全文获取类型
收费全文 | 1163篇 |
免费 | 156篇 |
国内免费 | 628篇 |
专业分类
安全科学 | 67篇 |
废物处理 | 21篇 |
环保管理 | 245篇 |
综合类 | 1130篇 |
基础理论 | 205篇 |
污染及防治 | 105篇 |
评价与监测 | 76篇 |
社会与环境 | 68篇 |
灾害及防治 | 30篇 |
出版年
2024年 | 16篇 |
2023年 | 62篇 |
2022年 | 107篇 |
2021年 | 115篇 |
2020年 | 110篇 |
2019年 | 89篇 |
2018年 | 69篇 |
2017年 | 95篇 |
2016年 | 73篇 |
2015年 | 81篇 |
2014年 | 98篇 |
2013年 | 126篇 |
2012年 | 101篇 |
2011年 | 106篇 |
2010年 | 79篇 |
2009年 | 64篇 |
2008年 | 73篇 |
2007年 | 82篇 |
2006年 | 67篇 |
2005年 | 42篇 |
2004年 | 31篇 |
2003年 | 31篇 |
2002年 | 22篇 |
2001年 | 21篇 |
2000年 | 23篇 |
1999年 | 15篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 18篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有1947条查询结果,搜索用时 993 毫秒
431.
县域土地复垦潜力分析方法研究 总被引:3,自引:0,他引:3
以山西省潞城市为研究区域,对土地复垦潜力补充调查、适宜性评价、潜力分级和其测算与分析方法、潜力的构成进行了研究。结果表明:在土地利用现状调查成果的基础上,进行待复垦土地资源数量、质量、分布调查,并将指数和法与适宜性调查相结合进行适宜性评价,用潜力系数进行潜力级别划分,是县域土地复垦潜力研究的有效方法。 相似文献
432.
Ryan N. Engstrom Allen S. Hope Douglas A. Stow George L. Vourlitis Walter C. Oechel 《Journal of the American Water Resources Association》2002,38(6):1647-1659
ABSTRACT: Average daily values of the Priestley‐Taylor coefficient (a) were calculated for two eddy covariance (flux) tower sites with contrasting vegetation, soil moisture, and temperature characteristics on the North Slope of Alaska over the 1994 and 1995 growing seasons. Because variations in a have been shown to be associated with changes in vegetation, soil moisture, and meteorological conditions in Arctic ecosystems, we hypothesized that a values would be significantly different between sites. Since variations in the normalized difference vegetation index (NDVI) follow patterns of vegetation community composition and state that are largely controlled by moisture and temperature gradients on the North Slope of Alaska, we hypothesized that temporal variations in a respond to these same conditions and thus co‐vary with NDVI. Significant differences in a values were found between the two sites in 1994 under average precipitation conditions. However, in 1995, when precipitation conditions were above average, no significant difference was found. Overall, the variations in a over the two growing seasons showed little relationship to the seasonal progression of the regional NDVI. The only significant relationship was found at the drier, upland study site. 相似文献
433.
Donald D. Adelman 《Journal of the American Water Resources Association》2003,39(5):1079-1092
ABSTRACT: Ground water irrigation pumpage of the High Plains Aquifer is controlled at the state level in Texas and Oklahoma but at the regional level in Kansas and Nebraska. Critical declines in the aquifer that threatened the reliability of local public water supply wells prompted Nebraska's Upper Republican Natural Resources District (URNRD) to mandate water restrictions in 1978. Under current regulations, irrigators may not extract more than 1,842 millimeters of water per certified hectare (ha) in any five‐year period. Meter monitoring ensures that irrigators comply with restrictions. Farmers now incorporate irrigation scheduling into their cropping practices in order to meet URNRD controls. This study examines whether irrigators are using ground water efficiently while complying with pumpage limits. Crop irrigation requirements (CIR) from 1986 to 1999 were derived from a water balance approach incorporating Penman‐Monteith evapotranspira‐tion (ET) calculations from weather data supplied by the High Plains Climate Center automated weather station network. A ratio of average water pumped per well to the CIR was developed to verify irrigation efficiency. Results indicate that irrigation applications were less than CIR during most irrigation seasons. Irrigation efficiency increases can be attributed to crop rotations, favorable growing season precipitation, use of ET estimates to schedule irrigation, and water allocations limited to less than all certified hectares. 相似文献
434.
435.
为了解石油工业区土壤中PAHs(多环芳烃)的污染特征、来源及潜在危害,选择兰州市西固区为研究区域,系统采集表层土壤样品及部分剖面样品,采用GC-MS检测方法,分析了土壤中PAHs的污染水平与分布、来源及潜在致癌风险. 结果表明:研究区表层(0~20 cm)土壤中w(∑PAHs)(22种PAHs的总质量分数)在535~32 300 μg/kg之间;PAHs在土壤剖面的纵向分布上主要集中在5~10 cm,在0~25 cm范围内变化不明显;表层土壤中PAHs主要以2~3环为主. 相关性分析显示,土壤中w(∑PAHs)与w(TOC)无显著的相关性,表明TOC并非影响土壤中PAHs持留的重要因素. 研究区土壤中PAHs主要来源于石油、生物质和煤炭的燃烧,∑TEQBaP (22种PAHs的毒性当量浓度,以苯并芘等效浓度计)平均值为190 μg/kg,表明土壤中PAHs的潜在致癌性较低. 相似文献
436.
437.
438.
本研究基于苏州市低碳试点工作实施方案,识别了苏州市重点减排领域,采用国家温室气体排放清单,估算了苏州"十二五"(2011—2015)期间碳排放量,并利用情景分析法预测了2016—2025年基准情景和综合减排情景碳排放趋势,分析了各重点排放领域减排贡献率。在此基础上,将减排策略按照自愿、监管、自愿与监管相结合的方式分别从不同利益相关群体进行梳理,分析不同群体减排潜力。结果表明:(1) 2015年,苏州市碳排放量约为2.35亿吨,2011—2015年,重点排放领域为工业能源消耗、建筑、交通、电力行业。(2)采用综合减排方案能在2020年左右达到峰值,之后缓慢下降,但交通部门碳排放仍有一定增加。(3)碳减排策略由多个利益相关群体共同作用产生减排贡献。对苏州市低碳试点方案的分析表明,当地政策制定者的减排贡献最高,其后是基础设施建设者和运营者,最后是基础设施使用者。 相似文献
439.
Variations among rice cultivars on root oxidation and Cd uptake 总被引:1,自引:1,他引:0
In order to understand the mechanisms on the variation between rice cultivars in Cd uptake and accumulation, two pot soil experiments were conducted with typical rice cultivars that varied greatly in soil Cd uptake. The experiments with six rice cultivars showed that the root oxidation abilities of rice differed with rice cultivars and also with types of the cultivars, the cultivars with indica consanguinity were significantly higher than the cultivars with japonica consanguinity. Root oxidation abilities of the rice cultivars correlated positively and significantly (P〈0.01) with their Cd concentrations and Cd quantity accumulations in rice plants. The experiments with two rice cultivars showed that significant differences also existed between the two cultivars in pot soil redox potentials, which of Shan you 63 (higher soil Cd accumulator) were significantly higher than that of Wu yun jing 7 (lower soil Cd accumulator) under different soil Cd levels, but the degrees of the differences varied with soil Cd levels. The differences were larger under soil Cd treatments than the control. The results indicate that root oxidation ability, especially in Cd contaminated soil, is one of the main mechanisms which dominate Cd uptake and accumulation by rice plant. 相似文献
440.