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81.
Reactively Compatibilized Cellulosic Polylactide Microcomposites 总被引:3,自引:0,他引:3
Birgit Braun John R. Dorgan Daniel M. Knauss 《Journal of Polymers and the Environment》2006,14(1):49-58
Poly(lactic acid) (PLA) possesses a suite of favorable material properties that are enabling its penetration into diverse
markets (e.g., as packaging material or textile fibers). In order to increase the range of applications for this material,
it is necessary to modify its properties and for certain applications, reduce its cost. The introduction of fibers into a
polymeric matrix is an established route towards property enhancement provided good dispersion and intimate interfacial adhesion
can be achieved. In addition, cellulosic microfibers are obtainable at low to moderate cost. In this study, reactive compatibilization
of cellulosic fibers with PLA is pursued. Hydroxyl groups available on the surface of cellulosic fibers are used to initiate
lactide polymerization. Various processing strategies are investigated: (1) blending preformed PLA with the fiber material,
(2) through a one-step process in which lactide is polymerized in the presence of the fibers alone, or (3) reactive compatibilization
in the presence of preformed high molecular weight polymer. The results show that materials prepared by simultaneous introduction
of lactide and preformed high molecular PLA at the beginning of the reaction possess superior mechanical properties compared
to composites made by either purely mechanical mixing or solely polymerization of lactide in the presence of fibers. The modulus
of materials containing 25% fibers which are prepared by reactive compatibilization of 30% preformed PLA and 70% lactide (30/70
P/L) improves by 53% compared to the homopolymer, whereas 36% reinforcement can be achieved upon purely mechanical mixing.
A further increase to 35% fiber loading leads to a reduction in modulus due to an excess in initiating groups. The same trend
was observed in systems containing 65% preformed PLA and 35% lactide (65/35 P/L) with an overall achievable reinforcement
that was slightly lower. 相似文献
82.
Birgit M. Braune Mark L. Mallory Scott A. Mabury 《Environmental pollution (Barking, Essex : 1987)》2010,158(12):3513-3519
Northern fulmars from two breeding colonies in the Canadian Arctic, Cape Vera and Prince Leopold Island, were analyzed for organochlorine pesticides, PCBs, perfluorinated compounds (PFCs) and total mercury (Hg). Hepatic concentrations of organochlorines and Hg were highest in the male fulmars from Cape Vera. Perfluorooctane sulfonate (PFOS) concentrations did not vary significantly between sexes or colonies. However, concentrations of the perfluorinated carboxylates (PFCAs) were higher in fulmars from Cape Vera than Prince Leopold Island. The C11-C15 PFCAs averaged 90% of the PFCA profile at both colonies. Polychorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and non-ortho PCBs (NO-PCBs) were measured only in birds from Prince Leopold Island. Concentrations of PCDDs, PCDFs, NO-PCBs and Toxic Equivalents (TEQs) did not differ significantly between sexes. ΣTEQ was comprised mainly of ΣTEQPCDF. Concentrations of Hg and the persistent halogenated compounds reported in this study were below published toxicological threshold values for wild birds. 相似文献
83.
Dana Kiessling Cornelia Schmidt-Hattenberger Hartmut Schuett Frank Schilling Kay Krueger Birgit Schoebel Erik Danckwardt Juliane Kummerow 《International Journal of Greenhouse Gas Control》2010,4(5):816-826
The feasibility of monitoring CO2 migration in a saline aquifer at a depth of about 650 m with cross-hole and surface–downhole electrical resistivity tomography (ERT) is investigated at the CO2SINK test site close to Ketzin (Germany). The permanent vertical electrical resistivity array (VERA) consists of 45 electrodes (15 in the injection well Ktzi201 and 15 in each of the two observation wells Ktzi200 and Ktzi202), successfully placed on the electrically insulated casings, in the depth range of about 590–740 m with a spacing of about 10 m. The three Ketzin wells are arranged as perpendicular triangle with distances of 50 and 100 m.First synthetic modelling studies indicate an increase of the electrical resistivity of about 200% caused by CO2 injection, corresponding to a bulk CO2 saturation of 50%, which is in good agreement with laboratory studies. Finite difference inversion of field data delivers three-dimensional resistivity distributions between the wells which are consistent with the reservoir modelling studies.To increase the limited observation area provided by the cross-hole measurements, additional surface–downhole measurements were deployed. A main CO2 migration in SE–NW direction is deduced from surface to downhole resistivity experiments.The first cross-hole time-lapse results show that the resolution and the coverage of the electrode array in the Ketzin setting are sufficient to resolve the expected resistivity changes on the characteristic length scale of the electrode array. Significant resistivity changes could be measured, however, detailed information on the CO2 plume could not be resolved yet by VERA under the existing geological circumstances. 相似文献
84.
北京夏季高温高湿和降水过程对大气颗粒物谱分布的影响 总被引:26,自引:8,他引:26
2004-07-13~2004-08-23使用TDMPS-APS系统在线测量颗粒物的数浓度谱分布,并于07-16~07-18选取了高温闷热夜晚、日间高温高湿和雨后晴朗干洁3种天气条件,使用多级串联撞击式采样器(MOUDI)测量颗粒物的质量浓度谱分布,结果表明,高温高湿天气条件下颗粒物的污染、尤其细粒子污染严重,导致很低的能见度(2.5km);PM1.8和PM10的质量浓度分别为170.68μg/m3和249.35μg/m3,细粒子质量浓度占PM10的68%;粒径为50~100nm颗粒物的数浓度最高,为2×104~3×104个/cm3;降雨过程对粗粒子和细粒子均有去除作用,对细粒子的去除作用尤为明显;降雨后PM10和PM1.8浓度分别比降雨前降低3倍和6倍;降雨过后的晴朗干洁天气有利于新粒子(3~20nm)的生成,生成的新粒子快速长大到50~100nm;随着污染物的累积,以后几天内又变为污染天气. 相似文献