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   2778篇
  免费   240篇
  国内免费   940篇
安全科学   275篇
废物处理   168篇
环保管理   213篇
综合类   1801篇
基础理论   381篇
环境理论   1篇
污染及防治   687篇
评价与监测   125篇
社会与环境   180篇
灾害及防治   127篇
  2024年   10篇
  2023年   50篇
  2022年   166篇
  2021年   164篇
  2020年   138篇
  2019年   120篇
  2018年   136篇
  2017年   152篇
  2016年   143篇
  2015年   167篇
  2014年   223篇
  2013年   293篇
  2012年   249篇
  2011年   265篇
  2010年   213篇
  2009年   205篇
  2008年   204篇
  2007年   143篇
  2006年   189篇
  2005年   112篇
  2004年   74篇
  2003年   75篇
  2002年   75篇
  2001年   63篇
  2000年   64篇
  1999年   47篇
  1998年   47篇
  1997年   29篇
  1996年   25篇
  1995年   35篇
  1994年   16篇
  1993年   14篇
  1992年   13篇
  1991年   11篇
  1990年   7篇
  1989年   6篇
  1988年   4篇
  1987年   2篇
  1986年   4篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
排序方式: 共有3958条查询结果,搜索用时 15 毫秒
971.

Shengjin Lake wetland is located in the middle and lower reaches of the Yangtze River in China. It is a typical lake-type wetland and is also an ideal place for rare cranes to overwintering. The changes of wetland landscape are closely related to the habitat quality of wintering cranes. It is of great significance to study the habitat change of wintering cranes in wetland for wetland ecological restoration and restoration. In this paper, we analyze four kinds of winter cranes and wetland landscape pattern types from the years 1986 to 2015. Also, we adopted the Pearson correlation analysis method to analyze the relationship between wetland landscape types and crane population, and the main landscape types of cranes habitat were obtained. We selected disturbance degree, food richness, vegetation cover, and hydrological condition as the main factors affecting wintering habitat of cranes. We established a habitat suitability index model for wintering cranes and generated habitat suitability assessment maps by ArcGIS. The results show that the change of landscape pattern in Shengjin Lake protected area was obvious, the number of wetland patches increased, the fragmentation degree of landscape increased, the landscape patch difference became smaller, and the diversity index and evenness index increased gradually. From 1986 to 2015, the number of wintering cranes decreased and the habitat suitability index of wintering cranes decreased from 0.845 to 0.465, and the habitat suitability of wintering cranes fell from 13,577.11 to 7424.42 ha, which showed the overall habitat deteriorated significantly and had a positive correlation between the crane population and habitat suitability.

  相似文献   
972.
Environmental Science and Pollution Research - A recent work has shown that hydrophobic organic compounds solubilized in the micelle phase of some nonionic surfactants present substrate toxicity to...  相似文献   
973.
In order to investigate the effect of feedstock ratios in biogas production, anaerobic co-digestions of rice straw with kitchen waste and pig manure were carried out. A series of single-stage batch mesophilic (37 ± 1 °C) anaerobic digestions were performed at a substrate concentration of 54 g/L based on volatile solids (VS). The results showed that the optimal ratio of kitchen waste, pig manure, and rice straw was 0.4:1.6:1, for which the C/N ratio was 21.7. The methane content was 45.9–70.0% and rate of VS reduction was 55.8%. The biogas yield of 674.4 L/kg VS was higher than that of the digestion of rice straw or pig manure alone by 71.67% and 10.41%, respectively. Inhibition of biogas production by volatile fatty acids (VFA) occurred when the addition of kitchen waste was greater than 26%. The VFA analysis showed that, in the reactors that successfully produced biogas, the dominant intermediate metabolites were propionate and acetate, while they were lactic acid, acetate, and propionate in the others.  相似文献   
974.
This work determined the influence of humic acid (HA) and fulvic acid (FA) on the interaction mechanism and microstructure of Ni(II) onto diatomite by using batch experiments, X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) methods. Macroscopic and spectroscopic experiments have been combined to see the evolution of the interaction mechanism and microstructure of Ni(II) in the presence of HA/FA as compared with that in the absence of HA/FA. The results indicated that the interaction of Ni(II) with diatomite presents the expected solution pH edge at 7.0, which is modified by addition of HA/FA. In the presence of HA/FA, the interaction of Ni(II) with diatomite increased below solution pH 7.0, while Ni(II) interaction decreased above solution pH 7.0. XPS analysis suggested that the enrichment of Ni(II) onto diatomite may be due to the formation of (≡SO)2Ni. EXAFS results showed that binary surface complexes and ternary surface complexes of Ni(II) can be simultaneously formed in the presence of HA/FA, whereas only binary surface complexes of Ni(II) are formed in the absence of HA/FA, which contribute to the enhanced Ni(II) uptake at low pH values. The results observed in this work are important for the evaluation of Ni(II) and related radionuclide physicochemical behavior in the natural soil and water environment.  相似文献   
975.
为了积极推进矿业领域循环经济的发展,开展国家级绿色矿山建设试点示范工作,2010年9月11—12日,由中国矿业联合会、国土资源部规划司联合主办的"2010年中国矿业循环经济论坛"在山西大同市召开,对矿业领域发展循环经济,建设国家级绿色矿山试点工作进行了交流和部署。根据国土资源部明确要求,中国矿业联合会要加快研究完善绿色矿山建设具体标准和办法,会同有关行业协会组织做好国家级试点矿山的推荐和评估工作,积极搭建绿色矿山建设交流与合作平台,为试点矿山提供经验交流和技术咨询等服务,切实承担起全面推进绿色矿山建设的业务支撑。此次会议之后,本刊记者就矿业领域发展循环经济,建设绿色矿山等问题专访了中国矿业联合会会长、全国政协人口资源环境委员会副主任李元。  相似文献   
976.
Abstract

A process on crystallized precipitation of ammonium by adding magnesium salt and phosphate was carried out to improve C/N ratio in swine wastewater. After completion of crystallized precipitation of ammonium, an intermittent aeration process with aeration and non‐aeration periods alternated at interval of 1:1 hr day‐1 is used for the improved swine wastewater (T‐N/BOD=0.14: BOD=8200 mg/liter and T‐N=1166 mg/liter). The results obtained from the experiment show that the removal ratios of T‐N and NH4‐N are 91% and 99%, respectively. T‐P is not removed, while the removal ratio of PO4‐P is 60% as 3% of CaCl2 liquid is added. The results also indicate that dilution with water is effective to improve the removal of phosphorus even if raw swine wastewater contains high concentrations of T‐N, T‐P, BOD, and TOC.  相似文献   
977.
基于徐州台和常熟台 2 套 VP 型宽频带倾斜仪记录到的 186 次同震形变波,统计分析其振幅-震级特征,分区对比研究其衰减关系,结合观测资料计算仪器特征参数,通过岩芯试验获取场地基岩性质,综合分析仪器观测效能。结果表明:(1)相比于常熟台,徐州台的 NS 向和 EW 向拟合均较为稳定,记震能力更好;(2)不同构造分区中拟合的振幅-震级关系,随着震中距增大,最大振幅幅值呈指数上升且拟合程度显著增强;(3)仪器基墩稳定性对同震响应存在一定的影响,基墩稳定性好,观测数据年零漂小,同震记录相对稳定;不同岩性的基墩对同震记录的敏感性存在差异,同震响应振幅与基墩弹性模量成反比。  相似文献   
978.
台风风场模型的研究对于台风风场极值风速、巨浪的精确预报以及与之相关的灾害评估研究是极具现实意义的。系统介绍了Kepert提出的台风风场线性解析模型和Foster提出的基于相似理论求解的半解析模型。在Kepert解析模型的基础上进行改进,引入沿高度变化湍流扩散系数模型和受速度影响的拖曳系数模型,用半解析的方法对风场进行求解。借助Dropsonde现场观测台风风速剖面数据对本文提出改进模型的准确性进行验证。利用三种理论模型对实测海上台风表面风场进行模拟,与H*wind风场数据进行比较,验证不同模型之间的差别,并定量分析不同模型对台风表面风场特性的模拟能力。  相似文献   
979.
基于高光谱遥感的沿海河口无机氮浓度空间分布特征解译   总被引:1,自引:0,他引:1  
张东  许勇  张鹰  李欢 《环境科学》2010,31(6):1435-1441
利用39组样本的野外实测光谱结合Hyperion影像资料,建立了高悬沙含量沿海河口可溶性无机氮(dissolved inorganic nitrogen,DIN)的高光谱定量遥感解译模型,实现DIN浓度空间分布规律的遥感反演及动态监测.研究发现,当悬沙浓度0.1kg/m3时,DIN浓度与悬沙含量之间呈显著的倒数相关关系,相关系数R2为0.617.据此首先将重采样处理后的野外实测光谱与同步DIN浓度数据进行统计相关分析,筛选出2个对DIN浓度变化敏感的波段,中心波长分别为630nm和804nm;然后利用波段反射率R804和R630计算出仿泥沙遥感参数因子R804×R630/(R804-R630),建立其与实测DIN浓度的非线性遥感模型,29组建模样本和10组检验样本的相关系数R2分别为0.746和0.67,DIN浓度平均绝对误差分别为109.07μg/L和147.58μg/L.将该非线性遥感模型应用于Hyperion影像,获得了射阳河口DIN浓度的空间分布特征,DIN浓度的变化范围为52~513μg/L.可以看出,在以悬沙为主要悬浮物的沿海河口,遥感解译得到的DIN浓度扩散趋势与潮流的运动以及悬沙的运移规律密切相关.因此,在无需了解水动力状况的条件下,高光谱遥感是对DIN浓度进行动态监测的有效手段.  相似文献   
980.
丹江口水库典型消落区土壤氮磷赋存形态及释放特征研究   总被引:9,自引:1,他引:8  
丹江口水库是南水北调中线工程水源地,调水工程使得水库蓄水并带来水库水位上升,新增淹没区不同土地利用类型土壤由于淹没浸泡可能使其中氮磷等营养物释放,对水库水质构成威胁.本文通过采集丹江口水库典型消落区5种土地利用类型(滩地、草地、荒地、耕地、果园)的表层土壤,选用磷形态标准测试方法(SMT)和氮形态分级浸取方法对消落区土壤氮磷赋存形态进行分析,同时进行土壤氮磷释放模拟实验来考察消落区土壤"淹没-落干"过程的氮磷释放特征.结果表明,东库湾消落区土壤磷素主要以钙结合态磷(Ca-P)存在,其占TP比例范围为54.7%~82.0%,平均值为69.1%.滩地、草地、荒地土壤生物可利用性磷(BAP)占TP比例也基本超过30%.土壤有机硫化物结合态氮(OSFN)含量在139.1~195.0 mg·kg-1之间,占TN比例范围为18.8%~27.0%,是土壤可转化态氮(TF-N)中主要的赋存形态.土壤释放模拟实验显示,耕地、果园这两类新增淹没区土壤在受淹后其更易向水体释放磷素,而消落区土壤氮素整体上呈现向水体缓慢释放的规律."淹没-落干"前后滩地、荒地的BAP含量下降超过20%,果园BAP含量也降低了16%,草地和耕地的BAP含量则维持相对稳定."淹水-落干"实验后耕地、果园土壤IEF-N含量分别下降22.6%、34.2%,这两类新增淹没区土壤在调水淹没后可能会向上覆水水体释放氮素.  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