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491.
Roger M. Evans 《Behavioral ecology and sociobiology》1996,39(3):203-209
American white pelicans (Pelecanus erythrorhynchos) lay two eggs but typically rear only one young owing to siblicidal brood reduction affecting the later-hatched, or B-chick.
When the A-offspring fails at an early age, the B-chick may survive as a replacement (insurance) offspring. Using a combination
of nests with natural and artificially manipulated hatching asynchrony, I examined the hypothesis that hatching asynchrony
in this species is adaptively tuned to permit B-chicks to survive during the time they are most likely to be needed as replacements,
with brood reduction following when they become redundant. Hatching asynchrony over the natural range of 0–4 days significantly
increased within-brood mass differentials and reduced B-chick lifespan. Full synchrony had a marginally negative effect on
A-chick mass. Greater asynchrony did not significantly affect the number of days B-chicks survived after hatching of the A-chick,
owing to a corresponding extension of time B-offspring were protected from harassment while still within the egg. This resulted
in a high probability (> 0.8) of B-chicks surviving through the initial period (5–7 days) of maximum early A-chick loss. Redundant
B-chicks were subject to heavy brood reduction, with both chicks likely to have survived at only one each of 94 natural and
84 manipulated (0, 2, and 4 days asynchrony) nests. Hatching asynchrony in American white pelicans, in combination with a
rapid development of senior chick siblicidal competence, appears to result in a time course of brood reduction appropriate
for an effective insurance reproductive strategy.
Received: 2 February 1996 /Accepted after revision: 18 May 1996 相似文献
492.
MANAGING UNDERGROUND STORAGE TANKS IN URBAN ENVIRONMENTS: A GEOGRAPHIC INFORMATION SYSTEMS APPROACH1
Paul F. Hudak Roger K. Speas F. Andrew Schoolmaster 《Journal of the American Water Resources Association》1995,31(3):439-445
ABSTRACT: Fuels contained in underground storage tanks (USTs) are a major source of soil and ground water contamination. Effective management of the problem at the urban level is difficult due to a large number of tanks and a vast array of factors (e.g., tank characteristics, geology) that determine environmental hazards. The problem is compounded by frequent abandonment and reuse of service stations, which makes it difficult to track the status of underground tanks. Geographic information systems (GIS) are ideally suited to organizing location and attribute data for variables that are pertinent to the UST management problem. A GIS-based UST management system was developed and applied to 136 current and former gasoline service stations in Denton, Texas. The system is effective for tank inventory and can be applied in a proactive fashion to identify potentially problematic facilities. In the event of a leak or spill, the management system can support the implementation of reactive measures to mitigate subsurface contamination. Potential beneficiaries of such a system include planning departments, environmental regulatory agencies, emergency management officials, lending institutions, gasoline distributors, and oil companies. 相似文献
493.
494.
J. Kent Mitchell Saied Mostaghimi Dale S. Freeny J. Roger McHenry 《Journal of the American Water Resources Association》1983,19(4):549-555
ABSTRACT The movement of fallout 137Cs carried by soil particles was studied as an indicator of erosion and sedimentation in the Allerton watersheds and 4-H Memorial Lake located near Monticello, Illinois. Sediment deposition was greater in the waterway draining from watershed IB than in the waterway from watershed IA. At the average rate of 2.3 cm/yr of sediment deposition in the lake (from 1954 to 1979), there will be a loss of over 2 meters of water depth in the next century. However, there appears to be a decreasing rate of sediment deposition in the 4-H Memorial Lake as a result of improved conservation practices on the watersheds and the increased effectiveness of vegetated waterways and buffers for retaining sediment. 相似文献
495.
Tapping the leakages: Methane losses, mitigation options and policy issues for Russian long distance gas transmission pipelines 总被引:1,自引:0,他引:1
Stefan Lechtenbhmer Carmen Dienst Manfred Fischedick Thomas Hanke Roger Fernandez Don Robinson Ravi Kantamaneni Brian Gillis 《International Journal of Greenhouse Gas Control》2007,1(4):387-395
The Russian natural gas industry is the world's largest producer and transporter of natural gas. This paper aims to characterize the methane emissions from Russian natural gas transmission operations, to explain projects to reduce these emissions, and to characterize the role of emissions reduction within the context of current GHG policy. It draws on the most recent independent measurements at all parts of the Russian long distance transport system made by the Wuppertal Institute in 2003 and combines these results with the findings from the US Natural Gas STAR Program on GHG mitigation options and economics.With this background the paper concludes that the methane emissions from the Russian natural gas long distance network are approximately 0.6% of the natural gas delivered. Mitigating these emissions can create new revenue streams for the operator in the form of reduced costs, increased gas throughput and sales, and earned carbon credits. Specific emissions sources that have cost-effective mitigation solutions are also opportunities for outside investment for the Joint Implementation Kyoto Protocol flexibility mechanism or other carbon markets. 相似文献
496.
Non-avian theropod dinosaurs attained large body sizes, monopolising terrestrial apex predator niches in the Jurassic–Cretaceous.
From the Middle Jurassic onwards, Allosauroidea and Megalosauroidea comprised almost all large-bodied predators for 85 million
years. Despite their enormous success, however, they are usually considered absent from terminal Cretaceous ecosystems, replaced
by tyrannosaurids and abelisaurids. We demonstrate that the problematic allosauroids Aerosteon, Australovenator, Fukuiraptor and Neovenator form a previously unrecognised but ecologically diverse and globally distributed clade (Neovenatoridae, new clade) with the
hitherto enigmatic theropods Chilantaisaurus, Megaraptor and the Maastrichtian Orkoraptor. This refutes the notion that allosauroid extinction pre-dated the end of the Mesozoic. Neovenatoridae includes a derived
group (Megaraptora, new clade) that developed long, raptorial forelimbs, cursorial hind limbs, appendicular pneumaticity and
small size, features acquired convergently in bird-line theropods. Neovenatorids thus occupied a 14-fold adult size range
from 175 kg (Fukuiraptor) to approximately 2,500 kg (Chilantaisaurus). Recognition of this major allosauroid radiation has implications for Gondwanan paleobiogeography: The distribution of early
Cretaceous allosauroids does not strongly support the vicariant hypothesis of southern dinosaur evolution or any particular
continental breakup sequence or dispersal scenario. Instead, clades were nearly cosmopolitan in their early history, and later
distributions are explained by sampling failure or local extinction. 相似文献
497.
Ako AA Shimada J Hosono T Ichiyanagi K Nkeng GE Fantong WY Eyong GE Roger NN 《Environmental geochemistry and health》2011,33(6):559-575
Groundwater quality of the Banana Plain (Mbanga, Njombe, Penja—Cameroon) was assessed for its suitability for drinking, domestic,
and agricultural uses. A total of 67 groundwater samples were collected from open wells, springs, and boreholes. Samples were
analyzed for physicochemical properties, major ions, and dissolved silica. In 95% of groundwater samples, calcium is the dominant
cation, while sodium dominates in 5% of the samples. Eighty percent of the samples have HCO3 as major anion, and in 20%, NO3 is the major anion. Main water types in the study area are CaHCO3, CaMgHCO3, CaNaHCO3, and CaNaNO3ClHCO3. CO2-driven weathering of silicate minerals followed by cation exchange seemingly controls largely the concentrations of major
ions in the groundwaters of this area. Nitrate, sulfate, and chloride concentrations strongly express the impact of anthropogenic
activities (agriculture and domestic activities) on groundwater quality. Sixty-four percent of the waters have nitrate concentrations
higher than the drinking water limit. Also limiting groundwater use for potable and domestic purposes are contents of Ca2+, Mg2+ and HCO3
− and total hardness (TH) that exceed World Health Organization (WHO) standards. Irrigational suitability of groundwaters in
the study area was also evaluated, and results show that all the samples are fit for irrigation. Groundwater quality in the
Banana Plain is impeded by natural geology and anthropogenic activities, and proper groundwater management strategies are
necessary to protect sustainably this valuable resource. 相似文献
498.
The frequently observed positive correlation between species diversity and community biomass is thought to depend on both the degree of resource partitioning and on competitive dominance between consumers, two properties that are also central to theories of species coexistence. To make an explicit link between theory on the causes and consequences of biodiversity, we define in a precise way two kinds of differences among species: niche differences, which promote coexistence, and relative fitness differences, which promote competitive exclusion. In a classic model of exploitative competition, promoting coexistence by increasing niche differences typically, although not universally, increases the "relative yield total", a measure of diversity's effect on the biomass of competitors. In addition, however, we show that promoting coexistence by decreasing relative fitness differences also increases the relative yield total. Thus, two fundamentally different mechanisms of species coexistence both strengthen the influence of diversity on biomass yield. The model and our analysis also yield insight on the interpretation of experimental diversity manipulations. Specifically, the frequently reported "complementarity effect" appears to give a largely skewed estimate of resource partitioning. Likewise, the "selection effect" does not seem to isolate biomass changes attributable to species composition rather than species richness, as is commonly presumed. We conclude that past inferences about the cause of observed diversity-function relationships may be unreliable, and that new empirical estimates of niche and relative fitness differences are necessary to uncover the ecological mechanisms responsible for diversity-function relationships. 相似文献
499.
Roger Matta Sabrine Tlili Serge Chiron St��phane Barbati 《Environmental Chemistry Letters》2011,9(3):347-353
The occurrence of bioactive trace pollutants such as pharmaceuticals in natural waters is an emerging issue. Numerous pharmaceuticals
are not completely removed in conventional wastewater treatment plants. Advanced oxidation processes may represent an interesting
alternative to completely mineralize organic trace pollutants. In this article, we show that sulfate radicals generated from
peroxymonosulfate/CoII are more efficient than hydroxyl radicals generated from the Fenton’s reagent (H2O2/FeII) for the degradation of the pharmaceutical compound, carbamazepine. The second-order rate constant for the reaction of SO4
·− with carbamazepine is 1.92·109 M−1 s−1. In laboratory grade water and in real urban wastewater, SO4
·− yielded a faster degradation of carbamazepine compared to HO· . Under strongly oxidizing conditions, a nearly complete mineralization of carbamazepine was achieved, while under mildly
oxidizing conditions, several intermediates were identified by LC–MS. These results show for the first time in real urban
wastewater that sulfate radicals are more selective than hydroxyl radicals for the oxidation of an organic pollutant and may
represent an interesting alternative in advanced oxidation processes. 相似文献
500.