首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   13556篇
  免费   280篇
  国内免费   1218篇
安全科学   341篇
废物处理   950篇
环保管理   1544篇
综合类   3283篇
基础理论   3752篇
污染及防治   2711篇
评价与监测   1199篇
社会与环境   1100篇
灾害及防治   174篇
  2024年   6篇
  2023年   51篇
  2022年   181篇
  2021年   186篇
  2020年   176篇
  2019年   141篇
  2018年   1602篇
  2017年   1547篇
  2016年   1330篇
  2015年   316篇
  2014年   260篇
  2013年   328篇
  2012年   791篇
  2011年   1658篇
  2010年   948篇
  2009年   856篇
  2008年   1148篇
  2007年   1515篇
  2006年   231篇
  2005年   180篇
  2004年   206篇
  2003年   212篇
  2002年   242篇
  2001年   146篇
  2000年   140篇
  1999年   108篇
  1998年   93篇
  1997年   88篇
  1996年   80篇
  1995年   68篇
  1994年   44篇
  1993年   39篇
  1992年   37篇
  1991年   16篇
  1990年   20篇
  1989年   16篇
  1988年   10篇
  1987年   3篇
  1986年   2篇
  1985年   5篇
  1984年   14篇
  1983年   10篇
  1982年   1篇
  1960年   1篇
  1935年   2篇
排序方式: 共有10000条查询结果,搜索用时 831 毫秒
851.

Background, aim, and scope  

Carbonyl compounds have been paid more and more attention because some carbonyl species have been proven to be carcinogenic or a risk for human health. Plant leaves are both an important emission source and an important sink of carbonyl compounds. But the research on carbonyl compounds from plant leaves is very scarce. In order to make an approach to the emission mechanism of plant leaves, a new method was established to extract carbonyl compounds from fresh plant leaves.  相似文献   
852.

Background, aim and scope  

European legislation stipulates that genetically modified organisms (GMO) have to be monitored to identify potential adverse environmental effects. A wealth of different types of monitoring data from various sources including existing environmental monitoring programmes is expected to accumulate. This requires an information system to efficiently structure, process and evaluate the monitoring data.  相似文献   
853.
废弃中药渣催化热解制取生物油的研究   总被引:1,自引:0,他引:1  
利用热重分析仪(TGA)对植物类中药渣的热解特性进行了研究,用Coats-Redfern积分法计算了其热解动力学参数,得出中药渣热解反应符合一级反应动力学方程,其活化能较低,为36.0kJ/mol。考察了热解温度对气体、液体、固体产物的影响,在723K时,液体产物生物油产率最高,为39%。以介孔分子筛SBA-15以及分别负载Al、Sn、Ni、Cu和Mg的SBA-15作为催化剂,研究催化热解对气体、液体、固体产率及生物油组分的影响。研究表明,Al-SBA-15的催化效果较好,液体产率最高,为36%;采用元素分析仪和热值测定仪,得到用Al-SBA-15作为催化剂时生物油的氧质量分数最低,低位热值最高。用GC/MS对生物油组分的分析结果表明,添加Al-SBA-15后,热解产物中脂肪族和芳香族化合物增加,而含氧化合物减少。  相似文献   
854.
855.
Soybean oil (SBO) was dimerized and the crude dimer acid product reacted with 1,2-phenylene diamine at 210 ± 5 °C under inert atmosphere to obtain fatty polyamide (FPA). The FPA was used to modify a commercial alkyd resin by reacting a mixture of the alkyd resin with 5 wt% of FPA at 120 °C for 80 min under inert atmosphere. The FTIR spectrum of the FPA modified resin showed evidence of higher degree of H-bonding than was found for the unmodified alkyd. White gloss coatings of 15, 20, 25, and 30% solids were formulated from the modified and unmodified resins and examined for performance with respect to: leveling, sag resistance, drying time, pigment settling, skinning tendency and film hardness. Results showed that the unmodified alkyd coatings exhibited good leveling but poor sag resistance at all solid contents. In contrast, FPA modified alkyd coatings combined good leveling with high sag resistance indicating their thixotropic nature. A strong tendency to pigment settling was observed for unmodified alkyd coatings but was not observed in the FPA modified alkyd coatings. The modified alkyd coatings showed skinning while the unmodified alkyd coatings did not skin. A 30% solids coating formulation of the FPA modified resin showed shorter surface dry time but longer hard dry time than the unmodified alkyd resin coating.  相似文献   
856.
A new aliphatic block copolyester was synthesized in bulk from transesterification techniques between poly((R)-3-hydroxybutyrate) (PHB) and poly(isosorbide succinate) (PIS). Additionally, other two block copolyesters were synthesized in bulk either from transesterification reactions involving PHB and poly(l-lactide) (PLLA) or from ring-opening copolymerization of l-lactide and hydroxyl-terminated PHB, as result of a previous transesterification reactions with isosorbide. Two-component blends of PHB and PIS or PLLA were also prepared as comparative systems. SEC, MALDI-TOF mass spectrometry (MALDI-TOFMS), 1H and 13C NMR spectroscopy, WAXD, solubility tests, and TG thermal analysis were used for characterization. The block copolymer structures of the products were evidenced by MALDI-TOFMS, 13C NMR, and WAXD data. The block copolymers and the corresponding binary blends presented different solubility properties, as revealed by solubility tests. Although the incorporation of PIS sequences into PHB main backbone did not enhance the thermal stability of the product, it reduced its crystallinity, which could be advantageous for faster biodegradation rate. These products, composed of PHB and PIS or PLLA sequences, are an interesting alternative in biomedical applications.  相似文献   
857.
An extracellular poly(3-hydroxybutyrate) (PHB) depolymerase produced by a thermotolerant fungal soil isolate, Aspergillus fumigatus 202, was purified and characterized. Maximum PHB depolymerase production was obtained at the end of 48 h with initial medium pH 7.0 and 45 °C in Bushnell Haas Minerals medium containing PHB as sole source of carbon. The PHB depolymerase was purified using size exclusion chromatography to a fold purification of 20.62 and 61.62% yield. SDS-PAGE and isoelectric focusing revealed the molecular weight and pI of the purified enzyme as 63,744 Da and 4.2, respectively. N-terminal amino acid sequence of purified enzyme was HAXDAYLVK. This non-glycosylated enzyme was most active at pH 9.0 and 45 °C. Purified enzyme was inactivated by N-bromosuccinimide and dithiothreitol suggesting the involvement of tryptophan residues and disulfide bonds at its active site. Nonionic detergents like Tween 20, Tween 80 and Triton X-100 inhibited the enzyme activity. Ions like Ca+2 and Mg+2 (5 mM) increased the enzyme activity 1.5 times. Fe+2 effectively inhibited the enzyme activity to 88% whereas Hg+2 completely inhibited the enzyme.  相似文献   
858.
This article investigates the effects of stone powder sludge on the microstructure and strength development of alkali-activated fly ash and blast furnace slag mixes. Stone powder sludge produced from a crushed aggregate factory was used to replace fly ash and granulated blast furnace slag at replacement ratios of 0%, 10%, 20%, and 30% by mass. The unit weight and compressive strength of the samples were measured, and scanning electron microscopy/energy dispersive spectroscopy and X-ray diffraction (XRD) analyses were performed. The test results indicated that the compressive strength of alkali-activated blast furnace slag mixes using stone powder sludge was higher than that of the alkali-activated blast furnace slag control mix, but the compressive strength of alkali-activated fly ash mixes decreased with increasing replacement ratio of stone powder sludge. Microscopy results indicated that for alkaliactivated blast furnace slag samples, broken surfaces were more evident than for the alkali-activated fly ash samples. For all XRD diagrams, broad and diffuse peaks were observed around 2θ = 35° (d = 2.96–3.03 Å), implying amorphous or short-ordering structure phases.  相似文献   
859.
日益增加的固体废弃物和工业废弃物已成为主要的社会问题。回收服务相对来说还很不足,导致很多废弃物只能进行简单的填埋、焚烧处理。这将导致严重的环境污染。借鉴国外一些发达国家废物管理领域的政策趋势,我国近年来出台了一系列关于电子废弃物管理的政策法规,但也暴露出正规的废物处理企业无法取得规模收益,入不敷出,电子废弃物处理基金的征收及补贴对象不明确等诸多问题。引入生产者责任延伸制将外部影响内部化,在理念和功能等方面适应了电子废弃物管理的需要。  相似文献   
860.

Purpose  

Besides classical organic pollutants and pesticides, pharmaceuticals and their residues have nowadays become recognized as relevant environmental contaminants. The risks of these chemicals for aquatic ecosystems are well known, but information about the pharmaca-plant interactions and metabolic pathways is scarce. Therefore, we investigate the process of uptake of acetaminophen (N-Acetyl-4-aminophenol) by Brassica juncea, drug-induced defense responses and detoxification mechanisms in different plant parts.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号