全文获取类型
收费全文 | 1254篇 |
免费 | 167篇 |
国内免费 | 238篇 |
专业分类
安全科学 | 254篇 |
废物处理 | 23篇 |
环保管理 | 150篇 |
综合类 | 741篇 |
基础理论 | 146篇 |
污染及防治 | 71篇 |
评价与监测 | 103篇 |
社会与环境 | 96篇 |
灾害及防治 | 75篇 |
出版年
2024年 | 3篇 |
2023年 | 23篇 |
2022年 | 43篇 |
2021年 | 67篇 |
2020年 | 59篇 |
2019年 | 68篇 |
2018年 | 50篇 |
2017年 | 62篇 |
2016年 | 81篇 |
2015年 | 65篇 |
2014年 | 74篇 |
2013年 | 92篇 |
2012年 | 125篇 |
2011年 | 91篇 |
2010年 | 72篇 |
2009年 | 72篇 |
2008年 | 42篇 |
2007年 | 80篇 |
2006年 | 79篇 |
2005年 | 58篇 |
2004年 | 46篇 |
2003年 | 41篇 |
2002年 | 24篇 |
2001年 | 25篇 |
2000年 | 20篇 |
1999年 | 35篇 |
1998年 | 26篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1980年 | 3篇 |
1977年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有1659条查询结果,搜索用时 31 毫秒
861.
862.
目的 探索当航空电连接器腐蚀退化时,其接触阻抗的变化规律,研究航空电连接器腐蚀退化对信号传输的影响规律。方法 首先对航空电连接器腐蚀退化的机理进行研究,建立其等效电路模型,然后分别对低频电连接器和射频电连接器进行仿真研究,提取阻抗参数,分析腐蚀退化对信号传输的影响规律。结果 接触电阻随着腐蚀程度的加深明显增大,接触电感随着腐蚀程度的加深变化不大,接触电容随着接触面腐蚀面积的增大而增大,随接触面间腐蚀厚度的增加而减小。接触电阻随频率的增加而增大,接触电感和接触电容随频率的增大基本保持不变。接触阻抗在低频时呈现感性特征,高频时呈现容性特征,阻抗幅值随频率的增加先增大、后减小,峰值出现在感性和容性转换频率处,腐蚀退化将使该转换频率减小。结论 对于低频信号,腐蚀退化将导致信号的衰减和延迟;对于高频信号,在转换频率处,信号的回波损耗、插入损耗和电压驻波比出现极值。 相似文献
863.
Stefano Raccanelli Vladimiro Bonamin Pietro Tundo 《Environmental science and pollution research international》2000,7(3):125-129
Venice is famous around the world for its uniqueness and architectural splendours, arts and the history of the “Serenissima
Repubblica”, as it was known in the past, but few are aware that Venice economy is strongly dependent on the industrial activities
based mainly on the adjacent Porto Marghera area. For many years, the lagoon that physically separates the city from the dry
land has avoided association between the concern connected with the pollution derived from these industrial activities and
the public perception of Venice. Since 1995, dioxins have appeared as a lagoon contaminant, and their presence, at such a
level requiring immediate “in depth” studies and interventions, has been fully realized for decades. 相似文献
864.
865.
Economic Growth and Marine Biodiversity: Influence of Human Social Structure on Decline of Marine Trophic Levels 总被引:2,自引:0,他引:2
Abstract: We assessed the effects of economic growth, urbanization, and human population size on marine biodiversity. We used the mean trophic level (MTL) of marine catch as an indicator of marine biodiversity and conducted cross-national time-series analyses (1960–2003) of 102 nations to investigate human social influences on fish catch and trends in MTL. We constructed path models to examine direct and indirect effects relating to marine catch and MTL. Nations' MTLs declined with increased economic growth, increased urbanization, and increased population size, in part because of associated increased catch. These findings contradict the environmental Kuznets curve hypothesis, which claims that economic modernization will reduce human impact on the environment. To make informed decisions on issues of marine resource management, policy makers, nonprofit entities, and professional societies must recognize the need to include social analyses in overall conservation-research strategies. The challenge is to utilize the socioeconomic and ecological research in the service of a comprehensive marine-conservation movement. 相似文献
866.
Michael E. Fraker 《Behavioral ecology and sociobiology》2008,62(7):1201-1205
The activity level of prey reflects a trade-off between predation risk and foraging gain. A number of theoretical and empirical
studies have shown that a prey's energetic state or the level of its resource should influence this trade-off (i.e., what
the optimal activity level at a level of predation risk is). Here, I show that the energetic state of prey may also influence
the duration of their antipredator behavioral response. Green frog tadpoles (Rana clamitans) reduced their activity level for a shorter time during exposure to the chemical cue of predatory larval dragonflies (Anax spp.) as their time since last feeding increased (i.e., as their energetic state decreased). Interestingly, the tadpoles
strongly reduced their activity level upon cue exposure in all treatments. Thus, the relative activity level of tadpoles at
different energetic states varied over time. 相似文献
867.
报道了1988年-1995年浙江省建筑材料中放射性水平和所致居民剂量的计算结果。采用高纯锗γ能谱法测定了该地区的6种,139个建筑材料样品中放射性核素含量,并收集了1984年以前该地区另外5种,77个建筑材料样品中的放射性水平数据。 相似文献
868.
西北主要城市生活用水中氡及其剂量当量研究 总被引:2,自引:0,他引:2
分析了生活用水对室内空气中氡的贡献,并估算了水中氡剂量当量的大小.研究表明,西北地区主要大城市生活用水中氡的浓度差异较大,其中宝鸡和咸阳两市居民自备井水中氡的浓度较高,兰州市水中氡的浓度最高.西北地区主要城市生活用水中氡的释放量占室内总氡的3.30—24.47%,水中氡剂量当量不大,最高值为环境天然辐射剂量当量的17%左右. 相似文献
869.
870.