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571.
Hai Gen Zuo Jian Xin Zhu Chun Rui Zhan Guo Yan Tang Ping Guo Yuan Long Wei Hai Long Zeng Hong Yang 《Environmental monitoring and assessment》2014,186(4):2399-2412
A new method has been developed to determine heptachlor and its metabolites heptachlor-exo-epoxide and heptachlor-endo-epoxide in pork. The pork samples were extracted with acetone–n-hexane (2:8, V:V) and cleaned up by gel permeation chromatography and florisil solid-phase extraction cartridge. The extract was then determined by gas chromatography equipped with electron capture detector (GC-ECD), followed by validation using gas chromatography–mass spectrometry (GC–MS) with negative chemical ionization. Linearity of calibration curves ranged from 0.01 to 0.5 mg L?1, with correlation coefficients of more than 0.9980 for GC-ECD and GC–MS, respectively. At spiked concentrations of 0.01, 0.05, and 0.1 mg kg?1, the average recovery and relative standard deviation values were 87.1–102.2 and 4.0–11.3 %, respectively. The limit of quantification for each analyte was 0.01 mg kg?1, which satisfied the current maximum residue limit permitted in pork. Our results showed that the method developed was successfully used to determine heptachlor and heptachlor epoxide residues in real pork samples. 相似文献
572.
北京市大气污染物浓度空间分布与优化布点研究 总被引:3,自引:3,他引:0
基于地统计学方法对北京市2012年11—12月的大气污染物SO2、NO2、PM10和PM2.5浓度数据进行了空间分析。结果表明,4种污染物浓度数据均符合正态分布,满足地统计学分析的使用条件且均呈现中等强度的变异性。4种污染物半变异函数的块金效应值分别是29%、24%、7%、4%,表现出很强的空间相关性。4种污染物长轴变程分别是63、58、62、90 km,短轴变程分别是31、37、48、50 km,空间分布呈现出各向异性,变程范围与中尺度天气系统相当。研究大气污染物的空间分布特性对于整体把握区域环境空气质量和监测点位优化十分重要,以北京市区域空气质量中PM2.5监测站点设置为例,其监测站点在长轴方向上的间隔设置应取20~25 km,短轴方向上布点间隔应为8~12 km。 相似文献
573.
Determination of emission of contaminant gases as ammonia, methane, or laughing gas from natural ventilated livestock buildings with large opening is a challenge due to the large variations in gas concentration and air velocity in the openings. The close relation between calculated animal heat production and the carbon dioxide production from the animals have in several cases been utilized for estimation of the ventilation air exchange rate for the estimation of ammonia and greenhouse gas emissions. Using this method, the problem of the complicated air velocity and concentration distribution in the openings is avoided; however, there are still some important issues remained unanswered: (1) the precision of the estimations, (2) the requirement for the length of measuring periods, and (3) the required measuring point number and location. The purpose of this work was to investigate how estimated average gas emission and the precision of the estimation are influenced by different calculation procedures, measuring period length, measure point locations, measure point numbers, and criteria for excluding measuring data. The analyses were based on existing data from a 6-day measuring period in a naturally ventilated, 150 milking cow building. The results showed that the methane emission can be determined with much higher precision than ammonia or laughing gas emissions, and, for methane, relatively precise estimations can be based on measure periods as short as 3 h. This result makes it feasible to investigate the influence of feed composition on methane emission in a relative large number of operating cattle buildings and consequently it can support a development towards reduced greenhouse gas emission from cattle production. 相似文献
574.
575.
为了实现废物资源综合利用,以橡胶对沥青的性能改善为基础,以废橡胶为原料,在轻组分助剂介质中采用微波降解和助溶处理技术制备沥青再生剂.通过正交实验设计,以再生沥青的针入度、延度、旋转薄膜烘箱老化(RTFOT)后的针入度比及残留延度为评价指标确定了再生剂原材料的合理配比及工艺条件,并进行了再生剂的效果试验.研究表明,最佳配比及条件为增塑剂DOP 40%,芳香油分糠醛抽出油40%,废橡胶粉20%,抗老剂添加量为以上总量的0.5%,微波功率为900 W,处理时间为10 min.再生效果试验表明,10%的再生剂用量可以有效补充老化沥青缺失的组分,恢复其胶体结构及流变性能. 相似文献
576.
577.
578.
Hongbin Zhan Zhang Wen Guanhua Huang Dongmin Sun 《Journal of contaminant hydrology》2009,107(3-4):162-174
This study deals with two-dimensional solute transport in an aquifer–aquitard system by maintaining rigorous mass conservation at the aquifer–aquitard interface. Advection, longitudinal dispersion, and transverse vertical dispersion are considered in the aquifer. Vertical advection and diffusion are considered in the aquitards. The first-type and the third-type boundary conditions are considered in the aquifer. This study differs from the commonly used averaged approximation (AA) method that treats the mass flux between the aquifer and aquitard as an averaged volumetric source/sink term in the governing equation of transport in the aquifer. Analytical solutions of concentrations in the aquitards and aquifer and mass transported between the aquifer and upper or lower aquitard are obtained in the Laplace domain, and are subsequently inverted numerically to yield results in the real time domain (the Zhan method). The breakthrough curves (BTCs) and distribution profiles in the aquifer obtained in this study are drastically different from those obtained using the AA method. Comparison of the numerical simulation using the model MT3DMS and the Zhan method indicates that the numerical result differs from that of the Zhan method for an asymmetric case when aquitard advections are at the same direction. The AA method overestimates the mass transported into the upper aquitard when an upward advection exists in the upper aquitard. The mass transported between the aquifer and the aquitard is sensitive to the aquitard Peclet number, but less sensitive to the aquitard diffusion coefficient. 相似文献
579.
Wang X Zheng Q Yao F Chen Z Feng Z Manning WJ 《Environmental pollution (Barking, Essex : 1987)》2007,148(2):390-395
Foliar applications of ethylenediurea (abbreviated as EDU) were made at 0, 150, 300 or 450 ppm to field-grown rice and wheat in the Yangtze Delta in China. Rice and wheat responded differently to ambient ozone and EDU applications. For wheat, some growth characteristics, such as yield, seed number per plant, seed set rate and harvest index, increased significantly at 300 ppm EDU treatment, while for rice no parameters measured were statistically different regarding EDU application. The reason may be that the wheat cultivar used may be more sensitive to ozone than the rice cultivar. EDU was effective in demonstrating ozone effects on the wheat cultivar, but not on the rice cultivar. Cultivar sensitivity might be an important consideration when assessing the effects of ambient ozone on plants. 相似文献
580.
中国水土流失的基本概况及其综合治理 总被引:15,自引:3,他引:12
水土流失是一个全球性的环境问题,给人类的生命和物质财产造成极大的危害与破坏。在现代社会,由于人口的持续增长、社会经济生产规模的不断扩大、植被破坏的急剧发展,对国家经济的发展构成了威胁。在上述背景下,本文在对以往研究结果进行综合分析的基础上,根据“再造一个山川秀美的西北地区”之要求,因地制宜地提出了我国水土流失的防治途径。 相似文献