首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   828篇
  免费   76篇
  国内免费   169篇
安全科学   30篇
废物处理   25篇
环保管理   44篇
综合类   384篇
基础理论   138篇
污染及防治   153篇
评价与监测   259篇
社会与环境   33篇
灾害及防治   7篇
  2024年   8篇
  2023年   15篇
  2022年   33篇
  2021年   34篇
  2020年   34篇
  2019年   25篇
  2018年   25篇
  2017年   40篇
  2016年   51篇
  2015年   48篇
  2014年   61篇
  2013年   120篇
  2012年   75篇
  2011年   91篇
  2010年   55篇
  2009年   62篇
  2008年   41篇
  2007年   51篇
  2006年   31篇
  2005年   30篇
  2004年   14篇
  2003年   18篇
  2002年   14篇
  2001年   12篇
  2000年   15篇
  1999年   6篇
  1998年   14篇
  1997年   10篇
  1996年   4篇
  1995年   11篇
  1994年   8篇
  1993年   9篇
  1992年   1篇
  1991年   2篇
  1990年   2篇
  1989年   1篇
  1987年   2篇
排序方式: 共有1073条查询结果,搜索用时 15 毫秒
91.
Fast pyrolysis of chicken manure produced two biooils (Fractions I and II) and a residual char. All four materials were analyzed by chemical methods, 13C and 1H Nuclear Magnetic Resonance Spectrometry (13C and 1H NMR), and Fourier Transform Infrared Spectrosphotometry (FTIR). The char showed the highest C content and the highest aromaticity. Of the two biooils Fraction II was higher in C, yield and calorific value but lower in N than Fraction I. The S and ash content of the two biooil fractions were low. The Cross Polarization Magic Angle Spinning (CP-MAS) 13C NMR spectrum of the initial chicken manure showed it to be rich in cellulose, which was a major component of sawdust used as bedding material. Nuclear Magnetic Resonance (NMR) spectra of the two biooils indicated that Fraction I was less aromatic than Fraction II. Among the aromatics in the two biooils, we were able to tentatively identify N-heterocyclics like indoles, pyridines, and pyrazines. FTIR spectra were generally in agreement with the NMR data. FTIR spectra of both biooils showed the presence of both primary and secondary amides and primary amines as well as N-heterocyclics such as pyridines, quinolines, and pyrimidines. The FTIR spectrum of the char resembled that of the initial chicken manure except that the concentration of carbohydrates was lower.  相似文献   
92.
Heavy metal distribution in medicinal plants is gaining importance not only as an alternative medicine, but also for possible concern due to effects of metal toxicity. The present study has been focused on emphasizing the heavy metal status and bioaccumulation factors of V, Mn, Fe, Co, Cu, Zn, Se (essential metals) and Cr, Ni, Cd, As and Pb (potentially toxic metals) in medicinal plants grown under two different environmental conditions e.g., near to Khetri copper mine and those in fertile soils of Haridwar, both in India, using Instrumental Neutron Activation Analysis (relative method) and Atomic Absorption Spectrometry. The copper levels in the medicinal plants from Khetri were found to be 3-4 folds higher (31.6–76.5 mg kg?1) than those from Haridwar samples (7.40–15.3 mg kg?1), which is correlated with very high copper levels (763 mg kg?1) in Khetri soil. Among various heavy metals, Cr (2.60–5.92 mg kg?1), Cd (1.47–2.97 mg kg?1) and Pb (3.97–6.63 mg kg?1) are also higher in concentration in the medicinal plants from Khetri. The essential metals like Mn (36.4–69.3 mg kg?1), Fe (192–601 mg kg?1), Zn (24.9–49.9 mg kg?1) and Se (0.13–0.91 mg kg?1) and potentially toxic metals like Ni (3.09–9.01 mg kg?1) and As (0.41–2.09 mg kg?1) did not show much variations in concentration in the medicinal plants from both Khetri and Haridwar. The medicinal plants from Khetri, e.g., Ocimum sanctum, Cassia fistula, Withania somnifera and Azadirachta Indica were found rich in Ca and Mg contents while Aloe barbadensis showed moderately high Ca and Mg. Higher levels of Ca-Mg were found to correlate with Zn (except Azadirachta Indica). The bioaccumulation factors (BAFS) of the heavy metals were estimated to understand the soil-to-plant transfer pattern of the heavy metals. Significantly lower BAF values of Cu and Cr were found in the medicinal plants from Khetri, indicating majority fraction of these metals are precipitated and were immobilized species unsuitable for plant uptake. Overall, Withania somnifera (Ashwagandha) showed very high metal bioaccumulation.  相似文献   
93.
针对绿藻,采用超声波提取,以荧光激发-发射波长差216nm,建立了同步荧光法测定绿藻叶绿素a含量的新方法,其线性范围为0.02~1.25 mg/L,检出限为1.6ug/L,加标回收率在97.0%~104%之间。与分光光度法测定叶绿素a的对比试验结果表明,两者无显著性差异,但该方法具有快速、灵敏,其他常见色素不干扰测定的优点,能够满足供水中绿藻叶绿素a含量快速检测的需要。  相似文献   
94.
Size-specific concentrations and bioaccessibility of polybrominated diphenyl ethers (PBDEs) in dust from air conditioner filters were measured, and the factors influencing the PBDE bioaccessibility were determined. Generally, the PBDE concentrations increased with decreasing dust particle size, and BDE209 (deca-BDE) was generally the predominant congener. The bioaccessibility ranged from 20.3% to 50.8% for tri- to hepta-BDEs, and from 5.1% to 13.9% for BDE209 in dust fractions of varied particle size. The bioaccessibility of most PBDE congeners decreased with increasing dust particle size. The way of being of PBDE (adsorbed to dust surface or incorporated into polymers) in dust significantly influenced the bioaccessibility. There was a significant negative correlation between the tri- to hepta-BDE bioaccessibility and organic matter (OM) contents in dust. Furthermore, tri- to hepta-BDE bioaccessibility increased with increasing polarity of OMs, while with decreasing aromaticity of OMs. The tri- to hepta-BDE bioaccessibility significantly positively correlated with the surface areas and pore volumes of dust. Using multiple linear regression analysis, it was found that the OM contents and pore volumes of dust were the most important factors to influence the tri- to hepta-BDE bioaccessibility and they could be used to estimate the bioaccessibility of tri- to hepta-BDEs according to the following equation: bioaccessibility (%) = 45.05 − 0.49 × OM% + 1.79 × pore volume. However, BDE209 bioaccessibility did not correlate to any of these factors.  相似文献   
95.
In this work, water and sediment samples were collected from three different stations located along the Sakarya river between May and September 2003. Lead, copper, chromium, zinc, nickel and cadmium concentrations were determined by using solvent extraction and flame atomic absorption spectrometric method. The results show that differences based upon sampling times, regions, sediment and water samples were observed. The mean levels of copper, nickel, chromium, lead, cadmium, zinc for sediment samples are; 4.630 μg g−1, 13.520 μg g−1, 8.780 μg g−1, 2.550 μg g−1, 9.990 μg g−1 and for water samples are; 0.851 μg g−1, 1.050 μg g−1, 0.027 μg g−1, 1.786 μg g−1, 0.236 μg g−1, 0.173 μg g−1, respectively.  相似文献   
96.
建立了用加速溶剂萃取仪(ASE)萃取、凝胶渗透色谱(GPC)净化、气相色谱/串联四极杆质谱多反应监测、同时测定土壤中17种有机氯农药和19种多氯联苯的方法.加标浓度在3.3μg/kg时的平均回收率在79.6%~93.2%之间,相对标准偏差在2.9%~13.0%之间,定量限在0.01~0.51μg/kg之间.在检测土壤样品中的有机氯农药和多氯联苯残留方面,Gc-QqQ-MS/MS相对于气相色谱/电子捕获检测器(GC-ECD)和GC-MS的选择离子检测(SIM)模式具有非常明显的优势,尤其是在低浓度水平的定性和定量方面.  相似文献   
97.
Cadmium and lead were determined simultaneously in seawater by differential pulse stripping voltammetry (DPSV) preceded by adsoptive collection of complexes with 8-hydroxyquinoline (oxine) on to a hanging mercury drop electrode (HMDE). In preliminary experiments the optimal analytical condition for oxine concentration was found to be 2.10−5 M, at pH 7.7, the accumulation potential was −1.1 V, and the initial scannig potential was −0.8 V. The peak potentials were found −0.652 V for Cd and −0.463 V for Pb At the 60 s accumalation time. The limit of detection (LOD) and limit of quantitatification (LOQ) were found to be by voltammetry as 0.588 and 1.959 μg l−1 (RSD, 5.50%) for Cd and 0.931 and 3.104 μg l−1 (RSD, 4.10%) for Pb at 60 s stirred accumulation time respectively. In these conditions the most of the seawater samples are amenable for direct voltammetric determination of cadmium and lead using a HMDE. An adsorptive stripping mechanism of the electrode reaction was proposed. For the comparison, seawater samples were also analysed by ICP-atomic emission spectrometry method (ICP-AES). The applied voltammetric technique was validated and good recoveries were obtained.  相似文献   
98.
The activity concentrations of soil samples collected from thirty different locations of Malwa region of Punjab were determined by using HPGe detector based on high-resolution gamma spectrometry system. The range of activity concentrations of 226Ra, 232Th and 40K in the soil from the studied areas varies from 18.37 Bq kg−1 (Sangrur) to 53.11 Bq kg−1 (Sitoguno), 57.28 Bq kg−1 (Dhanola) to 148.28 Bq kg−1 (Sitoguno) and 211.13 Bq kg−1 (Sunam) to 413.27 Bq kg−1 (Virk Khera) with overall mean values of 35 Bq kg−1, 80 Bq kg−1and 317 Bq kg−1 respectively. The absorbed dose rate calculated from activity concentration of 226Ra, 232Th and 40K ranges between 8.47 and 24.48, 35.68 and 92.38, and 8.74 and 17.11 nGy h−1, respectively. The total absorbed dose in the study area ranges from 58.08 nGy h−1 to 130.85 nGy h−1 with an average value of 79.11 nGy h−1. The calculated values of external hazard index (Hex) for the soil samples of the study area range from 0.35 to 0.79. Since these values are lower than unity, therefore, according to the Radiation Protection 112 (European Commission. Radiation Protection 112 1999) report, soil from these regions is safe and can be used as a construction material without posing any significant radiological threat to population.  相似文献   
99.
水中氨氮含量是反应水质状况的重要指标。文章对测定水中氨氮气相分子吸收光谱法(标准号HJ/T195-2005)进行了改进试验研究。第一,对氧化剂的配比进行了改进,使氨氮的测定范围扩展至100μg。第二,对标准HJ/T195-2005中直接使用亚硝酸钠标准溶液做标准曲线的处理方式也做了探讨。通过一系列对比实验认为,应用硫酸铵标准溶液做工作曲线更加准确合理。最后应用改进后的气相分子吸收光谱法和纳氏比色法或滴定法对多种实际废水样品进行同时测定。结果表明,改进后的气相分子吸收光谱法测定氨氮的范围更宽,灵敏度更高和准确度更好。  相似文献   
100.
通过传统单波长激发/发射荧光光谱法与恒能量同步荧光光谱法进行对比,对大气颗粒物中多环芳烃(PAHs)进行了定性定量分析,采用恒能量同步荧光光谱法在不同能量差下建立了15种典型PAHs成分的恒能量同步荧光法的标准谱库.在各PAHs在最佳能量差下进行定量分析,结果表明,除苊荧光信号响应较差外,其余PAHs的LOD和LOQ分别为0.0580~3.18、0.232~12.7 ng·mL~(-1).15种PAHs的空白和一定浓度下的加标回收率范围在82.8%~120.0%,相对标准偏差范围在0.51%~5.87%之间,以恒能量同步荧光光谱进行了兰州地区大气颗粒物中15种PAHs分布特征分析.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号