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91.
When the development of gap models began about three decades ago, they became a new category of forest productivity models. Compared with traditional growth and yield models, which aim at deriving empirical relationships that best fit data, gap models use semi-theoretical relationships to simulate biotic and abiotic processes in forest stands, including the effects of photosynthetic active radiation interception, site fertility, temperature and soil moisture on tree growth and seedling establishment. While growth and yield models are appropriate to predict short-term stemwood production, gap models may be used to predict the natural course of species replacement for several generations. Because of the poor availability of historical data and knowledge on species-specific allometric relationships, species replacement and death rate, it has seldom been possible to develop and evaluate the most representative algorithms to predict growth and mortality with a high degree of accuracy. For this reason, the developers of gap models focused more on developing simulation tools to improve the understanding of forest succession than predicting growth and yield accurately.In a previous study, the predictions of simulations in two southeastern Canadian mixed ecosystem types using the ZELIG gap model were compared with long-term historical data. This exercise highlighted model components that needed modifications to improve the predictive capacity of ZELIG. The updated version of the model, ZELIG-CFS, includes modifications in the modelling of crown interaction effects, survival rate and regeneration. Different algorithms representing crown interactive effects between crowns were evaluated and species-specific model components that compute individual-tree mortality probability rate were derived. The results of the simulations were compared using long-term remeasurement data obtained from sample plots located in La Mauricie National Park of Canada in Quebec. In the present study, three forest types were studied: (1) red spruce-balsam fir-yellow birch, (2) yellow birch-sugar maple-balsam fir, and (3) red spruce-balsam fir-white birch mixed ecosystems. Among the seven algorithms that represented individual crown interactions, two better predicted the changes in basal area and individual-tree growth: (1) the mean available light growing factor (ALGF), which is computed from the proportion of light intercepted at different levels of individual crowns adjusted by the species-specific shade tolerance index, and (2) the ratio of mean ALGF to crown width. The long-term predicted patterns of change in basal area were consistent with the life history of the different species. 相似文献
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Exposure to environmental contaminants has been shown to alter normal thyroid function in various wildlife species, including the American alligator (Alligator mississippiensis). Abnormalities in circulating levels of the thyroid hormone thyroxine (T4) have been reported in juvenile alligators from several contaminated lakes in Florida. To further elucidate these functional thyroid abnormalities, this study examines the structure of thyroids and circulating T4 concentrations from juvenile alligators collected from three sites of varying contamination on Lake Okeechobee, Florida. The following variables were used to characterize thyroid morphology: epithelial cell height, width and area, percent colloid, and follicle area. These variables were compared among study sites and between genders. No difference was detected in epithelial cell height, epithelial cell area, or follicle area among the sites, whereas significant differences in epithelial cell width (p=0.02) and percent colloid (p=0.008) were found. Animals from the most contaminated site (Belle Glade) had significantly greater epithelial cell widths and significantly less colloid present in their follicles compared to animals from the reference site (West). Gender did not have a significant interaction with site for any variable measured. Thyroxine (T4) concentrations were elevated in the intermediately contaminated site (Conservation Area 3A) compared to the other sites (p<0.0001). It is proposed that the disruptions seen in Lake Okeechobee alligators are due to disruptions at both the thyroid and extra-thyroidal tissues. 相似文献
95.
Wasps robbing food from ants: a frequent behavior? 总被引:1,自引:0,他引:1
Food robbing, or cleptobiosis, has been well documented throughout the animal kingdom. For insects, intrafamilial food robbing
is known among ants, but social wasps (Vespidae; Polistinae) taking food from ants has, to the best of our knowledge, never
been reported. In this paper, we present two cases involving social wasps robbing food from ants associated with myrmecophytes.
(1) Polybioides tabida F. (Ropalidiini) rob pieces of prey from Tetraponera aethiops Smith (Formicidae; Pseudomyrmecinae) specifically associated with Barteria fistulosa Mast. (Passifloraceae). (2) Charterginus spp. (Epiponini) rob food bodies from myrmecophytic Cecropia (Cecropiaceae) exploited by their Azteca mutualists (Formicidae; Dolichoderinae) or by opportunistic ants (that also attack cleptobiotic wasps). We note here that
wasps gather food bodies (1) when ants are not yet active; (2) when ants are active, but avoiding any contact with them by
flying off when attacked; and (3) through the coordinated efforts of two to five wasps, wherein one of them prevents the ants
from leaving their nest, while the other wasps freely gather the food bodies. We suggest that these interactions are more
common than previously thought. 相似文献
96.
Sheila M. Holmes Adam D. Gordon Edward E. Louis Steig E. Johnson 《Behavioral ecology and sociobiology》2016,70(11):1949-1960
97.
Andrea L. Baden Patricia C. Wright Edward E. Louis Jr. Brenda J. Bradley 《Behavioral ecology and sociobiology》2013,67(12):1939-1950
Communal nesting, where several mothers regularly pool and cooperatively rear offspring, is unusual in mammals. This type of crèching behavior is especially rare among primates, with the notable exceptions of humans, some nocturnal strepsirrhines, and—as we show in this study—black-and-white ruffed lemurs (Varecia variegata). Here, we combine data on nesting behavior, genetic relatedness, and infant survivorship to describe variation in ruffed lemur infant care and to examine the potential benefits of ruffed lemur communal breeding. Reproductive events were rare, and females produced litters (synchronously) only once in 6 years of observation. We show that not all mothers participate in communal crèches, but those that did had greater maternal success; communal breeders spent more time feeding and their offspring were more likely to survive. Although cooperating mothers were often related, females also cooperated with non-kin, and those who shared infant care responsibilities had greater maternal success than mothers who did not participate. If there is indeed a causal link between maternal cooperation and reproductive success, this unusual behavior, like that of human communal rearing, may have evolved via some combination of kin selection and mutualism. 相似文献
98.
Bird disturbance by human activities is one of the impacts related to human presence at conservation sites in Brittany (France). This paper is an attempt at reviewing this relatively unknown problem through the results of an international bibliographical review and of a regional inquiry conducted in close collaboration with managers of the conservation areas in Brittany. These two approaches will help to demonstrate the extent and complexity of the human / fauna interactions, as well as to take stock of the state of research in this field and, last but not least, to highlight the difficulties managers of conservation sites are facing to deal with this new issue. For the managers, bird disturbance is indeed the most important impact related to human attendance on conservation sites in Brittany. 相似文献
99.
三丁基锡(TBT)是一种常见于船舶防污涂料中的有机锡化合物。尽管该化学物已于2008年被禁用,但在ports和港口等海上交通区域仍可检出致毒水平(浓度)的TBT。一项补救方案在新西兰的一个港口实施,以将TBT和铜的浓度降低到可接受的(浓度)值。这项研究使用分析化学和桡足类生物测试相结合的方法评估了该方案的有效性。在港口内的三个空间梯度上采集沉积物和水样,并在修复前后测定了有机锡和金属含量。利用底栖和浮游桡足类生物测试估算了沉积物和淘析样品的毒性。虽然底泥样品的急性毒性在修复后减少,但对底栖桡足类的繁殖率仍有影响。本研究所采用的方法有望评估沿海地区修复过程的效果。 相似文献
100.