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71.
Differences in particle size distribution between runoff standards and unknown samples affect the accuracy of estimation of total suspended solids (TSS) concentration using the nephelometric turbidity (NTU) method. The objective was to quantify the effects of a sucrose solution as suspending medium and contrasting particle size distribution on nephelometric turbidity and accuracy of TSS estimation. Nineteen benchmark soils varying in texture and color were divided into particle size distribution of <250 and <2000 microm. Soils from these two aggregate classes were then made into suspension ranging from 0.2 to 15 g L-1 using distilled deionized water. Runoff suspensions ranging from 0.2 to 21 g L-1 were also collected from different watersheds. Turbidity of soil and runoff suspensions was measured in sucrose solution and in distilled deionized water. The sucrose solution density ranged from 1.10 to 1.30 kg L-1. Increasing sucrose solution density decreased turbidity. The TSS concentration was most sensitive to changes in turbidity with the 1.30 kg L-1 sucrose solution. Using the 1.30 kg L-1 sucrose solution, particle size bias and error of TSS estimates were decreased by at least 20% compared to distilled deionized water. Reduction in refraction index differences between the suspended particles and sucrose solution combined with reduced particle settling and reduced Brownian motion resulted in dampening the effects of particle size distribution. We propose a sucrose solution of 1.30 kg L-1 as a better suspending medium to dampen the effect of particle size distribution and thus improve suspension TSS concentration estimation. 相似文献
72.
Andrew M. Robbins Tara S. Stoinski Katie A. Fawcett Martha M. Robbins 《Behavioral ecology and sociobiology》2009,63(4):477-489
Socioecological models indicate that the group structure and female dispersal patterns of primates are determined primarily by the abundance and distribution of food, predation pressures, and infanticide risks. In response to those influences, females of folivorous primates are considered relatively free to disperse into groups with the optimal size and structure. Yet some folivores live in small groups despite a potentially higher risk of predation, an apparent inconsistency known as the folivore paradox. This paper examines the female dispersal of a folivorous primate, the Virunga mountain gorillas. Mountain gorillas currently have no natural predators, but this species presents a different version of the folivore paradox: why do 50–60% of females reside in smaller one-male groups despite a higher risk of infanticide? In this study, females left one-male groups more frequently than multimale groups, but transfer destinations were not consistently biased toward multimale groups and those groups did not have higher immigration rates. We found no evidence of dispersal to avoid feeding competition within large groups, even as they have become three to five times larger than average. Thus, the lack of a consistent bias toward multimale groups was not because they are typically larger than one-male groups. Instead, the apparent inconsistencies may reflect limited female transfer opportunities, other influences on dispersal, and possibly an evolutionary disequilibrium in which current behavior does not optimize fitness. 相似文献
73.
Martha P. GarcÍa De Llasera Adriana RodrÍguez-Castillo Luz E. Vera-Avila 《Journal of environmental science and health. Part. B》2013,48(6):615-627
The effect of organic matter on the solid-phase extraction (SPE) efficiency for pesticides belonging to different chemical groups (urea-derivatives, carbamates and triazines) and having different polarities, was simultaneously studied for the first time in pure and simulated water samples. SPE was carried out in precolumns packed with C18 silica or styrene-divinylbenzene copolymer PLRP-S phases on-line coupled to high performance liquid chromatography (HPLC) analysis. Retention factors in water (k'W) were estimated for 25 compounds and used for the calculation of the theoretical breakthrough volume (VbT) in pure water. Experimental breakthrough volumes (VbE) were first determined using purified and deionized water as the matrix for selected compounds having VbT < 500 mL; then, the same water with an added humic acid sodium salt (HA) at 0.4–5.6 mg/L of dissolved organic carbon (DOC) content, was used as the matrix for compounds having VbE < 500 mL in pure water. Several polar pesticides showed negative linear or logarithmic VbE curves depending on HA content; their recoveries were also determined in environmental samples having low dissolved organic carbon values, between 0.5–6.4 mg/L. A similar behavior was observed for these compounds in simulated and natural water samples, where DOC concentration and the percolated volume (Vp) mainly determine the solute recoveries values. However, the variation of recoveries as a function of DOC content could be negative or null depending on the two examined conditions (Vp lower or larger than VbE in pure water). Results demonstrated that breakthrough volume must always be considered to correctly interpret the participation of dissolved humic material on the SPE efficiency of organic micropollutants in water. 相似文献
74.
A study of 13 small (less than 7.5 km2) watersheds on Mt. Desert Island, Maine, was conducted from January 1999 to September 2000 to determine nutrient export delivery
to coastal waters around the island, and to determine whether a series of wildfires in 1947 have affected nutrient export
in burned watersheds. Nutrient export (nitrate–nitrogen, total nitrogen, total phosphorus) was determined for each watershed
during the study period, and was normalized by watershed area. The yield of nitrate–nitrogen (N) ranged from 10 to 140 kg/km2/year. Total N yield ranged from 42 to 250 kg/km2/year. Total phosphorus (P) yield ranged from 1.4 to 7.9 kg/km2/year. Watersheds entirely within Acadia National Park (lacking human land-based nutrient sources) exported significantly
less total N and total P than watersheds that were partly or entirely outside the park boundary. Nitrate–N export was not
significantly different in these two groups of watersheds, perhaps because atmospheric deposition is a dominant source of
nitrate in the study area. No relation was observed between burn history and nutrient export. Any effect of burn history may
be masked by other landscape-level factors related to nutrient export. 相似文献
75.
Jeffrey S. Brown Martha Sutula Chris Stransky John Rudolph Earl Byron 《Journal of the American Water Resources Association》2010,46(2):367-385
Brown, Jeffrey S., Martha Sutula, Chris Stransky, John Rudolph, and Earl Byron, 2010. Sediment Contaminant Chemistry and Toxicity of Freshwater Urban Wetlands in Southern California. Journal of the American Water Resources Association (JAWRA) 46(2):367-384. DOI: 10.1111/j.1752-1688.2009.00407.x Abstract: Wetlands provide many critical functions in urban ecosystems, including habitat for wetland-dependent fauna and enhancement of water quality. Interest in restoring or creating wetlands to enhance these functions is increasing due to the scale and extent of wetland loss and water quality problems associated with urbanization. One of the most pressing questions associated with urban wetland restoration is the extent to which urban wetlands tend to concentrate contaminants, and if so, whether an associated risk to wildlife exists. The goal of this study was to better understand these potential risks, and the associated tradeoffs with using wetlands to treat urban runoff. Sediment toxicity, contaminant chemistry, and macroinvertebrate (MI) community metrics were measured in 21 southern California wetlands that receive urban runoff as their primary water source. MI organisms in 18 of the 21 urban wetlands examined were considered to be at risk due to sediment contaminant concentrations and toxicity. Most of the sites were either toxic to the amphipod Hyalella azteca, exceeded a sediment quality guideline, or both. Sediment chemistry and toxicity identification evaluation studies suggest that pyrethroid pesticides may have been responsible for much of the toxicity documented in this study. The mean Probable Effects Concentration quotient (an index of degree of sediment contamination) was found to negatively correlate with MI diversity in these wetlands suggesting that toxicity was affecting organisms at the base of the food chain in these wetlands. 相似文献
76.
OBJECTIVES: Most states now have lengthy learner periods for young, beginning drivers as part of their graduated driver licensing (GDL) systems. Although parents play a vital role during the learner stage of GDL by supervising driving practice, virtually nothing is known about the nature and quality of parental supervision. The objectives of this study were to investigate parents' supervisory behavior and parent-teen relationships during the learner stage of graduated licensing and to evaluate two approaches for assisting parents in supervising their teenager's early driving experience. METHODS: Families of teenagers applying for a learner permit received either a booklet describing highly structured practice sessions for beginning drivers, a series of "tip sheets" offering more generalized guidance, or no special materials. Questionnaires were sent separately to parents and teenagers three to six months after teenagers obtained their permit. RESULTS: Of 1,190 participating families, 653 parents (55%) and 609 teenagers (51%) responded. Both parents and teenagers perceived parents as supportive and helpful during driving sessions. Parents often demonstrated positive behaviors, such as complimenting their teenager and pointing out possible hazards; they also exhibited less desirable behaviors, such as raising their voice, but these were less frequent. A majority of parents (71%) and teenagers (52%) reported that they enjoyed spending this time together. About four months after obtaining a permit, most parents believed their teenager did not yet have enough experience and was not ready to drive unsupervised. Although the reported behaviors are encouraging, within-family agreement was low on most items. Finally, efforts to assist parents proved unsuccessful. Although parents thought the booklet and tip sheets were helpful, most used these materials only in a general way. CONCLUSIONS: The extended learning experience required by GDL programs is a positive experience for many families. However, finding a method for helping parents achieve maximum benefits during this process will be challenging. The results also suggest that current requirements in the learner phase of most state GDL systems (six months; 30-50 hours) may be inadequate to ensure that teenagers obtain a sufficient amount of experience to begin driving safely on their own. 相似文献
77.
78.
Edward Wright Andrew M. Robbins Martha M. Robbins 《Behavioral ecology and sociobiology》2014,68(6):957-970
Socioecological models predict that contest competition for clumped foods can lead to higher energy intake and lower energy expenditure for higher-ranking individuals. Here, we examine the relationships between dominance rank and energy intake and expenditure of female mountain gorillas in Bwindi Impenetrable National Park, Uganda (Gorilla beringei beringei). Bwindi gorillas have weak dominance relationships, feed on nonreproductive plant parts throughout the year, and consume fruit when it is seasonally available. We used behavioral observations on one group of gorillas and nutritional analysis of their major food items to calculate energy intake rates and estimated energy expenditure. Using linear mixed models, we found a significant positive relationship between dominance rank and energy intake rates, due to higher-ranking females having faster ingestion rates, rather than consuming foods with higher energy concentrations. Lower-ranking females did not spend significantly more time feeding to compensate for their lower energy intake rates. Lower-ranking females spent significantly more time traveling than higher-ranking females, leading to a negative relationship between dominance rank and energy expenditure. The combined results revealed a significant positive relationship between dominance rank and energy balance. Higher-ranking females did not spend longer feeding on fruit than lower-ranking ones, and the relationship between dominance rank and energy intake rates was not stronger when fruit was available. According to socioecological models, these results suggest that contest competition may be occurring with both fruit and nonreproductive plant parts, which would be consistent with growing evidence that nonreproductive plant parts can be contestable. 相似文献
79.
As settled juveniles and adults, blue rockfish (Sebastes mystinus) are nonmigratory inhabitants of kelp and rocky reef habitats along the California coast, USA, and prior to settlement, they
possess a pelagic larval and juvenile stage lasting 3–5 months. A previous study of adults revealed two cryptic species within
S. mystinus and evidence of reproductive isolation in a region where both cryptic adults co-occur. Given this pattern of reproductive
isolation, we investigated the degree of hybridization or introgression in individual year-classes shortly after juvenile
settlement in two different years (2001 and 2002). Using microsatellite markers, we found little indication of hybridization
in new juvenile year-classes despite an adult population that comprised both cryptic species. However, we found an average
of two percent of hybrid or introgressed individuals in regions with a low frequency of one of the two species. Therefore,
while the lack of hybrids or introgression supports the hypothesis of reproductive isolation between the cryptic species within
S. mystinus, the age-structured analysis also revealed a spatial pattern of low-frequency differences in the number of introgressed individuals.
These results suggest that reproductive barriers may breakdown when one of the two species predominates the regional adult
gene pool. 相似文献
80.
The conservation of rare plant species hinges on our ability to identify the underlying mechanisms that limit rare plant populations. Theory on rarity suggests that both predispersal seed predation and competition can be important mechanisms influencing abundance and/or distribution of rare plant populations. Yet few studies have tested these interactions, and those that have evaluated each mechanism independently. Astragalus sinuatus Piper (Whited's milkvetch) is a narrow endemic plant species restricted to eight populations within a 10-km2 area in eastern Washington. We used experimental and observational methods to test the effects of native insect predispersal seed predators and an invasive grass (Bromus tectorum L. [cheatgrass]) on seed set and population density of A. sinuatus. We quantified per capita seed production and pod predation rates across four sites and among four years. Seed predation rates were high across four sites (66-82%) and all years (65-82%). Experimental reduction of predispersal seed predators significantly increased per capita seed set of A. sinuatus (164-345%) at two experimental sites. Concurrently, two seed addition experiments demonstrated the effect of seed loss and presence of B. tectorum on seedling recruitment and establishment of A. sinuatus over four growing seasons. In the first seed addition experiment, we found no difference in recruitment and establishment between low (40) and high (120) seed addition levels. In the second addition experiment (one level of addition; 40 seeds), we found that recruitment and survivorship increased 200% in plots where B. tectorum was removed compared to plots where B. tectorum was present. Thus, seed addition had no impact in the presence of B. tectorum; conversely, in the absence of B. tectorum, seed addition was highly effective at increasing population numbers. Results suggest that, in areas where B. tectorum is present, recruitment is site limited, and it is seed limited when B. tectorum is absent. We recommend that managers reduce B. tectorum in an effort to increase population growth of A. sinuatus; in areas where B. tectorum is absent, short-term reduction of insect predators should be considered as a strategy to increase population growth of this rare species. 相似文献