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991.
992.
在众多的媒体上,补钙的宣传铺天盖地、气势汹汹;而在很多人的内心里,补钙的问题挥之不去、疑虑重重。补还是不补?先慢下定论,且让我们共同探讨一下补钙的利与弊、难和易、必要及可能,希望让您既不用再做补钙的“门外汉”,也不用再让难补的钙只停留在体外,“钙”莫能外,概莫能外。 相似文献
993.
Liangliang Wei Kun Wang Qingliang Zhao Chunmei Xie Wei Qiu Ting Jia 《环境科学学报(英文版)》2011,23(7):1057-1065
Fly ash was used as a low-cost adsorbent for removing dissolved organic matter (DOM) in secondary effluent. Batch experiments were
conducted under various adsorbent dosages, pH, contact time, temperatures and DOM fractional characteristics. Under the optimum
conditions of fly ash dosage of 15 g/L, temperature of 303 K and contact time of 180 min, a removal of 22.5% of the dissolved
organic carbon (DOC), 23.7% of UV-254, 25.9% of the trihalomethanes precursors in secondary effluent was obtained. The adsorption
of DOM fractions onto fly ash all followed the pseudo second-order kinetic model, and the hydrophilic fraction adsorption by fly
ash also fitted the intraparticle diffusion model quite well. Freundlich and Langmuir models were applicable to the fly ash adsorption
and their constants were evaluated. The maximum adsorption capacities of the adsorptions revealed that fly ash was more effective
in adsorbing hydrophilic fraction than the acidic fractions. Structure changes of the DOM fractions after fly ash adsorption were also
characterized via spectrum analyzing. Those mechanisms presented critical step toward improved efficiencies of fly ash adsorption via
further surface-modification. 相似文献
994.
One potential drawback of compost-based passive bioreactors, which is a promising biotechnology for acid mine drainage (AMD)
treatment, is the transport of dissolved organic matter (DOM)-metal complexes in surface waters. To address this problem, the objective
of this study was to assess the maximum capacity of organic substrates to release soluble DOM-metal complexes in treated water.
The reactivities of DOM in maple wood chips and sawdust, composted poultry manure, and leaf compost were quantified toward
Cd2+, Ni2+, Fe2+, and Cu2+ using fluorescence quenching. The DOM showed the highest reactivity toward Fe, but a limited number
of available sites for sorption, whereas DOM-Cd complexes exhibited the lowest fluorescence quenching. Overall, the DOM from a
mixture of wastes formed higher concentrations of DOM-metal complexes relative to sole substrates. Among DOM-metal complexes,
the concentrations of DOM-Ni complexes were the highest. After reaching steady-state, low concentrations of DOM-metal complexes
were released in treated water, which is in agreement with theoretical predictions based on geochemical modeling. Therefore, in addition
to physicochemical characterization, fluorescence quenching technique is recommended for the substrate selection of bioreactors. 相似文献
995.
Mineral materials as feasible amendments to stabilize heavy metals
in polluted urban soils 总被引:2,自引:0,他引:2
Four minerals, agricultural limestone (AL), rock phosphate (RP), palygorskite (PG), and calcium magnesium phosphate (CMP),
were evaluated by means of chemical fractions of heavy metals in soils and concentrations of heavy metals in leachates from columns
to determine their ability to stabilize heavy metals in polluted urban soils. Two urban soils (calcareous soil and acidic soil) polluted
with cadmium, copper, zinc and lead were selected and amended in the laboratory with the mineral materials) for 12 months. Results
indicated that application of the mineral materials reduced exchangeable metals in the sequence of Pb, Cd > Cu > Zn. The reduction of
exchangeable fraction of heavy metals in the soils amended with di erent mineral materials followed the sequence of CMP, PG > AL
> RP. Reductions of heavy metals leached were based on comparison with cumulative totals of heavy metals eluted through 12 pore
volumes from an untreated soil. The reductions of the metals eluted from the calcareous soil amended with the RP, AL, PG and CMP
were 1.98%, 38.89%, 64.81% and 75.93% for Cd, 8.51%, 40.42%, 60.64% and 55.32% for Cu, 1.76%, 52.94%, 70.00% and 74.12%
for Pb, and 28.42%, 52.74%, 64.38% and 49.66% for Zn. Those from the acidic soil amended with the CMP, PG, AL, and RP were
25.65%, 68.06%, 78.01% and 79.06% for Cd, 26.56%, 49.64%, 43.40% and 34.68% for Cu, 44.44%, 33.32%, 61.11% and 69.44%
for Pb, and 18.46%, 43.77%, 41.98% and 40.68% for Zn. The CMP and PG treatments were superior to the AL and RP for stabilizing
heavy metals in the polluted urban soils. 相似文献
996.
In Rhodopseudomonas palustris, an arsM gene, encoding bacterial and archaeal homologues of the mammalian Cyt19 As(III)
S-adenosylmethionine methytransferase, was regulated by arsenicals. An expression of arsM was introduced into strains for the
methylation of arsenic. When arsM was expressed in Sphingomonas desiccabilis and Bacillus idriensis, it had 10 folds increase
of methyled arsenic gas compared to wild type in aqueous system. In soil system, about 2.2%–4.5% of arsenic was removed by
biovolatilization during 30 days. This study demonstrated that arsenic could be removed through volatilization from the contaminated
soil by bacteria which have arsM gene expressed. These results showed that it is possible to use microorganisms expressing arsM as an
inexpensive, efficient strategy for arsenic bioremediation from contaminated water and soil. 相似文献
997.
Involvements of chloride ion in decolorization of Acid Orange 7 by activated peroxydisulfate or peroxymonosulfate oxidation 总被引:1,自引:0,他引:1
The effects of Cl- on the decolorization of AO7 by SO4·- based-peroxydisulfate or peroxymonosulfate oxidation under various activated conditions were different. 相似文献
998.
999.
1000.
镇雄县煤矿废水未经处理或只经过简单的沉淀处理直接外排,造成惨重后果。为了防止这种恶性循环继续发生,结合镇雄县地域经济、社会环境和废水的污染性质,提出了经济适用的煤矿废水污染治理技术方案。经实践,取得了良好的效果。 相似文献