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561.
562.
分析评价了几种典型化学条件对腐殖酸絮凝体构造的影响.研究结果表明,在pH=5.0低投药量下以共聚络合为主要混凝机理所形成的絮凝体结构密实,粒径分布均匀,强度大.而pH=5高投药量以及pH=7.0两种情况下的混凝机理都是以吸附和网扫絮凝为主,此时形成的絮凝体构造特征相似,尽管尺寸较大,但是结构松散,强度较小.针对水中常见的主量阴阳离子,分析探讨了典型离子对絮凝体构造特征的影响.研究表明,Cl-在腐殖酸水样中的存在对絮凝体构造基本没有影响,而SO24-和SiO23-在水样中的存在可使腐殖酸絮凝体尺寸增加0.05—0.13 mm左右,但结构比较开放松散,同时絮凝体的黏结力(即抗剪切力)大大削弱,降低了约0.018—0.047 N·m-2,并且SO24-对腐殖酸絮体构造的影响大于SiO23-对其的影响.然而,引入阳离子会对絮凝体的构造起到不同程度的改善作用.其中以Ca2+、Mg2+为代表的高价阳离子对絮凝体构造影响较大,形成的絮凝体结构密实,尺寸较大,抗剪切能力强.高价阳离子的存在会使絮凝体的粒径增加0.08—0.15 mm,抗剪切力增加0.002—0.013 N·m-2,而以K+、Na+为代表的低价阳离子对絮凝体构造的影响较小. 相似文献
563.
Hyperaccumulation of metals by plants involves at least three processes: efficient absorption by roots, efficient root-to-shoot translocation and hypertolerance through internal detoxification. In this study, Thlaspi caerulescens was separately exposed to Cd and Zn at 0, 50, 100 and 200 μ M for 7 d to monitor plant responses in hydroponics. Significant dose-dependent accumulation was observed for both metals, mainly in roots (up to 3.2 and 9.2 mg g ?1 for Cd and Zn, respectively). However, Cd was more phytotoxic in terms of plant growth and photosynthesis. This higher toxicity was also evidenced by MetPLATE bioassay. Root exudation was significantly correlated to Cd and Zn translocation (r>0.85) proving its involvement in facilitating metal uptake. As for antioxidative responses, plants reacted to Cd and Zn by broadly exhibiting an elevation of glutathione reductase activity before declining at 200 μ M due to higher phytotoxicity. By contrast, superoxide dismutase activity was unlikely to be affected by both metals. Root-to-shoot apoplastic flow was traced using a fluorescent dye (trisodium-8-hydroxy-1,3,6-pyrenetrisulfonic acid; PTS), whose concentration in leaves increased to a certain extent with Cd and Zn accumulation, indicating that heavy metals have a comparable effect to drought or salinity in promoting the passive diffusion of water and solutes. Nevertheless, Cd at 200 μ M hindered the diffusion of PTS and consequently affected the apoplastic transport in plants. 相似文献
564.
Kalantari Soltanieh Sadraddin Saadati Karim Kalantari Soltanieh Sina Heydarpour Pouria 《毒物与环境化学》2013,95(5):1017-1023
Currently, attention has shifted to chronic or subclinical disorders attributed to lead (Pb) exposure. The aim of this study was to determine delta-aminolevulinic acid (δ-ALA) levels in urine of Angooran Lead &; Zinc Company workers. This cross-sectional study was conducted on 170 workers, in which 24 h urinary samples were collected and δ-ALA levels were measured spectrophotometrically. Questionnaire forms were completed indicating age, location, and duration of work. The mean δ-ALA level in urine was 5.44 mg L?1. δ-ALA levels were correlated with age, location, and duration of work in the company. The mean δ-ALA level in the urine of workers was in the upper limit of normal ranges. δ-ALA level in urine may not be the best discriminating factor of Pb exposure from the baseline to the high levels, but is recommended as a regular and routine test for all Pb-exposed workers in addition to the measurement of Pb in blood for subjects with higher δ-ALA levels. 相似文献
565.
The photocatalytic degradation of the organo-phosphorous pesticide phosphamidon at low concentration in aqueous solution on Ag-doped ZnO nanorods was investigated. Nanosized Ag-doped ZnO rods were synthesized by using a microwave assisted aqueous method. High molecular weight polyvinyl alcohol was used as a stabilizing agent. Composition and structure were investigated using energy-dispersive X-ray spectroscopy (EDAX) and X-ray diffraction (XRD). The XRD pattern reveals that ZnO nanorods are of hexagonal wurtzite structure. The average crystallite size calculated from Scherrer's relation was found to be 30?nm. The effects of catalyst loading, pH value, and initial concentration of phosphamidon on the photocatalytic degradation efficiency using Ag-doped ZnO nanorods as a photocatalyst have been discussed. The results revealed that Ag-doped ZnO nanorods with a diameter of 30?nm showed highest photocatalytic activity at a surface density of 1?g?dm?3. The catalyst doped with 0.2?mol% Ag is effective for the degradation of phosphamidon with visible light. This opens a new possibility to decompose pesticides that are present in wastewater. 相似文献
566.
Pot and hydroponic trials as well as tests on samples collected in a mining area and in two different urban sites of Tuscany were carried out on Arum italicum Mill (Italian arum) plants. Zinc and cadmium contents were determined by differential pulse anodic stripping voltammetry (DPASV) in different organs of about 180 samples. After 65 days treatment, zinc and cadmium median contents in leaves of plants grown hydroponically in solutions containing both metals at different concentrations fell within the range of 281-2022 and 8.3-45.1 μg g-1 (dry weight), respectively. Some Italian arum plants were also cultivated in pots in the presence or absence of malate or citrate in order to evaluate the role of these ligands in zinc and cadmium accumulation. Citrate enhanced cadmium uptake compared to malate. 相似文献
567.
568.
We report for the first time the use of beetroot fibers to eliminate heavy metals from polluted water. This biomass is used to remove lead, copper and zinc ions. The kinetics and beetroot fibers fixation capacities of lead, zinc and copper according to various physico‐chemical parameters such as pH, and the concentration of metal solutions were studied. The experiments were carried out in a laboratory column with fixed bed. For kinetic studies, samples of metal solutions were taken at regular intervals and measured by atomic absorption spectrometry. pH at 6.6 shows a maximum retention of the above cited metals by beetroot fibers (98%, 92%, 90% respectively). Quantity of cations retained by this biomass in simple and mixture solution is respectively estimated to be 23.6, 14.02 and 14.64 mg/g. Results indicate the usefulness of this biomass in the remediation of water contaminated by heavy metals by a rapid, practical and efficient method. 相似文献
569.
Nineteen years (1980–1998) of precipitation chemistry data from a site in Alaska are examined for trends using a least squares general linear model. The annual concentrations of SO2– 4 show a significant decreasing trend at 0.001 level and the annual change in concentration is —0.012mg 1–1 yr–1. The annual concentrations of NO – 3 show an increasing tendency non‐significant. The annual base cation concentrations show a clear significant decreasing trend at 0.001 level and the decrease is —0.009mg 1–1 yr–1. Ca2+ concentrations exhibit a significant decreasing trend at 0.001 level and the annual change of concentration is —0.003 mg 1–1 yr–1. Mg2+ and Na+ concentrations show a significant decreasing trend at 0.01 level and the annual change is —0.001 mg1–1 yr–1 for Mg2+ and —0.004 mg1–1 yr–1 for Na+. K+ concentrations are characterised by a decreasing trend, significant at 0.05 level. K+ concentrations have decreased —0.002mg1–1 yr–1. The strongest rates of concentration decline for base cations, Ca2+, Mg2+, K+ and Na+ occurred in fall and winter season. The annual values of pH show a decreasing trend non‐significant. The values of pH oscillate between 5.1 and 5.6 during the period considered. 相似文献
570.
Yifei SUN Xin FU Wei QIAO Wei WANG Tianle ZHU Xinghua LI 《Frontiers of Environmental Science & Engineering》2013,7(6):827-832
Activated carbon (AC)-supported copper or zinc made from ion exchange resin (IRCu-C and IRZn-C) have an increased metal load of 557.3 mg·g^-1 and 502.8 mg·g^-1 compared to those prepared by the traditional method involving impregnation with AC and copper (II) citrate or zinc citrate solution (LaCu-C and LaZn-C) of 12.9 mg·g^-1 and 46.0 mg·g^-1 respectively. When applied to decompose 2,2',4,4',5,5'-hexachlorobiphenyl at 250 ℃, IRCu-C achieved higher activity of 99.0% decomposition efficiency than LaCu-C of 84.7%, IRZn-C of 90.5% and LaZn-C of 62.7%. When the reaction temperature rose to 350 ℃, all the four kinds of reactants can decompose PCB- 153 with efficiency above 90%. Further, X-ray photoelec- tron spectroscopy characterization of IRCu-C before and after the reaction indicated transformation of 19.1% of Cu atoms into Cu^2+, illustrating that Cu is the active ingredient or electron donor promoting the decomposition of PCB- 153. The mechanism underlying this process differs from a traditional H donor. However, there is no significant change on the surface of IRZn-C before and after the reaction, suggesting that Zn acts as catalyst during the process of PCB-153 decomposition. 相似文献