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排序方式: 共有168条查询结果,搜索用时 234 毫秒
21.
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Marion Valeix Hervé Fritz Andrew J. Loveridge Zeke Davidson Jane E. Hunt Felix Murindagomo David W. Macdonald 《Behavioral ecology and sociobiology》2009,63(10):1483-1494
A central question in the study of predator–prey relationships is to what extent prey behaviour is determined by avoidance
of predators. Here, we test whether the long-term risk of encountering lions and the presence of lions in the vicinity influence
the behaviour of large African herbivores at waterholes through avoidance of high-risk areas, increases in group size, changes
in temporal niche or changes in the time spent in waterhole areas. In Hwange National Park, Zimbabwe, we monitored waterholes
to study the behaviour of nine herbivore species under different risks of encountering lions. We radio-collared 26 lions in
the study area which provided the opportunity to monitor whether lions were present during observation sessions and to map
longer-term seasonal landscapes of risk of encountering lions. Our results show that the preferred prey species for lions
(buffalo, kudu and giraffe) avoided risky waterholes. Group size increased as encounter risk increased for only two species
(wildebeest and zebra), but this effect was not strong. Interestingly, buffalo avoided the hours of the day which are dangerous
when the long-term and short-term risks of encountering lions were high, and all species showed avoidance of waterhole use
at night times when lions were in the vicinity. This illustrates well how prey can make temporal adjustments to avoid dangerous
periods coinciding with predator hunting. Additionally, many herbivores spent more time accessing water to drink when the
long- and short-term risks of encountering lions were high, and they showed longer potential drinking time when the long-term
risk of encountering lions was high, suggesting higher levels of vigilance. This study illustrates the diversity of behavioural
adjustments to the risk of encountering a predator and how prey respond differently to temporal variations in this risk. 相似文献
23.
E. A. Perry G. B. Stenson S. E. Bartlett W. S. Davidson S. M. Carr 《Marine Biology》2000,137(1):53-58
Harp seals (Pagophilus groenlandicus Erxleben, 1777) comprise three populations based upon whelping areas in the Greenland Sea, White Sea, and Northwest Atlantic.
The last comprises two subpopulations, one whelping in the Gulf of St. Lawrence (“Gulf ”) and one on the pack ice of the southern
Labrador/northern Newfoundland coastal shelf (“Front”). A total of 40 female seals from the four whelping areas were collected
during the 1990 and 1992 whelping seasons. DNA sequence variation was examined in a 307 bp region of the mitochondrial cytochrome
b gene. Eleven variable nucleotide positions defined 13 genotypes: a significant fraction of the genotypic variance (F
ST=0.12, or 0.09 as measured by Weir's coancestry coefficient θ) is attributable to differentiation between Northwest and Northeast
Atlantic populations. There was no significant differentiation between the two whelping areas in the Northwest Atlantic, or
between the Greenland Sea and White Sea. These findings suggest significant reproductive isolation exists between trans-Atlantic
breeding populations.
Received: 18 January 1999 / Accepted: 22 February 2000 相似文献
24.
Morillo E Romero AS Maqueda C Madrid L Ajmone-Marsan F Grcman H Davidson CM Hursthouse AS Villaverde J 《Journal of environmental monitoring : JEM》2007,9(9):1001-1008
The purpose of this study was to determine the degree of contamination with polycyclic aromatic hydrocarbons (PAHs) in samples of urban soil from three European cities: Glasgow (UK), Torino (Italy) and Ljubljana (Slovenia). Fifteen PAHs (naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene, indeno[1,2,3-c,d]pyrene) were measured in urban soil samples, using harmonised sampling, sample extraction and analyte quantification methods. Although the mean concentration of each PAH in urban soils of each city showed a wide range of values, high levels of contamination were only evident in Glasgow, where the sum of concentrations of 15 PAHs was in the range 1487-51,822 microg kg(-1), cf. ranges in the other two cities were about ten-fold lower (89.5-4488 microg kg(-1)). The three predominant PAHs were phenanthrene, fluoranthene and pyrene, with the sum of these compounds about 40% of the total PAH content. These data, together with some special molecular indices based on ratios of selected PAHs, suggest pyrogenic origins, especially motor vehicle exhausts, to be the major sources of PAHs in urban soils of the three cities. The largest concentrations for PAHs were often found in sites close to the historic quarters of the cities. Overall, the different climatic conditions, the organic carbon contents of soil, and the source apportionment were the dominant factors affecting accumulation of PAHs in soil. 相似文献
25.
Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials 总被引:47,自引:0,他引:47
Rauret G López-Sánchez JF Sahuquillo A Rubio R Davidson C Ure A Quevauviller P 《Journal of environmental monitoring : JEM》1999,1(1):57-61
The Standards, Measurements and Testing Programme (formerly BCR) of the European Commission proposed a three-step sequential extraction procedure for sediment analysis, following extensive expert consultations and two interlaboratory studies. This scheme was recently used to certify the extractable trace element contents of a sediment reference material (CRM 601). Although this procedure offers a means to ensure the comparability of data in this field, some difficulties concerning the interlaboratory reproducibility still remain, and a new project is currently being conducted to determine the causes of poor reproducibility in the extraction scheme. The final objective of the project is the certification of new sediment and soil reference materials for their extractable contents of Cd, Cr, Cu, Ni, Pb and Zn. This paper presents the results of a small-scale interlaboratory study, which aimed to test a revised version of the extraction schemes by comparing the original and the modified protocols using the CRM 601 sample. This work offers an improvement to the BCR sequential extraction procedure through intercomparison exercises. This improved procedure will allow the obtaining of CRMs to validate analytical data in the analysis of soils and sediments, and it will also facilitate comparability of data in the European Union. 相似文献
26.
27.
Phaeocystis pouchetii (Hariot) Lagerheim is widely distributed in polar waters, and forms massive near-surface blooms in the marginal ice-edge zone around Antarctica during spring and summer. UV irradiance in the Antarctic marine environment is reportedly as high in October and November as in mid-summer due to stratospheric ozone depletion. Because of the location and timing of theP. pouchetii bloom, this prymnesiophyte will be exposed to high levels of UV-B (280 to 320 nm) radiation. Colourless water-soluble compounds, produced by the colonial stage in the life cycle of this alga, absorb strongly between 250 and 370 nm, with absorbance maxima at 271 and 323 nm. The concentration of these compounds in culturedP. pouchetii depends on the strain, stage in the life cycle, and presence of bacteria. As well as conferring substantial protection to this alga, these substances may also provide UV protection to other organisms present in the water column. 相似文献
28.
29.
J. M. Davidson Timothy R. B. Johnson Jr. David T. Rigdon Barry H. Thompson 《黑龙江环境通报》1984,4(5):355-363
Obstetric ultrasonography has made the prenatal diagnosis of gastroschisis and omphalocele more common. We present illustrative cases 2nd review the ultrasonographic features. Because of the increased risk of concomitant abnormalities (including trisomies) with omphalocele, full evaluation is indicated when this diagnosis is suspected. Recent perinatal approaches to delivery have favoured caesarean section. without scientific evidence that outcome is improved. Our experience. as well as a review of the literature, suggests that the outcome for vaginally delivered infants is acceptable. A prospective study of this question is needed. 相似文献
30.