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151.
Claudia von Brömssen Jens Fölster Martyn Futter Kerstin McEwan 《Environmental monitoring and assessment》2018,190(9):558
Long-term water quality monitoring is of high value for environmental management as well as for research. Artificial level shifts in time series due to method improvements, flaws in laboratory practices or changes in laboratory are a common limitation for analysis, which, however, are often ignored. Statistical estimation of such artefacts is complicated by the simultaneous existence of trends, seasonal variation and effects of other influencing factors, such as weather conditions. Here, we investigate the performance of generalised additive mixed models (GAMM) to simultaneously identify one or more artefacts associated with artificial level shifts, longitudinal effects related to temporal trends and seasonal variation, as well as to model the serial correlation structure of the data. In the same model, it is possible to estimate separate residual variances for different periods so as to identify if artefacts not only influence the mean level but also the dispersion of a series. Even with an appropriate statistical methodology, it is difficult to quantify artificial level shifts and make appropriate adjustments to the time series. The underlying temporal structure of the series is especially important. As long as there is no prominent underlying trend in the series, the shift estimates are rather stable and show less variation. If an artificial shift occurs during a slower downward or upward tendency, it is difficult to separate these two effects and shift estimates can be both biased and have large variation. In the case of a change in method or laboratory, we show that conducting the analyses with both methods in parallel strongly improves estimates of artefact effects on the time series, even if certain problems remain. Due to the difficulties of estimating artificial level shifts, posterior adjustment is problematic and can lead to time series that no longer can be used for trend analysis or other analysis based on the longitudinal structure of the series. Before carrying out a change in analytic method or laboratory, it should be considered if this is absolutely necessary. If changes cannot be avoided, the analysis of the two methods considered, or the two laboratories contracted, should be run in parallel for a considerable period of time so as to enable a good assessment of changes introduced to the data series. 相似文献
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153.
Regional Environmental Change - Seasonal runoff generation in a headwater (~100 km2) of the mountainous Sugnugr Basin, situated within the discontinuous permafrost zone of... 相似文献
154.
AbstractThis paper addresses the relevance of the demand side for the achievement of sustainable transport in urban areas. The underlying thesis is that a better understanding of user habits, perceptions and attitudes with its specific dynamics is essential for a successful design of targeted transport policies. In line with this, the paper at hand is based on research that aims at improving the knowledge of urban-transport-related habits and attitudes of young adults. The results of three interview meetings that were held in Karlsruhe, Budapest, and Copenhagen with participants aged between 20 and 30 are presented. Background of the interviews is a range of studies that indicate that young people in urban areas seem to be less interested in cars than the generation before. And indeed, the interview meetings reveal that participants had a rather pragmatic attitude towards transport modes. They wished a transport system that is flexible, convenient and cheap. Despite many differences, most participants showed rather positive attitudes towards policies supporting alternatives to car-based transport. However, it will be crucial for policy shaping to what extent the observed behaviour patterns and attitudes will persist over time. 相似文献
155.
Jens Schirmel 《Journal of Coastal Conservation》2011,15(1):159-162
In Europe, acidic coastal dunes are threatened by the invasion of the exotic moss Campylopus introflexus. While the effect of the moss encroachment on the vegetation is well analysed, knowledge of possible impact on arthropods
is lacking. Thus, an experiment was conducted in acidic coastal dunes on the Baltic island of Hiddensee, Germany. Myrmeleotettix maculatus, a common Orthoptera species of open and dry habitats, was sampled by pitfall trapping in eleven plots invaded by C. introflexus and in eleven native, non-invaded plots rich in lichens. Overall, 826 individuals of M. maculatus were captured (266 nymphs, 560 adults). Mean number of adults was significantly higher in native plots. This maybe explained
by a higher proportion of grasses (food supply), a higher availability of shelter (from predators, weather), or more favourable
microclimate conditions in native plots and a higher mortality rate in invaded plots. However, mean number of both young and
old nymphs did not differ significantly between both types. This could imply that invaded areas at least serve as favourable
oviposition sites and larval habitats. The observed negative effect of the moss invasion on M. maculatus remains to be studied on other arthropods. 相似文献
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159.
An isobole-based statistical model and test for synergism/antagonism in binary mixture toxicity experiments 总被引:4,自引:0,他引:4
Helle Sørensen Nina Cedergreen Ib M. Skovgaard Jens C. Streibig 《Environmental and Ecological Statistics》2007,14(4):383-397
Synergism and antagonism are often defined in relation to the model of Concentration Addition (CA). Hence, it is vital for
the conclusion of mixture toxicity studies to be able to test whether an observed deviation from CA reflects a true deviation
or whether it is simply due to random variation. In this paper we consider a non-linear regression model for the classical
ray designs for binary mixture experiments. The model combines dose–response curves for each mixture in the experiment with
an isobole model, describing possible deviations from CA. The method allows us to test whether the chosen isobole model is
reasonable for the data and to test the hypothesis of CA. Furthermore, it provides us with a measure of the degree of synergism/antagonism.
The method is flexible since both the dose–response relationships and the isobole model can be chosen arbitrarily. We demonstrate
the use of the method on datasets where combinations of pesticides are tested on a floating plant, Lemna minor, and an algae, Pseudokirchneriella subcapitata. Furthermore, we conduct a simulation study in order to explore the power with which a specific deviation from CA can be
distinguished in different test-systems. 相似文献
160.
Hanne Marie Kvamsdal Jens Hetland Geir Haugen Hallvard F. Svendsen Fredrik Major Vemund Kårstad Göran Tjellander 《International Journal of Greenhouse Gas Control》2010,4(4):613-622
A post-combustion CO2 capture process intended for offshore operations has been designed and optimised for integration with a natural gas-fired power plant on board a floating structure developed by the Norway-based company Sevan Marine ASA—designated Sevan GTW (gas-to-wire). The concept is constrained by the structure of the floater carrying a SIEMENS modular power system rated at 450 MWe, with a capture rate of 90% and CO2 compression (1.47 Mtpa) for pipeline pressure at 12 MPa. A net efficiency of 45% (based on a lower heating value) is estimated for the system with CO2 capture, thus suggesting that the post-combustion CO2 capture system is accountable for a fuel penalty of nine percentage points.The rationale behind the technology selection is the urgency of replacing the dispersed aero-derivative gas turbines which power the offshore oil and gas production units in Norwegian waters with near-zero emission power.As (inherently) fresh water usually constitutes a limiting factor in sea operations, efforts are made to obtain a neutral water balance to obtain an optimal design. This is primarily achieved by controlling the cleaned flue gas temperature at the top of the absorber column. 相似文献