全文获取类型
收费全文 | 1726篇 |
免费 | 130篇 |
国内免费 | 319篇 |
专业分类
安全科学 | 200篇 |
废物处理 | 62篇 |
环保管理 | 154篇 |
综合类 | 924篇 |
基础理论 | 288篇 |
污染及防治 | 308篇 |
评价与监测 | 73篇 |
社会与环境 | 110篇 |
灾害及防治 | 56篇 |
出版年
2024年 | 1篇 |
2023年 | 16篇 |
2022年 | 55篇 |
2021年 | 60篇 |
2020年 | 55篇 |
2019年 | 51篇 |
2018年 | 55篇 |
2017年 | 52篇 |
2016年 | 51篇 |
2015年 | 88篇 |
2014年 | 94篇 |
2013年 | 131篇 |
2012年 | 121篇 |
2011年 | 161篇 |
2010年 | 127篇 |
2009年 | 119篇 |
2008年 | 134篇 |
2007年 | 138篇 |
2006年 | 135篇 |
2005年 | 111篇 |
2004年 | 74篇 |
2003年 | 68篇 |
2002年 | 59篇 |
2001年 | 50篇 |
2000年 | 35篇 |
1999年 | 32篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 15篇 |
1994年 | 8篇 |
1993年 | 16篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1982年 | 1篇 |
排序方式: 共有2175条查询结果,搜索用时 109 毫秒
991.
992.
Hua Fang Yu L. Han Yuan M. Yin Xiang X. Jin Shao Y. Wang Fei F. Tang 《Journal of environmental science and health. Part. B》2013,48(8):609-615
Substantive addition of antibiotic-contaminated manure to agricultural soil may lead to “persistent” residues of antibiotics and may affect soil health. Therefore, this study examines the effects of repeated manure treatments containing sulfadiazine (SDZ) and chlortetracycline (CTC) residues, both individually and combined, on the functional diversity and structure of soil microbial communities in the soils under laboratory conditions. The average well color development (AWCD), Simpson diversity index (1/D, dominant populations), Shannon-Wiener diversity index (H′, richness), and McIntosh diversity index (U, evenness) in the antibiotics-treated soils decreased in the first 60-day treatment and then gradually recovered or even exceeded the initial level in the unamended soils with increasing treatment frequency. A total of 11 specific bands in temperature gradient gel electrophoresis (TGGE) profiles were observed and sequence analyzed for five repeated treatments, and most of them belonged to the phyla Firmicutes, Actinobacteria, and Proteobacteria. These results indicate that repeated treatments of manure containing SDZ and CTC residues can alter soil microbial community structure, although they have a temporary suppression effect on soil microbial functional diversity. 相似文献
993.
为更准确预测煤与瓦斯突出强度,在组合算法和径向基函数(RBF)神经网络的基础上,建立变权重RBF组合模型。首先,选取最具代表性的3种单项模型:BP神经网络、支持向量回归机(SVR)、免疫遗传算法(IGA),分别建模后对样本序列进行预测,并重构预测结果数据。以重构后的预测序列为输入层,突出强度为输出层,对变权重RBF组合模型进行训练,获得各单项模型的动态权值,从而建立动态变权重RBF组合模型,最后对突出强度进行预测。结果表明:变权重RBF组合模型预测结果的平均相对误差为2.621 2%,优于各单项模型、定权重组合模型以及数据不重构组合模型。 相似文献
994.
995.
Xinchuang Wang Guofan Shao Hua Chen Bernard J. Lewis Guang Qi Dapao Yu Li Zhou Limin Dai 《Environmental management》2013,52(3):612-620
Monitoring the dynamics of forest biomass at various spatial scales is important for better understanding the terrestrial carbon cycle as well as improving the effectiveness of forest policies and forest management activities. In this article, field data and Landsat image data acquired in 1999 and 2007 were utilized to quantify spatiotemporal changes of forest biomass for Dongsheng Forestry Farm in Changbai Mountain region of northeastern China. We found that Landsat TM band 4 and Difference Vegetation Index with a 3 × 3 window size were the best predictors associated with forest biomass estimations in the study area. The inverse regression model with Landsat TM band 4 predictor was found to be the best model. The total forest biomass in the study area decreased slightly from 2.77 × 106 Mg in 1999 to 2.73 × 106 Mg in 2007, which agreed closely with field-based model estimates. The area of forested land increased from 17.9 × 103 ha in 1999 to 18.1 × 103 ha in 2007. The stabilization of forest biomass and the slight increase of forested land occurred in the period following implementations of national forest policies in China in 1999. The pattern of changes in both forest biomass and biomass density was altered due to different management regimes adopted in light of those policies. This study reveals the usefulness of the remote sensing-based approach for detecting and monitoring quantitative changes in forest biomass at a landscape scale. 相似文献
996.
Optimal Land Use Management for Soil Erosion Control by Using an Interval-Parameter Fuzzy Two-Stage Stochastic Programming Approach 总被引:2,自引:1,他引:1
Soil erosion is one of the most serious environmental and public health problems, and such land degradation can be effectively mitigated through performing land use transitions across a watershed. Optimal land use management can thus provide a way to reduce soil erosion while achieving the maximum net benefit. However, optimized land use allocation schemes are not always successful since uncertainties pertaining to soil erosion control are not well presented. This study applied an interval-parameter fuzzy two-stage stochastic programming approach to generate optimal land use planning strategies for soil erosion control based on an inexact optimization framework, in which various uncertainties were reflected. The modeling approach can incorporate predefined soil erosion control policies, and address inherent system uncertainties expressed as discrete intervals, fuzzy sets, and probability distributions. The developed model was demonstrated through a case study in the Xiangxi River watershed, China’s Three Gorges Reservoir region. Land use transformations were employed as decision variables, and based on these, the land use change dynamics were yielded for a 15-year planning horizon. Finally, the maximum net economic benefit with an interval value of [1.197, 6.311] × 109 $ was obtained as well as corresponding land use allocations in the three planning periods. Also, the resulting soil erosion amount was found to be decreased and controlled at a tolerable level over the watershed. Thus, results confirm that the developed model is a useful tool for implementing land use management as not only does it allow local decision makers to optimize land use allocation, but can also help to answer how to accomplish land use changes. 相似文献
997.
998.
土壤水分管理对甲烷和氧化亚氮排放的影响 总被引:5,自引:0,他引:5
为控制农田温室气体排放的途径提供依据,通过实验室培养的方法测定了不同水分管理条件下CH4和N2O的排放,干旱处理(60%-70%WFP)和长期淹水土样在施肥后的Eh变化。最终得出:稻田CH4和N2O排放之间存在着互为消长的关系(R2=0.609),CH4和N2O的排放是水肥共同作用的结果,水分管理通过Eh来影响气体排放,有机质是造成前后期排放浓度差异的主要原因。 相似文献
999.
为解决具有轮换更新环节的应急物资政企协同预置储备优化问题,探讨轮换更新环节中的操作过程及成本构成,构建轮换更新费用的应急物资政企协同预置储备优化模型,并以美国东南部墨西哥湾飓风灾害为背景设计3组数值算例,采用Python语言编码模型并调用Gurobi求解器的方式进行算例优化求解。研究结果表明:合同期内,应急物资的轮换更新次数无论多少,需要支出的差价(折旧)补贴普遍较高;轮换更新频次不会影响库存维持成本,但会影响储备库与企业的协同关系。 相似文献
1000.
为研究横向风作用下喷口间距对射流扩散火焰特征的影响,以双喷口火焰为研究对象,利用CCD摄像机拍摄火焰几何形态,研究横向风条件下喷口间距对火焰形态演化、火焰长度和火焰吹熄极限的影响。研究结果表明:喷口间距较小时,2束火焰因空气夹带竞争和压差作用,彼此相互倾斜融合,火焰融合概率随喷口间距增加而逐渐降低,火焰临界融合间距随横向风的增加先增大后减小;由于火焰的空气夹带和热反馈处于较高水平,2束火焰被少量拉伸,火焰长度先增加后减小;喷口间距较小时,火焰吹熄极限显著增加。 相似文献