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501.
建立了吹脱捕集气相色谱法测定水中7种挥发性卤代烃的分析方法。对色谱条件、吹脱时间、实验用水等进行了探讨,同时对分析参数如线性相关性、相对标准偏差、最低检出限及加标回收率进行了评价。结果表明,采用吹脱捕集气相色谱法,在1.0μg/L~20.0μg/L范围内,7种卤代烃的质量浓度和峰面积呈良好的线性关系;10.0μg/L的7种挥发性卤代烃标准溶液经重复7次测定,其相对标准偏差为1.30%~8.71%;水样的加标回收率在86.3%~110%之间;最低检出限在0.17μg/L~0.96μg/L之间,该方法已成功地应用于饮用水和地表水中挥发性卤代烃的定性定量测定,结果令人满意。 相似文献
502.
503.
Fabrice Vinatier Françoise LescourretPierre-François Duyck Philippe Tixier 《Agriculture, ecosystems & environment》2012,146(1):52-59
The development of alternative pest-control strategies based on the spatial design of cropping systems requires a thorough understanding of the spatial links between the pest and its environment. Mechanistic models, especially individual-based models (IBMs), are powerful tools for integrating key behaviours, such as habitat selection and dispersal, with spatial heterogeneity. In this paper, we used an IBM calibrated and evaluated from real data to represent the spatial dynamics of the banana weevil in relation to the cropping system. We considered crop fragmentation and mass trapping as tools for suppressing pest numbers. Our simulation results showed that manipulating crop residues in the area surrounding each pheromone trap greatly improved trap efficiency. For an intensive banana plantation in fallow, traps were most effective when situated at the transition zone between banana area and fallow so as to maximize the trapping of weevils escaping the fallow. The model also showed that weevil numbers decreased when fragmentation of banana plantations was reduced. 相似文献
504.
505.
采用改进的Tessier连续萃取法对表层沉积物中重金属(内源体系:Fe、Mn、Cu、Zn和Pb;外源体系:掺杂Cu、Zn和Pb后的Fe、Mn、Cu、Zn和Pb)一定时间(45d)内的形态分布进行分析,探讨了混合菌对体系中重金属形态及生物有效性的影响。混合菌的加入促进了沉积物中Fe向可交换态、碳酸盐结合态的转变,Fe的生物有效性显著提高;混合菌的掺杂导致了Mn向稳定态的移动,体系中Mn的各形态除可交换态含量均有所提高,且混合菌可以提高Mn的生物有效性;混合菌的存在增加了内源体系中Zn的铁锰氧化态稳定性,外源体系中混合菌的添加促进了其活化作用,与混合菌前33d降低金属有效性相矛盾;混合菌加入使内源体系中Pb残渣态和外源体系中有机质结合态升高,与混合菌加大Pb的有效性不吻合;混合菌可导致内源体系Cu的铁锰氧化物含量增加和铁锰氧化物态下降、Cu的生物有效性提高,而外源体系中前Cu的碳酸盐结合态上升,混合菌降低了Cu生物有效性。 相似文献
506.
Contaminated groundwater and a riverine sediment core heavily affected by the same industrial point source were analysed for
hexachlorocyclohexanes (HCH) and its degradation products. A detailed quantification by GC/MS revealed contamination levels
up to 730 μg/L and 396 ng/g in sum for the water and sediment samples, respectively. The isomer pattern differed significantly
in both compartments. The ground water samples were depleted in γ-HCH, whereas a significant loss of α-HCH was evident in
the sediments as compared to the technical composition. The data obtained revealed interesting insights into the transformation
behaviour and fate of HCH mixtures in anaerobic environmental compartments. In the affected groundwater system an ongoing
microbial degradation was pointed out by the identification of indicative anaerobic metabolites. On the contrary in the sedimentary
system a high environmental stability or rather a hindered degradation was observed as indicated by unaltered concentration
levels as compared to production rates as well as by the absence of metabolites. Interestingly, the environmental fate of
HCH in subaquatic sediments as well as in anaerobic ground water differs highly in contrast to the behaviour in anaerobic
soil or surface water systems. Further on, it has to be stated, that the knowledge about the long-term behaviour of HCH residues
in sedimentary material under anaerobic conditions is rather limited so far. 相似文献
507.
The distribution of lignin in sediment is a useful tool for tracing the transport of land-derived organic matter in an aquatic
environment. Tetramethylammonium hydroxide (TMAH) flash chemopyrolysis, or chemolysis followed by GC–MS analysis can be used
for evaluating the origin of organic carbon in sediments. TMAH chemopyrolysis or chemolysis of organic matter produces a myriad
of semi-volatile products. Among these products are methylated phenols which are an indirect measure of lignin in sediment.
In this study, total organic carbon, elemental carbon, and lignin were measured in Lake Mead sediments. This study indicates
that terrestrial runoff makes a contribution to Lake Mead sediments, and that this contribution is most apparent in sediment
that is close to the Las Vegas Wash. Two chemolysis methods (on-line and off-line) were examined and compared for detection
of lignin phenols. The results from these sediment cores indicate that comparable results can be obtained from the two approaches,
although detection levels are significantly lower for the off-line approach. 相似文献
508.
Abstract: The emerging world crisis created by declining fish stocks poses a challenge to resource users and managers. The problem is particularly acute in poor nations, such as those in East Africa, where fishing is an important subsistence activity but high fishing intensity and use of destructive gear have resulted in declining catches. In this context developing effective management strategies requires an understanding of how fishers may respond to declines in catch. We examined the readiness of 141 Kenyan fishers to stop fishing under hypothetical scenarios of declines in catch and how socioeconomic conditions influenced their decisions. As expected, the proportion of fishers that would exit the fishery increased with magnitude of decline in catch. Fishers were more likely to say they would stop fishing if they were from households that had a higher material style of life and a greater number of occupations. Variables such as capital investment in the fishery and the proportion of catch sold had weak, nonsignificant relationships. Our finding that fishers from poorer households would be less likely to exit a severely declining fishery is consistent with the literature on poverty traps, which suggests the poor are unable to mobilize the necessary resources to overcome either shocks or chronic low-income situations and consequently may remain in poverty. This finding supports the proposition that wealth generation and employment opportunities directed at the poorest fishers may help reduce fishing effort on overexploited fisheries, but successful interventions such as these will require an understanding of the socioeconomic context in which fishers operate. 相似文献
509.
510.
Hierarchical modeling of the dilute transport of suspended sediment in open channels 总被引:1,自引:1,他引:0
We propose, discuss and validate a theoretical and numerical framework for sediment-laden, open-channel flows which is based
on the two-fluid-model (TFM) equations of motion. The framework models involve mass and momentum equations for both phases
(sediment and water) including the interactive forces of drag, lift, virtual mass and turbulent dispersion. The developed
framework is composed by the complete two-fluid model (CTFM), a partial two-fluid model (PTFM), and a standard sediment-transport
model (SSTM). Within the umbrella of the Reynolds-Averaged Navier-Stokes (RANS) equations, we apply K–ε type closures (standard and extended) to account for the turbulence in the carrier phase (water). We present the results
of numerical computations undertaken by integrating the differential equations over control volumes. We address several issues
of the theoretical models, especially those related to coupling between the two phases, interaction forces, turbulence closure
and turbulent diffusivities. We compare simulation results with various recent experimental datasets for mean flow variables
of the carrier as well as, for the first time, mean flow of the disperse phase and turbulence statistics. We show that most
models analyzed in this paper predict the velocity of the carrier phase and that of the disperse phase within 10% of error.
We also show that the PTFM provides better predictions of the distribution of sediment in the wall-normal direction as opposed
to the standard Rousean profile, and that the CTFM is by no means superior to the PTFM for dilute mixtures. We additionally
report and discuss the values of the Schmidt number found to improve the agreement between predictions of the distribution
of suspended sediment and the experimental data. 相似文献