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91.
Stéphane Bernard Loïc Youinou Philippe Gillard 《Journal of Loss Prevention in the Process Industries》2013,26(6):1493-1500
Pulverized materials such as metallic or polymer powders play a considerable role in many industrial processes. Their use requires the introduction of preventive safeguards to control the plant's safety.PA12 polymer powder processing by laser sintering is characteristic of this tendency. The present work concerns PA12 powder (bimodal particle size distribution: 10 μm and 55 μm) and relates to explosion sensitivity and the thermal degradation of this powder, which can occur during laser sintering. Minimum Ignition Energy is determined using a modified Hartmann tube combined with the Langlie method developed in the PRISME Laboratory. This study shows the influence of parameters such as distance between the electrodes, powder concentration and arc power on MIE values. Theses parameters vary in the range of 3–6 A for the current intensity of the spark and the electrode gap in the range of 2.5–4 mm. The MIE is obtained for a spark gap of 3 mm and current intensity of the 4 A spark in our device. It shows that the MIE is less than 40 mJ for concentrations approaching 1000 g/m3. At lower concentrations (under 150 g/m3) the MIE increases but discrepancies in measurements appear, probably because of the static electricity that creates strong irregularities in dust dispersion. The second part of this study concerns the thermal degradation of the PA12 which is performed by thermogravimetric experiments coupled with mass spectrometric (MS) analysis for gas investigation. The mass loss measurement combined with the gas analysis allows the principal stages of degradation to be determined so as to calculate the kinetics parameter PA12. Experiments have been performed for different heating rates between 1 and 30 K min?1 and the reproducibility of experiments has been verified. The activation energy is determined using two methods: Freidman and KAS. For a reaction rate of between 0.2 and 0.6, the activation energy is nearly constant. The KAS method gives a value of Ea = 250 kJ mol?1 and the Friedman method gives Ea = 300 kJ mol?1. The gas analysis by MS shows that oxidation begins at over 350 °C and finishes at under 650 °C with the formation of CO2 and H2O. Other major peaks with an m/z ratio of 29, 28 and 30 are noticed in this range of temperature. They show the presence of intermediate species such as C2H6, NO or CH2O. The presence of HCN is also detected (m/z ratio of 27). 相似文献
92.
Albert C. F. Lam Daniel H. C. Chan Tony M. F. Tong Mary H. Y. Tang Steven Y. F. Lo Ivan F. M. Lo Stephen T. S. Lam 《黑龙江环境通报》2006,26(11):1018-1020
We present the first confirmed case by molecular analysis of a metaphyseal chondrodysplasia, McKusick type, in a 22-week fetus. Two novel compound heterozygous mutations, 64T> A and 79G > T, were found in the highly conserved regions of the RMRP gene. Twenty-two heterozygous g.1018 T> C mutations, two homozygous g.1018 T> C mutations, two heterozygous insertion mutations g.799_g.800insC and one heterozygous insertion mutation g.849_g.850insT were found among 100 normal controls. Careful radiological examination of the fetus for skeletal dysplasia allowed definitive diagnosis, proper genetic counselling and future prenatal diagnosis. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
93.
Ryan Plummer Jonas Velaniškis Danuta de Grosbois Reid D. Kreutzwiser Rob de Loë 《Environmental Science & Policy》2010,13(6):535-548
While new environmental policies and procedures often are developed incrementally, they can also result from crises or other significant events. In situations where policies and procedures are introduced in response to a crisis, questions about the strengths and weaknesses of existing mechanisms, and the extent to which they can be used to address concerns, may be ignored. This paper explores the complexities of introducing new policies and processes where planning systems and procedures already exist. Drinking water source protection policies that are being developed in response to the tragic events in Walkerton, Ontario, Canada serve as the context for the inquiry. Three case study watersheds were selected to reflect the diversity of municipal jurisdictions and water supply systems in Ontario. A content analysis was undertaken on regulatory and non-regulatory policy documents to determine the extent to which they addressed elements of the multi-barrier approach for drinking water safety. Findings from the research reveal considerable evidence of the multi-barrier approach in the policy and guiding documents analyzed. Policy development in response to a crisis can advance progress on the issue of drinking water safety and coincide with emerging governance strategies. Policy effectiveness may be enhanced by considering existing policies as well as contextual and jurisdictional differences. 相似文献
94.
Diversity trends in Neogene European ungulates and rodents: large-scale comparisons and perspectives
The ungulate and rodent fossil records are often used independently to understand mammalian evolutionary history. Few studies
have directly compared both records over long time periods and large geographic areas. Here, we compiled two datasets of European
fossil localities containing rodents and/or ungulates over 20 My (Early Miocene–Early Pliocene) and processed the data with
the same methodology. We counted the raw diversity and calculated a measure of evenness (Pielou’s index). After controlling
for potential biases on diversity estimators, we identify the evenness index as a more reliable estimator bringing interesting
insights into the way both mammal groups are structured by biotic or abiotic factors. In this study, we consider that an uneven
distribution of the species richness among families, when only some families successfully diversify within the “continental-scale
community”, represents a lower adaptability of this community to the environmental context. Pielou’s index is used to estimate
this adaptability through time. The responses of ungulates and rodents to environmental changes are very divergent, especially
facing the climatic changes known since the Middle Miocene. The general patterns suggest that rodent broad-scale assemblages
are affected by all kinds of perturbations, even short biotic and abiotic events, but show a better adaptability when facing
long-term abiotic changes. Unlike rodents, the ungulate assemblages show more stability in periods of relative environmental
stability but show less adaptability to long-term climatic changes. Life-history traits of mammals can help explain patterns
of diversity and biogeography at different spatial scales and may probably partly explain the opposite patterns evidenced
here. 相似文献
95.
Simultaneous removal of chromium and arsenate from contaminated
groundwater by ferrous sulfate: Batch uptake behavior 总被引:1,自引:0,他引:1
Chromium and/or arsenate removal by Fe(II) as a function of pH, Fe(II) dosage and initial Cr(VI)/As(V) ratio were examined in
batch tests. The presence of arsenate reduced the removal e ciency of chromium by Fe(II), while the presence of chromate significantly
increased the removal e ciency of arsenate by Fe(II) at pH 6–8. In the absence of arsenate, chromium removal by Fe(II) increased to
a maximum with increasing pH from 4 to 7 and then decreased with a further increase in pH. The increment in Fe(II) dosage resulted
in an improvement in chromium removal and the improvement was more remarkable under alkaline conditions than that under acidic
conditions. Chromium removal by Fe(II) was reduced to a larger extent under neutral and alkaline conditions than that under acidic
conditions due to the presence of 10 mol/L arsenate. The presence of 20 mol/L arsenate slightly improved chromium removal by
Fe(II) at pH 3.9–5.8, but had detrimental e ects at pH 6.7–9.8. Arsenate removal was improved significantly at pH 4–9 due to the
presence of 10 mol/L chromate at Fe(II) dosages of 20–60 mol/L. Elevating the chromate concentration from 10 to 20 mol/L
resulted in a further improvement in arsenate removal at pH 4.0–4.6 when Fe(II) was dosed at 30–60 mol/L. 相似文献
96.
97.
China has seen rapid economic growth over the past two decades, but severe environmental problems have accompanied this, such as the looming danger of Asian Brown Clouds. This paper analyzes the regional development of China by examining economic performance and environmental factors. Technical efficiency and productivity changes in 31 regions of China are computed for the period 1997–2001. In the case of regional GDP, the fast-developing eastern (coastal) regions experience higher technical efficiency and productivity growth than the inland central and western regions. When environmental factors are incorporated, the eastern regions still perform better than inland regions, both from static and dynamic analysis. This phenomenon is termed the 'double deterioration' of the inland areas in China. Double deterioration is attributed to the lack of economic resources to replace highly-polluting production equipment and technology in those less developed regions. 相似文献
98.
Giovanni Lo Iacono 《Environmental Fluid Mechanics》2009,9(3):341-357
Rice’s theory for the statistical properties of random noise currents has been employed in the context of concentration fluctuations
in dispersing plumes. Within this context, the theory has been extended to calculate the distribution of excursion times above
a small threshold for arbitrary spacings between an up-crossing and the successive down-crossing. This approach has then been
applied to a second-order stochastic model for the evolution of odour concentrations and their time derivative (simple model),
and to the superstatistics extension of this model [Reynolds (2007) Phys. Fluids]. In agreement with the measurements of Yee and coworkers [Yee et al. (1993) Boundary-Layer Meteorol. 65, Yee et al. (1994) J. Appl. Meteorol. 33 ], both formulations predict a distribution of excursion times that can be well approximated by a power-law profile with
exponent close to −3/2. For the superstatistical model the power-law profile extends over approximately three or more decades,
for the simple model this range is smaller. Compared to the simple model, predictions for the superstatistical model are in
a better agreement with the measurements. 相似文献
99.
Monitoring the toxicity of phenolic chemicals to activated sludge using a novel optical scanning respirometer. 总被引:3,自引:0,他引:3
This paper reports the development of optical scanning respirometer for determining the toxicity of chemicals to activated sludge. The respirometer is used to measure the dissolved oxygen concentration by monitoring the luminescence intensity of ruthenium dye immobilized in a polymer film in contact with the wastewater sample. The intensity is related to the extent of oxygen quenching of luminescence. The toxicity of chemicals can be evaluated by measuring the inhibition on respiration rate of microorganism using the scanning respirometer. The IC50 values (concentration of a chemical that exhibits 50% respiration inhibition) of various phenolic chemicals in activated sludge were determined. The performance of this method is compared with other toxicity methods. The experimental results indicate that the reproducibility and sensitivity of this respirometer are reasonably good. 相似文献
100.
L. Donald Duke Thomas S. Lo Michelle W Turner 《Journal of the American Water Resources Association》1999,35(4):821-836
ABSTRACT: This research evaluated concentration data for selected water quality parameters in selected California urban separate storm sewer systems during storm event discharges and during dry weather conditions. We used existing monitoring data from multiple regulatory agencies and municipalities originally collected for compliance or local characterization, which allowed systematic assessment of seasonal patterns over a wide region. Long term mean concentration for most parameters in most streams was higher during storm discharges than during dry weather flows to at least 95 percent confidence in 20 of 45 comparative evaluations, and lower statistical confidence in 22 other comparisons. Some regional differences emerged: in four evaluated streams in the San Francisco Bay Area, total concentration of lead, copper and zinc were lower during dry weather than during storm flows to at least 99.9 percent confidence, with only one exception; while the other four evaluated California streams showed the same tendency, but to much lower statistical confidence. 相似文献