全文获取类型
收费全文 | 390篇 |
免费 | 8篇 |
国内免费 | 8篇 |
专业分类
安全科学 | 38篇 |
废物处理 | 14篇 |
环保管理 | 89篇 |
综合类 | 48篇 |
基础理论 | 78篇 |
环境理论 | 1篇 |
污染及防治 | 96篇 |
评价与监测 | 27篇 |
社会与环境 | 9篇 |
灾害及防治 | 6篇 |
出版年
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 10篇 |
2013年 | 34篇 |
2012年 | 12篇 |
2011年 | 32篇 |
2010年 | 21篇 |
2009年 | 21篇 |
2008年 | 24篇 |
2007年 | 17篇 |
2006年 | 29篇 |
2005年 | 20篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有406条查询结果,搜索用时 218 毫秒
381.
A two-dimensional infiltration experiment was conducted to investigate and quantify the effect of spatial wettability variations on DNAPL migration and entrapment in saturated sands. Experimental observations of tetrachloroethylene (PCE) infiltration showed that organic-wet sand lenses acted as very effective capillary barriers, retaining PCE and inhibiting its downward migration. A multiphase numerical simulator was used to model this sand box experiment. The simulator incorporates wettability-modified van Genuchten and Brooks-Corey capillary pressure/saturation relationships as well as Burdine and Mualem relative permeability relationships. PCE mass distributions, estimated by image analysis of digital photographs taken during the infiltration event, were compared to simulation results. Although both relative permeability models were qualitatively able to predict the PCE retention in the organic-wet layers, simulations with the Mualem model failed to capture the observed rate of PCE migration. A traditional multiphase simulator, incorporating water-wet capillary retention relations, failed to predict both PCE pathways and retention behavior. This study illustrates the potential influence of subsurface wettability variations on DNAPL migration and entrapment and supports the use of modified capillary relations in conjunction with the Burdine model in multiphase flow simulators. 相似文献
382.
383.
Sygna Linda Fuglestvedt Jan S. Aaheim H. Asbjørn 《Mitigation and Adaptation Strategies for Global Change》2002,7(1):45-62
This article looks at the ability of Global Warming Potentials (GWPs) towork as indicators of equivalence for temperature development and damagecosts. We look at two abatement scenarios that are equivalent when using100-year GWPs: one scenario reduces short-lived gases, mainly methane(CH4); the other scenario reduces carbon dioxide (CO2).Despite their equivalence in terms of CO2 equivalents, the scenariosdo not result in equal rates or levels of temperature change. The disparitiescontinue as we move further down the chain of causality toward damagecosts, measured either in terms of rate of climate change or level of climatechange. Compared to the CH4 mitigation scenario, the CO2mitigation scenario gives present value costs 1.3 and 1.5 times higher forlevel- and rate-dependent damage costs, respectively, assuming a discountrate of 3%. We also test the GWPs for other time horizons and theconclusions remain the same; using GWP as an index to reflect equivalentclimate effects and damage costs from emissions is questionable. 相似文献
384.
Boris M. Petrikovsky MD Phd Margaret I. Cuomo Elizabeth P. Schneider Linda J. Wyse Harris L. Cohen Martin Lesser 《黑龙江环境通报》1995,15(9):827-829
The aim was to assess the role that fetal bladder size has in the determination of fetal hydronephrosis. Forty-three fetuses were evaluated for fetal hydronephrosis in the second trimester of pregnancy. Anteroposterior measurements of the renal pelvis were obtained with a full bladder and again when the bladder emptied in each fetus. Statistical analysis was performed using the Spearman rank order correlation coefficient to assess the relationship between bladder status and renal dilation. The anteroposterior size of the fetal renal pelvis diminished from 6.8 ± 1.8 mm on a full bladder scan to 4.5 ± 1.6 mm when the bladder was emptied (P<0.001). Fifty-three per cent of the fetuses whose renal pelvic measurements were 5 mm or more on a full bladder scan had normal-appearing renal pelvises when their bladders emptied. The status of the fetal bladder should be considered when evaluating fetal hydronephrosis. 相似文献
385.
Linda A. Whittingham 《Behavioral ecology and sociobiology》1989,25(1):73-80
Summary The effect of brood size and female nesting status on male parental behavior was investigated in red-winged blackbirds Agelaius phoeniceus using brood size manipulation experiments. Male redwings allocated parental effort on the basis of brood size and nestling age. Males began assisting females only at nests with at least three offspring older than three days. Female nesting status had no singificant influence on male parental care. When females were unable to meet a brood's demand for food, males assisted females with nestling feeding. Females did not reduce the amount of food delivered to nestlings when males assisted. The amount of food brought to nestlings by the male was additional to the amount of food provided by the female. Male assistance increased fledgling success. When female provisioning was sufficient to meet a brood's demand for food males did not assist. The value of male parental care varied inversely with the ability of the female to meet nestling food demands. The ability of unassisted females to provide sufficient food and to raise a brood of nestlings successfully appeared to be influenced by resource abundance. 相似文献
386.
Summary Vocalizations of free-ranging North Atlantic pilot whales were studied in different behavioral contexts to gain insight into the function and biological significance of different sound types. Simple whistles (with no frequency inflections) were heard more frequently when whales were milling, a restful behavior type. During surface active behavior, energetic, often coordinated activity probably representing feeding, many sound types, especially complex whistles (with more frequency inflections) and pulsed sounds, occurred with greater frequency than when this behavior was absent. Greater numbers of most whistle types were produced when whales were spread over a larger area and when more subgroups were present. Thus, in pilot whales, there is a significant relationship between their sounds and their behavior, with vocalizations possibly serving to maintain contact and coordinate movements of the herd.
Offprint requests to: L.S. Weilgart at the current address 相似文献
387.
Thomas C. Edwards Jr. D. Richard Cutler Niklaus E. Zimmermann Linda Geiser Gretchen G. Moisen 《Ecological modelling》2006
We evaluated the effects of probabilistic (hereafter DESIGN) and non-probabilistic (PURPOSIVE) sample surveys on resultant classification tree models for predicting the presence of four lichen species in the Pacific Northwest, USA. Models derived from both survey forms were assessed using an independent data set (EVALUATION). Measures of accuracy as gauged by resubstitution rates were similar for each lichen species irrespective of the underlying sample survey form. Cross-validation estimates of prediction accuracies were lower than resubstitution accuracies for all species and both design types, and in all cases were closer to the true prediction accuracies based on the EVALUATION data set. We argue that greater emphasis should be placed on calculating and reporting cross-validation accuracy rates rather than simple resubstitution accuracy rates. Evaluation of the DESIGN and PURPOSIVE tree models on the EVALUATION data set shows significantly lower prediction accuracy for the PURPOSIVE tree models relative to the DESIGN models, indicating that non-probabilistic sample surveys may generate models with limited predictive capability. These differences were consistent across all four lichen species, with 11 of the 12 possible species and sample survey type comparisons having significantly lower accuracy rates. Some differences in accuracy were as large as 50%. The classification tree structures also differed considerably both among and within the modelled species, depending on the sample survey form. Overlap in the predictor variables selected by the DESIGN and PURPOSIVE tree models ranged from only 20% to 38%, indicating the classification trees fit the two evaluated survey forms on different sets of predictor variables. The magnitude of these differences in predictor variables throws doubt on ecological interpretation derived from prediction models based on non-probabilistic sample surveys. 相似文献
388.
There is a lack of research on the effects of logging on Canadian amphibians. We compared the abundance of terrestrial salamanders in old-growth forests with that in young and mature post-harvest stands. We also measured habitat features of amphibians and contrasted these with old-growth and harvested stands to assess the effects of forest harvest. Quadrat searches demonstrated that clearcut harvesting reduces terrestrial amphibian populations by up to 70% in coastal old-growth forests. We suggest that this reduction results from a decrease in availability of moist microhabitats. Salamander densities within 10 meters of streams in managed stands were similar to those near and away from streams in old growth. We recommend that forest managers recognize the needs of terrestrial amphibians and help maintain amphibian populations by preserving cool, moist habitats. This can be accomplished within cutblocks by (1) maintaining an even distribution of logs and snags as stable, moist microhabitats; (2) retaining some understory as sources of shade, and (3) preserving streamside buffers. Managers must also ensure some level of landscape connectivity to enable climate-sensitive amphibians to disperse and recolonize marginal habitats. 相似文献
389.
Relatedness, polyandry and extra-group paternity in the cooperatively-breeding white-browed scrubwren (Sericornis frontalis ) 总被引:3,自引:0,他引:3
Linda A. Whittingham Peter O. Dunn Robert D. Magrath 《Behavioral ecology and sociobiology》1997,40(4):261-270
We used DNA fingerprinting to examine the genetic parentage and mating system of the cooperatively breeding white-browed
scrubwren, Sericornis frontalis, in Canberra, Australia. Our analyses revealed a remarkable variety of mating tactics and social organization. Scrubwrens
bred in pairs or multi-male groups that consisted of a female and two or more males. Females were always unrelated to the
pair male or alpha (dominant) male. Among multi-male groups we found three different mating tactics. Firstly, when alpha and
beta (subordinate) males were unrelated, they usually shared paternity in the brood. This resulted in both males gaining reproductive
benefits directly. Secondly, when beta males were not related to the female but were related to the alpha males, beta males
sired offspring in some broods. In this situation, beta males gained reproductive benefits both directly and potentially indirectly
(through the related alpha male). Thirdly, when beta males were related to the female or both the female and alpha male, they
remained on their natal territory and did not sire any offspring. Thus beta males gained only indirect reproductive benefits.
Overall, when group members were related closely, the dominant male monopolized reproductive success, whereas when the members
were not related closely the two males shared paternity equally. This positive association between monopolization of reproduction
and relatedness is predicted by models of reproductive skew, but has not been reported previously within a single population
of birds. Other cooperatively breeding birds with both closely related and unrelated helpers may show a similar variety of
mating tactics. Finally, we found that extra-group paternity was more common in pairs (24% of young) than in multi-male groups
(6%), and we discuss three possible reasons for this difference.
Received: 21 May 1996 / Accepted after revision: 14 December 1996 相似文献
390.
How Climate and Vegetation Influence the fire Regime of the Alaskan Boreal Biome: The Holocene Perspective 总被引:2,自引:0,他引:2
Feng Sheng Hu Linda B. Brubaker Daniel G. Gavin Philip E. Higuera Jason A. Lynch T. Scott Rupp Willy Tinner 《Mitigation and Adaptation Strategies for Global Change》2006,11(4):829-846
We synthesize recent results from lake-sediment studies of Holocene fire-climate-vegetation interactions in Alaskan boreal
ecosystems. At the millennial time scale, the most robust feature of these records is an increase in fire occurrence with
the establishment of boreal forests dominated by Picea mariana: estimated mean fire-return intervals decreased from ≥300 yrs to as low as ∼80 yrs. This fire-vegetation relationship occurred
at all sites in interior Alaska with charcoal-based fire reconstructions, regardless of the specific time of P. mariana arrival during the Holocene. The establishment of P. mariana forests was associated with a regional climatic trend toward cooler/wetter conditions. Because such climatic change should
not directly enhance fire occurrence, the increase in fire frequency most likely reflects the influence of highly flammable
P. mariana forests, which are more conducive to fire ignition and spread than the preceding vegetation types (tundra, and woodlands/forests
dominated by Populus or Picea glauca). Increased lightning associated with altered atmospheric circulation may have also played a role in certain areas where
fire frequency increased around 4000 calibrated years before present (BP) without an apparent increase in the abundance of
P. mariana. When viewed together, the paleo-fire records reveal that fire histories differed among sites in the same modern fire regime
and that the fire regime and plant community similar to those of today became established at different times. Thus the spatial
array of regional fire regimes was non-static through the Holocene. However, the patterns and causes of the spatial variation
remain largely unknown. Advancing our understanding of climate-fire-vegetation interactions in the Alaskan boreal biome will
require a network of charcoal records across various ecoregions, quantitative paleoclimate reconstructions, and improved knowledge
of how sedimentary charcoal records fire events.
In this paper, charcoal refers to macroscopic (≥180 μm) as opposed to microscopic (< 180 μm) particles unless indicated otherwise.
Radiocarbon ages were converted to calibrated years before AD 1950 using the atmospheric calibration data set (Stuiver et
al. 1998). 相似文献