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排序方式: 共有356条查询结果,搜索用时 31 毫秒
331.
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J L Moore S M Howden G M McKeon J O Carter J C Scanlan 《Environment international》2001,27(2-3):147-153
This study outlines the development of an approach to evaluate the sources, sinks, and magnitudes of greenhouse gas emissions from a grazed semiarid rangeland dominated by mulga (Acacia aneura) and how these emissions may be altered by changes in management. This paper describes the modification of an existing pasture production model (GRASP) to include a gas emission component and a dynamic tree growth and population model. An exploratory study was completed to investigate the likely impact of changes in burning practices and stock management on emissions. This study indicates that there is a fundamental conflict between maintaining agricultural productivity and reducing greenhouse gas emissions on a given unit of land. Greater agricultural productivity is allied with the system being an emissions source while production declines and the system becomes a net emissions sink as mulga density increases. Effective management for sheep production results in the system acting as a net source (approximately 60-200 kg CO2 equivalents/ha/year). The magnitude of the source depends on the management strategies used to maintain the productivity of the system and is largely determined by starting density and average density of the mulga over the simulation period. Prior to European settlement, it is believed that the mulga lands were burnt almost annually. Simulations indicate that such a management approach results in the system acting as a small net sink with an average net absorption of greenhouse gases of 14 kg CO2 equivalents/ha/year through minimal growth of mulga stands. In contrast, the suppression of fire and the introduction of grazing results in thickening of mulga stands and the system can act as a significant net sink absorbing an average of 1000 kg CO2 equivalents/ha/year. Although dense mulga will render the land largely useless for grazing, land in this region is relatively inexpensive and could possibly be developed as a cost-effective carbon offset for greenhouse gas emissions elsewhere. These results also provide support for the hypothesis that changes in land management, and particularly, suppression of fire is chiefly responsible for the observed increases in mulga density over the past century. 相似文献
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335.
Food availability and physiological state of sea urchin larvae (<Emphasis Type="Italic">Strongylocentrotus purpuratus</Emphasis>) 总被引:2,自引:2,他引:0
Food availability is highly variable in the ocean. Many species of marine invertebrates have a larval form that depends upon
exogenous nutrients for growth, yet there are few biochemical and physiological indices for determining changes in the nutritional
status of larvae. In this study, the effects of food availability on biochemical compositions and metabolic processes of larvae
of the sea urchin, Strongylocentrotus purpuratus, were determined. Larvae were cultured under different food concentrations (fed-to-excess and unfed) and a suite of biological
processes assayed, ranging from measurements at the level of the whole organism to that of specific molecules. These data
were normalized to DNA content (an index of cell number) to allow comparisons of physiological rates in larvae of different
sizes. Changes in the following were measured during larval growth: free amino acid pool, protein, lipid classes (cholesterol,
free fatty acids, hydrocarbons, phospholipids, triacylglycerol), enzyme activities (Na+, K+-ATPase and citrate synthase), and respiration rates. In growing larvae, the two key components that showed differential cell-specific
content relative to unfed larvae were glycine in the free amino acid pool and phospholipids. Additionally, several lipid classes
were detectable only in fed larvae (cholesterols, free fatty acids, and hydrocarbons). While triacylglycerols were present
in eggs and utilized during pre-feeding development, they were not re-accumulated at detectable levels in feeding larvae.
Respiration rates, protein content, and enzyme activities were all similar on a cell-specific basis, showing that these variables
did not provide useful indices of differences in physiological state between fed and unfed larvae. In contrast, measurements
of the cell-specific content of glycine and certain lipid classes did provide useful indices of physiological state of larvae.
Application of these indices could potentially allow for determinations of nutritional state of larvae in the ocean. 相似文献
336.
Mohamed E Sarhan Richard E Howitt Charles V Moore 《Journal of Environmental Economics and Management》1979,6(1):69-84
A simultaneous equation model of the behavior of a mosquito abatement district based on biological and economic data is presented. Results indicate high long term costs if heavy reliance on chemical pesticide control methods continue, due to a pesticide resistance buildup in the mosquito populations. Physical source reduction methods were shown to be more efficient both in the short and long run. A linear programming model is presented which optimizes the inix of chemical and physical control methods. Results indicate increasing costs of mosquito abatement as pesticide effectiveness declines. 相似文献
337.
Wesley M. Knapp Anne Frances Reed Noss Robert F. C. Naczi Alan Weakley George D. Gann Bruce G. Baldwin James Miller Patrick McIntyre Brent D. Mishler Gerry Moore Richard G. Olmstead Anna Strong Kathryn Kennedy Bonnie Heidel Daniel Gluesenkamp 《Conservation biology》2021,35(1):360-368
Extinction rates are expected to increase during the Anthropocene. Current extinction rates of plants and many animals remain unknown. We quantified extinctions among the vascular flora of the continental United States and Canada since European settlement. We compiled data on apparently extinct species by querying plant conservation databases, searching the literature, and vetting the resulting list with botanical experts. Because taxonomic opinion varies widely, we developed an index of taxonomic uncertainty (ITU). The ITU ranges from A to F, with A indicating unanimous taxonomic recognition and F indicating taxonomic recognition by only a single author. The ITU allowed us to rigorously evaluate extinction rates. Our data suggest that 51 species and 14 infraspecific taxa, representing 33 families and 49 genera of vascular plants, have become extinct in our study area since European settlement. Seven of these taxa exist in cultivation but are extinct in the wild. Most extinctions occurred in the west, but this outcome may reflect the timing of botanical exploration relative to settlement. Sixty-four percent of extinct plants were single-site endemics, and many occurred outside recognized biodiversity hotspots. Given the paucity of plant surveys in many areas, particularly prior to European settlement, the actual extinction rate of vascular plants is undoubtedly much higher than indicated here. 相似文献
338.
Nathalie Hilmi Denis Allemand Sam Dupont Alain Safa Gunnar Haraldsson Paulo A. L. D. Nunes Chris Moore Caroline Hattam Stéphanie Reynaud Jason M. Hall-Spencer Maoz Fine Carol Turley Ross Jeffree James Orr Philip L. Munday Sarah R. Cooley 《Marine Biology》2013,160(8):1773-1787
Ocean acidification is increasingly recognized as a component of global change that could have a wide range of impacts on marine organisms, the ecosystems they live in, and the goods and services they provide humankind. Assessment of these potential socio-economic impacts requires integrated efforts between biologists, chemists, oceanographers, economists and social scientists. But because ocean acidification is a new research area, significant knowledge gaps are preventing economists from estimating its welfare impacts. For instance, economic data on the impact of ocean acidification on significant markets such as fisheries, aquaculture and tourism are very limited (if not non-existent), and non-market valuation studies on this topic are not yet available. Our paper summarizes the current understanding of future OA impacts and sets out what further information is required for economists to assess socio-economic impacts of ocean acidification. Our aim is to provide clear directions for multidisciplinary collaborative research. 相似文献
339.
Battaleb-Looie S Moore F Jacks G Ketabdari MR 《Environmental geochemistry and health》2012,34(5):641-650
The present study is the first attempt to put forward possible source(s) of fluoride in the Dashtestan area, Bushehr Province, southern Iran. In response to reports on the high incidence of dental fluorosis, 35 surface and groundwater samples were collected and analysed for fluoride. The results indicate that dissolved fluoride in the study area is above the maximum permissible limit recommended by the World Health Organization (WHO). An additional 35 soil and rock samples were also collected and analysed for fluoride, and rock samples were subjected to petrographic investigations and X-ray diffraction. The results of these analyses show that the most likely source for fluoride in the groundwater is from clay minerals (chlorite) and micas (muscovite, sericite, and biotite) in the soils and rocks in the area. We also note that due to the high average temperatures all year round and excessive water consumption in the area, the optimum fluoride dose level should be lower than that recommended by the WHO. 相似文献
340.
Using the functional response of a consumer to predict biotic resistance to invasive prey 总被引:1,自引:0,他引:1
Predators sometimes provide biotic resistance against invasions by nonnative prey. Understanding and predicting the strength of biotic resistance remains a key challenge in invasion biology. A predator's functional response to nonnative prey may predict whether a predator can provide biotic resistance against nonnative prey at different prey densities. Surprisingly, functional responses have not been used to make quantitative predictions about biotic resistance. We parameterized the functional response of signal crayfish (Pacifastacus leniusculus) to invasive New Zealand mud snails (Potamopyrgus antipodarum; NZMS) and used this functional response and a simple model of NZMS population growth to predict the probability of biotic resistance at different predator and prey densities. Signal crayfish were effective predators of NZMS, consuming more than 900 NZMS per predator in a 12-h period, and Bayesian model fitting indicated their consumption rate followed a type 3 functional response to NZMS density. Based on this functional response and associated parameter uncertainty, we predict that NZMS will be able to invade new systems at low crayfish densities (< 0.2 crayfish/m2) regardless of NZMS density. At intermediate to high crayfish densities (> 0.2 crayfish/m2), we predict that low densities of NZMS will be able to establish in new communities; however, once NZMS reach a threshold density of -2000 NZMS/m2, predation by crayfish will drive negative NZMS population growth. Further, at very high densities, NZMS overwhelm predation by crayfish and invade. Thus, interacting thresholds of propagule pressure and predator densities define the probability of biotic resistance. Quantifying the shape and uncertainty of predator functional responses to nonnative prey may help predict the outcomes of invasions. 相似文献