全文获取类型
收费全文 | 2270篇 |
免费 | 190篇 |
国内免费 | 537篇 |
专业分类
安全科学 | 386篇 |
废物处理 | 70篇 |
环保管理 | 502篇 |
综合类 | 1030篇 |
基础理论 | 210篇 |
污染及防治 | 376篇 |
评价与监测 | 95篇 |
社会与环境 | 109篇 |
灾害及防治 | 219篇 |
出版年
2024年 | 8篇 |
2023年 | 36篇 |
2022年 | 71篇 |
2021年 | 85篇 |
2020年 | 92篇 |
2019年 | 59篇 |
2018年 | 67篇 |
2017年 | 96篇 |
2016年 | 126篇 |
2015年 | 119篇 |
2014年 | 142篇 |
2013年 | 157篇 |
2012年 | 163篇 |
2011年 | 173篇 |
2010年 | 140篇 |
2009年 | 140篇 |
2008年 | 105篇 |
2007年 | 154篇 |
2006年 | 133篇 |
2005年 | 138篇 |
2004年 | 93篇 |
2003年 | 88篇 |
2002年 | 76篇 |
2001年 | 69篇 |
2000年 | 85篇 |
1999年 | 45篇 |
1998年 | 28篇 |
1997年 | 32篇 |
1996年 | 20篇 |
1995年 | 37篇 |
1994年 | 19篇 |
1993年 | 28篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1973年 | 3篇 |
1972年 | 7篇 |
1971年 | 9篇 |
1970年 | 3篇 |
排序方式: 共有2997条查询结果,搜索用时 0 毫秒
141.
固定污染源氨气的手工监测,干扰因素较多,其中采样环节尤为关键。实验通过催化氧化-化学发光法考察不同采样管线材质对氨气的吸附效果,离子色谱法考察化学吸收法采集氨气的吸收瓶类型、采样流量、吸收液种类、吸收液浓度及体积等采样条件对氨气吸收效率的影响。实验表明,316 L不锈钢与聚四氟乙烯对氨气的吸附较小,氨气的采样流量不宜超过1.0 L/min,棕色气泡式吸收瓶更适用于氨气样品的采集,磷酸溶液作吸收液对氨气的吸收效率较好,对于低浓度的氨气样品,应采用低流量长时间采集。 相似文献
142.
143.
针对长江上游金沙江下游区域近几年6月和10月出现的较剧烈的水资源丰枯转换现象,以2018年金沙江下游来水过程作为研究案例,考虑金沙江下游流域来水组成及水利工程建设情况,从区间流量分析及上游水库群调蓄影响分析两方面开展了研究工作。研究结果表明:金沙江下游流域丰枯转换主要影响因素为三堆子流量变化,三堆子至溪洛渡区间流量变化影响较小。在6月,上游水库群调蓄对金沙江下游流域丰枯转换影响较大,10月影响相对较小。相关研究成果可为溪洛渡-向家坝梯级水库调度计划制订及实际调度工作提供参考。 相似文献
144.
F. Le Ber C. Lavigne K. Adamczyk F. Angevin N. Colbach J.-F. Mari H. Monod 《Ecological modelling》2009
Neutral landscape models are not frequently used in the agronomical domain, whereas they would be very useful for studying given agro-ecological or physical processes. Contrary to ecological neutral landscape models, agricultural models have to represent and manage geometrical patches and thus should rely on tessellation methods. We present a three steps approach that aimed at simulating such landscapes. Firstly, we characterized the geometry of three real field patterns; secondly, we generated simulated field patterns with two tessellation methods attempting to control the value of some of the observed characteristics and, thirdly, we evaluated the simulated field patterns. For this evaluation, we considered that good simulated field patterns should capture characteristics of real landscapes that are important for the targeted agro-ecological process. Real landscapes and landscapes simulated using either a Voronoi or a rectangular tessellation were thus compared when used as input data within a gene flow model. The results showed that neither tessellation method captured field shapes correctly, thus leading to over or (small) under estimation of gene flow. The Voronoi tessellation, though, performed better than the rectangular tessellation. Possible research directions are proposed to improve the simulated patterns, including the use of post-processing, the control of cell orientation or the implementation of other tessellation techniques. 相似文献
145.
EcoTroph (ET) is a model articulated around the idea that the functioning of aquatic ecosystems may be viewed as a biomass flow moving from lower to higher trophic levels, due to predation and ontogenetic processes. Thus, we show that the ecosystem biomass present at a given trophic level may be estimated from two simple equations, one describing biomass flow, the other their kinetics (which quantifies the velocity of biomass transfers towards top predators). The flow kinetic of prey partly depends on the abundance of their predators, and a top-down equation expressing this is included in the model. Based on these relationships, we simulated the impact on a virtual ecosystem of various exploitation patterns. Specifically, we show that the EcoTroph approach is able to mimic the effects of increased fishing effort on ecosystem biomass expected from theory. Particularly, the model exhibits complex patterns observed in field data, notably cascading effects and ‘fishing down the food web’. EcoTroph also provides diagnostic tools for examining the relationships between catch and fishing effort at the ecosystem scale and the effects of strong top-down controls and fast-flow kinetics on ecosystems resilience. Finally, a dynamic version of the model is derived from the steady-state version, thus allowing simulations of time series of ecosystem biomass and catches. Using this dynamic model, we explore the propagation of environmental variability in the food web, and illustrated how exploitation can induce a decrease of ecosystem stability. The potential for applying EcoTroph to specific ecosystems, based on field data, and similarities between EcoTroph and Ecopath with Ecosim (EwE) are finally discussed. 相似文献
146.
Noam Leader Eli Geffen Ofer Mokady Yoram Yom-Tov 《Behavioral ecology and sociobiology》2008,62(8):1299-1305
Geographic variation in vocalizations is widespread in passerine birds, but its origins and maintenance remain unclear. In
this study, we test the hypothesis that song dialect, a culturally transmitted trait, is related to the population genetic
structure of the orange-tufted sunbird, Nectarinia osea. To address this, we compared mitochondrial DNA (mtDNA) sequence variation together with allele frequencies at five microsatellite
loci from an urban population of sunbirds exhibiting two distinct song dialects on a microgeographic scale. Our findings reveal
no association between dialect membership and genetic composition. All genetic measures, from both mitochondrial and nuclear
DNA, indicate high levels of gene flow between both dialect populations. The low F
ST values obtained from mtDNA and microsatellite analysis imply that the variation among dialects does not account for more
than 2%, at best, of the overall genetic variation found in the entire population. These measures fall well within the range
of similar measures obtained in other studies of species exhibiting vocal dialects, most of which fail to detect any dialect-based
genetic differentiation. The persistence of dialects in the orange-tufted sunbird may thus best be explained by dispersal
of individuals across dialect boundaries and possibly from surrounding areas, followed by postdispersal vocal matching. Because
genetic structuring appears weaker than cultural structure in this species, we discuss the behavioral mechanisms underlying
dialect maintenance in the presence of apparent gene flow. 相似文献
147.
Mariana Valdez-Castillo Sonia Arriaga 《Frontiers of Environmental Science & Engineering》2021,15(3):43
148.
聚丙烯酰胺对聚合物驱含油污水中油珠沉降分离的影响 总被引:37,自引:1,他引:37
研究发现阴离子聚丙烯酰胺(HPAM)对聚合物驱含油污水处理有正反2方面影响.聚合物能增加污水粘度,降低油珠上浮速度,而且聚合物能增加油水界面水膜强度,延缓油珠聚并时间,这是聚合物对油珠沉降分离的不利影响;同时,聚丙烯酰胺具有絮凝性,能将水中油珠连接到一起,有利于油珠聚并.当聚丙烯酰胺相对分子质量为2.72×106,浓度小于800mg/L时,絮凝作用大于粘度作用,有利于油珠的沉降分离.初始油珠粒径小是聚合物驱含油污水难处理的主要原因.横向流除油器可以加速油珠聚并,缩短沉降时间,适合处理聚合物驱含油污水. 相似文献
149.
甘肃舟曲三眼峪沟泥石流粗大颗粒冲击力特征分析 总被引:2,自引:0,他引:2
本文通过对甘肃省舟曲县城后山三眼峪沟特大泥石流灾害的现场调查获取了舟曲三眼峪泥石流沟相关资料,并根据这些收集整理的资料分别对三眼峪沟及其支沟(大峪沟、小峪沟)泥石流动力学重要参数-冲击力,进行计算与特征分析,该参数计算结果对该沟泥石流防治工程参数设计有一定的参考作用,对灾区灾后重建有重要意义。分析发现泥石流流通区最大颗粒冲击力比堆积区的大,而堆积区粗大颗粒的冲击力呈先增大后减小的趋势并与粗大颗粒的最大直径呈单调线性关系;堆积区的粗大颗粒形态主要为棱柱状(长方体、立方体)、角锥状、菱形状。最后以利子依达沟为例对计算结果进行简要评估,并在上述计算与特征分析的基础上提出三眼峪泥石流沟针对性防灾减灾建议。 相似文献
150.