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801.
Jinxi SONG Xunhong CHEN Cheng CHENG 《Frontiers of Environmental Science & Engineering》2010,4(3):340-348
In the Elkhorn River, burrows, tubes, and sediment mounds created by invertebrate bioturbation were observed in the exposed streambed and commonly concentrated on the fine-sediment patches, which consist of silt, clay, and organic matter. These invertebrate activities could loosen the thin layer of clogging sediments and result in an increase of pore size in the sediments, leading to greater vertical hydraulic conductivity of the streambed (K v ). The measurements of the vertical hydraulic gradient across the submerged streambed show that vertical flux in the hyporheic zone can alter directions (upward versus downward) for two locations only a few meters apart. In situ permeameter tests show that streambed K v in the upper sediment layer is much higher than that in the lower sediment layer, and the calculated K v in the submerged streambed is consistently greater than that in the clogged sediments around the shorelines of the sand bars. Moreover, a phenomenon of gas bubble release at the water-sediment interface from the subsurface sediments was observed in the groundwater seepage zone where flow velocity is extremely small. The bursting of gas bubbles can potentially break the thin clogging layer of sediments and enhance the vertical hydraulic conductivity of the streambed. 相似文献
802.
Exchange of trace gases between the oceans and the atmosphere affects the atmospheric content and cycling of a range of chemical
species which are related to climate change, ozone layer depletion, acid deposition, eutrophication, atmospheric particle
formation, photo-oxidants, trace metals and persistent organic pollutants (POPs). The effects and impacts of air–sea exchange
of these gases can be local, regional and global. Until now, most of the research has concentrated on the sea–air exchange
of trace gases in the open ocean. The flux rates of the trace gases from the coastal waters to the air are much higher than
the rates for the open ocean and the contribution of the coastal areas to the total oceanic emissions of these trace gases
can be significant on a global scale. This contribution can be as high as 50% and more for nitrous oxide and COS. Concerning
the contribution of the trace gas production in the coastal areas to the total global production of these gases, it can be
concluded that this contribution seems to be below 2% except for nitrous oxide. However, it should be pointed out that on
the local and even regional scale the emissions in the coastal areas can be very important, contributing substantially to
the total emission of these gases in a studied area. Thus, there is a need to carry out studies in the future with the aim
to provide more accurate understanding of the production and sea–air exchange processes for these gases around the world.
Electronic Publication 相似文献
803.
Malcolm S. Cresser 《Water, Air, & Soil Pollution: Focus》2007,7(1-3):407-412
Numerous assumptions have been made over the past 17 years when calculating critical loads for soils, both for acidity (based
upon base cation steady state mass balances (SMB)) and for N (eutrophication, based upon N mass balances), often without all the assumptions being explicitly stated. The tacit assumptions that the author believes to be implicit in the SMB approach
are critically reviewed, with particular reference to upland regions where slope processes are highly significant. It is concluded
that many of them cannot be justified, especially those that involve ignoring many key processes known to be important to
biogeochemical cycling and soil evolution in upland catchments. The evidence presented suggests that critical loads of acidity
and of N for soils should be based upon effective pollutant and, for acidity, also effective base cation deposition concentrations,
rather than upon pollutant deposition fluxes. This is because of the dominant role of cation exchange equilibria, rather than
weathering rate, in regulation of the pH and base status of the more acidification-sensitive soils, and because of the importance
of transport down slope of base cations, alkalinity and N species. 相似文献
804.
Gkhan Ekrem Üstün Seval Kutlu Akal Solmaz Akn Birgül 《Resources, Conservation and Recycling》2007,52(2):425-440
Regeneration studies of wastewater effluent from an organized industrial district (OID) for possible reuse in textile industry as process water was investigated. Advanced treatment methods including Fenton process, polyaluminium chloride (PAC) coagulation and ion exchange were applied on OID effluent. In Fenton process removal efficiencies for suspended solids (SS), chemical oxygen demand (COD), SAC436 (spectral absorption coefficient), SAC525 and SAC620 were determined 61%, 36%, 35%, 49% and 67%, respectively. After Fenton process, wastewater samples were coagulated with PAC. Optimum removal efficiencies for SS, COD, Fe ion, SAC436, SAC525 and SAC620 were determined 83%, 18%, 93%, 32%, 36% and 58%, respectively. Ion exchange experiments were conducted on chemically coagulated wastewater samples to improve the quality of wastewater. Optimum dosage of resins was determined. The experiments revealed that 1:1 resin ratio (20 mL H-type resin:20 mL OH-type resin) gave the best removal rates for the parameters considered in this study. Study results indicated that quality of the wastewater was suitable for the process water characteristics of textile industry and unit wastewater treatment cost was determined as 2.54 €/m3. 相似文献
805.
脉冲喷吹滤筒除尘器在低尘环境中应用的可行性分析 总被引:1,自引:0,他引:1
为拓宽脉冲喷吹滤筒除尘器的应用范围,结合目前低浓度粉尘环境中特别是在空调净化系统中除尘、净化技术的发展和滤筒式除尘技术的优点,通过对脉冲喷吹滤筒除尘器在低浓度粉尘环境中的应用分析,特别是在空调净化系统中的应用分析,说明脉冲喷吹滤筒除尘器可以解决目前低浓度粉尘环境特别是空调净化系统中存在的一系列问题,对低浓度粉尘环境具有很好的除尘净化效果,且适合低浓度粉尘环境的特殊要求,在低浓度粉尘环境中应用时具有可行性和可靠性,从而进一步拓宽脉冲喷吹滤筒除尘器的应用范围。 相似文献
806.
807.
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809.
The study examined the adsorption of Pb(II) ions from aqueous solution onto chitosan, chitosan-GLA and chitosan-alginate beads. Several important parameters influencing the adsorption of Pb(II) ions such as initial pH, adsorbent dosage and different initial concentration of Pb(II) ions were evaluated. The mechanism involved during the adsorption process was explored based on ion exchange study and using spectroscopic techniques. The adsorption capacities obtained based on non-linear Langmuir isotherm for ch... 相似文献
810.
Assessment of the nitrogen and carbon budget of two managed temperate grassland fields 总被引:1,自引:0,他引:1
Christof Ammann Christoph Spirig Jens Leifeld Albrecht Neftel 《Agriculture, ecosystems & environment》2009,133(3-4):150
Greenhouse gas budgets as well as the productivity of grassland systems are closely related to the carbon (C) and nitrogen (N) cycles. Within the framework of the CarboEurope and NitroEurope projects we have measured C and N exchange on the field scale at the grassland site Oensingen previously converted from arable rotation. The site is located on the Swiss Central Plateau and consists of two parallel fields of equal size. One field was subjected to intensive management with average nitrogen input of 230 kg-N ha−1 year−1 and 4–5 cuts per year, and the other to an extensive management with no fertilisation and less frequent cutting. The total C budget of the fields was assessed by measuring the CO2 exchange by eddy covariance and analysing the carbon import by manure application and export by harvest. The N budget of the managed grassland is more complex. Besides the management related import and export, it includes gaseous exchange in many different forms (NO, NO2, HNO3, N2O, NH3, N2) needing different analytical techniques, as well as input by rain and leaching of N-compounds with the soil water. The main (“level-3”) field sites in the NitroEurope project are supposed to measure 95% of the N fluxes at the field scale. For several of the N fluxes specific measurements have been performed for 1 year or longer at the site. Some of the remaining N budget components (dry and wet deposition) could be estimated from results of a national deposition network, while other components (NH3 and N2 emission) were estimated based on literature parameterisations. However, we found indications that the (systematic) uncertainties of these estimated N-fluxes are large and that it is important to make site-specific measurement for all relevant budget components. The suitability of corresponding experimental methods is discussed.Analysis of the C budget over a 6-year period (2002–2007) showed a significant mean difference between the two newly established grassland fields with a likely net carbon loss for the extensive management and a net sequestration for the intensive management. Since the C/N ratio of the soil organic matter of the grassland is constrained in a rather narrow range around 9.3, the change in the soil carbon pool is supposed to be accompanied by a corresponding change in the N storage. This approach provided an alternative method to check the N budget of the two grassland fields derived from the individual N fluxes. 相似文献