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271.
Summary. The furoquinoline alkaloids skimmianine and dictamnine were tested for effects on the feeding and growth of larvae of the
generalist lepidopteran, Spodoptera litura. Skimmianine was further investigated for toxic and phototoxic effects on the larvae of Trichoplusia ni, also a generalist species. In feeding experiments with S. litura, growth and consumption of larvae decreased with increasing concentration of furoquinolines; skimmianine caused a greater
reduction in growth than dictamnine. In T. ni, dietary skimmianine reduced growth and consumption; when administered topically, it significantly reduced consumption but
without a concomitant reduction in growth. Phototoxicity of skimmianine was not apparent in T. ni because UV light failed to increase the negative effects of the alkaloid on larvae. 相似文献
272.
Summary The songs of two species of wrens, Thryothorus sinaloa and T. felix, are less similar than previously believed. We have found that song structure, bout patterning, and other aspects of singing behavior are widely divergent between the two species, which are sympatric over much of their ranges. The nature of these differences supports the hypothesis of contrast reinforcement in bird song. Further evidence is provided by essentially parallel differences in another pair of sympatric species, T. pleurostictus and T. maculipectus. A cluster analysis of song form of the above four species plus one other, T. ludovicianus, suggests that those species which are allopatric are the most similar in song form, while sympatric species are the most dissimilar. We relate various features of singing behavior in the two species to some aspects to their ecology, and examine relationships among various song parameters within the genus Thryothorus. The parallel differences in pairs of sympatric Thryothorus in structure of song units, temporal organization of song, and duetting, along with the close correlation of groups of song parameters in the five species of Thryothorus leads us to propose that strategies or adaptive complexes of singing characteristics may exist in the genus. 相似文献
273.
Craig A. Walling Nick J. Royle Neil B. Metcalfe Jan Lindström 《Behavioral ecology and sociobiology》2007,61(7):1007-1014
It is well documented that poor early nutrition can have profound negative effects on adult life-history traits. However,
it has also been demonstrated that organisms can undergo compensatory resource allocation strategies (such as an accelerated
growth rate) if food availability improves, so as to mitigate the effects of the poor early conditions. Previous research
has indicated that elevated growth rates can incur costs in the longer term, such as an increased rate of senescence and shorter
lifespan. We tested whether a phase of compensatory growth after a period of reduced food availability earlier in life affected
the sexual attractiveness of adult male green swordtails Xiphophorus helleri, a species in which it has previously been documented that females prefer larger-bodied and longer-tailed males. The experiment
compared the attractiveness of size-matched brothers that had experienced contrasting growth trajectories as juveniles; the
experiments were initially conducted in the middle of a male’s sexually reproductive life and were then repeated towards the
very end of life. At both ages, males that had undergone compensatory growth were equally as attractive as their brothers
that had grown normally. These results suggest that the growth compensation benefits males through an increase in their attractiveness
over that which they would have had if they had remained on their original growth trajectory. The lack of change in relative
attractiveness with age indicates that the compensation does not cause greater deterioration in secondary sexual characters
at older ages than in continuously well-fed males. 相似文献
274.
The historical record of PAH, PCB, trace metal and fly-ash particle deposition at a remote lake in north-west Scotland 总被引:4,自引:0,他引:4
Sediment cores taken from the deep basin of Loch Coire nan Arr in north-west Scotland were dated using 210Pb calibrated spheroidal carbonaceous particle (SCP) profiles and analysed for trace metals, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). These data show that the site is one of the least contaminated by atmospheric pollution in the UK. Peak concentrations of PAHs were found to be equivalent to background values at sites in the English Lake District. The date of concentration maxima for SCP, PCB and some metals were in agreement with previously published polychlorinated dibenzo-p-dioxin/polychlorinated dibenzofuran (PCDD/F) data suggesting long-range industrial sources. The date of individual PAH concentration maxima were earlier, but concomitant with each other, possibly suggesting the influence of a local source. Comparison with remote European mountain lakes shows Loch Coire nan Arr to be one of the least contaminated sites in Europe with respect to PCBs, but more contaminated with respect to PAHs. 相似文献
275.
Dickey CA Heal KV Cape JN Stidson RT Reeves NM Heal MR 《Journal of environmental monitoring : JEM》2005,7(2):137-144
Soil is an important compartment in the environmental cycling of trichloroacetic acid (TCA), but soil TCA concentration is a methodologically defined quantity; analytical methods either quantify TCA in an aqueous extract of the soil, or thermally decarboxylate TCA to chloroform in the whole soil sample. The former may underestimate the total soil TCA, whereas the latter may overestimate TCA if other soil components (e.g. humic material) liberate chloroform under the decarboxylation conditions. The aim of this work was to show that extraction and decarboxylation methods yield different TCA concentrations because the decarboxylation method can also determine "bound" TCA. Experiments with commercial humic acid solutions showed there was no additional chloroform formation under decarboxylation conditions, and that all TCA in a TCA-humic acid mixture could be quantitatively determined (108 +/- 13%). Anion exchange resin was used as a provider of solid-phase TCA binding; only 5 +/- 1% of a TCA solution mixed with the resin was present in the aqueous extract subsequently separated from the resin, yet the decarboxylation method yielded mass balance (123 +/- 22%) with TCA remaining in the resin. In aqueous extraction of a range of soil samples (with or without added TCA spike), the decarboxylation method was able to satisfactorily account for TCA in the extractant + residue post-extraction, compared with whole-soil TCA (+ spike) pre-extraction: e.g. mass balances for unspiked soil from Sikta spruce and larch forest were 99 +/- 8% and 93 +/- 6%, respectively, and for TCA-spiked forest and agricultural soils were 114 +/- 13% and 102 +/- 2%. In each case recovery of TCA in the extractant was substantially less than 100%(<20% for unspiked soils, <55% for spiked soils). Extraction efficiencies were generally lower in more organic soils. The results suggest that analytical methods which utilise aqueous extraction may underestimate whole-soil TCA concentrations. Application of both methodologies together may enhance insight into TCA behaviour in soil. 相似文献
276.
277.
Adger W. Neil Kelly P. Mick 《Mitigation and Adaptation Strategies for Global Change》1999,4(3-4):253-266
The objective of this paper is to outline a conceptual model of vulnerability to climate change as the first step in appraising and understanding the social and economic processes which facilitate and constrain adaptation. Vulnerability as defined here pertains to individuals and social groups. It is the state of individuals, of groups, of communities defined in terms of their ability to cope with and adapt to any external stress placed on their livelihoods and well-being. This proposed approach puts the social and economic well-being of society at the centre of the analysis, thereby reversing the central focus of approaches to climate impact assessment based on impacts on and the adaptability of natural resources or ecosystems and which only subsequently address consequences for human well-being. The vulnerability or security of any group is determined by the availability of resources and, crucially, by the entitlement of individuals and groups to call on these resources. This perspective extends the concept of entitlements developed within neo-classical and institutional economics. Within this conceptual framework, vulnerability can be seen as a socially-constructed phenomenon influenced by institutional and economic dynamics. The study develops proxy indicators of vulnerability related to the structure of economic relations and the entitlements which govern them, and shows how these can be applied to a District in coastal lowland Vietnam. This paper outlines the lessons of such an approach to social vulnerability for the assessment of climate change at the global scale. We argue that the socio-economic and biophysical processes that determine vulnerability are manifest at the local, national, regional and global level but that the state of vulnerability itself is associated with a specific population. Aggregation from one level to another is therefore not appropriate and global-scale analysis is meaningful only in so far as it deals with the vulnerability of the global community itself. 相似文献
278.
David J. H. Brock David Bedgood Caroline Hayward Neil J. Carbarns Christine Gosden 《黑龙江环境通报》1984,4(4):261-266
Measurement of the microvillar enzymes, γ-glutamyltranspeptidase (GGTP), aminopeptidase M (APM) and alkaline phosphatase (ALP), in amniotic fluid supernatant has been proposed as a method for the early prenatal diagnosis of cystic fibrosis. The activities of these enzymes in a series of other fetal abnormalities have now been examined. GGTP activities were below the 5th percentile in 28 out of 54 cases of trisomy 21 and 9 of 14 cases of trisomy 18, while APM values were below this cut-off in 26 of 54 cases of trisomy 21 and 8 of 14 cases of trisomy 18. Abnormal ALP isoenzyme ratios were found in 6 of 54 cases of trisomy 21 and 4 of 14 cases of trisomy 18. If prenatal cytogenetic studies are routinely carried out on amniotic fluid cells, the occasional confounding effect of abnormal microvillar enzymes associated with fetal trisomies rather than with cystic fibrosis should be avoided. 相似文献
279.
The potential damages of climate change and climate variability are dependent upon the responses or adaptations that people make to their changing environment. By adapting the management of resources, the mix and methods of producing goods and services, choices of leisure activities, and other behavior, people can lessen the damages that would otherwise result. A framework for assessing the benefits and costs of adaptation to both climate change and climate variability is described in the paper. The framework is also suitable for evaluating the economic welfare effects of climate change, allowing for autonomous adaptation by private agents. The paper also briefly addresses complications introduced by uncertainty regarding the benefits of adaptation and irreversibility of investments in adaptation. When investment costs are irreversible and there is uncertainty about benefits, the usual net present value criterion for evaluating the investment gives the wrong decision. If delaying an adaptation project is possible, and if delay will permit learning about future benefits of adaptation, it may be preferable to delay the project even if the expected net present value is positive. Implications of this result for adaptation policy are discussed in the paper. 相似文献
280.
Viorel?BlujdeaEmail author David?Neil?Bird Gerald?Kapp Martin?Burian Ilie?Silvestru?Nuta Liviu?Ciuvat 《Mitigation and Adaptation Strategies for Global Change》2011,16(4):463-476
Initiatives for reducing anthropogenic greenhouse gas emissions from deforestation and degradation require transparent and
robust methodologies for the estimation of emissions reduction or removal. Although carbon (C) stock change in degradation
and devegetation by remote sensing are becoming increasingly powerful, the drivers of degradation, wood collection and harvest
dynamics, cannot be understood without “on the ground” sampling. A methodological tool for the quantitative and qualitative
analysis of forest degradation is proposed as developed based on a research on the stump history in the black locust degrading
stands sampled in southwest Romania. Based on the survey of stumps, the cutting regime and wood extraction is determined over
a past period of some 15 years. Stump age classification comprises multiple qualitative criteria (i.e. bark features; adherence
of sprouts; cut edge features; etc.). The method allows for a quantitative assessment of wood removal over time, and is suitable
for the development of a dynamic baseline and monitoring of degradation avoidance activities. 相似文献