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   414篇
  免费   3篇
  国内免费   4篇
安全科学   39篇
废物处理   33篇
环保管理   34篇
综合类   48篇
基础理论   92篇
污染及防治   135篇
评价与监测   26篇
社会与环境   14篇
  2021年   4篇
  2020年   7篇
  2019年   8篇
  2018年   16篇
  2017年   8篇
  2016年   12篇
  2015年   13篇
  2014年   15篇
  2013年   31篇
  2012年   24篇
  2011年   35篇
  2010年   20篇
  2009年   21篇
  2008年   23篇
  2007年   19篇
  2006年   29篇
  2005年   23篇
  2004年   15篇
  2003年   18篇
  2002年   9篇
  2001年   5篇
  2000年   2篇
  1999年   6篇
  1997年   2篇
  1996年   2篇
  1995年   4篇
  1994年   2篇
  1993年   4篇
  1992年   2篇
  1991年   2篇
  1990年   5篇
  1989年   2篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   2篇
  1977年   1篇
  1969年   1篇
  1960年   1篇
  1959年   3篇
  1958年   1篇
  1957年   1篇
  1954年   1篇
  1936年   1篇
排序方式: 共有421条查询结果,搜索用时 171 毫秒
191.
The tendency to aggregate with conspecifics is a common type of social behavior, and interspecific differences in degree of sociality may indicate that evolutionary changes in sociality have been shaped by past selection pressures. A pre-requisite for such evolutionary change is that the behavior in question has an additive genetic basis. I investigated parent-offspring resemblance in two characteristics of sociality (colony size and nearest neighbor distance) in the semi-colonial barn swallow Hirundo rustica. Heritability estimates of these phenotypic characters were statistically significant. Offspring that were transferred to foster nests as part of brood size manipulation or cross-fostering experiments resembled their original parents more than their foster parents with respect to sociality. There was little evidence of phenotypic characteristics of mothers being significantly related to colony size or nearest neighbor distance of their offspring. Maintenance of genetic variation in sociality in this species may be related to the facts that the relationship between reproductive success and colony size differs among years, and that individuals differing in phenotypic quality have different optimal colony sizes.  相似文献   
192.
193.
The utilization of forest residues for bioenergy in Norway is foreseen to increase due to the government call to double bioenergy output by 2020 to thirty Tera-Watt hours. This study focuses on the climate impacts of bioenergy utilization where four forest residue extraction scenarios at clear-cut are considered: i) 75 % above ground residues (branches, (25 %) foliage, tops); ii) 75 % above and below ground residues (branches, tops, (25 %) foliage, stumps, coarse and small roots); iii) extracting 100 % of all available forest residue; and iv) leaving all residues in the forest. The Yasso07 soil-carbon model was utilized to quantify the carbon flux to the atmosphere due to the forest residues that are left in the forest in each scenario. The climate impact potential for each scenario was then calculated for the carbon-flux neutral Norway Spruce (Picea abies) forest system in five regions of Norway. The biogenic carbon dioxide emissions associated to decomposition upon forest floor, procurement losses and bioenergy conversion are included in these calculations. Results suggest that if such bioenergy can directly replace a fossil source of energy, the utilization of this biomass was found to be climatically beneficial in most fossil energy replacement cases and time horizons when compared to leaving the residues in the forest. Integrated global temperature change displacement factors have been developed which have been used to estimate the magnitude of this climate change mitigation over a particular time horizon.  相似文献   
194.
Learning from incidents is considered a very important source for learning and improving safety in the process industries. However, the effectiveness of learning from reported incidents can often be questioned. Therefore, there is a need to be able to evaluate the effectiveness of learning from incidents, and for that purpose we need methods and tools. In this paper, a method is described for evaluating the effectiveness of learning, based on the idea of “level of learning” of the lessons learned. The level of learning is expressed in terms of how broadly the lesson learned is applied geographically, how much organizational learning is involved and how long-lasting the effect of learning is. In the 6-step method, the incidents reported in a typical incident learning system are evaluated both for the actual and the potential level of learning in a semi-quantitative way with different tools. The method was applied in six process industries on a large number of incidents. The method was found to be very useful and to give insights of aspects that influence the learning from incidents.  相似文献   
195.
The occurrence of male pregnancy in the family Syngnathidae (seahorses, pipefishes, and sea dragons) provides an exceptionally fertile system in which to investigate issues related to the evolution of parental care. Here, we take advantage of this unique reproductive system to study the influence of maternal body size on embryo survivorship in the brood pouches of pregnant males of the broad-nosed pipefish, Syngnathus typhle. Males were mated with either two large females, two small females, a large then a small female, or a small then a large female. Our results show that offspring survivorship depends on an interaction between female body size and the number of eggs transferred by the female. Eggs of larger females deposited in large numbers are more likely to result in viable offspring than eggs of smaller females laid in large numbers. However, when females deposited smaller numbers of eggs, the eggs from smaller females were more likely to produce viable offspring compared to those from larger females. We found no evidence that this result was based on mating order, the relative sizes of competing females, or egg characteristics such as dry weight of eggs. Additionally, male body size did not significantly influence the survivorship of offspring during brooding. Our results suggest that the factors underlying offspring survivorship in pipefish may be more complex than previously believed, with multiple factors interacting to determine the fitness of individual offspring within the broods of pregnant males.  相似文献   
196.
This paper presents an approach for inventory compilation and adjustment of double counting in tiered hybrid life cycle inventories (LCIs). The combination of input–output and physical inventory data on coefficient level is a convenient way of constructing a hybrid LCI that has both good detail and completeness. The proposed approach formalizes how to deal with partially overlapping data in inventory compilation. This particular approach requires that the issue of double counting is resolved in a consistent manner. Algorithms for identifying and adjusting for double counting are developed. Identification is performed based on a structural path analysis (SPA). Two algorithms for adjustment are presented. The first method is relatively simple to implement but has limitations to its applicability when performing a detailed assessment. The second method is more complex to implement but provides results that allow for more comprehensive structural inventory analysis. Numerical examples are provided in Appendix.  相似文献   
197.
Hole-nesting habits of redstarts Phoenicurus phoenicurus make laying difficult for parasitic cuckoo Cuculus canorus females and eviction of host eggs difficult for the cuckoo hatchling, causing fitness costs of cuckoo parasitism to be lower than those reported for open nesting hosts. Redstarts have recognition problems when confronted with real cuckoo eggs showing a perfect mimicry with their own eggs since they never eject when parasitized with perfect mimetic cuckoo eggs but instead desert the nest. Here we use a cost-benefit model to assess the effects of parasitism costs and the probability of being parasitized to estimate the reproductive success of redstarts when accepting or rejecting in the presence or absence of parasitism. Baseline data for model calculations come from this and a previous study on a cuckoo parasitized redstart population in Finland. When desertion implies a loss of 50%, we found that below a threshold value of 20% parasitism redstarts should accept cuckoo eggs since the costs of rejection exceed the benefits, whereas above this threshold they should reject. Interestingly, as the cost of desertion increases the threshold value, it should pay the redstart to reject increasingly at an exponential rate. Our field observations on natural parasitism and experiments with artificial cuckoo eggs confirmed the predictions from the model when hatching failures of the cuckoo were taken into account. Therefore, the low cost imposed by cuckoo parasitism in the system, and the presumably high cost of desertion as a response to parasitism favours acceptance over rejection for a wide range of parasitism pressures. This finding could explain the low rejection rate of real cuckoo eggs found in the redstart despite the presumably long history of a coevolutionary relationship with the cuckoo in Finland.  相似文献   
198.
During the last decade, systems analysis has become a more frequently used tool in municipal waste management. This paper investigates how one such analysis, carried out in a Swedish county, was perceived by local municipal officers and politicians as support in the decision-making process. A questionnaire was sent to municipal officers and politicians in local government committees and municipal councils. The respondents considered the most important aspects in evaluating scenarios to be: possibilities for municipal co-operation to minimize cost and negative environmental influence; sound working conditions for refuse disposal personnel; low emissions of greenhouse gases; keeping household economy in mind; and using technologies that are known and reliable. Aspects of relatively low importance were the number of locally generated job opportunities, and minimizing work efforts for the households. The study also showed differences between male and female respondents and between politicians and municipal officers, on how scenarios were valued and on which aspects of the systems analysis were of greatest importance for this valuation. Respondents, on average, were satisfied with the systems analysis, and its usefulness as a decision-support tool. However, more work should be carried out to explain and present the results of the systems analysis to further improve its usefulness.  相似文献   
199.
于2017年在四川省宜宾市采集黑冠夜鹭(Nycticorax nycticorax)卵样30枚(包括9枚无胚卵和21枚胚胎卵),分析了样品中有机氯农药(OCPs)的残留状况.结果表明,宜宾夜鹭卵中检出了8种OCPs残留物,总含量为4.76~97.9 ng·g~(-1)(以湿重计).其中,p,p′-滴滴伊(p,p′-DDE)含量最高((20±18) ng·g~(-1)),其次为六氯苯(HCB,(5.3±3.4) ng·g~(-1))和β-六六六(β-HCH,(1.1±0.8) ng·g~(-1));滴滴涕类(∑DDTs)中的稳定代谢物p,p′-DDE和六六六类(∑HCHs)中的稳定同分异构体β-HCH占比均在99%以上.p,p′-滴滴涕(p,p′-DDT)和p,p′-DDE在无胚卵蛋液中的残留水平比在胚胎卵蛋液中更高一些,而反式九氯则相反,其余OCPs无差别,这说明鹭卵在孵化过程中p,p′-DDT可能易于代谢,而稳定的p,p′-DDE更容易向胚胎传递.宜宾夜鹭卵中p,p′-DDE的最高含量为84 ng·g~(-1),远低于鹭科繁殖效应阈值(1000 ng·g~(-1)).总体上,夜鹭卵中OCPs的赋存状况较好地反映出长江上游地区OCPs污染水平较低,对夜鹭繁殖的影响较小.  相似文献   
200.
Harnessing the economic potential of the oceans is key to combating poverty, enhancing food security, and strengthening economies. But the concomitant risk of intensified resource extraction to migratory species is worrying given these species contribute to important ecological processes, often underpin alternative livelihoods, and are mostly already threatened. We thus sought to quantify the potential conflict between key economic activities (5 fisheries and hydrocarbon exploitation) and sea turtle migration corridors in a region with rapid economic development: southern and eastern Africa. We satellite tracked the movement of 20 loggerhead (Caretta caretta) and 14 leatherback (Dermochelys coriacea) turtles during their postnesting migrations. We used movement‐based kernel density estimation to identify migration corridors for each species. We overlaid these corridors on maps of the distribution and intensity of economic activities, quantified the extent of overlap and threat posed by each activity on each species, and compared the effects of activities. These results were compared with annual bycatch rates in the respective fisheries. Both species’ 3 corridors overlapped most with longline fishing, but the effect was worse for leatherbacks: their bycatch rates of approximately 1500/year were substantial relative to the regional population size of <100 nesting females/annum. This bycatch rate is likely slowing population growth. Artisanal fisheries may be of greater concern for loggerheads than for leatherbacks, but the population appears to be withstanding the high bycatch rates because it is increasing exponentially. The hydrocarbon industry currently has a moderately low impact on both species, but mining in key areas (e.g., Southern Mozambique) may undermine >50 years of conservation, potentially affecting >80% of loggerheads, 33% of the (critically endangered) leatherbacks, and their nesting beaches. We support establishing blue economies (i.e., generating wealth from the ocean), but oceans need to be carefully zoned and responsibly managed in both space and time to achieve economic (resource extraction), ecological (conservation, maintenance of processes), and social (maintenance of alternative livelihood opportunities, alleviate poverty) objectives.  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