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691.
Douglas F. Bertram 《Conservation biology》1995,9(4):865-872
I examined the decline of Ancient Murrelets ( Synthliboramphus antiquus ), a small, burrow-nesting seabird, at Langara Island. The island's seabird colony was historically one of the largest colonies of Ancient Murrelets in British Columbia—perhaps in the world—with an estimated 200,000 nesting pairs. I reviewed historical information and compared the results of surveys from 1981 and 1988 that employed the same census protocol. The extent of the colony, a potential index of population size, declined from 101 ha in 1981 to 48 ha in 1988. Burrow density increased during the same period, however, suggesting that the colony bad consolidated. In 1988, the population estimate was 24,200 ± 4000 (S.E.) breeding pairs compared to 22,000 ± 3700 in 1981. in 1988, 29% of the burrows that were completely searched contained bones of Ancient Murrelets. Bones were most common in burrows located in abandoned areas of the colony and were least common where burrow occupancy was high. The discovery of adult Ancient Murrelets killed in their burrows by introduced rats, combined with the high proportion of burrows with bones, suggests that rats ( Rattus rattus and R. norvegicus ) have contributed significantly to the decline of the population. In addition, the presence and activities of a salmon-fishing fleet in the 1950s and 1960s may also be linked to the decline of the Langara Ancient Murrelet population during that period because these fisheries are known to have caused heavy mortality through fatal light attraction and drowning in gill nets. The combined effects of ongoing predation by introduced rats and—to a lesser extent—previous, episodic fishery-induced mortality are probable causes for the population decline. 相似文献
692.
The abundance of exotic plants is thought to be limited by competition with resident species (including plants and generalist herbivores). In contrast, observations in semiarid Chile suggest that a native generalist rodent, the degu (Octodon degus), may be facilitating the expansion of exotic annual plants. We tested this hypothesis with a 20-year data set from a World Biosphere Reserve in mediterranean Chile. In this semiarid environment, rainfall varies annually and dramatically influences cover by both native and exotic annual plants; degu population density affects the composition and cover of exotic and native annual plants. In low-rainfall years, cover of both native and exotic herbs is extremely low. Higher levels of precipitation result in proportional increases in cover of all annual plants (exotic and native species), leading in turn to increases in degu population densities, at which point they impact native herbs in proportion to their greater cover, indirectly favoring the expansion of exotic plants. We propose that bottom-up control of consumers at our site results in top-down indirect facilitation of invasive annual herbs, and that this pattern may be general to other semiarid ecosystems. 相似文献
693.
A wide variety of hypotheses has been proposed to explain the structural diversity in bird song repertoires. Song diversity
is frequently described in terms of song “types” or within-type “variants.” Male Puget Sound white-crowned sparrows, Zonotrichia leucophrys pugetensis, produce variants of their single adult song type by altering the number of repetitions of syllables in the terminal trill.
We tested whether variation in trill length correlated with distance to the receiver and with signaling context as predicted
by the eavesdropping avoidance hypothesis and the strategic signaling hypothesis. In accordance with the eavesdropping avoidance
hypothesis, males sang variants with shorter trills, and sang quieter and less frequently when near their mate during the
incubation phase than during spontaneous singing while unpaired. Males also sang variants with short trills, but at a high
rate and variable amplitude when within 10 m of an opponent during close male–male territorial interactions. In agreement
with the strategic signaling hypothesis, males decreased trill length immediately before chasing an opponent, but did not
change length consistently prior to flight. We conclude that the occurrence of short quiet songs sung near the mate agrees
with predictions of the eavesdropping avoidance hypothesis, while short songs sung near other males are best explained by
the strategic signaling hypothesis. Trill length variation may be a conventional signal of aggressive intentions in male–male
contests stabilized by receiver-imposed retaliation costs. 相似文献
694.
695.
Zachary Douglas Cole Holly M. Donohoe Michael L. Stellefson 《Environmental management》2013,51(3):511-523
The interactive capacity of the Internet offers benefits that are intimately linked with contemporary research innovation in the natural resource and environmental studies domains. However, e-research methodologies, such as the e-Delphi technique, have yet to undergo critical review. This study advances methodological discourse on the e-Delphi technique by critically assessing an e-Delphi case study. The analysis suggests that the benefits of using e-Delphi are noteworthy but the authors acknowledge that researchers are likely to face challenges that could potentially compromise research validity and reliability. To ensure that these issues are sufficiently considered when planning and designing an e-Delphi, important facets of the technique are discussed and recommendations are offered to help the environmental researcher avoid potential pitfalls associated with coordinating e-Delphi research. 相似文献
696.
Paul Kirshen Chris Watson Ellen Douglas Allen Gontz Jawon Lee Yong Tian 《Mitigation and Adaptation Strategies for Global Change》2008,13(5-6):437-451
With dense population and development along its coastline, the northeastern United States is, at present, highly vulnerable to coastal flooding. At five sea level stations in the United States, from Massachusetts to New Jersey, sea level rise (SLR) trends and tidal effects were removed from the hourly sea level time series and then frequency analysis was performed on the positive remaining anomalies that represent storm surge heights. Then using eustatic SLR estimates for lower and higher greenhouse gas emissions scenarios and assumed trends in local sea level rise, new recurrence intervals were determined for future storm surges. Under the higher emissions scenario, by 2050, the elevation of the 2005 100-year event may be equaled or exceeded at least every 30 years at all sites. In more exposed US cities such as Boston, Massachusetts and Atlantic City, New Jersey, this could occur at the considerably higher frequency of every 8 years or less. Under the lower emissions scenario, by 2050, the elevation of the 2005 100-year event may be equaled or exceeded at least every 70 years at all sites. In Boston and Atlantic City, this could occur every 30 years or less. 相似文献
697.
Kitto ME Fielman EM Haines DK Menia TA Bari A 《Journal of environmental radioactivity》2008,99(8):1255-1257
Methods currently approved for the measurement of radon ((222)Rn) in water in New York State are liquid scintillation counting and emanation into alpha-scintillation cells. A passive system using an electret ion chamber (EIC) was evaluated as an alternative for the measurement of radon in water. Over 130 water samples from a community water supply containing 32BqL(-1) and 30 standards containing 686BqL(-1) were measured using the EIC method over 1- to 4-day exposure times. For comparison, identical samples were measured using liquid scintillation counting. Results of duplicate samples were typically within 5% for liquid scintillation counting and within 10% for the EIC. With respect to accuracy, the EIC produced results that were consistently low by 11-15%. 相似文献
698.
Stephanie J. Perles Tyler Wagner Brian J. Irwin Douglas R. Manning Kristina K. Callahan Matthew R. Marshall 《Environmental management》2014,54(3):641-655
Forests are socioeconomically and ecologically important ecosystems that are exposed to a variety of natural and anthropogenic stressors. As such, monitoring forest condition and detecting temporal changes therein remain critical to sound public and private forestland management. The National Parks Service’s Vital Signs monitoring program collects information on many forest health indicators, including species richness, cover by exotics, browse pressure, and forest regeneration. We applied a mixed-model approach to partition variability in data for 30 forest health indicators collected from several national parks in the eastern United States. We then used the estimated variance components in a simulation model to evaluate trend detection capabilities for each indicator. We investigated the extent to which the following factors affected ability to detect trends: (a) sample design: using simple panel versus connected panel design, (b) effect size: increasing trend magnitude, (c) sample size: varying the number of plots sampled each year, and (d) stratified sampling: post-stratifying plots into vegetation domains. Statistical power varied among indicators; however, indicators that measured the proportion of a total yielded higher power when compared to indicators that measured absolute or average values. In addition, the total variability for an indicator appeared to influence power to detect temporal trends more than how total variance was partitioned among spatial and temporal sources. Based on these analyses and the monitoring objectives of the Vital Signs program, the current sampling design is likely overly intensive for detecting a 5 % trend·year?1 for all indicators and is appropriate for detecting a 1 % trend·year?1 in most indicators. 相似文献
699.
Online crowdfunding can help address the perennial financial shortfalls in environmental conservation and management. Although many online crowdfunding campaigns fail to collect any funds due to not achieving their targets, little is known about what drives success. To address this knowledge gap, we applied a mixed-methods approach to data from 473 successful and failed campaigns hosted on the online crowdfunding platform Readyfor. We found that fundraising performance varied by topic, with campaigns on pet animal management outperforming those focussed on landscape management and sustainable use. We also found that marketing strategies associated with online findability and increased reach through social networks, increased fundraising success. However, the existence of other environmental campaigns running simultaneously, reduced the chance of success, which implies that the selecting popular topics does not always increase the likelihood of success due to increased competition. Wider applications of marketing could enhance the ability of environmental crowdfunding campaigns to raise funds.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01522-0. 相似文献
700.
An experiment was conducted to determine the influence the time of brush-cutting can have on plant regrowth and attractiveness
to herbivores that browse in linear corridors. The influence of cutting time on leaf flush and senescence, shoot morphometry,
and biomass was measured for 3 consecutive years after initial brush-cutting. Results indicate that morphological and phenological
attributes of three woody deciduous plants were influenced by the timing of brush-cutting for up to 3 years after initial
cutting. Brush-cutting generally stimulated plants to produce larger than normal shoots and delay leaf senescence. The degree
to which plants were affected, however, varied with the timing of initial cutting and the species in question. Generally,
plants cut later in the year resprouted more vigorously and were taller in the third year after cutting but produced less
overall biomass than when cut earlier. In the years following brush-cutting, plants cut earlier flushed leaves earlier in
the spring but delayed leaf senescence in the fall when compared to uncut controls. Results of these trials suggest that brush-cutting
time influences plant response and several plant attributes known to influence plant attractiveness to moose and other herbivores.
We therefore recommend that roadside and railside vegetation management plans consider the influence of cutting time on plant
regrowth. Such considerations can ensure that brush is cut to reduce the attractiveness of plant regrowth in these linear
corridors, reduce the utilization of such brush by herbivores, and, as such, mitigate collision risk between motorists and
herbivores such as moose. 相似文献