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本文从价格视角将我国稀土市场结构的变化历程划分为不同阶段,分别从理论和现实视角上探讨了在国际、国内都是完全竞争市场,国际市场垄断、国内市场完全竞争,国际市场完全竞争、国内市场垄断,国际、国内都是垄断市场条件下稀土最优开采路径及最优耗竭时间,并通过设定参数判断其相对大小关系。发现在一定的假设条件下,开采前期当国内和国际市场都是完全竞争时,稀土最优开采量是最大的;当国内和国际市场都是垄断时,稀土最优开采量是最小的;其他两种市场情况下稀土最优开采量居于中间,当国际市场是稀土的主要消费地时,国际竞争-国内垄断市场情况下稀土最优开采量大于国际垄断-国内竞争市场情况下稀土最优开采量,反之,国际垄断-国内竞争市场情况下稀土最优开采量大于国际竞争-国内垄断市场情况下稀土最优开采量。 相似文献
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Hamide Elvan Bayrak Mehmet Tufekci Hacer Bayrak Celal Duran Mustafa Soylak 《毒物与环境化学》2017,99(4):590-600
A simple and sensitive solid phase extraction method was developed for simultaneous separation and preconcentration of gold and palladium ions with N-(4-methylphenyl)-2-{[(4-phenyl-5-pyridine-4-yl-4H-1,2,4-triazol-3-yl)thio]acetyl}hydrazine carbo thioamide complex on Amberlite XAD-1180 resin before their determination by flame atomic absorption spectrometry. Some analytical parameters such as HNO3 concentration of the sample solution, amount of complexing agent, sample volume, eluent type and volume, effects of foreign ions and adsorption capacity of the resin were investigated for quantitative recovery of gold and palladium ions. The effects of some anions and cations were also examined. Under optimum conditions, the detection limits for gold and palladium ions were found to be 0.29 and 0.19 μg L?1, respectively. The preconcentration factor for gold and palladium was 250. After being validated by standard addition and analysis of standard reference material, the procedure was successfully applied to the analysis of sea and stream water, anodic slime, gold ore, soil and electronic waste. 相似文献
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《Environmental Forensics》2013,14(4):313-317
Supercritical fluid extraction (SFE) was investigated to evaluate its potential for obtaining high quality chromatographic fingerprints from soils encountered in environmental investigations. While the volatile and semivolatile fractions of light nonaqueous phase liquid (LNAPL) samples can be “fingerprinted” in a single chromatographic run, it is commonly not possible to obtain samples of LNAPL in the locations of interest. For this and other reasons, it was desirable to develop this method (SFE) of soil extraction, which allows chromatographic fingerprinting of the same quality routinely obtained with LNAPL so that environmental forensic investigations could be extended to areas beyond those containing LNAPL in monitoring wells. In this study, SFE was compared to conventional dichloromethane extraction. Both artificially spiked soil and soil from petroleum release sites were tested. Since water can be a problem when using the SFE method, particular attention was given to handling soils with high moisture contents. The SFE extracts showed excellent retention of low molecular components, including pentanes. Gas chromatography of SFE extracts yielded molecular distributions that showed no significant bias toward either low or high molecular weight components. These results show that SFE can be used to obtain an unbiased, single-run chromatographic “fingerprint” of both volatile and semivolatile hydrocarbons in contaminated soil samples. 相似文献
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To evaluate the genotoxic risk that contaminated sediment could constitute for benthic organisms, three contaminated (VA, VC and VN) and one uncontaminated (RN) sediment samples were collected in the Berre lagoon (France). Potentially bioavailable contaminants in sediments were obtained using sediment extraction with synthetic seawater adjusted to pH 4 or pH 6, simulating the range of pH prevailing in the digestive tract of benthic organisms. The genotoxic activities of these extracts were evaluated by three short-term bioassays: the Salmonella mutagenicity test using the Salmonella typhimurium strain TA102, the alkaline comet assay and the micronucleus assay on the Chinese Hamster Ovary cells CHO-K1. Results of the Salmonella mutagenicity assay detected a mutagenic response for RN extract at pH 6, and for VA extract at pH 4. Results of the comet and micronucleus assays detected low genotoxic/clastogenic activities for VA and VC extracts at pH 6 and higher activities for RN, VA and VC extracts at pH 4. To identify if metals (Al, Fe, Mn, As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn) were involved in these genotoxic activities, their concentrations were determined in the extracts, and their speciation was assessed by thermodynamic calculations. Results showed that extracts from sites VA, VC and VN generally presented the highest trace metal contents for both extractants, while the site RN presented lower trace metal contents but the highest Fe and Mn contents. Thermodynamic calculations indicated that Fe, Mn, As and in a lower extend Co, Ni and Zn were mainly present under free forms in extracts, and were consequently, more likely able to induce a genotoxic effect. Results globally showed no correspondence between free metal contents and genotoxic activities. They suggested that these positive results could be due to uncharacterized compounds, acting as direct genotoxic agents or enhancing the genotoxic properties of analyzed metals. 相似文献
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Akira Sano Makoto KanomataHiroki Inoue Norio SugiuraKai-Qin Xu Yuhei Inamori 《Chemosphere》2012,89(10):1243-1247
The objective of the present study was to establish an alkali extraction technology for FePO4-containing sewage sludge obtained from a wastewater treatment system that includes phosphorous removal by iron electrolysis. By clarifying the extraction properties of phosphorous, organic matter, and inorganic matter, conditions for alkali extraction were optimized. As a result, it was suggested that unheated phosphorous extraction would be superior for FePO4-containing sewage sludge. And, extraction methods and sewage sludge properties were also compared, and the noteworthy result that extraction of metals can be suppressed to extremely low amounts with alkali extraction as compared with acid extraction was obtained. A new insight was also gained that, as compared with the use of incinerated ash reported in previous studies, alkali extraction was more efficient when raw sewage sludge was used. 相似文献
99.
聚环氧琥珀酸萃取锰泥残渣中铬的研究 总被引:1,自引:0,他引:1
聚环氧琥珀酸(PESA)是一种具有无磷及非氮结构、环境友好型水溶性聚合物,且具有螯合多价金属阳离子的性能和可生物降解性的特征,选取其作为锰泥残渣中铬的螯合萃取剂,研究了不同pH、螯合萃取剂剂量、搅拌时间下PESA对铬的萃取率。结果表明:(1)最佳萃取条件为pH=4、PESA剂量30mg/g、搅拌时间60min;在最佳萃取条件下,铬的萃取率可达95%。(2)从结构上看,PESA是由醚基和羧基基团组成的高分子聚合物,羧基基团是与金属离子作用的主要官能团,它对Ca2+、Mg2+、Zn2+、Cr(Ⅲ)、Cr(Ⅵ)和Pb2+等有较强的螯合能力;从溶液的配位角度看,PESA与金属有较强的结合能力。因此,PESA对锰泥残渣中的铬有萃取作用。 相似文献
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