, Cd, Pb, and Hg were similar to that reported for other lakes globally. Concentrations of K, Mg, Na, Li, Ga, and Ag were greater than the average, whereas those of Cr, Ni, and Cu were lower. Cluster analysis (CA) and positive matrix factorization (PMF) yielded accordant results for the source apportionment of PCBs. The technical PCBs and microbial degradation accounted for 34.2 % and 65.8 % of total PCBs using PMF, and PMF revealed that natural and anthropogenic sources of heavy metals accounted for 38.1 % and 61.8 %, respectively. CA indicated that some toxic heavy metals (e.g., Cd, In, Tl, and Hg) were associated with Ca–Na–Mg minerals rather than Fe–Mn minerals. The uncorrelated results between organic matter revealed by pyrolysis technology and heavy metals might be caused by the existence of competitive adsorption between organic matter and minerals. PCBs and heavy metals were coupling discharge without organochlorine pesticides (OCPs), but with polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers (PBDEs). No sediment sample exceeded the toxic threshold for dioxin-like PCBs (dl-PCBs) set at 20 pg toxicity equivalency quantity (TEQ)?g?1, (max dl-PCBs, 10.9 pg TEQ g?1). However, concentrations of Ag, Cd, and Hg were at levels of environmental concern. The sediment in the drinking water source area (DWSA) was threatened by heavy metals from other areas, and some fundamental solutions were proposed to protect the DWSA. 相似文献
250.