全文获取类型
收费全文 | 3800篇 |
免费 | 346篇 |
国内免费 | 1403篇 |
专业分类
安全科学 | 235篇 |
废物处理 | 151篇 |
环保管理 | 698篇 |
综合类 | 2528篇 |
基础理论 | 554篇 |
污染及防治 | 803篇 |
评价与监测 | 306篇 |
社会与环境 | 223篇 |
灾害及防治 | 51篇 |
出版年
2024年 | 5篇 |
2023年 | 50篇 |
2022年 | 109篇 |
2021年 | 123篇 |
2020年 | 119篇 |
2019年 | 138篇 |
2018年 | 153篇 |
2017年 | 169篇 |
2016年 | 237篇 |
2015年 | 218篇 |
2014年 | 276篇 |
2013年 | 345篇 |
2012年 | 363篇 |
2011年 | 384篇 |
2010年 | 304篇 |
2009年 | 401篇 |
2008年 | 226篇 |
2007年 | 267篇 |
2006年 | 256篇 |
2005年 | 247篇 |
2004年 | 168篇 |
2003年 | 151篇 |
2002年 | 131篇 |
2001年 | 110篇 |
2000年 | 96篇 |
1999年 | 91篇 |
1998年 | 65篇 |
1997年 | 56篇 |
1996年 | 57篇 |
1995年 | 66篇 |
1994年 | 37篇 |
1993年 | 27篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有5549条查询结果,搜索用时 15 毫秒
991.
以自制Ti基Ru O2-Ir O2镀层形稳电极为阳极,采用电催化氧化处理偶氮染料甲基橙模拟废水。以硫酸钠为支持电解质,在自然p H条件下分别考察了电解时间、电极间距、电流密度和电解质浓度等因素对甲基橙去除率的影响,并分析其原因。实验结果表明,在自然p H、电极间距为1.0 cm、电流密度为30.0 m A/cm2、电解质硫酸钠浓度为20.0 g/L、电解1.0h,甲基橙去除率高达90.0%以上。因此,电催化氧化法作为一种高效、简便的染料废水处理技术,具有一定的应用潜力。 相似文献
992.
首先将聚乙二醇单甲基甲醚酯(PEGMA)接枝到聚醚砜(PES)上得到PES-g-PEGMA,然后利用溶液共混的方法,将聚氯乙烯(PVC)与PES-g-PEGMA共混,通过溶剂-非溶剂扩散诱导相分离法(NIPS)制备PVC/PES-g-PEGMA共混膜。在此基础上对PVC/PES-g-PEGMA共混膜的断面和表面微观结构、水通量、截留率、机械性能及耐污染等性能进行测试,并采用接触角,含水率(EWC),X射线光电子能谱仪(XPS)来表征PES-g-PEGMA的质量百分含量对PVC/PES-g-PEGMA共混膜亲水性的影响。结果表明,PVC/PES-g-PEGMA共混膜水通量,亲水性较纯PVC有很大程度的提高。耐污染性实验表明,随着PES-g-PEGMA的增加,耐污染性逐渐增强。实验结果同时也表明,该共混体系最佳共混比为7∶3。 相似文献
993.
为探讨Cu2+、p H和流速对固定化斜生栅藻去除畜禽废水中NH+4-N、TP效果的影响,在实验室条件下模拟实际污水处理过程,并采用正交实验方案对结果进行分析。结果表明低质量浓度Cu2+(0~0.05 mg/L)改善藻的净化效果,高质量浓度Cu2+(0.50~5.00 mg/L)抑制藻的净化效果;在p H较高的条件下(p H=9),固定化斜生栅藻的净化效果明显提高;流速对结果没有明显影响。通过正交实验,得出固定化斜生栅藻去除畜禽废水中NH+4-N、TP的优化条件如下:Cu2+质量浓度为0.05 mg/L,p H为9,流速为0.3 m/s。此时NH+4-N去除率为96.11%,TP去除率为97.53%。 相似文献
994.
利用化学沉淀法制备磁性四氧化三铁/石墨烯(Fe3O4/GE)纳米复合材料,并将其与H2O2构成非均相Fenton体系用于催化降解水中微量的17β-雌二醇(E2),研究了初始p H值,初始H2O2浓度,催化剂用量对E2降解的影响。结果表明,Fe3O4/GE纳米复合材料在无需外加光源的条件下能够有效催化降解E2。在p H 7.0,E2初始浓度为1 mg/L,初始H2O2浓度为15 mmol/L,Fe3O4/GE投加量为15 mg/L的条件下,反应8 h后可去除92.9%的E2。Fe3O4/GE具有便捷的磁分离特性和稳定的催化活性,经过7次循环使用后对E2的降解效率仍保持在91.5%左右。 相似文献
995.
采用等体积浸渍法制备了负载型有序介孔Fe-Ce/MCM-41催化剂。研究了该催化剂降解甲基橙的适宜工艺条件,并采用XPS,XRD,TEM技术对该催化剂进行了表征。实验结果表明,该催化剂Fenton氧化降解甲基橙的较适宜工艺条件为:溶液pH 5.0、甲基橙溶液初始质量浓度100 mg/L、催化剂加入量2.0 g/L、H_2O_2浓度20 mmol/L,在此适宜条件下反应120 min时,甲基橙去除率接近100%。表征结果显示:Fe-Ce/MCM-41催化剂主要由铁、铈、氧、碳4种元素组成;铁与铈的摩尔比接近3∶1;铁和铈主要以Fe_3O_4和CeO_2的形态存在于催化剂表面。 相似文献
996.
S.M. Pan S.G. TimsX.Y. Liu L.K. Fifield 《Journal of environmental radioactivity》2011,102(10):930-936
A sediment core collected from the sub-aqueous delta of the Yangtze River estuary was subjected to analyses of 137Cs and plutonium (Pu) isotopes. The 137Cs was measured using γ-spectrometry at the laboratories at the Nanjing University and Pu isotopes were determined with Accelerator Mass Spectrometry (AMS), measurements made at the Australian National University. The results show considerable structure in the depth concentration profiles of the 137Cs and 239+240Pu. The shape of the vertical 137Cs distribution in the sediment core was similar to that of the Pu. The maximum 137Cs and 239+240Pu concentrations were 16.21 ± 0.95 mBq/g and 0.716 ± 0.030 mBq/g, respectively, and appear at same depth. The average 240Pu/239Pu atom ratio was 0.238 ± 0.007 in the sediment core, slightly higher than the average global fallout value. The changes in the 240Pu/239Pu atom ratios in the sediment core indicate the presence of at least two different Pu sources, i.e., global fallout and another source, most likely close-in fallout from the Pacific Proving Grounds (PPG) in the Marshall Islands, and suggest the possibility that Pu isotopes are useful as a geochronological tool for coastal sediment studies. The 137Cs and 239+240Pu inventories were estimated to be 7100 ± 1200 Bq/m2 and 407 ± 27 Bq/m2, respectively. Approximately 40% of the 239+240Pu inventory originated from the PPG close-in fallout and about 50% has derived from land-origin global fallout transported to the estuary by the river. This study confirms that AMS is a useful tool to measure 240Pu/239Pu atom ratio and can provide valuable information on sedimentary processes in the coastal environment. 相似文献
997.
In order to measure groundwater age and design nuclear waste disposal sites, it is important to understand the sorption behavior of tritium on soils. In this study, batch tests were carried out using four soils from China: silty clays from An County and Jiangyou County in Sichuan Province, both of which could be considered candidate sites for Very Low Level Waste disposal; silty sand from Beijing; and loess from Yuci County in Shanxi Province, a typical Chinese loess region. The experimental results indicated that in these soil media, the distribution coefficient of tritium is slightly influenced by adsorption time, water/solid ratio, initial tritium specific activity, pH, and the content of humic and fulvic acids. The average distribution coefficient from all of these influencing factors was about 0.1-0.2 mL/g for the four types of soil samples. This relatively modest sorption of tritium in soils needs to be considered in fate and transport studies of tritium in the environment. 相似文献
998.
Oikawa S Watabe T Inatomi N Isoyama N Misonoo J Suzuki C Nakahara M Nakamura R Morizono S Fujii S Hara T Kido K 《Journal of environmental radioactivity》2011,102(3):302-310
A radioactivity survey was launched in 1991 to determine the background levels of 239+240Pu in the marine environment off a commercial spent nuclear fuel reprocessing plant before full operation of the facility. Particular attention was focused on the 240Pu/239Pu atom ratio in seawater and bottom sediment to identify the origins of Pu isotopes. The concentration of 239+240Pu was almost uniform in surface water, decreasing slowly over time. Conversely, the 239+240Pu concentration varied markedly in the bottom water and was dependent upon the sampling point, with higher concentrations of 239+240Pu observed in the bottom water sample at sampling points having greater depth. The 240Pu/239Pu atom ratio in the seawater and sediment samples was higher than that of global fallout Pu, and comparable with the data in the other sea area around Japan which has likely been affected by close-in fallout Pu originating from the Pacific Proving Grounds. The 240Pu/239Pu atom ratio in bottom sediment samples decreased with sea depth. The land-originated Pu is not considered as the reason of the increasing 239+240Pu concentration and also decreasing the 240Pu/239Pu atom ratio with sea depth, and further study is required to clarify it. 相似文献
999.
The vertical distribution of the 236U/238U isotopic ratio was investigated in soil samples from three different locations on La Palma (one of the seven Canary Islands, Spain). Additionally the 240Pu/239Pu atomic ratio, as it is a well establish tool for the source identification, was determined. The radiochemical procedure consisted of a U separation step by extraction chromatography using UTEVA® Resin (Eichrom Technologies, Inc.). Afterwards Pu was separated from Th and Np by anion exchange using Dowex 1x2 (Dow Chemical Co.). Furthermore a new chemical procedure with tandem columns to separate Pu and U from the matrix was tested. For the determination of the uranium and plutonium isotopes by alpha spectrometry thin sources were prepared by microprecipitation techniques. Additionally these fractions separated from the soil samples were measured by Accelerator Mass Spectrometry (AMS) to get information on the isotopic ratios 236U/238U, 240Pu/239Pu and 236U/239Pu, respectively. The 236U concentrations [atoms/g] in each surface layer (∼2 cm) were surprisingly high compared to deeper layers where values around two orders of magnitude smaller were found. Since the isotopic ratio 240Pu/239Pu indicated a global fallout signature we assume the same origin as the probable source for 236U. Our measured 236U/239Pu value of around 0.2 is within the expected range for this contamination source. 相似文献
1000.
改革开放以来中国能源效率不断地提高,但是在某些年份存在波动现象.采用非线性分形理论及分形分析R/S方法,科学定量地描述了中国以及各个地区能源效率的演变趋势.首先采用分形理论对1978-2008年的中国能源效率时间序列数据进行研究,结果显示,中国能源效率发展演变存在Hurst现象,具有明显的分形特征.并依照“五年计划”来划分时间序列样本为研究区间,结合“五年计划”详尽地解释说明了中国能源效率变动的原因.然后将数据扩大为样本期为1995-2008年29地区的面板数据,采用面板变系数模型进一步对各个地区的能源效率进行分析,发现除海南外其他地区的能源效率演变过程中具有明显的持续性规律,各个地区能源效率将继续保持增长.西部6个地区以及东北三省的能源效率演变趋势高于全国水平,说明“西部大开发”战略和“振兴东北”战略都已经显效. 相似文献