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301.
302.
Hydraulic conductivity and sorption coefficients for chlorinated hydrocarbons (chloroform, carbon tetrachloride and tetrachloroethylene) were evaluated for 216 sediment samples collected across a 15 m transect and a 21 m depth interval in a contaminated aquifer near Schoolcraft, Michigan. Relationships between hydraulic conductivity, linear sorption partition coefficients, grain size classes, and spatial location were investigated using linear regression analysis and geostatistical techniques. Clear evidence of layering was found in sorption properties, hydraulic conductivity and grain sizes. Conductivity correlated well with grain size, as expected, but sorption varied inversely with grain size, contrary to some previous reports. No significant correlation was found between sorption properties and hydraulic conductivity. This is likely due to the unexpected presence of small amounts of highly sorptive coal-like solids, which dominate the sorption behavior but have little effect on conductivity. The results demonstrate that recent findings regarding the high sorption capacity of coal materials found in soils can exert a controlling influence on contaminant transport. Designers of in situ remediation systems should be cautioned that 1) it is not reasonable to assume that sorption capacity and hydraulic conductivity are related, 2) sorption capacity and hydraulic conductivity are critical measurements for contaminant site characterization and subsequent transport modeling, 3) estimating sorption capacity from organic carbon measurement may lead to greater errors than performing sorption isotherms, and 4) it is more important to characterize vertical heterogeneity rather than horizontal heterogeneity because both sorption and hydraulic conductivity are correlated across longer distances in the horizontal plane. 相似文献
303.
304.
VanStone N Przepiora A Vogan J Lacrampe-Couloume G Powers B Perez E Mabury S Sherwood Lollar B 《Journal of contaminant hydrology》2005,78(4):431-325
Stable carbon isotopic analysis, in combination with compositional analysis, was used to evaluate the performance of an iron permeable reactive barrier (PRB) for the remediation of ground water contaminated with trichloroethene (TCE) at Spill Site 7 (SS7), F.E. Warren Air Force Base, Wyoming. Compositional data indicated that although the PRB appeared to be reducing TCE to concentrations below treatment goals within and immediately downgradient of the PRB, concentrations remained higher than expected at wells further downgradient (i.e. >9 m) of the PRB. At two wells downgradient of the PRB, TCE concentrations were comparable to upgradient values, and delta13C values of TCE at these wells were not significantly different than upgradient values. Since the process of sorption/desorption does not significantly fractionate carbon isotope values, this suggests that the TCE observed at these wells is desorbing from local aquifer materials and was present before the PRB was installed. In contrast, three other downgradient wells show significantly more enriched delta13C values compared to the upgradient mean. In addition, delta13C values for the degradation products of TCE, cis-dichloroethene and vinyl chloride, show fractionation patterns expected for the products of the reductive dechlorination of TCE. Since concentrations of both TCE and degradation products drop to below detection limit in wells within the PRB and directly below it, these downgradient chlorinated hydrocarbon concentrations are attributed to desorption from local aquifer material. The carbon isotope values indicate that this dissolved contaminant is subject to local degradation, likely due to in situ microbial activity. 相似文献
305.
Mariusz O. Jedrysek 《Environmental Chemistry Letters》2005,3(3):100-112
Microbial oxidation of organic compounds (including methane), in freshwater sediments, may result in precipitation of carbonates,
which may become an important geochemical archive of paleoenvironmental variations. Most probably low δ13C value in calcite in eutrophic systems results from an advanced oxidation of organic compounds in turbulent or/and sulphate-rich
conditions. Likewise, high δ13C value in calcite from organic-rich sediments may evidence low redox potential of the freshwater system. Oxidation of methane
and organic matter results in significant isotope effects in sulphates dissolved in water. Therefore, to better understand
the origin of carbon isotope signal in carbonates, concentration and stable isotope measurements in dissolved sulphate (water
column), bubble methane and calcite (freshwater sediments) have been carried out in 24 lakes, 2 ponds and 4 rivers in Poland.
The highest concentration of sulphate has been detected in rivers (85.47 SO4
2− mg/l) and an artificial lake (70.30 SO4
2− mg/l) located in the extremely SO4
2−-polluted region called the “Black Triangle”. The lowest concentration of sulphate is found in dystrophic and mountain lakes
(from 0.5 SO4
2− to about 3 mg/l). The lowest δ34S(SO4
2−) and δ18O(SO4
2−) values occur in unpolluted lakes in eastern Poland (−0.94 and 1.38‰, respectively). The highest S and O isotopic ratios
are found in a polluted lake in western Poland (δ14S(SO4
2)=12.95‰) and in a dystrophic lake in eastern Poland (δ18O(SO4
2) = 16.15‰) respectively. It is proposed that δ34SO4
2− and (18O(SO4
2−) values in lakes represent a good tool to assess and quantify anthropogenic impact by acid precipitation and to monitor variations
in the trophic state and redox processes controlled by biodegradation of organic compounds in sediments and water column.
In general, increasing depth (up to 12 m) of the water column is associated with decreasing trend the δ13C(CH4) value from about –35 to about –78‰. However, δ13C value in sedimentary calcite (δ13C vary from –10 to 0.5‰) shows opposite trends as compared to the corresponding methane. This is probably due to redox processes
and distribution of heavy isotopes between methane and calcite. Likewise, turbulent water (river) show high δ13C value in methane and low δ13C value in calcite—this is probably due to an enhanced oxidation of methane producing 13C-depleted CO2. In contrast to clean lakes, it is observed that an increase of the δ13C(CH4) value occurs with increasing depth of the water column in a strongly SO4
2−-contaminated lake. This is probably due to a loss of biological buffering potential of the lake accompanied by an active
oxidation of methane precursors. 相似文献
306.
青岛市生态足迹动态研究 总被引:3,自引:2,他引:3
利用生态足迹和生态承载力度量和评价1995—2004年间的青岛市可持续发展程度。结果发现,随着经济的发展和社会的进步青岛市的生态足迹显著上升,各类用地都呈现增加趋势,耕地增加程度最大,而水域则表现出不稳定;承载力明显下降,其中主要是耕地承载力下降,林地、水域等其他用地则有相对的提高。生态足迹和承载力的变化造成生态赤字进一步加大。将单位生态足迹内产生的GDP作为生态效率,可以发现青岛市的生态效率呈现增加趋势,表明青岛市的资源利用效率明显增加。按照1995到2004年的发展趋势,青岛在未来十年的生态赤字将进一步加大,通过科学技术提高生态效率是青岛降低生态赤字的主要途径。文章首次分析了青岛市的生态足迹动态,提出了降低生态赤字的途径,为青岛市的可持续发展提供了理论参考。 相似文献
307.
Analysis of leakage in carbon sequestration projects in forestry: a case study of upper magat watershed,Philippines 总被引:2,自引:0,他引:2
Rodel D. Lasco Florencia B. Pulhin Renezita F. Sales 《Mitigation and Adaptation Strategies for Global Change》2007,12(6):1189-1211
The role of forestry projects in carbon conservation and sequestration is receiving much attention because of their role in
the mitigation of climate change. The main objective of the study is to analyze the potential of the Upper Magat Watershed
for a carbon sequestration project.
The three main development components of the project are forest conservation: tree plantations, and agroforestry farm development.
At Year 30, the watershed can attain a net carbon benefit of 19.5 M tC at a cost of US$ 34.5 M.
The potential leakage of the project is estimated using historical experience in technology adoption in watershed areas in
the Philippines and a high adoption rate. Two leakage scenarios were used: baseline and project leakage scenarios. Most of
the leakage occurs in the first 10 years of the project as displacement of livelihood occurs during this time. The carbon
lost via leakage is estimated to be 3.7 M tC in the historical adoption scenario, and 8.1 M tC under the enhanced adoption
scenario. 相似文献
308.
采用混凝、氧化的方法对精研精抛清洗废液进行处理,对絮凝过程中所用的6种混凝剂的投加量pH值和氧化过程中的氧化试剂H2O2的投加量分别进行了筛选,同时简单地分析了反应机理.经混凝氧化处理后,COD值由1200mg/mL降至500mg/mL左右,COD去除率达95%;最后进行活性炭吸附,COD值达到国家排放标准. 相似文献
309.
理论等温方程式在CS2—ACF静态吸附体系的应用 总被引:3,自引:0,他引:3
测定了CS_2蒸气在4种ACF(活性炭纤维)和GAC(粒状活性炭)上的若干吸附等温线。用BET方程、H-J方程和D-A方程对CS_2-ACF静态吸附体系进行了处理。结果表明,除H-J方程外,其它两个方程适用良好。通过理论等温方程式,求出了吸附剂的比表面积和微孔体积。 相似文献
310.