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181.
Evaluating non-equilibrium solute transport in small soil columns 总被引:11,自引:0,他引:11
Kamra SK Lennartz B Van Genuchten MT Widmoser P 《Journal of contaminant hydrology》2001,48(3-4):189-212
Displacement studies on leaching of bromide and two pesticides (atrazine and isoproturon) were conducted under unsaturated steady state flow conditions in 24 small undisturbed soil columns (5.7 cm in diameter and 10 cm long) each collected from two sites differing in soil structure and organic carbon content in North Germany. There were large and irregular variabilities in the characteristics of both soils, as well as in the shapes of breakthrough curves (BTCs) of different columns, including some with early breakthrough and increased tailing, qualitatively indicating the presence of preferential flow. It was estimated that one preferential flow column (PFC) at site A, and four at site B, contributed, respectively to 11% and 58% of the accumulated leached fraction and to more than 80% of the maximum observed standard deviation (SD) in the field-scale concentration and mass flux of pesticides at two sites. The bromide BTCs of two sites were analyzed with the equilibrium convection-dispersion equation (CDE) and a non-equilibrium two-region/mobile-immobile model. Transport parameters of these models for individual BTCs were determined using a curve fitting program, CXTFIT, and by the time moment method. For the CDE based equilibrium model, the mean values of retardation factor, R, considered separately for all columns, PFCs or non-preferential flow columns (NPFCs) were comparable for the two methods; significant differences were observed in the values of dispersion coefficients of two sites using the two estimation methods. It was inferred from the estimated parameters of non-equilibrium model that 5-12% of water at site A, and 12% at site B, was immobile during displacement in NPFCs. The corresponding values for PFCs of two sites were much larger, ranging from 25% to 51% by CXTFIT and from 24% to 72% by the moment method, suggesting the role of certain mechanisms other than immobile water in higher degrees of non-equilibrium in these columns. Peclet numbers in PFCs of both sites were consistently smaller than five, indicating the inadequacy of the non-equilibrium model to incorporate the effect of all forms of non-equilibrium in PFCs. Overall, the BTCs of individual NPFCs, PFCs and of field average concentration at the two sites were better reproduced with parameters obtained from CXTFIT than by the moment method. The moment method failed to capture the peak concentrations in PFCs, but tended to describe the desorption and tail branches of BTCs better than the curve fitting approach. 相似文献
182.
This laboratory study investigated the kinetics of leaf and DNA content decomposition in two varieties of tomato (Palmiro and Admiro) after incubation in soil for 35 days. Results revealed that the decrease of dry matter in leaves in both varieties did not follow a single exponential function and was better described by a double exponential model. Composite half-decrease times were 3.4 and 2.4 days for Palmiro and Admiro respectively. The same pattern was observed for DNA mass loss, although this was closer to a single exponential model with composite half-decrease times of 1.5 and 1.4 days. Genomic analysis showed that DNA in dried leaves at room temperature (not inoculated in the soil), remains intact or presents a weak degradation, and DNA extracted from leaves inoculated in non-sterile soil showed degradation after two days. These results indicate that before release an important quantity of DNA may be degraded inside plant tissues during decomposition in soil. 相似文献
183.
184.
Dale R. Van Stempvoort James Armstrong Bernhard Mayer 《Journal of contaminant hydrology》2007,92(3-4):184-207
Despite a rapid expansion over the past decade in the reliance on intrinsic bioremediation to remediate petroleum hydrocarbon plumes in groundwater, significant research gaps remain. Although it has been demonstrated that bacterial sulfate reduction can be a key electron accepting process in many petroleum plumes, little is known about the rate of this reduction process in plumes derived from crude oil and gas condensates at cold-climate sites (mean temperature <10 degrees C), and in complex hydrogeological settings such as silt/clay aquitards. In this field study, sulfate was injected into groundwater contaminated by gas condensate plumes at two petroleum sites in Alberta, Canada to enhance in-situ bioremediation. In both cases the groundwater near the water table had low temperature (6-9 degrees C). Monitoring data had provided strong evidence that bacterial sulfate reduction was a key terminal electron accepting process (TEAP) in the natural attenuation of dissolved hydrocarbons at these sites. At each site, water with approximately 2000 mg/L sulfate and a bromide tracer was injected into a low-sulfate zone within a condensate-contaminant plume. Monitoring data collected over several months yielded conservative estimates for sulfate reduction rates based on zero-order kinetics (4-6 mg/L per day) or first-order kinetics (0.003 and 0.01 day(-1)). These results favor the applicability of in-situ bioremediation techniques in this region, under natural conditions or with enhancement via sulfate injection. 相似文献
185.
Gia Thanh Nguyen Jian Pu Takayuki Miura Hiroaki Ito Shinobu Kazama Yoshimitsu Konta An Van Le Toru Watanabe 《Food and environmental virology》2018,10(1):61-71
This study investigated the level of norovirus contamination in oysters collected at a lagoon receiving urban drainage from Hue City for 17 months (August 2015–December 2016). We also investigated the genetic diversity of norovirus GI and GII in oyster and wastewater samples by using pyrosequencing to evaluate the effect of urban drainage on norovirus contamination of oysters. A total of 34 oyster samples were collected at two sampling sites (stations A and B) in a lagoon. Norovirus GI was more frequently detected than GII (positive rate 79 vs. 41%). Maximum concentrations of GI and GII were 2.4 × 105 and 2.3 × 104 copies/g, respectively. Co-contamination with GI and GII was observed in 35% of samples. Norovirus GII concentration was higher at station A in the flood season than in the dry season (P = 0.04, Wilcoxon signed-rank test). Six genotypes (GI.2, GI.3, GI.5, GII.2, GII.3, and GII.4) were identified in both wastewater and oyster samples, and genetically similar or identical sequences were obtained from the two types of samples. These observations suggest that urban drainage and seasonal flooding contribute to norovirus contamination of oysters in the study area. 相似文献
186.
Thomas Fellmann Peter Witzke Franz Weiss Benjamin Van Doorslaer Dusan Drabik Ingo Huck Guna Salputra Torbjörn Jansson Adrian Leip 《Mitigation and Adaptation Strategies for Global Change》2018,23(3):451-468
Taking the European Union (EU) as a case study, we simulate the application of non-uniform national mitigation targets to achieve a sectoral reduction in agricultural non-carbon dioxide (CO2) greenhouse gas (GHG) emissions. Scenario results show substantial impacts on EU agricultural production, in particular, the livestock sector. Significant increases in imports and decreases in exports result in rather moderate domestic consumption impacts but induce production increases in non-EU countries that are associated with considerable emission leakage effects. The results underline four major challenges for the general integration of agriculture into national and global climate change mitigation policy frameworks and strategies, as they strengthen requests for (1) a targeted but flexible implementation of mitigation obligations at national and global level and (2) the need for a wider consideration of technological mitigation options. The results also indicate that a globally effective reduction in agricultural emissions requires (3) multilateral commitments for agriculture to limit emission leakage and may have to (4) consider options that tackle the reduction in GHG emissions from the consumption side. 相似文献
187.
John S. McLaren Todd V. Royer Robert W. Van Kirk Melissa L. Muradian 《Journal of the American Water Resources Association》2019,55(5):1323-1334
This study seeks to improve understanding of temperature patterns in reservoir outflows. We examined water temperatures in an irrigation storage reservoir, Island Park Reservoir, and its outflow, Henry’s Fork of the Snake River in eastern Idaho. Our objectives were to (1) quantify the extent to which daily temperature ranges in the reservoir outflow deviated from other reaches of the Henry’s Fork, and (2) test whether the reservoir’s net volume change during the summer — expressed as the volume of water remaining in the reservoir on September 1 — predicted mean summer temperature in the outflow. Two years of temperature data showed dampened diel temperature cycles in the reservoir outflow. Model selection with 17 years of climatic, hydrologic, and reservoir management variables found mean summer temperature in the outflow was best predicted by September 1 reservoir volume and average summer air temperature. Two years of weekly reservoir thermal profiles indicated large changes in reservoir volume eliminated cool hypolimnetic water and encouraged mixing, allowing warm epilimnetic water to be discharged into the outflow. Increases in future drought frequency and severity and increases in summer air temperatures could increase the frequency of occurrence of high mean summertime water temperatures in the outflow. Our study provides important information for local managers by quantifying influences on outflow temperatures and the downstream river ecosystem. 相似文献
188.
Anh Van Ngo Ha Thi Nguyen Chieu Van Le Rajeev Goel Mitsuharu Terashima Hidenari Yasui 《Journal of Material Cycles and Waste Management》2016,18(2):239-247
Microbial response on volatile fatty acids (VFAs) is a key for methane fermentation processes since accumulation of VFAs often causes an acidic failure, especially treating such organics as food wastes composed of mostly readily biodegradable materials. To evaluate the impact of VFA accumulation, a lab-scale continuous experiment was performed for 110 days with sequential feeding of heterogeneous food wastes. When the volumetric loading rate was increased from 6 to 8 kg-COD/m3/day, a sudden decrease of methane production was observed with an accumulation of acetate and propionate in the fermenter. After discontinuation of feeding for 10 days, the digestate in the fermenter was centrifuged and washed with tap water to reduce the VFAs to be acceptable concentration below 1000 mg-COD/L. Nevertheless, no recovery of methane production was observed and VFA concentrations consistently increased. To model the event, a modification of ADM1 was made assuming the methanogens in the fermenter were irreversibly inactivated under very high VFA. Also considering the different nature of the fed food wastes over 11 samples, decomposition kinetics of individual food wastes were manipulated. The modified ADM1 with methanogenic activity decay reasonably reproduced the responses for soluble material concentrations and methane gas production rate over the experimental period. 相似文献
189.
Paolo Ciavola Oscar Ferreira Piet Haerens Mark Van Koningsveld Clara ArmaroliAuthor vitae 《Environmental Science & Policy》2011,14(7):924-933
This paper describes the MICORE approach to quantify for nine field sites the crucial storm related physical hazards (hydrodynamic as well as morphodynamic) in support of early warning efforts and emergency response.As a first step historical storms that had a significant morphological impact on a representative number of sensitive European coastal stretches were reviewed and analysed in order to understand storm related morphological changes and how often they occur around Europe. Next, an on-line storm prediction system was set up to enable prediction of storm related hydro- and morphodynamic impacts. The system makes use of existing off-the-shelf models as well as a new open-source morphological model. To validate the models at least one year of fieldwork was done at nine pilot sites. The data was safeguarded and stored for future use in an open database that conforms to the OpenEarth protocols.To translate quantitative model results to useful information for Civil Protection agencies the Frame of Reference approach (
[Van Koningsveld et al., 2005]
and
[Van Koningsveld et al., 2007]
) was used to derive Storm Impact Indicators (SIIs) for relevant decision makers. The acquired knowledge is expected to be directly transferred to the civil society trough partnerships with end-users at the end of the MICORE project. 相似文献
190.
Trophic ecology of Rimicaris exoculata : a combined lipid abundance/stable isotope approach 总被引:1,自引:0,他引:1
The alvinocaridid shrimp Rimicaris exoculata is an abundant component of the biota of Mid-Atlantic Ridge hydrothermal vents. To determine the nutritional strategy of
this organism, we analysed the molecular abundance and carbon isotopic composition of its phospholipid fatty acids. High abundances
of n-7 fatty acids (>40% total fatty acids) were observed in R. exoculata muscle tissues, in bacterial epibionts scraped from its gill bailers, and from the bacterially infested metal sulphides that
the shrimp ingest. The phospholipid fatty acid abundance data indicates that the bacteria in the sulphides are closely related
to the bacterial epibiota inhabiting the shrimp gill bailers, carapace and other body parts. Compound specific δ13C analyses of the phospholipid fatty acids gave average values of −12‰ for the epibiont bacteria and −21‰ for the sulphide
bacteria. This difference may be largely due to the expression of different forms of RuBisCO (Forms I and II) which fractionate
against 13C to different extents. Carbon limitation within the shrimp epibiont population may be an additional factor. The δ13C values (mean = −13‰) of the saturated and monounsaturated fatty acids isolated from the muscle tissues of R. exoculata were very close to those of the epibionts, indicating that the predominant source of dietary carbon for the shrimp is their
epibionts, with a lesser contribution from free-living bacteria. The δ13C values (−26‰) of shrimp cholesterol were much more negative than those of the fatty acids, and this cholesterol is likely
to have derived from the oceanic photic zone.
Received: 26 June 1997 / Accepted: 6 November 1998 相似文献