全文获取类型
收费全文 | 334篇 |
免费 | 12篇 |
国内免费 | 16篇 |
专业分类
安全科学 | 9篇 |
环保管理 | 50篇 |
综合类 | 49篇 |
基础理论 | 181篇 |
污染及防治 | 29篇 |
评价与监测 | 12篇 |
社会与环境 | 22篇 |
灾害及防治 | 10篇 |
出版年
2023年 | 5篇 |
2022年 | 1篇 |
2021年 | 8篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 13篇 |
2012年 | 4篇 |
2011年 | 36篇 |
2010年 | 23篇 |
2009年 | 43篇 |
2008年 | 35篇 |
2007年 | 24篇 |
2006年 | 17篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 1篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有362条查询结果,搜索用时 31 毫秒
1.
Abstract: The sustainability of seed extraction from natural populations has been questioned recently. Increased recruitment failure under intense seed harvesting suggests that seed extraction intensifies source limitation. Nevertheless, areas where more seeds are collected tend to also have more intense hunting of seed-dispersing animals. We studied whether such hunting, by limiting disperser activity, could cause quantitative dispersal limitation, especially for large crops and for crops in years of high seed abundance. In each of four Carapa procera (Meliaceae) populations in French Guiana and Surinam, two with hunting and two without, we compared seed fate for individual trees varying in crop size in years of high and low population-level seed abundance. Carapa seeds are a nontimber forest product and depend on dispersal by scatter-hoarding rodents for survival and seedling establishment. Hunting negatively affected the proportion of seeds dispersed and caused greater numbers of seeds to germinate or be infested by moths below parent trees, where they would likely die. Hunting of seed-dispersing animals disproportionally affected large seed crops, but we found no additional effect of population-level seed abundance on dispersal rates. Consistently lower rates of seed dispersal, especially for large seed crops, may translate to lower levels of seedling recruitment under hunting. Our results therefore suggest that the subsistence hunting that usually accompanies seed collection is at the cost of seed dispersal and may contribute to recruitment failure of these nontimber forest products. Seed extraction from natural populations may affect seedling recruitment less if accompanied by measures adequately incorporating and protecting seed dispersers. 相似文献
2.
Kristina?D.?RothleyEmail author Charlene?Rae 《Environmental Modeling and Assessment》2005,10(2):107-113
In this paper we apply graph theory in a reserve selection exercise to explore the tradeoffs between maintaining connectivity and minimizing the total area of a protected area network. Rather than focus on a single organism, we used a multi-species approach and looked at the tradeoff curves for organisms with varying dispersal abilities. We first generated the tradeoff curves using a graph-based metric to determine the importance of individual patches for maintaining connectivity. We then performed an analogous set of analyses using patch size as a surrogate measure of importance. 相似文献
3.
The increasing use of the landscape by humans has led to important diminutions of natural surfaces. The remaining patches
of wild habitat are small and isolated from each other among a matrix of inhospitable land-uses. This habitat fragmentation,
by disabling population movements and stopping their spread to new habitats, is a major threat to the survival of numerous
plant and animal species. We developed a general model, adaptable for specific species, capable of identifying suitable habitat
patches within fragmented landscapes and investigating the capacity of populations to move between these patches. This approach
combines GIS analysis of a landscape, with spatial dynamic modeling. Suitable habitat is identified using a threshold area
to perimeter ratio. Potential movement pathways of species between habitat patches are modeled using a cellular automaton.
Habitat connectivity is estimated by overlaying habitat patches with movement pathways. The maximum potential population is
calculated within and between connected habitat patches and potential risk of inbreeding within meta-populations is considered.
The model was tested on a sample map and applied to scenario maps of predicted land-use change in the Peoria Tri-county region
(IL). It (1) showed area of natural area alone was insufficient to estimate the consequences on animal populations; (2) underscored
the necessity to use approaches investigating the effect of land-use change spatially through the landscape and the importance
of considering species-specific life history characteristics; and (3) highlighted the model's potential utility as an indicator
of species likelihood to be affected negatively by land-use scenarios and therefore requiring detailed investigation. 相似文献
4.
朱喜 《环境监测管理与技术》1996,8(5):18-19
监测结果表明,梅梁湖水体TP,TN含量分别为0.1mg/L和3.4mg/L藻类生物量达9-13亿个细胞/L,富营养化相当严重,污染的主要原因,工农业,渔业,畜牧业和生活污水的直接排放,使水全营养盐含量较高,藻类大量繁殖,可采用“控源截汛”,“清除淤泥”,“调水搞活”及生物治理等综合性措施,对梅梁湖的富营养化进行了治理。 相似文献
5.
6.
随着人类环境意识的觉醒与升华,引发了对自身生存环境的更深层次的思考。本文就环境承载力的内涵与外延以及它既会造成贫困又可解脱贫困的关键作用进行了研究和探讨。 相似文献
7.
The adaptive significance of male polymorphism in the acarid mite Caloglyphus berlesei 总被引:5,自引:0,他引:5
Jacek Radwan 《Behavioral ecology and sociobiology》1993,33(3):201-208
Summary Two forms of males occur in the acarid mite, Caloglyphus berlesei. One of them uses its thickened third pair of legs to kill other males; the other, without modified legs, does not attack other males. Previous studies have shown that the form of the male is environmentally determined: fighter males develop only at low population densities and their development can be suppressed by substances emanating from dense colonies. In this study, the duration of development, longevity and virility of the two male morphs were measured. The only significant difference was that fighters had a shorter development time between the two last moults. In another experiment, two groups of colonies were maintained under the same conditions but had different numbers of individuals: small colonies contained 2 fighters and 2 non-fighters, whereas large colonies contained 30 males of each type. The relative reproductive success of both morphs was estimated from numbers of matings. In small colonies, the estimated reproductive success (ERS) was significantly higher for fighters than for non-fighters, mainly because in over 50% of these colonies a single fighter male managed to kill all the rival males and monopolize the females. The opposite was true in large colonies, in which non-fighters achieved significantly higher ERS, mainly because the fighters were killed in fights more often than the non-fighters. This implies that the ratio of costs to benefits obtained by adopting the fighter-male strategy increases with the number of rival males, which may explain conditional male development in C. berlesei. 相似文献
8.
Due to a number of factors outlined in this article, the issue of population growth is excluded from the sustainability discussion. In this article, we explore some of the ethical presumptions that underlie the issues linking population growth and sustainability. Critics argue that action to address population creates social and economic segregation, and portray overpopulation concerns as being “anti-poor,” “anti-developing country,” or even “antihuman.” Yet, de-linking demographic factors from sustainability concerns ignores significant global realities and trends, such as the ecological limits of the Earth, the welfare and long-term livelihood of the most vulnerable groups, future prospects of humanity, as well as the ecosystems that support society. 相似文献
9.
IAN BRECKHEIMER NICK M. HADDAD WILLIAM F. MORRIS ANNE M. TRAINOR WILLIAM R. FIELDS R. TODD JOBE BRIAN R. HUDGENS AARON MOODY JEFFREY R. WALTERS 《Conservation biology》2014,28(6):1584-1593
Conserving or restoring landscape connectivity between patches of breeding habitat is a common strategy to protect threatened species from habitat fragmentation. By managing connectivity for some species, usually charismatic vertebrates, it is often assumed that these species will serve as conservation umbrellas for other species. We tested this assumption by developing a quantitative method to measure overlap in dispersal habitat of 3 threatened species—a bird (the umbrella), a butterfly, and a frog—inhabiting the same fragmented landscape. Dispersal habitat was determined with Circuitscape, which was parameterized with movement data collected for each species. Despite differences in natural history and breeding habitat, we found substantial overlap in the spatial distributions of areas important for dispersal of this suite of taxa. However, the intuitive umbrella species (the bird) did not have the highest overlap with other species in terms of the areas that supported connectivity. Nevertheless, we contend that when there are no irreconcilable differences between the dispersal habitats of species that cohabitate on the landscape, managing for umbrella species can help conserve or restore connectivity simultaneously for multiple threatened species with different habitat requirements. Definición y Evaluación del Concepto de Especie Paraguas para Conservar y Restaurar la Conectividad de Paisajes 相似文献
10.
NICK M. HADDAD LARS A. BRUDVIG ELLEN I. DAMSCHEN DANIEL M. EVANS BRENDA L. JOHNSON DOUGLAS J. LEVEY JOHN L. ORROCK JULIAN RESASCO LAUREN L. SULLIVAN JOSH J. TEWKSBURY STEPHANIE A. WAGNER AIMEE J. WELDON 《Conservation biology》2014,28(5):1178-1187
Despite many studies showing that landscape corridors increase dispersal and species richness for disparate taxa, concerns persist that corridors can have unintended negative effects. In particular, some of the same mechanisms that underlie positive effects of corridors on species of conservation interest may also increase the spread and impact of antagonistic species (e.g., predators and pathogens), foster negative effects of edges, increase invasion by exotic species, increase the spread of unwanted disturbances such as fire, or increase population synchrony and thus reduce persistence. We conducted a literature review and meta‐analysis to evaluate the prevalence of each of these negative effects. We found no evidence that corridors increase unwanted disturbance or non‐native species invasion; however, these have not been well‐studied concerns (1 and 6 studies, respectively). Other effects of corridors were more often studied and yielded inconsistent results; mean effect sizes were indistinguishable from zero. The effect of edges on abundances of target species was as likely to be positive as negative. Corridors were as likely to have no effect on antagonists or population synchrony as they were to increase those negative effects. We found 3 deficiencies in the literature. First, despite studies on how corridors affect predators, there are few studies of related consequences for prey population size and persistence. Second, properly designed studies of negative corridor effects are needed in natural corridors at scales larger than those achievable in experimental systems. Third, studies are needed to test more targeted hypotheses about when corridor‐mediated effects on invasive species or disturbance may be negative for species of management concern. Overall, we found no overarching support for concerns that construction and maintenance of habitat corridors may result in unintended negative consequences. Negative edge effects may be mitigated by widening corridors or softening edges between corridors and the matrix. Other negative effects are relatively small and manageable compared with the large positive effects of facilitating dispersal and increasing diversity of native species. Efectos Negativos Potenciales de los Corredores 相似文献