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   1233篇
  免费   54篇
  国内免费   398篇
安全科学   82篇
废物处理   65篇
环保管理   99篇
综合类   652篇
基础理论   225篇
污染及防治   396篇
评价与监测   52篇
社会与环境   39篇
灾害及防治   75篇
  2023年   17篇
  2022年   62篇
  2021年   47篇
  2020年   30篇
  2019年   34篇
  2018年   46篇
  2017年   50篇
  2016年   46篇
  2015年   72篇
  2014年   85篇
  2013年   115篇
  2012年   113篇
  2011年   112篇
  2010年   90篇
  2009年   77篇
  2008年   90篇
  2007年   77篇
  2006年   90篇
  2005年   57篇
  2004年   34篇
  2003年   40篇
  2002年   41篇
  2001年   39篇
  2000年   29篇
  1999年   30篇
  1998年   23篇
  1997年   27篇
  1996年   19篇
  1995年   18篇
  1994年   13篇
  1993年   18篇
  1992年   12篇
  1991年   6篇
  1990年   5篇
  1989年   6篇
  1988年   3篇
  1987年   4篇
  1986年   2篇
  1982年   1篇
  1981年   2篇
  1971年   1篇
  1969年   1篇
  1962年   1篇
排序方式: 共有1685条查询结果,搜索用时 31 毫秒
541.
A MOUDI-120 sampler was used in Beijing to collect multi-stage samples in the summer and winter of 2013 to 2015. Thirty-three sample sets were collected during the daytime,nighttime, and different pollution levels. The actual relative humidity in the impactors was calculated for the first time. The carbonaceous components(organic and elemental carbon,OC and EC, respectively) and water-soluble inorganic ions(Na~+, NH_4~+, K~+, Mg~(2+), Ca~(2+), Cl~-, NO_3~-,and SO_4~(2-)) were analyzed in each sample. The characteristics of the mass concentration distribution and charge balance were discussed. On the basis of relative humidity in the impactors, aerosols less than 1.0 μm were sampled under relatively dry conditions in most cases. The concentration levels for the chemical species were higher in the winter than in the summer. Three modes(condensation mode, droplet mode, and coarse mode) could be identified from the distributions of NH_4~+, NO_3~-, SO_4~(2-), Cl~-, K~+, OC and EC. The distribution characteristics for the pollution dissipation process were different from the pollution accumulation process. NO_3~-and NO_2~-contributed most of the negative electric charges in the stage below 0.1 μm. In the condensation mode, the cations were dominated by NH_4~+, which was sufficient to balance the anions. In the droplet mode of the heavily polluted samples,the ammonium was not sufficient to balance the anions. In the coarse mode, the positive electric charges were primarily composed of metal cations. The analyzed anions were not sufficient to neutralize the measured cations.  相似文献   
542.
长江口沉积物重金属赋存形态及风险特征   总被引:7,自引:1,他引:6  
基于长江口沉积物8种重金属(As、Cd、Cr、Cu、Hg、Ni、Pb、Zn)总量与形态在丰、平、枯水期以及14个典型点位的分布特征,通过平衡分配法建立了长江口沉积物质量基准(SQGs),并以此评价长江口沉积物重金属生态风险,揭示重金属生态风险与其形态特征间的相关关系.结果表明,除Cd之外,长江口沉积物重金属以残渣态为主导形态,尤其是As、Cr、Hg,其残渣态含量均为90%以上.长江口As、Cd、Cr、Cu、Hg、Ni、Pb、Zn的沉积物质量基准分别为43.29、0.672、79.65、19.08、0.569、339.09、30.87、411.36μg·g~(-1).Cu的生态风险程度最高,对水生生物具有较大的毒性影响,应当引起重视.河口上游受到长江径流影响大,在丰水期风险较高,在平水期和枯水期则风险偏低;而下游受上海等城市排污影响较大,风险较高(尤其在平水期和枯水期).8种重金属的生态风险与赋存形态之间表现出3种不同的相关关系.  相似文献   
543.
Hao GY  Goldstein G  Sack L  Holbrook NM  Liu ZH  Wang AY  Harrison RD  Su ZH  Cao KF 《Ecology》2011,92(11):2117-2130
Woody hemiepiphytic species (Hs) are important components of tropical rain forests, and they have been hypothesized to differ from non-hemiepiphytic tree species (NHs) in adaptations relating to water relations and carbon economy; but few studies have been conducted comparing ecophysiological traits between the two growth forms especially in an evolutionary context. Using common-garden plants of the genus Ficus, functional traits related to plant hydraulics and carbon economy were compared for seven NHs and seven Hs in their adult terrestrial "tree-like" growth phase. We used phylogenetically independent contrasts to test the hypothesis that differences in water availability selected for contrasting suites of traits in Hs and NHs, driving evolutionary correlations among functional traits including hydraulic conductivity and photosynthetic traits. Species of the two growth forms differed in functional traits; Hs had substantially lower xylem hydraulic conductivity and stomatal conductance, and higher instantaneous photosynthetic water use efficiency. Leaf morphological and structural traits also differed strikingly between the two growth forms. The Hs had significantly smaller leaves, higher leaf mass per area (LMA), and smaller xylem vessel lumen diameters. Across all the species, hydraulic conductivity was positively correlated with leaf gas exchange indicating high degrees of hydraulic-photosynthetic coordination. More importantly, these correlations were supported by correlations implemented on phylogenetic independent contrasts, suggesting that most trait correlations arose through repeated convergent evolution rather than as a result of chance events in the deep nodes of the lineage. Vatiation in xylem hydraulic conductivity was also centrally associated with a suite of other functional traits related to carbon economy and growth, such as LMA, water use efficiency, leaf nutrient concentration, and photosynthetic nutrient use efficiency, indicating important physiological constraints or trade-offs among functional traits. Shifts in this trait cluster apparently related to the adaptation to drought-prone canopy growth during the early life cycle of Hs and clearly affected ecophysiology of the later terrestrial stage of these species. Evolutionary flexibility in hydraulics and associated traits might be one basis for the hyper-diversification of Ficus species in tropical rain forests.  相似文献   
544.
从生物氧化提金废液中回收砷的热力学分析及试验   总被引:3,自引:0,他引:3  
对生物氧化提金废液中的砷、铁进行分离后得到砷的富集液,利用水合肼湿法提取单质砷.进行了水合肼还原砷酸钠制备单质砷的热力学分析,考察了pH值、水合肼过量系数、水合肼的稀释倍数、温度、超声功率等工艺参数对砷一次回收率的影响.结果表明,当温度70℃,pH=7,超声功率为160W时,砷一次还原率可达62.9%,再用40%的次亚...  相似文献   
545.
崖角藤的化学成分   总被引:1,自引:0,他引:1  
从天南星科崖角藤茎95%乙醇提取物中分离得到10个化合物,通过波谱数据鉴定为羽扇豆醇乙酸酯(1)、羽扇豆醇(2)、β-谷甾醇(3)、桦木醇(4)、桦木酸(5)、硬脂酸(6)、ficubee A(7)、ficubee B(8)、artelastin(9)和β-胡萝卜苷(10).  相似文献   
546.
长期施肥对旱地红壤肥力和酶活性的影响   总被引:2,自引:0,他引:2  
为了明确不同施肥种类对旱地红壤肥力与酶活性的影响,以30年(1981年至今)长期定位试验地为基础,研究不同施肥处理(CK,N,NP,NPK,2倍NPK,猪粪,NPK+猪粪)旱地红壤玉米田耕层(0~20 cm)土壤酶活性与养分的变化趋势及其相关性。结果表明:1)全N含量各处理间差异不显著,单施N肥显著增加土壤速效N,施有机肥处理(NPK+猪粪,猪粪)土壤的pH值、有机质、全P、速效P均显著增加;2)除了2倍NPK处理土壤脲酶活性最高外,施有机肥土壤的转化酶、脱氢酶、酸性磷酸酶、过氧化氢酶活性也较其他处理显著增加;3)酸性磷酸酶、过氧化氢酶、脱氢酶、脲酶与全N、有机质、速效N呈显著或极显著正相关;因此,红壤旱地通过长期施用有机肥或与无机肥配施,不仅能显著提高土壤肥力,而且能增加土壤酶活性,从而显著提高土壤持续生产力。  相似文献   
547.
热防护服是热环境下人体安全防护的主要装备,其标准的科学性和系统性对热环境下的人体安全防护具有重要的支持作用.国外对热防护服相关的技术标准予以充分重视,以性能测试技术方法为主体,建立了较为科学、完善的标准,并体现出新的发展趋势.通过对国外热防护服技术标准的调研,总结性能测试标准的共性内容,包括主要性能测试方法、实验设备、实验步骤、烧伤评估、人体模型和测试报告等.整套防护服装的性能测试技术及标准是研究的重点,出汗暖体假人将在防护服装性能测试领域被更为广泛的应用.最后,提出我国研制热防护服性能测试技术标准的建议.  相似文献   
548.
通过对大连市两大典型社区老龄者的抽样调查,运用阶层回归分析法分析了深度休闲活动对老龄者幸福感的影响。研究结果表明,深度休闲活动与老龄者的幸福感有显著的正向关系,深度休闲包含的坚持不懈、个人努力、认同感、职业生涯性、休闲利益、亚文化等价值面,对形成老龄者幸福感的身体健康、心理健康、人际互动、充实感、成就感、归属感方面都有着不同程度的正向影响。  相似文献   
549.
Abstract

This paper presents the results of a national project investigating Australian local government (LG) attempts to deliver beneficial environmental outcomes. It briefly describes the extensive environmental planning, management and protection roles played by Australian LGs. It notes that these roles are poorly documented within the academic literature, and makes a case for fundamental research to better understand LGs and their work from the inside. It describes this project's use of grounded theory methods in gathering and analysing 34 case studies of Australian LG environmental initiatives. The inside perspectives represented by the papers show that Australian LG environmental work:
  • extends beyond its statutory requirements;

  • is novel and creative;

  • endures by balancing ecological, social and economic values;

  • demonstrates different patterns depending on its planning, management or protection focus; and

  • usually involves environmental strategists with long-term, passionate commitments to local environmental values.

  相似文献   
550.
在实地调查研究的基础上,分析了巴河上游流域地段的景观结构功能与演替及流域治理存在的问题,切中流域生态环境变化的要害——水土流失问题。在区内景观带自然分异的基础上,进行了流域景观生态设计。  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