全文获取类型
收费全文 | 4477篇 |
免费 | 559篇 |
国内免费 | 2198篇 |
专业分类
安全科学 | 327篇 |
废物处理 | 57篇 |
环保管理 | 458篇 |
综合类 | 3562篇 |
基础理论 | 1589篇 |
污染及防治 | 459篇 |
评价与监测 | 286篇 |
社会与环境 | 323篇 |
灾害及防治 | 173篇 |
出版年
2024年 | 29篇 |
2023年 | 155篇 |
2022年 | 252篇 |
2021年 | 310篇 |
2020年 | 301篇 |
2019年 | 277篇 |
2018年 | 260篇 |
2017年 | 317篇 |
2016年 | 339篇 |
2015年 | 368篇 |
2014年 | 312篇 |
2013年 | 401篇 |
2012年 | 445篇 |
2011年 | 471篇 |
2010年 | 335篇 |
2009年 | 350篇 |
2008年 | 276篇 |
2007年 | 358篇 |
2006年 | 261篇 |
2005年 | 248篇 |
2004年 | 176篇 |
2003年 | 165篇 |
2002年 | 119篇 |
2001年 | 99篇 |
2000年 | 101篇 |
1999年 | 71篇 |
1998年 | 61篇 |
1997年 | 60篇 |
1996年 | 60篇 |
1995年 | 50篇 |
1994年 | 45篇 |
1993年 | 35篇 |
1992年 | 28篇 |
1991年 | 20篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1971年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有7234条查询结果,搜索用时 46 毫秒
991.
三江平原小叶章湿地土壤硫的组成与垂直分布 总被引:2,自引:0,他引:2
以三江平原小叶章湿地为对象,对比研究了典型草甸小叶章湿地和沼泽化草甸小叶章湿地土壤硫的组成与垂直分布特征.结果表明,在2种小叶章湿地类型中,土壤总硫含量分别为303.39~520.83和303.74~1 219.81 mg·kg-1,平均值为391.62和513.03 mg·kg-1,均低于世界平均土壤硫含量(700 mg·kg-1).硫主要富集在土壤表层,且主要以有机硫形式存在,有机硫占总硫比例约为90%,而在有机硫中,则以碳键硫所占比例最大,占总硫比例分别为45.34%和37.24%.沼泽化草甸小叶章湿地土壤各形态硫含量及其变异性均高于典型草甸小叶章湿地.在2种湿地土壤中各形态硫都具有明显的垂直分布特征和变异性.土壤有机质含量是影响硫含量的重要因素,同时也受到土壤各粒级含量的影响,并且土壤各形态硫含量之间存在一定的相关关系. 相似文献
992.
三峡库区太阳能资源基本特征及其演变 总被引:1,自引:0,他引:1
利用1961-2007年的日照时数建模计算了三峡库区的太阳辐射,在此基础上对库区的太阳能资源作了全面分析和评价。结果表明:库区年总辐射量介于3200~4400MJ/m2,与德国等太阳能利用大国相当;“下游多,上游少”是资源空间分布的基本特征,且在秋、冬季差异更为明显;资源的年变化具有“夏大冬小”的特点,同时呈典型“双峰结构”,最大和次大峰值分别出现在8月和5月;库区上游太阳能季节差异大,而中、下游四季差异相对较小;库区太阳辐射以散射辐射为主(平均为64%),上游尤其明显;1961-2007年,资源量与直射比均呈明显下降趋势,且在夏、冬季下降尤为显著,分析表明这与轻雾日数和霾日数的增加有关;自20世纪90年代初起,资源量开始回升,有利于库区太阳能的开发利用。 相似文献
993.
994.
Fluoride concentration of groundwater reserves occurs in many places in the world. A critical area for such contamination
in India is alluvial soil of the plain region, consisting of five blocks (Jhajjar, Bahadurgarh, Beri, Matanhail, and Sahalawas)
of the Jhajjar District adjacent to the National Capital Territory of India, New Delhi. The purpose of this study was to assess
the association between water fluoride levels and prevalence of dental fluorosis among school children of the Jhajjar District
of Haryana, India. The fluoride content in underground drinking water sources was found to vary in villages. Hence, the villages
were categorized as high-fluoride villages (1.52–4.0 mg F/l) and low/normal-fluoride villages (0.30–1.0 mg F/l). The source
of dental fluorosis data was school-going children (7–15 years) showing different stages and types of fluorosis who were permanent
resident of these villages. The fraction of dental fluorosis-affected children varied from 30% to 94.85% in the high-fluoride
villages and from 8.80% to 28.20% in the low/normal-fluoride villages. The results of the present study revealed that there
existed a significant positive correlation between fluoride concentration in drinking water and dental fluorosis in high-fluoride
villages (r = 0.508; p < 0.001) and insignificant correlation in low-fluoride villages. 相似文献
995.
针对500kV变电站内产生较高工频磁场强度的电气设备——35kV并联电抗器,研究不同类型、不同排列方式下35kV并联电抗器周围工频电磁场分布规律。结果表明,35kV并联电抗器的电磁场强度随着离开电抗器中心距离的增加而降低,三角形排列的电抗器磁场强度大于水平排列的。 相似文献
996.
997.
N. F. Chernousova 《Russian Journal of Ecology》2001,32(2):122-125
The long-term population dynamics of rodent communities in park forests of Yekaterinburg was studied. The results showed that deep population depressions occurring in natural communities are not characteristic of the urban communities. In the urban environment, the density of rodents is always maintained at a relatively high level due to the appearance of species that are atypical for the natural communities. This fact deserves attention in view of the increasing risk of tick-borne encephalitis (TBE) in the region, as a high rodent abundance may provide for the maintenance of a stable TBE focus in the city. 相似文献
998.
香港汀角红树植物、沉积物及双壳类动物重金属含量 总被引:14,自引:0,他引:14
汀角有香港面积最大的硬底质红树林,作者调查了该红树林区沉积物、红树植物以及双壳类动物体内重金属(Cu、Pb、Zn和Ni)的含量.总体看,沉积物中重金属含量与其他地点相比较低,红树植物根际沉积物中重金属含量高于光滩.红树植物组织内重金属含量较低,体内Pb、Zn的含量均低于根际沉积物,但对Cu、Ni有一定的富集,Cu可在根部和叶内富集,而Ni只在根部富集,并束缚于此.双壳类动物对4种重金属的吸收存在较大差异,Zn、Cu的富集明显高于Pb和Ni的富集程度.5种动物中又以岩蠔最高,体内的Zn、Cu分别达到3913, 378mg/g.从重金属含量看,作为食用动物有一定的风险. 相似文献
999.
PCDDs/DF and Co-PCB (dioxin) formations were studied with ash from a newly developed gasification and melting process for
municipal solid waste. Ash samples were heated in a laboratory-scale fixed-bed reactor. Emphasis was placed on the effects
of the type and composition of ash, temperatures, gas residence time, and gaseous organic precursors. Investigations using
macroscopic and homologue distribution analyses led to the following conclusion. The ash from the gasification–melting process
had the ability to generate dioxins in flue gas. A possible carbon source is unburned carbon in the ash samples, although
this was very low (less than 0.01%). An experimental result that the level of dioxins generated from preheated fly ash obtained
from a conventional incinerator was much lower than that from nonheated fly ash supported this conclusion. Dioxin concentrations
obviously showed temperature dependence and peaked at 350°C. Dioxins formed in a gasification–melting process ash were readily
desorbed from the surface, probably because of the low carbon content of the ash. There was no experimental evidence that
gaseous organic precursors fed to the reactor generated dioxins. Therefore, an organic precursor was not essential for the
formation of dioxins. A good linear relationship obtained between PCDDs/DFs and gas residence time also supported the assumption.
Received: February 14, 2000 / Accepted: June 30, 2000 相似文献
1000.