全文获取类型
收费全文 | 453篇 |
免费 | 29篇 |
国内免费 | 47篇 |
专业分类
安全科学 | 5篇 |
废物处理 | 2篇 |
环保管理 | 127篇 |
综合类 | 134篇 |
基础理论 | 199篇 |
污染及防治 | 19篇 |
评价与监测 | 14篇 |
社会与环境 | 24篇 |
灾害及防治 | 5篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 18篇 |
2018年 | 8篇 |
2017年 | 14篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 15篇 |
2013年 | 32篇 |
2012年 | 19篇 |
2011年 | 22篇 |
2010年 | 13篇 |
2009年 | 21篇 |
2008年 | 20篇 |
2007年 | 21篇 |
2006年 | 40篇 |
2005年 | 29篇 |
2004年 | 28篇 |
2003年 | 25篇 |
2002年 | 11篇 |
2001年 | 28篇 |
2000年 | 17篇 |
1999年 | 21篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有529条查询结果,搜索用时 0 毫秒
451.
Linking Wild and Captive Populations to Maximize Species Persistence: Optimal Translocation Strategies 总被引:2,自引:0,他引:2
BRIGITTE TENHUMBERG§ REW J. TYRE KATRIONA SHEA† HUGH P. POSSINGHAM‡ 《Conservation biology》2004,18(5):1304-1314
Abstract: Captive breeding of animals is widely used to manage endangered species, frequently with the ambition of future reintroduction into the wild. Because this conservation measure is very expensive, we need to optimize decisions, such as when to capture wild animals or release captive-bred individuals into the wild. It is unlikely that one particular strategy will always work best; instead, we expect the best decision to depend on the number of individuals in the wild and in captivity. We constructed a first-order Markov-chain population model for two populations, one captive and one wild, and we used stochastic dynamic programming to identify optimal state-dependent strategies. The model recommends unique sequences of optimal management actions over several years. A robust rule of thumb for species that can increase faster in captivity than in the wild is to capture the entire wild population whenever the wild population is below a threshold size of 20 females. This rule applies even if the wild population is growing and under a broad range of different parameter values. Once a captive population is established, it should be maintained as a safety net and animals should be released only if the captive population is close to its carrying capacity. We illustrate the utility of this model by applying it to the Arabian oryx ( Oryx leucoryx ). The threshold for capturing the entire Arabian oryx population in the wild is 36 females, and captive-bred individuals should not be released before the captive facilities are at least 85% full. 相似文献
452.
Centennial Decline in the Trophic Level of an Endangered Seabird after Fisheries Decline 总被引:1,自引:0,他引:1
Abstract: Coastal marine ecosystems worldwide have undergone such profound transformations from overfishing that trophic interactions observed today might be artifacts of these changes. We determined whether the trophic level of an endangered seabird, the Marbled Murrelet ( Brachyramphus marmoratus ), has declined over the past 100 years after the collapse of Pacific sardine ( Sardinops sadax ) fisheries in the late 1940s and the recent declines of similar fisheries in central California. We compared stable-isotope signatures of δ15 N and δ13 C in feathers of museum specimens collected before fisheries decline with values in murrelet feathers collected recently. Values of δ15 N in prebreeding diets declined significantly, 1.4‰ or 38% of a trophic level, over the past century during cool ocean conditions and by 0.5‰ during warm conditions, whereas postbreeding values of δ15 N were nearly constant. The δ13 C values in prebreeding diets declined by 0.8‰, suggesting an increased importance of krill in modern compared with historic prebreeding diets, but postbreeding diets did not change. Stable-isotope mixing models indicated that the proportion of energetically superior, high-trophic-level prey declined strongly whereas energetically poor, low-trophic-level and midtrophic-level prey increased in the prebreeding diet in cool years when murrelet reproduction was likely to be high. Decreased prey resources have caused murrelets to fish further down on the food web, appear partly responsible for poor murrelet reproduction, and may have contributed to its listing under the U.S. Endangered Species Act. 相似文献
453.
以1号冷冻保存(-20℃)的齿突蟾标本为材料,建立一种动物肌肉线粒体DNA的快捷提取方法.取10 g冷冻保存的肌肉组织,在研钵中剪碎,液氮研磨成粉;然后加SE缓冲液混匀,转入10 mL离心管静置10 min;上清液转入2 mL的Eppendorf管,1 000×g离心10 min,取上清液,再12 000×g离心15 min,沉淀即为线粒体;最后用SDS碱裂解法分离得到mtDNA.图1参3 相似文献
454.
三波长红外法测定水中石油类和动植物油 总被引:1,自引:0,他引:1
根据油的种类,性质及水中的分布情况,采用优级纯四氯化碳多次萃取,将油从水中提取出来,包含石油类和动物物油,动物物油属极性物质,可被硅酸吸附,石油类不被吸附,在红外三波长,波数分别为2930cm^-1,2960cm^-1,3030cm^-1处被吸收,准确测定这三个波数特征谱带的总和,从而准确测定水中石油类和动植物油。 相似文献
455.
Robert L. Parsons James W. Pease Darrell J. Bosch 《Journal of the American Water Resources Association》1995,31(6):1079-1087
ABSTRACT: EPIC, a soil erosion/plant growth simulation model, is used to simulate nitrogen losses for 120 randomly selected and previously surveyed cropland sites. Simulated nitrogen losses occur through volatilization, surface water and soil runoff, subsurface lateral flow, and leaching. Physical and crop management variables explain a moderate but significant proportion of the variation in nitrogen losses. Site slope and tillage have offsetting effects on surface and ground water losses. Nitrogen applications in excess of agronomic recommendations and manure obtained off the farm and applied to the sites are significant contributors to nitrogen losses. Farm characteristics such as production of confined livestock, total manure nitrogen available, and farm income per cropland acre explain a relatively large portion of the variability in manure nitrogen applied to survey sites. The results help to identify farm characteristics that can be used to target nutrient management programs. Simulation modeling provides a useful tool for investigating variables which contribute to agricultural nitrogen losses. 相似文献
456.
D. G. M. Wood-Gush K. Vestergaard 《Journal of Agricultural and Environmental Ethics》1989,2(2):161-169
Exploratory behavior is considered under the following categories: (1) extrinsic exploration in which the animal seeks information about conventional reinforcers such as food, (2) intrinsic exploration which is directed toward stimuli which may have no biological significance, further divided into inspective and inquisitive exploration. In the former the animal inspects a particular object; in the latter, the animal performs behavior to make a change in its environment, rather than merely responding to a change. Extrinsic exploration is synonymous with the ethological term, appetitive behavior. It is shown that much of the behavior indicative of frustration reported in intensively housed animals occurs when the appetitive component of a drive rather than the consummatory component, is prevented. Consideration of inspective exploration is necessary for good husbandry practice, for fear is an important competing response. Inquisitive exploration has not been widely investigated in infraprimate species, but the authors present several possible examples in the species of common agricultural animals. However, they suggest that the propensity to show this type of exploration may vary between closely related species. In environments barren to the extent of stifling exploration, animals may develop apathy, and its relevance to animal welfare is discussed. 相似文献
457.
GORDON B. BAUER 《Conservation biology》2005,19(6):1779-1789
Abstract: Restrictions on training potentially releasable animals such as those undergoing rehabilitation care or wild-caught captives have limited our understanding of sensory processes, cognition, and physiology important for conservation of species. It is common practice among several U.S. federal agencies to limit training of animals available for release. The behavioral argument justifying this practice is that training habituates subjects to people and conditions them to associate people with rewards such as food; habituation to and positive associations with people will lead animals into dangerous situations after their release. If under special circumstances research training is permitted, all trained behaviors must be extinguished before release because behaviors will transfer to the natural setting. Research on animal learning and memory indicates that these may not be accurate scenarios. A review of the literature on habituation, classical and instrumental conditioning, and compound conditioning suggests that learning within a research setting does not add to learning that already occurs in procedures associated with basic feeding and care. In fact, animals probably learn less about people in a training setting. Furthermore, context-specific effects on memory limit behavior transfer from captive to natural settings. Extinction is strongly susceptible to context effects, which suggests that extinction does not effectively transfer to the postrelease setting. Counterintuitively, extinction of responses to experimental stimuli under some circumstances may enhance undesirable learning about humans. Under those circumstances in which isolation from human contact is difficult or undesirable, behavioral research can present an ideal format for minimizing learning about humans and provide biological information important for conservation. 相似文献
458.
Elemental Conservation Units: Communicating Extinction Risk without Dictating Targets for Protection
Abstract: Conservation biologists mostly agree on the need to identify and protect biodiversity below the species level but have not yet resolved the best approach. We addressed 2 issues relevant to this debate. First, we distinguished between the abstract goal of preserving the maximum amount of unique biodiversity and the pragmatic goal of minimizing the loss of ecological goods and services given that further loss of biodiversity seems inevitable. Second, we distinguished between the scientific task of assessing extinction risk and the normative task of choosing targets for protection. We propose that scientific advice on extinction risk be given at the smallest meaningful scale: the elemental conservation unit (ECU). An ECU is a demographically isolated population whose probability of extinction over the time scale of interest (say 100 years) is not substantially affected by natural immigration from other populations. Within this time frame, the loss of an ECU would be irreversible without human intervention. Society's decision to protect an ECU ought to reflect human values that have social, economic, and political dimensions. Scientists can best inform this decision by providing advice about the probability that an ECU will be lost and the ecological and evolutionary consequences of that loss in a form that can be integrated into landscape planning. The ECU approach provides maximum flexibility to decision makers and ensures that the scientific task of assessing extinction risk informs, but remains distinct from, the normative social challenge of setting conservation targets. 相似文献
459.
M.B.M. Bracke J.H.M. Metz A.A. Dijkhuizen B.M. Spruijt 《Journal of Agricultural and Environmental Ethics》2001,14(3):321-337
Due to increasing empiricalinformation on farm animal welfare since the1960s, the prospects for sound decisionmakingconcerning welfare have improved. This paperdescribes a strategy to develop adecision-making aid, a decision support system,for assessment of farm-animal welfare based onavailable scientific knowledge. Such a decisionsupport system allows many factors to be takeninto account. It is to be developed accordingto the Evolutionary Prototyping Method, inwhich an initial prototype is improved inreiterative updating cycles. This initialprototype has been constructed. It useshierarchical representations to analysescientific statements and statements describingthe housing system. Welfare is assessed fromwhat is known about the biological needs of theanimals, using a welfare model in the form of atree that contains these needs as welfarecomponents. Each state of need is assessedusing welfare relevant attributes of thehousing system and weighting factors.Attributes are measurable properties of thehousing system. Weighting factors are assignedaccording to heuristic rules based on theprinciple of weighting all components(attributes and needs) equally, unless thereare strong reasons to do otherwise. Preliminarytests of the prototype indicate that it may bepossible to perform assessment of farm-animalwelfare in an explicit way and based onempirical findings. The procedure needs to berefined, but its prospects are promising. 相似文献
460.
Eileen O'Rourke 《Journal of Agricultural and Environmental Ethics》2000,13(1):144-165
This paper is concerned with changing social representations of the ``wild,' in particular wild animals. We argue that within a contemporary Western context the old agricultural perception of wild animals as adversarial and as a threat to domestication, is being replaced by an essentially urban fascination with certain emblematic wild animals, who are seen to embody symbols of naturalness and freedom. On closer examination that carefully mediatized ``naturalness' may be but another form of domestication. After an historical overview of the human-animal, domestic-wild construction, an anthropological approach is used to interpret the social representation of wild animals held by different social actors – farmers, hunters, and tourists – within the context of an inhabited National Park, that of the Cévennes in south east France. Within the Park, the domestic and the wild, along with agriculture, hunting, conservation, re-introduced wild animals, and tourists co-habit. It is argued that changes in the representation of ``wildness' may well be an important indicator ofchanges in the social representation of nature. 相似文献