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803.
Plant polyphenols are involved in important ecosystem processes and may affect nutrient cycling. Previous investigations have demonstrated detrimental effects of suboptimal sample treatment on the quantity of extractable plant polyphenols. We compared leaf polyphenol concentrations of 20 tree species from East China in two sample sets collected under different conditions: (a) according to established protocols and stored more than three years, (b) under conditions optimised for leaf polyphenols. We investigated the variance brought about by suboptimal sample handling as compared to the variance caused by the taxonomic range of species. Family-affiliation explained the largest proportion of variance, whereas sample handling had only minor effects. Reducing the taxonomic range increased the impact of differences in sample handling. Additionally, we showed that the concentrations of leaf polyphenols were phylogenetically more conserved than other leaf traits. Non-metric-multi-dimensional scaling revealed similar ordination patterns for leaf polyphenol concentrations in both sample sets with both ordinations being closely correlated. Finally, we computed separate ordinations including an extended set of leaf traits and found that both analyses led to similar ecological conclusions. Consequently, in studies comprising a wide taxonomic range, the adverse effects of suboptimal sample handling may be overridden by the variation brought about by phylogeny. 相似文献
804.
Cruz C Bio AM Jullioti A Tavares A Dias T Martins-Loução MA 《Environmental pollution (Barking, Essex : 1987)》2008,154(3):414-423
Heterogeneity and dynamics of eight soil surface characteristics essential for plants—ammonium and nitrate concentrations, water content, temperature, pH, organic matter, nitrification and ammonification rates—were studied in a Mediterranean-type ecosystem on four occasions over a year. Soil properties varied seasonally and were influenced by plant species. Nitrate and ammonium were present in the soil at similar concentrations throughout the year. The positive correlation between them at the time of greatest plant development indicates that ammonium is a readily available nitrogen source in Mediterranean-type ecosystems. The results presented here suggest that plant cover significantly affects soil surface characteristics. 相似文献
805.
长江三角洲港口群的功能定位探析 总被引:5,自引:1,他引:5
根据国际海洋运输船舶大型化和集装箱化的趋势,为积极应对来自亚太地区各港口的挑战,总结和分析了长江三角洲地区港口群的发展现状,即各港口都取得了较大的发展,特别是宁波和上海两港口的集装箱吞吐量增长很快。但是,上海港的发展受制于航道水深水足和缺乏深水大港,南京以下各港中存在因重复建设而导致岸线浪费和恶性竞争的问题,宁波港的主要制约在于箱源腹地有限和陆上集疏运条件亟待完善。同时,还提出了各自的解决对策。为应对我国加入WTO后国际航运面临的严峻挑战和尽快实施国家战略,该地区应当形成代表国家参与国际航运竞争的以上海为中心、苏南和浙北为两翼的组合港式国际航运中心。其中,形成合理竞争与协调分工的长江三角洲港口群则是当务之急。鉴于此,各港口的功能定位可以是,上海港要尽快建成国际级的集装箱枢纽港,长江沿岸港口(南京以下各港口)要逐步形成协同发展的内支线港和喂给港,宁波、舟山等港口要建设成为上海港的中转港和深水外港。 相似文献
806.
长江源自然保护区生态环境状况及功能区划分 总被引:1,自引:0,他引:1
长江源区是长江流域的特殊生态功能区 ,也是我国最重要的生态功能区之一。其生态环境的好坏 ,不仅关系到当地人民的生存与发展 ,而且会影响整个长江流域的可持续发展。简要介绍了长江源区的基本概况 ,分析了源区目前存在冰川退缩、冻土退化、草场退化、土地沙化、湖泊萎缩、生物多样性遭受破坏等主要生态环境问题。造成这种状况的有自然因素 ,也有人为因素 ,自然原因占主导地位 ,而人为因素加剧了生态环境的恶化。赞成在长江源区建立国家级自然保护区 ,提出了建设长江源自然保护区功能区的思想 ,认为保护区应重点保护水源地、生物多样性和特殊生态系统。在野外调查的基础上 ,建议将保护区划分成 5个核心区 ,3个缓冲区和 2个实验区。核心区生物多样性最丰富 ,生态系统的代表性最强 ,水源涵养作用最大 ,生态系统受人类干扰和破坏程度最小。 相似文献
807.
Objective: Drivers’ use of lane departure warning and prevention systems is lower than use of other crash avoidance technologies and varies significantly by manufacturer. One factor that may affect use is how well a system prevents unintended departures. The current study evaluated the performance of systems that assist in preventing departures by providing steering or braking input in a 2016 Chevrolet Malibu, 2016 Ford Fusion, 2016 Honda Accord, and 2018 Volvo S90. These vehicles were selected because a prior observational study found that the percentage of privately owned vehicles that had lane departure prevention systems turned on varied among these 4 automakers.Method: In each vehicle, a test driver induced 40 lane drifts on left and right curves by steering the vehicle straight into the curve so that vehicles departed in the opposite direction and 40 lane drifts on straightaways by slight steering input to direct the vehicle to left and right lane markers.Results: Vehicles from automakers with higher observed lane departure prevention use rates (Volvo, Chevrolet) featured systems that provided steering input earlier and more often avoided crossing lane markers by more than 35?cm compared to vehicles from automakers with lower observed use rates (Ford, Honda).Conclusion: The study identified functional characteristics (i.e., timing of steering input, prevention of departures more than 35?cm) of lane departure prevention systems that were strongly associated with observed activation of these systems in privately owned vehicles. Although this relationship does not imply causation, the findings support the hypothesis that functional characteristics of lane departure prevention systems affect their use. Designers may be able to use these results to maximize driver acceptance of future implementations of lane departure prevention. 相似文献
808.
中国荒漠化气候类型划分方法的初步探讨 总被引:23,自引:1,他引:23
在同一气候资料的基础上 ,分别应用Thornthwaite公式和Penman公式计算了潜在蒸散 ,并据此计算湿润指数 ,划分了我国的荒漠化气候类型区 ,并确定了荒漠化潜在发生范围 ,同时对上述两种方法在我国荒漠化气候类型区划中的适用性进行了比较分析。结果表明 ,对我国而言 ,Penman公式法比Thornthwaite公式法更具有合理性。根据Penman公式法的区划结果 ,我国荒漠化潜在发生范围约为4 2 4万km2 ,占国土面积的 4 4 .1% ,分布于全国 19个省 (自治区、直辖市 )。 相似文献
809.
从全国范围环境区划的角度,阐述了环境区划的理论基础──环境地域分异理论和社会-经济-自然复合生态系统理论,探讨了环境区划的原则,提出了国家级环境区划的方法以及环境区划的等级体系标准与指标体系。 相似文献
810.
冷冻法在有机废水处理方面取得了良好的应用效果,但其分离机理缺乏深入的研究。为深入研究冷冻法对有机污染物的处理效果及分离机理,采用悬浮冷冻结晶法,对废水中己烷、正己酸、正己醇和正己醛4种具有不同官能团的有机物污染物进行分离实验,并采用量子化学方法计算了氢键结合能,进一步探讨了有机物官能团对冰晶杂质浓度的影响机理。悬浮结晶实验结果表明,废水中己烷、正己酸、正己醇和正己醛的去除率分别可达67.07%、87.75%、94.71%和95.32%。量子化学计算结果表明,极性有机物官能团和水分子间缔结的氢键结合能越大,其对应的冰晶杂质浓度越高,从而导致有机物去除率越低。正己醛3种极性有机物(正己酸、正己醇和正己醛)中和水分子间氢键结合能最小,对应的去除率最高。而己烷作为非极性有机物,无法和水分子间缔结产生氢键,因而极易在悬浮结晶时析出,与悬浮冰晶混合于溶液上层,故其去除率最低。以上研究结果从分子水平加深了对冷冻法在有机废水处理中作用机理的理解,可为该技术在水处理领域的深入研究提供参考。 相似文献