全文获取类型
收费全文 | 983篇 |
免费 | 33篇 |
国内免费 | 8篇 |
专业分类
安全科学 | 56篇 |
废物处理 | 45篇 |
环保管理 | 257篇 |
综合类 | 85篇 |
基础理论 | 260篇 |
环境理论 | 3篇 |
污染及防治 | 206篇 |
评价与监测 | 68篇 |
社会与环境 | 35篇 |
灾害及防治 | 9篇 |
出版年
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 16篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 31篇 |
2015年 | 31篇 |
2014年 | 26篇 |
2013年 | 63篇 |
2012年 | 59篇 |
2011年 | 59篇 |
2010年 | 40篇 |
2009年 | 61篇 |
2008年 | 69篇 |
2007年 | 59篇 |
2006年 | 57篇 |
2005年 | 32篇 |
2004年 | 43篇 |
2003年 | 39篇 |
2002年 | 37篇 |
2001年 | 9篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 18篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有1024条查询结果,搜索用时 281 毫秒
961.
Nadon MO Baum JK Williams ID McPherson JM Zgliczynski BJ Richards BL Schroeder RE Brainard RE 《Conservation biology》2012,26(3):493-503
Sharks and other large predators are scarce on most coral reefs, but studies of their historical ecology provide qualitative evidence that predators were once numerous in these ecosystems. Quantifying density of sharks in the absence of humans (baseline) is, however, hindered by a paucity of pertinent time-series data. Recently researchers have used underwater visual surveys, primarily of limited spatial extent or nonstandard design, to infer negative associations between reef shark abundance and human populations. We analyzed data from 1607 towed-diver surveys (>1 ha transects surveyed by observers towed behind a boat) conducted at 46 reefs in the central-western Pacific Ocean, reefs that included some of the world's most pristine coral reefs. Estimates of shark density from towed-diver surveys were substantially lower (<10%) than published estimates from surveys along small transects (<0.02 ha), which is not consistent with inverted biomass pyramids (predator biomass greater than prey biomass) reported by other researchers for pristine reefs. We examined the relation between the density of reef sharks observed in towed-diver surveys and human population in models that accounted for the influence of oceanic primary productivity, sea surface temperature, reef area, and reef physical complexity. We used these models to estimate the density of sharks in the absence of humans. Densities of gray reef sharks (Carcharhinus amblyrhynchos), whitetip reef sharks (Triaenodon obesus), and the group "all reef sharks" increased substantially as human population decreased and as primary productivity and minimum sea surface temperature (or reef area, which was highly correlated with temperature) increased. Simulated baseline densities of reef sharks under the absence of humans were 1.1-2.4/ha for the main Hawaiian Islands, 1.2-2.4/ha for inhabited islands of American Samoa, and 0.9-2.1/ha for inhabited islands in the Mariana Archipelago, which suggests that density of reef sharks has declined to 3-10% of baseline levels in these areas. 相似文献
962.
Plants are expected to differentially allocate resources to reproduction, growth, and survival in order to maximize overall fitness. Life history theory predicts that the allocation of resources to reproduction should occur at the expense of vegetative growth. Although it is known that both organism size and resource availability can influence life history traits, few studies have addressed how size dependencies of growth and reproduction and variation in resource supply jointly affect the coupling between growth and reproduction. In order to understand the relationship between growth and reproduction in the context of resource variability, we utilize a long-term observational data set consisting of 670 individual trees over a 10-year period within a local population of Bursera simaruba (L.) Sarg. We (1) quantify the functional form and variability in the growth-reproduction relationship at the population and individual-tree level and (2) develop a theoretical framework to understand the allometric dependence of growth and reproduction. Our findings suggest that the differential responses of allometric growth and reproduction to resource availability, both between years and between microsites, underlie the apparent relationship between growth and reproduction. Finally, we offer an alternative approach for quantifying the relationship between growth and reproduction that accounts for variation in allometries. 相似文献
963.
Current taxonomy indicates a single global species of the Great Barracuda (Sphyraena barracuda) despite differences in color and behavior between Atlantic and Pacific forms. To investigate these differences and qualify
the dispersal characteristics of this unique coastal–pelagic teleost (bony fish), we conducted a global phylogeographic survey
of 246 specimens from thirteen sampling locations using a 629-base pair fragment of mtDNA cytochrome b. Data indicate high overall gene flow in the Indo-Pacific over large distances (>16,500 km) bridging several biogeographic
barriers. The West Atlantic population contains an mtDNA lineage that is divergent from the Indo-Pacific (d = 1.9%), while the East Atlantic (N = 23) has two mutations (d = 0.6%) apart from the Indo-Pacific. While we cannot rule out distinct evolutionary partitions among ocean basins based on
behavior, coloration, and near-monophyly between Atlantic and Indo-Pacific subpopulations, more investigation is required
before taxonomic status is revised. Overall, the pattern of high global dispersal and connectivity in S. barracuda more closely resembles those reported for large oceanic predators than reef-associated teleosts. 相似文献
964.
Predicting spread is a central goal of invasion ecology. Within marine systems, researchers have increasingly made use of
oceanographic circulation models to estimate currents and track species dispersal. However, the accuracy of these models for
predicting biological patterns, particularly for non-native species, has generally not been validated. Particularly, we wished
to examine the ability of models to predict physical and biological processes, which jointly determine the spread of marine
larval organisms. We conducted two empirical studies—a recruitment study and a drift card study—along the coast of New England,
USA, focusing on two invaders of concern—the European green crab (Carcinus maenas) and the Asian shore crab (Hemigrapsus sanguineus), to explicitly evaluate the ability of oceanographic models to predict patterns of spread. We used data from the large-scale
drift card study to validate our ability to capture dispersal patterns driven purely by physical processes. Next, we conducted
a recruitment study to evaluate our ability to reproduce patterns of biological dispersal. We were generally capable of reproducing
drift cards patterns—suggesting that the physical mechanics in the model were predictive. However, predicted biological patterns
were inconsistent—we were able to predict dispersal patterns for H. sanguineus but not for C. maenas. Our results highlight the importance of validating models and suggest that more work is necessary before we can reliably
use oceanographic models to predict biological spread of intertidal organisms. 相似文献
965.
We tested for unintended mercury contamination problems associated with estuarine floodplain restoration projects of the Louisiana coastal zone, USA. Barataria Bay and Breton Sound are two neighboring deltaic estuaries that were isolated by levees from the Mississippi River about 100 years ago. These estuaries recently have been reconnected to the nutrient-rich Mississippi River, starting major river diversion (input) flows in 1991 for Breton Sound and in 2004 for Barataria Bay. We collected > 2100 fish over five years from 20 stations in these estuaries to test two hypotheses about Hg bioaccumulation: (H1) Background Hg bioaccumulation in fish would be highest in low-salinity upper reaches of estuaries, and (H2) recent river inputs to these upper estuarine areas would increase Hg bioaccumulation in fish food webs. For H1, we surveyed fish Hg concentrations at several stations along a salinity gradient in Barataria Bay in 2003-2004, a time when this estuary lacked strong river inputs. Results showed that average Hg concentrations in fish communities were lowest (150 ng/g dry mass) in higher salinity areas and -2.4x higher (350 ng/g) in low-salinity oligohaline and freshwater upper reaches of the estuary. For H2, we tested for enhanced Hg bioaccumulation following diversion onset in both estuaries. Fish communities from Breton Sound that had long-term (> 10 years) diversion inputs had -1.7x higher average Hg contents of 610 ng/g Hg vs. 350 ng/g background values. Shorter-term diversion inputs over 2-3 years in upper Barataria Bay did not result in strong Hg enrichments or stable C isotope increases seen in Breton Sound, even though N and S stable-isotope values indicated strong river inputs in both estuaries. It may be that epiphyte communities on abundant submerged aquatic vegetation (SAV) are important hotspots for Hg cycling in these estuaries, and observed lesser development of these epiphyte communities in upper Barataria Bay during the first years of diversion inputs may account for the lessened Hg bioaccumulation in fish. A management consideration from this study is that river restoration projects may unintentionally fertilize SAV and epiphyte-based food webs, leading to higher Hg bioaccumulation in river-impacted floodplains and their food webs. 相似文献
966.
How complex do models need to be to predict dispersal of threatened species through matrix habitats?
Hudgens BR Morris WF Haddad NM Fields WR Wilson JW Kuefler D Jobe T 《Ecological applications》2012,22(5):1701-1710
Persistence of species in fragmented landscapes depends on dispersal among suitable breeding sites, and dispersal is often influenced by the "matrix" habitats that lie between breeding sites. However, measuring effects of different matrix habitats on movement and incorporating those differences into spatially explicit models to predict dispersal is costly in terms of time and financial resources. Hence a key question for conservation managers is: Do more costly, complex movement models yield more accurate dispersal predictions? We compared the abilities of a range of movement models, from simple to complex, to predict the dispersal of an endangered butterfly, the Saint Francis' satyr (Neonympha mitchellii francisci). The value of more complex models differed depending on how value was assessed. Although the most complex model, based on detailed movement behaviors, best predicted observed dispersal rates, it was only slightly better than the simplest model, which was based solely on distance between sites. Consequently, a parsimony approach using information criteria favors the simplest model we examined. However, when we applied the models to a larger landscape that included proposed habitat restoration sites, in which the composition of the matrix was different than the matrix surrounding extant breeding sites, the simplest model failed to identify a potentially important dispersal barrier, open habitat that butterflies rarely enter, which may completely isolate some of the proposed restoration sites from other breeding sites. Finally, we found that, although the gain in predicting dispersal with increasing model complexity was small, so was the increase in financial cost. Furthermore, a greater fit continued to accrue with greater financial cost, and more complex models made substantially different predictions than simple models when applied to a novel landscape in which butterflies are to be reintroduced to bolster their populations. This suggests that more complex models might be justifiable on financial grounds. Our results caution against a pure parsimony approach to deciding how complex movement models need to be to accurately predict dispersal through the matrix, especially if the models are to be applied to novel or modified landscapes. 相似文献
967.
Susan L. Balenger L. Scott Johnson Brian S. Masters 《Behavioral ecology and sociobiology》2009,63(3):403-411
Ornamental traits are thought to evolve because they give individuals an advantage in securing multiple mates. Thus, the presence
of ornamentation among males in many monogamous bird species presents something of a conundrum. Under certain conditions,
extra-pair paternity can increase the variance in reproductive success among males, thus increasing the potential for sexual
selection to act. We addressed this possibility in the mountain bluebird (Sialia currucoides), a socially monogamous songbird in which males possess brilliant ultraviolet (UV)-blue plumage. Specifically, we asked whether
a male’s success at siring offspring within his own nest and within the nests of other males was related to his coloration.
In pairwise comparisons, males that sired extra-pair offspring were not more colorful than the males that they cuckolded.
However, males that sired at least one extra-pair offspring were, on average, brighter and more UV-blue than males that did
not sire extra-pair offspring. Brighter, more UV-blue males sired more offspring both with their own mate and tended to sire
more offspring with extra-pair mates and thus sired more offspring overall. Our results support the hypothesis that the brilliant
UV-blue ornamental plumage of male mountain bluebirds evolved at least in part because it provides males with an advantage
in fertilizing the eggs of multiple females. 相似文献
968.
Despite the important roles played by parasites in local population dynamics and community structure of marine ecosystems,
there is a lack of information on the geographical variation in infection levels displayed by particular host–parasite species
combinations. This study examines geographical variation in infection levels by the metacercarial stages of trematode parasites
in crustacean and bivalve second intermediate hosts. Analyses were based on a dataset compiled from the literature, consisting
of 164 local samples representing 49 host–parasite species pairs for crustaceans, and 338 entries representing 36 host–parasite
species pairs for bivalves. The analyses indicate that for all measures of infection levels [prevalence (percentage of individuals
infected), intensity (mean no. of metacercariae per infected individual), abundance (mean no. of metacercariae across all
individuals in a sample)], there was statistically significant repeatability of infection values within host–parasite species
pairs. However, it is only for values of intensity and abundance of infection in crustacean hosts that the repeatability was
strong; this suggests that infection levels are specific properties of crustacean–trematode species pairs, showing significant
consistency across localities despite spatial variation in abiotic and biotic conditions. Although the magnitude of variation
in infection levels within parasite species pairs (measured as coefficients of variation) was independent of scale in crustacean
hosts, infection levels in bivalves increased in variability at large (>100 km) spatial scales. These results suggest that
there is a considerable geographical consistency in parasite load, especially in crustacean hosts, which should lead to consistent
ecological and ecosystem effects of marine trematodes.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
969.
Maria de Lourdes Melo Zurita Brian Cook Dana C. Thomsen Paul G. Munro Timothy F. Smith John Gallina 《Disasters》2018,42(3):571-589
This paper explores how social networks and bonds within and across organisations shape disaster operations and strategies. Local government disaster training exercises serve as a window through which to view these relations, and ‘social capital’ is used as an analytic for making sense of the human relations at the core of disaster management operations. These elements help to expose and substantiate the often intangible relations that compose the culture that exists, and that is shaped by preparations for disasters. The study reveals how this social capital has been generated through personal interactions, which are shared among disaster managers across different organisations and across ‘levels’ within those organisations. Recognition of these ‘group resources’ has significant implications for disaster management in which conducive social relations have become paramount. The paper concludes that socio‐cultural relations, as well as a people‐centred approach to preparations, appear to be effective means of readying for, and ultimately responding to, disasters. 相似文献
970.
Recent years have witnessed the growth of new information technologies and their applications to various disciplines. The
goal of this paper is to demonstrate how the two innovative methods, upper level set scan (ULS) hotspot detection and the
multicriteria prioritization scheme, facilitate population health and break new ground in public health surveillance. It is
believed that the social environment (i.e. social conditions and social capital) is one of the determinants of human health.
Using infant health data and 10 additional indicators of social environment in the 159 counties of Georgia, ULS identified
52 counties that are in double jeopardy (high infant mortality and a high rate of low infant birth weight). The multicriteria
ranking scheme suggested that there was no conspicuous spatial cluster of ranking orders, which improved the traditional decision
making by visual geographic cluster. Both hotspot detection and ranking methods provided an empirical basis for re-allocating
limited resources and several policy implications could be drawn from these analytic results. 相似文献