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   181篇
  免费   16篇
  国内免费   1篇
安全科学   1篇
废物处理   2篇
环保管理   66篇
综合类   11篇
基础理论   92篇
环境理论   1篇
污染及防治   10篇
评价与监测   7篇
社会与环境   6篇
灾害及防治   2篇
  2023年   2篇
  2022年   4篇
  2021年   4篇
  2020年   6篇
  2019年   3篇
  2018年   5篇
  2017年   3篇
  2016年   4篇
  2015年   8篇
  2014年   3篇
  2013年   6篇
  2012年   6篇
  2011年   3篇
  2010年   6篇
  2009年   5篇
  2008年   6篇
  2007年   7篇
  2006年   6篇
  2005年   8篇
  2004年   4篇
  2003年   10篇
  2002年   3篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1998年   8篇
  1997年   4篇
  1996年   5篇
  1995年   3篇
  1994年   6篇
  1993年   1篇
  1992年   1篇
  1991年   2篇
  1990年   2篇
  1989年   11篇
  1988年   7篇
  1987年   4篇
  1986年   2篇
  1984年   1篇
  1983年   1篇
  1982年   4篇
  1981年   2篇
  1980年   3篇
  1979年   2篇
  1975年   2篇
  1970年   1篇
  1968年   1篇
  1962年   1篇
  1957年   3篇
  1955年   2篇
排序方式: 共有198条查询结果,搜索用时 31 毫秒
181.
In avian species whose chicks show facultative siblicide, attacks increase with food deprivation. In species that show obligate siblicide, this causal relationship is not expected, but no test has been made. When we composed artificial pairs of young brown boobies, Sula leucogaster (an obligately siblicidal species), and supplied variable amounts of food to the older nestlings in each pair, food ingestion was related to the most intense form of attack, pushes, which can cause death by expelling the broodmate from the nest. The less food an older nestling ingested, the more time it spent active and the greater its rate and absolute frequency of pushes, and the more often it expelled its nestmate. Hence, deficient food provision to older nestlings could precipitate siblicidal expulsion of broodmates. Younger nestmates were aggressive too, and the more they were pushed and expelled, the more they pecked. Aggression of senior brown-booby broodmates may be flexible and food sensitive in order to optimize the timing of siblicide or to make siblicide weakly facultative.Communicated by R. Gibson  相似文献   
182.
183.
The photodegradation of the herbicides atrazine and ametryn with visible light in aerated neutral aqueous solutions and 5, 10, 15, 20-tetrakis (2,6-dichloro-3-sulfophenyl) porphyrin or 5, 10, 15, 20-tetrakis (4-sulfophenyl) porphyrin as sensitizers are reported for the first time. Our findings show that the degradation percentage reached 30% for atrazine and 63% for ametryn. The final photoproducts were characterized as dealkylated s-triazines. Photolysis of the pesticides in the presence of a singlet oxygen quencher showed only a minor contribution of this type of mechanism, while a bimolecular quenching reaction between the triplet state of the sensitizer and the pesticides is excluded by flash photolysis studies. It is proposed that the mechanism may involve the formation of a superoxide radical anion from the triplet state of the sensitizer and molecular oxygen, followed by a radical decomposition pathway. Selected article from 1st International Meeting on Photochemistry, Photocatalysis and Environmental Applications, Agadir, 2006, organised by Prof. Dr. Ait Ichou, University Ibn Zohr, Agadir, Morocco  相似文献   
184.
The function of hatching asynchrony in the blue-footed booby   总被引:3,自引:0,他引:3  
The blue-footed booby (Sula nebouxii) commonly hatches two eggs 4 days apart; then the senior (first-hatched) chick aggressively dominates the other and sometimes kills it. Two hypotheses explaining the function of the hatching interval were tested by creating broods with synchronous hatching: the facultative brood reduction hypothesis of Lack (1954) and the sibling rivalry reduction hypothesis of Hahn (1981). The results contradicted most predictions of both hypotheses: synchronous broods formed an aggressive hierarchy similarly to asynchronous broods (controls), and subordinate chicks grew poorly (Fig. 1) and died frequently, similarly to junior chicks in control broods. However, compared with synchronous broods, asynchronous broods showed less aggression (Fig. 2), diminished food allocation to subordinate chicks (Fig. 3) and less total food consumption (30% fewer feeds at age 0–10 days). These behavioral comparisons took into account the different ages of chicks in different treatments. The results suggest that natural asynchrony makes brood reduction more efficient and decreases the costs of sibling aggression to parents, in terms of their future survival or fecundity, as proposed by Mock and Ploger (1987). Further, in exaggeratedly asynchronous broods (8-day hatch interval) junior chicks suffered more aggression (Fig. 4) and grew more slowly than junior chicks in control broods. This result supports the hypothesis of optimal hatch asynchrony of Mock and Ploger (1987).  相似文献   
185.
The Nottingham Cycle Friendly Employers Project studied the effectiveness of measures to promote cycling to work by eight large city employers under the 1995 governmentfunded Cycle Challenge. Progress was monitored by 'before' and 'after' surveys, by examination of the measures, and by discussions with the employers. Overall cycling awareness and activity were increased by the project: 42% of employees said their cycle commuting had increased. The main influences, about equally, were providing workplace cycling facilities, a house or job move making cycling more attractive, and heightened awareness of the importance of regular exercise for health. The most welcomed and best used measures were secure cycle parking, showering and changing facilities, and cycle purchase loans.  相似文献   
186.
187.
A number of distinct definitions ofsustainable agriculture have been proposed. In this paper we criticize two such definitions, primarily for conflating sustainability with other objectives such as economic viability and ecological integrity. Finally, we propose and defend a definition which avoids our objections to the other definitions.  相似文献   
188.
Reims was in the direct line of fire throughout the First World War and suffered almost complete destruction. Planning for reconstruction proved controversial and grand designs were only implemented in part, with the help of government funds, important reconstruction cooperatives and American aid. The new Reims involved additional and wider thoroughfares, an enormous array of new public and private buildings in the city centre, and almost a dozen highly distinctive garden suburbs, built by private and municipal housing authorities. By 1926 the city had virtually regained its 1911 population level, but painstaking reconstruction of many historic buildings was not to be completed until well into the 1930s. The architectural legacy of the interwar period, especially that of the Art Deco movement, has been analysed thoroughly and appreciated more positively in recent years.  相似文献   
189.
190.
Large-scale catastrophic events, although rare, lie generally beyond the control of local management and can prevent marine reserves from achieving biodiversity outcomes. We formulate a new conservation planning problem that aims to minimize the probability of missing conservation targets as a result of catastrophic events. To illustrate this approach we formulate and solve the problem of minimizing the impact of large-scale coral bleaching events on a reserve system for the Great Barrier Reef, Australia. We show that by considering the threat of catastrophic events as part of the reserve design problem it is possible to substantially improve the likely persistence of conservation features within reserve networks for a negligible increase in cost. In the case of the Great Barrier Reef, a 2% increase in overall reserve cost was enough to improve the long-run performance of our reserve network by >60%. Our results also demonstrate that simply aiming to protect the reefs at lowest risk of catastrophic bleaching does not necessarily lead to the best conservation outcomes, and enormous gains in overall persistence can be made by removing the requirement to represent all bioregions in the reserve network. We provide an explicit and well-defined method that allows the probability of catastrophic disturbances to be included in the site selection problem without creating additional conservation targets or imposing arbitrary presence/absence thresholds on existing data. This research has implications for reserve design in a changing climate.  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