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   243篇
  免费   88篇
  国内免费   81篇
安全科学   23篇
废物处理   7篇
环保管理   31篇
综合类   153篇
基础理论   117篇
污染及防治   43篇
评价与监测   13篇
社会与环境   17篇
灾害及防治   8篇
  2024年   1篇
  2023年   1篇
  2022年   5篇
  2021年   6篇
  2020年   9篇
  2019年   14篇
  2018年   77篇
  2017年   12篇
  2016年   13篇
  2015年   13篇
  2014年   21篇
  2013年   33篇
  2012年   27篇
  2011年   25篇
  2010年   16篇
  2009年   23篇
  2008年   16篇
  2007年   10篇
  2006年   5篇
  2005年   5篇
  2004年   5篇
  2003年   12篇
  2002年   8篇
  2001年   6篇
  2000年   4篇
  1999年   6篇
  1998年   2篇
  1997年   5篇
  1996年   3篇
  1995年   7篇
  1994年   5篇
  1993年   4篇
  1991年   1篇
  1990年   3篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1984年   1篇
  1983年   3篇
  1982年   1篇
  1980年   1篇
排序方式: 共有412条查询结果,搜索用时 15 毫秒
171.
内分泌干扰物莠去津对鲫鱼血清激素的影响   总被引:3,自引:1,他引:3  
为了研究低剂量条件下,内分泌干扰物莠去津对鲫鱼血清激素的影响,探讨其作用机理和剂量-效应关系,同时筛选出敏感的生物标志物,实验以除草剂莠去津对鲫鱼进行低剂量染毒(染毒浓度0~3mg·L-1),采用放射免疫法测定莠去津长期暴露下(60d)幼年雄性鲫鱼血清中性激素(17β-雌二醇(E2)、睾酮(T))及甲状腺激素(促甲状腺激素(TSH)、三碘甲状腺原氨酸(T3))的浓度,并将测定结果与空白对照及溶剂对照进行比较.结果发现:1)莠去津长期暴露下,各处理组鲫鱼血清E2浓度普遍升高,0.023、0.094、1.500、3.000mg·L-1组与空白对照相比,升高显著(p<0.05);2)各处理组鲫鱼血清T浓度与空白对照相比均无显著性差异(p>0.05);3)莠去津长期暴露下,低浓度莠去津组(0.006、0.023mg·L-1组)鲫鱼血清TSH浓度与空白对照相比差异不显著(p>0.05),而高浓度莠去津组(0.094、1.500、3.000mg·L-1组)则显著降低(p<0.05);4)类似地,莠去津长期暴露下,低浓度莠去津组(0.006、0.023、0.094、0.375、1.500mg·L-1组)鲫鱼血清T3浓度与空白对照相比差异不显著(p>0.05),只有高浓度莠去津组(3.000mg·L-1组)显著升高(p<0.05).实验结果表明,低剂量长期暴露下,莠去津对鲫鱼体内性激素及甲状腺激素具有一定的干扰作用,尤其是对17β-雌二醇影响更为显著,因此,17β-雌二醇可作为评价农药内分泌干扰效应的生物标志物.  相似文献   
172.
A possible aerobic degradative pathway for polyacrylate was examined with trimer (1,3,5-pentane tricarboxylic acid; PTCA)-utilizing bacteria. A few metabolic products from PTCA accumulated in culture filtrates and reaction mixtures of washed cells. Fraction A was detected as a main metabolite by high-performance liquid chromatography. A small amount of fraction B was concomitant with fraction A. Another fraction, C, was also detected. These compounds were suggested by liquid chromatography-mass spectrometry analyses to be 1,3,5-(1- or 2-pentene)tricarboxylic acid (fraction A or B) and 1,3,5-(2-oxopentane)tricarboxylic acid (fraction C). Fraction A was quickly further metabolized by washed cells, but fraction B was only gradually degraded. From these results, the metabolic pathway for polyacrylate is suggested to be quite similar to-oxidation for saturated fatty acids. The degradation of PTCA by washed cells was slower than that by growing cells and was inhibited by 5 mM NaN3. This suggests that the metabolism is linked to a respiratory chain or energy-producing system of bacteria which can aerobically assimilate PTCA.Paper presented at the Bio/Environmentally Degradable Polymer Society—Second National Meeting, August 19–21, 1993, Chicago, Illinois.  相似文献   
173.
在对水中总硬度测定条件进行分析、比较的基础上,针对测定过程中经常出现的问题提出一些看法及解决方法,并进行了探讨。  相似文献   
174.
采用直接法和后嫁接法成功制备出骨架掺杂Al原子,孔道表面接枝大位阻含胺基基团的双功能介孔硅基吸附材料.采用SAXRD、TEM、FTIR、NH3-TPD等手段对合成材料进行表征,结果表明合成的双功能AN-SBA-15具有有序的二维六方介孔结构,孔道表面的Al-OH与胺基不会发生自发复合反应.对模拟废水中Cd~(2+)和Cr_2O_7~(2-)的同时吸附去除实验研究表明AN-SBA-15具备同时吸附废水中Cd~(2+)和Cr_2O_7~(2-)离子的能力,吸附最佳pH值为5.0,吸附在40 min就达到平衡.AN-SBA-15对Cd~(2+)和Cr_2O_7~(2-)离子的吸附符合Langmuir模型,属于单层吸附.由Langmuir模型拟合出的AN-SBA-15对Cd~(2+)和Cr_2O_7~(2-)离子的最大吸附容量分别为125.9 mg·g~(-1)和156.5 mg·g~(-1).此外AN-SBA-15具备良好的脱附再生能力.  相似文献   
175.
成分复杂的垃圾渗滤液经处理后,研究其中残留的极低浓度的酚类环境内分泌干扰物的雌激素效应及其对生态环境的毒性作用具有非常重要的实际价值.本文选择对雌激素敏感的MCF-7人类乳腺癌细胞进行体外培养,将老龄渗滤液原液、经过内部微电解(IME)和内部微电解结合芬顿试剂(IME-Fenton)处理后的渗滤液酚类提取液稀释10~107倍,采用MTT法测定MCF-7细胞的增殖和细胞划痕损伤实验评价渗滤液中酚类物质的雌激素效应,并探讨了活性炭在反应中对酚类物质的去除效果.结果表明,渗滤液中酚类提取物对MCF-7细胞增殖在浸染72 h后达到最大;与渗滤液原液相比,渗滤液经IME和IME-Fenton处理后,最大增殖效应分别下降了85%和110%,酚类提取物减缓了MCF-7细胞的迁移速度;活性炭对渗滤液中酚的吸附主要发生在反应前30 min,渗滤液经活性炭吸附后的酚类提取物稀释10~107倍仍表现出细胞毒性.渗滤液经IME-Fenton处理后降低了酚类物质进入环境引起的危害,MCF-7细胞增殖和细胞划痕也为检测浓度低至10-15g·L-1的酚类雌激素提供新方法.  相似文献   
176.
本文描述了采用SIEMENS S7 414-5H CPU和WINCC等自动化产品实现再加热步进炉的自动控制。网络拓扑结合了Profibus-DP冗余现场总线和以太网(TCP/IP),使用STEP7编程实现了双交叉PID,使用WINCC软件实现了各工艺子系统画面以及参数监控、报表打印等功能。实现了用户控温节能的目的。  相似文献   
177.
Assessment of water resources requires reliable rainfall data, and rain gauge networks may not provide adequate spatial representation due to limited point measurements. The Tropical Rainfall Measuring Mission (TRMM) provides rainfall data at global scale, and has been used with good results. However, TRMM data are an indirect measurement of rainfall, and therefore must be validated for its proper use. In this work, a validation scheme was designed and implemented to compare the TRMM Version 7 (V7) monthly rainfall product at different time frames with data measured in two hydrologic subregions of the Santiago River Basin (SRB) in Mexico: Río Alto Santiago and Río Bajo Santiago (RBS). Additionally, three physio‐climatic regions provide an assessment of the interplay of topography, distance from coastal regions, and seasonal weather patterns on the correspondence between both datasets. The TRMM V7 rainfall product exhibited good agreement with the rain gauge data particularly for the RBS and for the whole SRB during wettest summer and autumn seasons. However, strong regional dependence was observed due to differences in climate and topography. Overall, in spite of some noted underestimations, the monthly TRMM V7 rainfall product was found to provide useful information that can be used to complement limited monitoring as is the case of RBS. An improved combined rainfall product could be generated and thus gaining the most benefits from both data sources.  相似文献   
178.
Surface air concentrations of 7Be at a number of stations in Oceania show a distinct annual cycle. We apply a sinusoidal model to describe this cycle. The results show that peak 7Be concentrations in surface air occur during early spring at tropical latitudes and during mid-to-late summer at middle latitudes. Comparison with available 90Sr surface air data for the southern hemisphere indicates that stratosphere-to-troposphere exchange is an active atmospheric process controlling the 7Be annual cycle throughout the Oceania region. Vertical transport of air within the troposphere also seems to influence the observed annual cycle. Seasonality in rainfall is not thought to control the annual cyclic behaviour of 7Be in surface air.  相似文献   
179.
The occurrence, distribution and nature of ambient thiobacilli along with their ability to oxidize different sulphur species under simulated natural and in vitro culture conditions were studied in the polluted and unpolluted sites of the River Ganga.

Thiobacillus thioparus, T. thiooxidans and T. denitrificans were isolated from the river water. the former two occurred in both polluted and unpolluted sites, while T. denitrificans occurred in polluted areas only. the paper pulp mill effluent discharge area contained the highest population of T. thioparus. the sewage drainage area showed relatively higher populations of T. thiooxidans and T. denitrificans.

The present study revealed that only biological oxidation of either thiosulphate or elemental sulphur occurred in the river water. All the thiobacilli screened oxidized thiosulphate, and three-fourths of them oxidized elemental sulphur. Some strains were found to be very good acidifiers. in spite of such acidification by the ambient thiobacilli, the pH of the river water remained alkaline. the specific rates of thiosulphate (0.18 -0.51 μMmolh-1 mg-1 cell) and sulphur (1.3 - 6.2 Normality day-1 mg-1 biomass) oxidations under simulated natural condition were found to be higher in polluted areas when compared with the unpolluted one (sulphur: 0.8 - 1.0 Normality day-1 mg-1).

Further, addition of thiouslphate or elemental sulphur in the river water in simulated in vitro condition resulted in the increase of respective oxidation rates. the variations in the natae of pollutants discharged into the river water influenced the oxidation rate of thiosulphate or sulphur.  相似文献   
180.
Fuel and leasable minerals mined in the United States have historically been subject to federal royalties while locatable minerals have not. In recent years there have been multiple attempts to alter this policy and subject locatable minerals to federal royalties as well; most recently the preliminary 2012 Obama budget included a gross royalty on hard-rock mining on public lands. This paper analyzes the issue of imposing such federal royalties from both a legal and economic perspective. From a legal perspective, it is argued that the state of western property rights precludes royalties on currently extant claims so revenues from a royalty would not be realized for many years. From an economic perspective, it is argued that the effect on revenue would be smaller than one might anticipate due to such a royalty crowding out state levies or encouraging vertical disintegration on the part of mining firms to avoid much of the burden of the royalty.  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