全文获取类型
收费全文 | 618篇 |
免费 | 28篇 |
国内免费 | 245篇 |
专业分类
安全科学 | 41篇 |
废物处理 | 38篇 |
环保管理 | 59篇 |
综合类 | 354篇 |
基础理论 | 125篇 |
污染及防治 | 197篇 |
评价与监测 | 16篇 |
社会与环境 | 38篇 |
灾害及防治 | 23篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 25篇 |
2021年 | 29篇 |
2020年 | 22篇 |
2019年 | 32篇 |
2018年 | 24篇 |
2017年 | 27篇 |
2016年 | 28篇 |
2015年 | 31篇 |
2014年 | 49篇 |
2013年 | 50篇 |
2012年 | 51篇 |
2011年 | 54篇 |
2010年 | 45篇 |
2009年 | 44篇 |
2008年 | 58篇 |
2007年 | 41篇 |
2006年 | 26篇 |
2005年 | 27篇 |
2004年 | 22篇 |
2003年 | 15篇 |
2002年 | 23篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 18篇 |
1998年 | 20篇 |
1997年 | 31篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
排序方式: 共有891条查询结果,搜索用时 405 毫秒
481.
The review analysis of twenty two irrigation efficiency (IE) studies carried out in the Ebro River Basin shows that IE is
low (average IE)avg(= 53%) in surface-irrigated areas with high-permeable and shallow soils inadequate for this irrigation system, high (IE)avg(= 79%) in surface-irrigated areas with appropriate soils for this system, and very high (IE)avg(= 94%) in modern, automated and well managed sprinkler-irrigated areas. The unitary salt (total dissolved solids) and nitrate
loads exported in the irrigation return flows (IRF) of seven districts vary, depending on soil salinity and on irrigation
and N fertilization management, between 3–16 Mg salt/ha⋅ year and 23–195 kg NO)3
−-N/ha⋅ year, respectively. The lower nitrate loads exported from high IE districts show that a proper irrigation design and
management is a key factor to reduce off-site nitrogen pollution. Although high IE’s also reduce off-site salt pollution,
the presence of salts in the soil or subsoil may induce relatively high salt loads (≥14 Mg/ha⋅ year) even in high IE districts.
Two important constrains identified in our revision were the short duration of most surveys and the lack of standards for
conducting irrigation efficiency and mass balance studies at the irrigation district level. These limitations {emphasize the
need for the establishment of a permanent and standardized network of drainage monitoring stations for the appropriate off-site
pollution diagnosis and control of irrigated agriculture. 相似文献
482.
Fertilizer leaching affects farm profitability and contributes to nonpoint-source pollution of receiving waters. This work aimed to establish nitrate nitrogen export from La Violada Gully in relation to nitrogen fertilization practices in its basin (La Violada Gully watershed, VGW, 19,637 ha) and especially in La Violada Irrigation District (VID, 5282 ha). Nitrogen (N) fertilization in VID (and VGW) was determined through interviews with local farmers for the hydrologic years 1995 and 1996 and NO3-N load in the gully was monitored from 1995 to 1998. The N fertilizer applied in VGW was 2175 Mg in 1995 and 2795 Mg in 1996. About 43% was applied in VID (945 Mg in 1995 and 1161 Mg in 1996). The most fertilized crop was corn: 398 kg N ha-1 (665 Mg) in 1995 and 453 kg N ha-1 (911 Mg) in 1996. Nitrogen fertilization was higher than N uptake for irrigated crops, especially for corn and rice. Nitrate N load in La Violada Gully averaged 427.4 Mg yr-1. Seventy-five percent of the exports took place during the irrigation season (321.8 Mg). During the non-irrigation season maximum NO3-N loads (3.1 Mg NO3-N d-1) were found after heavy rains following the N side-dressing of wheat in the rain-fed area of VGW (February). During the irrigation season NO3-N load was determined by outflow from the district (caused by irrigation) and to a lesser extent by changes in NO3 concentration (caused by fertilization), showing peaks in April (pre-sowing corn N fertilization and first irrigations) and June to August (highest irrigation months and corn side-dress N applications, maximum 6.3 Mg NO3-N d-1 in July). Adjusting N fertilization to crops' needs, improving irrigation efficiencies, and better scheduling N fertilization and irrigation in corn could reduce N export from VID. 相似文献
483.
Salt loading in irrigation return flows contributes to the salinization of the receiving water bodies, particularly when originated in salt-affected areas as frequently found in the middle Ebro River basin (Spain). We determined the salt loading in La Violada Gully from the total dissolved solids (TDS) and flows (Q) during the 1995 to 1998 hydrological years. Since this gully collects flows from various sources, an end-member mixing analysis (EMMA) was performed to quantify the drainage flow from La Violada Irrigation District (VID). Three flow components were identified in La Violada Gully: drainage waters from VID (Qd); tail-waters from irrigation ditches, spill-over, and seepage from the Monegros Canal (Qo); and ground water inflows (Qg) originating in the dryland watershed. Gypsum in the soils of VID was the main source for salts in La Violada Gully (flow-weighted mean TDS=1720 mg L-1, dominated by sulfate and calcium). The contribution of Qg to the total gully flow during the 1996 irrigation season was low (6.5% of the total flow). The 1995 to 1998 annual salt load average in La Violada Gully was 78 628 Mg, 71% of which was exported during the irrigation season. The 1995 to 1998 irrigation season salt load average in Qd was 43 015 Mg (77% of the total load). Thus, irrigated agriculture in VID was the main source of salt loading in this gully, with a yield of 11.1 Mg of salts per hectare of irrigated land for the irrigation season. Efficient irrigation systems and irrigation management practices that reduce Qd are key factors for controlling off-site salt pollution of these gypsum-rich irrigated areas. 相似文献
484.
Seasonal variation, source, and regional representativeness of the background aerosol from two remote sites in western China 总被引:1,自引:0,他引:1
Wenjun Qu Dan Wang Yaqiang Wang Lifang Sheng Gang Fu 《Environmental monitoring and assessment》2010,167(1-4):265-288
Using observations from two remote sites during July 2004 to March 2005, we show that at Akdala (AKD, 47° 06′ N, 87° 58′ E, 562 m asl) in northern Xinjiang Province, there were high wintertime loadings of organic carbon (OC), elemental carbon (EC), and water-soluble (WS) ${\rm SO}_{4}^{2-}$ , ${\rm NO}_{3}^{2-}$ , and ${\rm NH}_{4}^{+}$ , which is similar to the general pattern in most areas of China and East Asia. However, at Zhuzhang (ZUZ, 28° 00′ N, 99° 43′ E, 3,583 m asl) in northwestern Yunnan Province, the aerosol concentrations and compositions showed little seasonal variation except for a decreasing trend of OC from August to autumn–winter. Additionally, the OC variations dominated the seasonal variation of PM10 (particles ≤10 μm diameter) level. Chemical characteristics combined with transport information suggested sea salt origin of ionic Na?+?, Mg2?+?, and Cl??? at ZUZ. At AKD, ionic Ca2?+?, Mg2?+?, Na?+?, and Cl??? primarily originated from salinized soil. Furthermore, the WS Ca2?+? contributions (5.4–6%) to the PM10 mass during autumn, winter, and early spring reflected a constant dust component. The results of this study indicated that both sites were regionally representative. However, the representative regions and scales of these background sites may vary seasonally as the regional atmospheric transport patterns change. Seasonal variations in the background aerosol levels from these two areas need to be considered when evaluating the regional climate effects of the aerosols. 相似文献
485.
Preparation and utilization of molecularly imprinted polymer for chlorsulfuron extraction from water, soil, and wheat plant 总被引:1,自引:0,他引:1
A molecularly imprinted polymer (MIP) was prepared using chlorsulfuron (CS), a herbicide as a template molecule, methacrylic acid as a functional monomer, ethylene glycol dimethacrylate (EDMA) as a cross-linker, methanol and toluene as a porogen, and 2,2-azobisisobutyronitrile as an initiator. The binding behaviors of the template chlorsulfuron and its analog on MIP were evaluated by equilibrium adsorption experiments, which showed that the MIP particles had specific affinity for the template CS. Solid-phase extraction (SPE) with the chlorsulfuron molecularly imprinted polymer as an adsorbent was investigated. The optimum loading, washing, and eluting conditions for chlorsulfuron molecularly imprinted polymer solid-phase extraction (CS-MISPE) were established. The optimized CS-MISPE procedure was developed to enrich and clean up the chlorsulfuron residue in water, soils, and wheat plants. Concentrations of chlorsulfuron in the samples were analyzed by HPLC-UVD. The average recoveries of CS spiked standard at 0.05~0.2 mg L(-1) in water were 90.2~93.3%, with the relative standard deviation (RSD) being 2.0~3.9% (n=3). The average recoveries of 1.0 mL CS spiked standard at 0.1~0.5 mg L(-1) in 10 g soil were 91.1~94.7%, with the RSD being 3.1~5.6% (n=3). The average recoveries of 1.0 mL CS spiked standard at 0.1~0.5 mg L(-1) in 5 g wheat plant were 82.3~94.3%, with the RSD being 2.9~6.8% (n=3). Overall, our study provides a sensitive and cost-effective method for accurate determination of CS residues in water, soils, and plants. 相似文献
486.
487.
488.
氯代苯及氯代酚类优先污染物好氧生物降解动力学的研究 总被引:2,自引:0,他引:2
利用测定微生物呼吸耗氧量的方法,对氯代苯及氯代酚类中的7种优先污染物,用经它们分别驯化的活性污泥对其好氧生物降解动力学进行了研究。 相似文献
489.
水中微量甲基膦酸类化合物的树脂富集与GC/MS分析 总被引:3,自引:0,他引:3
本文使用三种阴离子交换树脂(即大孔弱碱型D-301-R,强碱型D-296,201X7)柱对水中微量甲基膦酸类化合物的富集方法进行了研究。含磷毒剂降解产物的水样用气相色谱/质谱法进行定性定量分析。结果表明,D-301-R阴离子交换树脂柱对甲基膦酸的富集回收率高于60%。 相似文献
490.