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111.
Francis K Wiese Julia K Parrish Christopher W Thompson Christina Maranto 《Ecological applications》2008,18(3):681-700
Predator-prey relationships are often altered as a result of human activities. Where prey are legally protected, conservation action may include lethal predator control. In the Columbia River basin (Pacific Northwest, USA and Canada), piscivorous predators have been implicated in contributing to a lack of recovery of several endangered anadromous salmonids (Oncorhynchus spp.), and lethal and nonlethal control programs have been instituted against both piscine and avian species. To determine the consequences of avian predation, we used a bioenergetics approach to estimate the consumption of salmonid smolts by waterbirds (Common Merganser, California and Ring-billed Gull, Caspian Tern, Double-crested Cormorant) found in the mid-Columbia River from April through August, 2002-2004. We used our model to explore several predator-prey scenarios, including the impact of historical bird abundance, and the effect of preserving vs. removing birds, on smolt abundance. Each year, <1% of the estimated available salmonid smolts (interannual range: 44,830-109,209; 95% CI = 38,000-137,000) were consumed, 85-98% away from dams. Current diet data combined with historical gull abundance at dams suggests that past smolt consumption may have been 1.5-3 times current numbers, depending on the assumed distribution of gulls along the reaches. After the majority (80%) of salmonid smolts have left the study area, birds switch their diet to predominantly juvenile northern pikeminnow (Ptychocheilus oregonensis), which as adults are significant native salmonid predators in the Columbia River. Our models suggest that one consequence of removing birds from the system may be increased pikeminnow abundance, which--even assuming 80% compensatory mortality in juvenile pikeminnow survival--would theoretically result in an annual average savings of just over 180,000 smolts, calculated over a decade. Practically, this suggests that smolt survival could be maximized by deterring birds from the river when smolts are present, allowing bird presence after the diet switch to act as a tool for salmonid-predator control, and conducting adult-pikeminnow control throughout. Our analysis demonstrates that identifying the strength of ecosystem interactions represents a top priority when attempting to manage the abundance of a particular ecosystem constituent, and that the consequences of a single-species view may be counterintuitive, and potentially counterproductive. 相似文献
112.
Costas A. Velis David C. Wilson Christopher R. Cheeseman 《Waste management (New York, N.Y.)》2009,29(4):1282-1290
The material recovery methods used by dust-yards in early 19th century London, England and the conditions that led to their development, success and decline are reported. The overall system developed in response to the market value of constituents of municipal waste, and particularly the high coal ash content of household ‘dust’. The emergence of lucrative markets for ‘soil’ and ‘breeze’ products encouraged dust-contractors to recover effectively 100% of the residual wastes remaining after readily saleable items and materials had been removed by the thriving informal sector. Contracting dust collection to the private sector allowed parishes to keep the streets relatively clean, without the need to develop institutional capacity, and for a period this also generated useful income. The dust-yard system is, therefore, an early example of organised, municipal-wide solid waste management, and also of public–private sector participation. The dust-yard system had been working successfully for more than 50 years before the Public Health Acts of 1848 and 1875, and was thus important in facilitating a relatively smooth transition to an institutionalised, municipally-run solid waste management system in England. The dust-yards can be seen as early precursors of modern materials recycling facilities (MRFs) and mechanical–biological treatment (MBT) plants; however, it must be emphasised that dust-yards operated without any of the environmental and occupational health considerations that are indispensable today. In addition, there are analogies between dust-yards and informal sector recycling systems currently operating in many developing countries. 相似文献
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Francesca Porri Gerardo I. Zardi Christopher D. McQuaid Sarah Radloff 《Marine Biology》2007,152(3):631-637
Settlement is a major determinant of intertidal populations. However, the energy costs of lost larvae are very high. Accordingly,
arrival and attachment on suitable substrata are essential requirements for species’ survival. On the intertidal, the presence
of cues left by adult or juvenile conspecifics could be vital for the successful establishment of larvae arriving on the shore.
Two mussel species, the indigenous Perna perna and the invasive Mytilus galloprovincialis, co-occur on the lower eulittoral zone on the south coast of South Africa. P.
perna dominates the low and M. galloprovincialis the high mussel zones, with co-existence in the mid mussel zone. This study tested the hypothesis of settlement selectivity
for conspecifics in these two mussel species, to understand whether the final adult distribution of mussels on the shores
is determined by active behavioural and chemical mechanisms. Preferential selection by larvae for conspecifics was tested
in the field during the peak settlement period in 2004 in natural mussel beds across zones and through manipulative experiments
in the mid-zone where the species co-exist. On natural beds, settlement was determined by counts of settlers attached over
48 h onto artificial collectors. Collectors were placed on beds of P. perna and M. galloprovincialis present at both high- and low-adult densities, as well as in mixed beds. On such natural beds, settlers of both species consistently
favored low-zone P. perna beds. Settlement patterns over 24 h onto experimentally created mussel patches consisting of P.
perna, M. galloprovincialis or the two species combined beds, set in the mixed zone, did not conform with the results of the natural beds study: settlers
of both species settled with no discrimination among different patches. The results indicate that mussels, which are sedentary,
lack attraction to conspecifics at settlement. This highlights the importance of tidal height in setting settlement rates,
and of post-settlement events in shaping populations of these broadcast spawners. 相似文献
116.
Christopher R. Smith 《Behavioral ecology and sociobiology》2007,61(9):1479-1487
Limitation of a necessary resource can affect an organism’s investment into growth and reproduction. Pogonomyrmex harvester ants store vast quantities of seeds in their nests that are thought to buffer the ants when external resources
are not available. This research uses externally controlled food availability to examine how resource shortage affects colony
investment, resource use, and resource distribution within the nest. Colonies were either starved or supplemented with resources
for 2 months, beginning at the onset of reproductive investment and ending immediately before nuptial flights. Fed colonies
invested more in overall production, proportionally more in reproduction relative to growth and in female reproductives relative
to males. Stored seeds in starved colonies did not buffer production in this study. However, worker fat reserves were depleted
in starved colonies, indicating that fat reserves fuel the spring bout of production. In starved colonies, worker fat reserves
were depleted evenly throughout the nest, distributing the burden of starvation on all workers regardless of caste and age.
A reallocation of diploid eggs into female workers rather than reproductives best explains the observed change in sex ratio
investment between treatments. The redistribution of resources into growth relative to reproduction in starved colonies is
consistent with life history theory for long-lived organisms, switching from current to future reproduction when resources
are scarce. 相似文献
117.
Alireza A. Shamshirsaz Kelsey A. Stewart Hadi Erfani Ahmed A. Nassr Nathan C. Sundgren Amy R. Mehollin-Ray Shaine A. Morris Jimmy Espinoza Magdalena Sanz Cortes Christopher Cassady Timothy C. Lee Eumenia C. Castro Olutoyin A. Olutoye Deepak K. Mehta Darrell Cass Oluyinka O. Olutoye Michael A. Belfort 《黑龙江环境通报》2019,39(4):287-292
118.
Jonathan A. Villines Carmen T. Agouridis Richard C. Warner Christopher D. Barton 《Journal of the American Water Resources Association》2015,51(6):1667-1687
Headwater streams have a significant nexus or physical, chemical, and/or biological connection to downstream reaches. Generally, defined as 1st‐3rd order with ephemeral, intermittent, or perennial flow regimes, these streams account for a substantial portion of the total stream network particularly in mountainous terrain. Due to their often remote locations, small size, and large numbers, conducting field inventories of headwater streams is challenging. A means of estimating headwater stream location and extent according to flow regime type using publicly available spatial data is needed to simplify this complex process. Using field‐collected headwater point of origin data from three control watersheds, streams were characterized according to a set of spatial parameters related to topography, geology, and soils. These parameters were (1) compared to field‐collected point of origin data listed in three nearby Jurisdictional Determinations, (2) used to develop a geographic information system (GIS)‐based stream network for identifying ephemeral, intermittent, and perennial streams, and (3) applied to a larger watershed and compared to values obtained using the high‐resolution National Hydrography Dataset (NHD). The parameters drainage area and local valley slope were the most reliable predictors of flow regime type. Results showed the high‐resolution NHD identified no ephemeral streams and 9 and 65% fewer intermittent and perennial streams, respectively, than the GIS model. 相似文献
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