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101.
Human influence on California fire regimes. 总被引:6,自引:0,他引:6
Alexandra D Syphard Volker C Radeloff Jon E Keeley Todd J Hawbaker Murray K Clayton Susan I Stewart Roger B Hammer 《Ecological applications》2007,17(5):1388-1402
Periodic wildfire maintains the integrity and species composition of many ecosystems, including the mediterranean-climate shrublands of California. However, human activities alter natural fire regimes, which can lead to cascading ecological effects. Increased human ignitions at the wildland-urban interface (WUI) have recently gained attention, but fire activity and risk are typically estimated using only biophysical variables. Our goal was to determine how humans influence fire in California and to examine whether this influence was linear, by relating contemporary (2000) and historic (1960-2000) fire data to both human and biophysical variables. Data for the human variables included fine-resolution maps of the WUI produced using housing density and land cover data. Interface WUI, where development abuts wildland vegetation, was differentiated from intermix WUI, where development intermingles with wildland vegetation. Additional explanatory variables included distance to WUI, population density, road density, vegetation type, and ecoregion. All data were summarized at the county level and analyzed using bivariate and multiple regression methods. We found highly significant relationships between humans and fire on the contemporary landscape, and our models explained fire frequency (R2 = 0.72) better than area burned (R2 = 0.50). Population density, intermix WUI, and distance to WUI explained the most variability in fire frequency, suggesting that the spatial pattern of development may be an important variable to consider when estimating fire risk. We found nonlinear effects such that fire frequency and area burned were highest at intermediate levels of human activity, but declined beyond certain thresholds. Human activities also explained change in fire frequency and area burned (1960-2000), but our models had greater explanatory power during the years 1960-1980, when there was more dramatic change in fire frequency. Understanding wildfire as a function of the spatial arrangement of ignitions and fuels on the landscape, in addition to nonlinear relationships, will be important to fire managers and conservation planners because fire risk may be related to specific levels of housing density that can be accounted for in land use planning. With more fires occurring in close proximity to human infrastructure, there may also be devastating ecological impacts if development continues to grow farther into wildland vegetation. 相似文献
102.
Anastasios I. Stamou Kimon Hadjibiros Andreas Andreadakis Alexandra Katsiri 《Environmental Modeling and Assessment》2007,12(3):157-170
A water quality model (MERES) is applied in the multi-purpose reservoir of Plastiras in Greece. The model was calibrated with
limited field data using the standard trial and error procedure; next, it was applied for four scenarios of reservoir operation,
which correspond to four values of minimum water levels (MWL). Model results were combined with landscape aesthetics to establish
a “safe” MWL in the reservoir. MWL was proposed to be +784 m, a value that ensures a very good water quality by retaining
the reservoir in the status of “a little beyond oligotrophic” and a very good quality of landscape with an acceptable area
of dead zones; it also ensures an annual release of 127.5 hm3 of water within a reliability level of 90%. This quantity can be considered as acceptable from the water supply point of
view. 相似文献
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Miguel A. Bedoya-Perez Alexandra J. R. Carthey Valentina S. A. Mella Clare McArthur Peter B. Banks 《Behavioral ecology and sociobiology》2013,67(10):1541-1553
The giving-up density (GUD) framework provides a powerful experimental approach with a strong theoretical underpinning to quantify foraging outcomes in heterogeneous landscapes. Since its inception, the GUD approach has been applied successfully to a vast range of foraging species and foraging scenarios. However, its application is not simple, as anyone who has tried to use it for the first time might attest. Limitations of the technique were noted at its conception, yet only the artificiality of the patches, the appropriateness of the food resource, and the possibility of multiple visiting foragers were identified. Here we show the current uses of GUD and outline the practical benefits as well as the often overlooked limitations of the technique. We define seven major points that need to be addressed when applying this methodology: (1) the curvilinearity between harvest rate and energy, (2) the energetic state of the forager, (3) the effect of group foraging, (4) food quality and substrate properties, (5) the predictability of the patch, (6) behavioral traits of the forager, and (7) nontarget species. We also suggest how GUD experiments can be enhanced by incorporating complementary methods (such as cameras) to better understand the foraging processes involved in the GUD itself. We conclude that the benefits of using GUD outweigh the costs, but that its limitations should not be ignored. Incorporating new methods when using GUD can potentially offer novel and important insights into the study of foraging behavior. 相似文献
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Regional Environmental Change - In order to combat hunger and feed a growing world population, adapt to climate change and reduce environmental impacts of unsustainable farming practices, the need... 相似文献
109.
Callaway RM Waller LP Diaconu A Pal R Collins AR Mueller-Schaerer H Maron JL 《Ecology》2011,92(12):2208-2213
The greater abundance of some exotic plants in their nonnative ranges might be explained in part by biogeographic differences in the strength of competition, but these competitive effects have not been experimentally examined in the field. We compared the effects of neighbors on the growth and reproduction of spotted knapweed (Centaurea stoebe) in Europe, where it is native, and in Montana, where it is invasive. There were strong negative competitive effects of neighboring vegetation on C. stoebe growth and reproduction in Europe. In contrast, identical experiments in Montana resulted in insignificant impacts on C. stoebe. Although the mechanisms that produce this dramatic biogeographic difference in competitive outcome remain unknown, our results indicate that differences in net competitive interactions between ranges may contribute to the striking dominance of C. stoebe in parts of North America. 相似文献
110.
Alexandra Bottcher Jorge Paulo Zolin Flávia Nogueira-de-Sá José Roberto Trigo 《Chemoecology》2009,19(1):63-66
The most frequently investigated defence mechanism among larvae of tortoise beetles is protection by faecal shields, which
generally present chemicals that are directly sequestered and/or modified from larval host-plants. In the present work we
investigate the tortoise beetle Chelymorpha reimoseri that feeds on the leaves of Ipomoea carnea fistulosa (Convolvulaceae), seeking for the importance of this mechanism to their larvae. We show that 4th instar larvae suffer low
predation regardless of the presence of shields in field and laboratory bioassays with ants and chicks. Chloroform extract
from larvae without shields provided high protection against predation as shown in bioassays in the field, as well as against
chicks, suggesting that C. reimoseri does not rely on the shield for protection. The aqueous extract of the shields did not show activity in such bioassays. The
compounds responsible for this protection have yet to be identified, and it remains an open question as to whether they are
sequestered from the host plant or de novo biosynthesized. This is the first record of chemical defence in cassidine beetles
without the need for faecal shields. These findings indicate that more attention should be paid to chemicals present in the
tissues of larvae and/or adults of tortoise beetles; the protective compounds sequestered from host plants or de novo biosynthesized
can provide an alternative or complementary strategy against predation in these insects. 相似文献