首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   434篇
  免费   16篇
  国内免费   9篇
安全科学   20篇
废物处理   17篇
环保管理   101篇
综合类   41篇
基础理论   146篇
环境理论   1篇
污染及防治   80篇
评价与监测   36篇
社会与环境   17篇
  2023年   4篇
  2022年   4篇
  2021年   4篇
  2020年   3篇
  2019年   8篇
  2018年   14篇
  2017年   8篇
  2016年   14篇
  2015年   13篇
  2014年   14篇
  2013年   31篇
  2012年   22篇
  2011年   33篇
  2010年   21篇
  2009年   21篇
  2008年   28篇
  2007年   37篇
  2006年   28篇
  2005年   7篇
  2004年   19篇
  2003年   12篇
  2002年   12篇
  2001年   12篇
  2000年   4篇
  1999年   9篇
  1998年   8篇
  1997年   4篇
  1996年   7篇
  1995年   3篇
  1994年   4篇
  1993年   4篇
  1992年   4篇
  1991年   6篇
  1990年   2篇
  1989年   2篇
  1988年   2篇
  1986年   3篇
  1985年   4篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   4篇
  1980年   6篇
  1979年   4篇
  1978年   4篇
  1977年   1篇
  1974年   1篇
  1973年   1篇
排序方式: 共有459条查询结果,搜索用时 281 毫秒
171.
Adaptive management implies a continuous knowledge‐based decision‐making process in conservation. Yet, the coupling of scientific monitoring and management frameworks remains rare in practice because formal and informal communication pathways are lacking. We examined 4 cases in Micronesia where conservation practitioners are using new knowledge in the form of monitoring data to advance marine conservation. These cases were drawn from projects in Micronesia Challenge jurisdictions that received funding for coupled monitoring‐to‐management frameworks and encompassed all segments of adaptive management. Monitoring in Helen Reef, Republic of Palau, was catalyzed by coral bleaching and revealed evidence of overfishing that led to increased enforcement and outreach. In Nimpal Channel, Yap, Federated States of Micronesia (FSM), monitoring the recovery of marine food resources after customary restrictions were put in place led to new, more effective enforcement approaches. Monitoring in Laolao Bay, Saipan, Commonwealth of the Northern Mariana Islands, was catalyzed by observable sediment loads from poor land‐use practices and resulted in actions that reduced land‐based threats, particularly littering and illegal burning, and revealed additional threats from overfishing. Pohnpei (FSM) began monitoring after observed declines in grouper spawning aggregations. This data led to adjusting marine conservation area boundaries and implementing market‐based size class restrictions. Two themes emerged from these cases. First, in each case monitoring was conducted in a manner relevant to the social and ecological systems and integrated into the decision‐making process. Second, conservation practitioners and scientists in these cases integrated culturally appropriate stakeholder engagement throughout all phases of the adaptive management cycle. More broadly, our study suggests, when describing adaptive management, providing more details on how monitoring and management activities are linked at similar spatial scales and across similar time frames can enhance the application of knowledge.  相似文献   
172.
173.
Parental investment decision rules: a test in bluegill sunfish   总被引:5,自引:1,他引:4  
Summary We review parental investment decision theory and provide an experimental test of the decision rule used by male bluegill sunfish (Lepomis macrochirus) in allocating parental investment to their young. The alternative decision rules tested are: (1) invest according to brood size (number) only; (2) invest according to past investment only; (3) invest according to both brood size and past investment; and (4) invest according to neither brood size nor past investment. By manipulating brood size independently of a male's cumulative investment in the brood, and by measuring each male's defensive behavior against a model predator, we found that male bluegill invest according to both brood size and past investment. This result is consistent with recent theory that past parental investment devalues adult future reproductive value, and that animals should therefore invest according to the value of their brood relative to that of their own expected future reproduction.  相似文献   
174.
Resources to develop proactive environmental programs compete directly with resources dedicated to the fundamental business of the company. Therefore, environmental managers need to prioritize environmental programs using the same criteria as the company as a whole; for many companies, this means measuring how well such programs meet and exceed customer expectations. We must define our customers, measure their expectations, analyze the results, develop programs in response, and finally measure the results of the program implementation. Although Apple has not completed this cycle, our customer definition and measurement systems are taking shape. This article explains how we define our customers, and how we measure their expectations through direct and indirect data collection mechanisms. It also outlines measurement results and our evolving program focus in response to those results.  相似文献   
175.
In birds, the position and extent of the region of binocular vision appears to be determined by feeding ecology. Of prime importance is the degree to which vision is used for the precise control of bill position when pecking or lunging at prey. In birds that do not require such precision (probe and filter-feeders), the bill falls outside the binocular field, which extends above and behind the head, thus providing comprehensive visual coverage. Flamingos Phoenicopteridae are highly specialised filter-feeders. They employ a unique technique that does not require accurate bill positioning in which the inverted head is placed between the feet. Feeding flamingos often walk forwards with the head pointing “backwards”. Here we show that in Lesser Flamingos Phoeniconaias minor visual fields are in fact the same as those of birds that feed by precision pecking and that feeding flamingos are blind in the direction of their walking. We suggest that this is due to the requirement for accurate bill placement when flamingos feed their chicks with “crop-milk”, and possibly when building their nest. We propose that chick-feeding may be the ultimate determinant of visual field topography in birds, not feeding ecology.  相似文献   
176.
Diffusion of dissolved oxygen through activated sludge flocs was studied, as it represents a potential mechanism for simultaneous nitrification and denitrification in activated sludge systems. Dissolved oxygen profiles through six floc particles collected at different times from a full-scale activated sludge plant demonstrated that that the dissolved oxygen concentration declines through all floc particles. For larger floc particles (2-mm diameter and greater), the dissolved oxygen concentration reached near-zero values at depths depending on process operating conditions. A mathematical model based on diffusion of dissolved oxygen, organic substrate (methanol), ammonia, nitrite, and nitrate through a spherical floc and consumption of dissolved oxygen by heterotrophs and autotrophs accurately predicted the dissolved oxygen profile and required adjustment of only one model parameter--the concentration of heterotrophs. A different dissolved oxygen decline pattern was exhibited for the smaller floc particles characterized, with the dissolved oxygen reaching a non-zero plateau toward the center of the floc. This pattern was not reproduced with the mathematical model developed and suggests that additional mechanisms are responsible for the transport of dissolved oxygen into the center of these flocs. Implications of these results regarding the occurrence of simultaneous nitrification and denitrification include consideration of the factors that affect floc size and distribution (simultaneous nitrification and denitrification is maximized with larger floc particles), coupling of the International Water Association (London) activated models to predict activated sludge composition with diffusion models to consider intrafloc effects, and the effects of substrate diffusion on the apparent half-saturation constant for various substrates in activated sludge systems.  相似文献   
177.
Although rewarded bees learn and remember colors and patterns, they have difficulty in learning to avoid negative stimuli such as decorated spider webs spun by Argiope argentata. A. argentata decorates its web with silk patterns that vary unpredictably (Fig. 1) and thus foraging insects that return to sites where spiders are found encounter new visual cues daily. Stingless bees can learn to avoid spider webs but avoidance-learning is slowed or inhibited by daily variation in web decorations (Figs. 3,4; Tables 1,2). In addition, even if bees learn to avoid decorated webs found in one location, they are unable to generalize learned-avoidance responses to similarly decorated webs found at other sites. A. argentata seems to have evolved a foraging behavior that is tied to the ways insects perceive and process information about their environment. Because of the evolutionary importance of bee-flower interdependence, the predatory behavior of web-decorating spiders may be difficult for natural selection to act against.  相似文献   
178.
Mutualistic relationships between ants and aphids are well studied but it is unknown if aphid-attending ants place a greater relative importance on defending aphids from aphid-predators or from competing ant colonies. We tested the hypothesis that aphid-attending ants defend their aphids against aphid-predators more aggressively than against ants from neighboring colonies. We conducted introduction trials by placing an individual non-predatory insect, an aphid-predator, or a foreign conspecific ant on the leaf of a resident ant. We found that ants did not attack non-predatory insects, but did attack competing ants and aphid-predators. When we presented resident ants with both the threats (i.e., predator and competitor) at the same time, residents always attacked potential competitors as opposed to aphid-predators. We suggest this behavior may reduce the likelihood of raids by neighboring colonies. Ants appear to balance both the energetic costs of making an attack and the costs associated with losing aphids to a predator, against the benefits of signaling their defensive ability to rivals and/or preventing rivals from gaining knowledge of a potential food resource.  相似文献   
179.
180.
Nest or roost temperature (T roost) is thought to impact reproductive fitness in many endotherms but few studies have directly tested the hypothesis that naturally occurring variability in nest or roost microclimate is large enough to affect reproductive success. We conducted a field experiment to test whether roost selection by cavity-dwelling, reproductive female big brown bats (Eptesicus fuscus) is more strongly influenced by roost microclimate or a physical characteristic of roosts that facilitates social thermoregulation (i.e., cavity volume). We quantified spatial variability in T roost within different-sized, unoccupied cavities and also recorded T roost in occupied vs unoccupied roost trees. We used equations relating energy use and ambient temperature for big brown bats to calculate values of daily energy expenditure from T roost data because energy is a currency that likely affects reproductive fitness. We found no difference between maximum and minimum T roost, spatial variability in T roost, or predicted energy expenditure in more-preferred vs less-preferred roosts. However, there was a significant difference between T roost and predicted energy expenditure when we compared occupied vs unoccupied roosts. The presence of bats increased T roost by as much as 7°C, and there was a significant positive correlation between the number of bats occupying a roost, maximum daily T roost, and energy savings. We calculate that, on average, a normothermic individual would save about 6.5 kJ/day (roughly 9% of the daily energy budget) by roosting in an occupied cavity relative to roosting alone and that savings may increase to 40 kJ/day (about 53% of the energy budget) for an individual roosting in a group of 45 bats. Our findings suggest that variability in microclimate among potential roost or nest sites may be less important to some cavity-dwelling endotherms than has been suggested in previous studies. Our results reinforce the importance of sociality and social thermoregulation to the roosting ecology of forest-living bats and socially roosting or nesting endotherms in general.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号