全文获取类型
收费全文 | 3501篇 |
免费 | 453篇 |
国内免费 | 1742篇 |
专业分类
安全科学 | 353篇 |
废物处理 | 155篇 |
环保管理 | 234篇 |
综合类 | 3106篇 |
基础理论 | 988篇 |
污染及防治 | 441篇 |
评价与监测 | 270篇 |
社会与环境 | 56篇 |
灾害及防治 | 93篇 |
出版年
2024年 | 14篇 |
2023年 | 96篇 |
2022年 | 194篇 |
2021年 | 206篇 |
2020年 | 193篇 |
2019年 | 191篇 |
2018年 | 180篇 |
2017年 | 228篇 |
2016年 | 242篇 |
2015年 | 271篇 |
2014年 | 306篇 |
2013年 | 402篇 |
2012年 | 400篇 |
2011年 | 316篇 |
2010年 | 270篇 |
2009年 | 289篇 |
2008年 | 242篇 |
2007年 | 270篇 |
2006年 | 245篇 |
2005年 | 173篇 |
2004年 | 162篇 |
2003年 | 155篇 |
2002年 | 105篇 |
2001年 | 98篇 |
2000年 | 78篇 |
1999年 | 75篇 |
1998年 | 62篇 |
1997年 | 52篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 28篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有5696条查询结果,搜索用时 484 毫秒
141.
Effectiveness of Africa's tropical protected areas for maintaining forest cover 总被引:1,自引:0,他引:1 下载免费PDF全文
The effectiveness of parks for forest conservation is widely debated in Africa, where increasing human pressure, insufficient funding, and lack of management capacity frequently place significant demands on forests. Tropical forests house a substantial portion of the world's remaining biodiversity and are heavily affected by anthropogenic activity. We analyzed park effectiveness at the individual (224 parks) and national (23 countries) level across Africa by comparing the extent of forest loss (as a proxy for deforestation) inside parks to matched unprotected control sites. Although significant geographical variation existed among parks, the majority of African parks had significantly less forest loss within their boundaries (e.g., Mahale Park had 34 times less forest loss within its boundary) than control sites. Accessibility was a significant driver of forest loss. Relatively inaccessible areas had a higher probability (odds ratio >1, p < 0.001) of forest loss but only in ineffective parks, and relatively accessible areas had a higher probability of forest loss but only in effective parks. Smaller parks less effectively prevented forest loss inside park boundaries than larger parks (T = ?2.32, p < 0.05), and older parks less effectively prevented forest loss inside park boundaries than younger parks (F2,154 = ?4.11, p < 0.001). Our analyses, the first individual and national assessment of park effectiveness across Africa, demonstrated the complexity of factors (such as geographical variation, accessibility, and park size and age) influencing the ability of a park to curb forest loss within its boundaries. 相似文献
142.
Biosorption efficiency of coir pith, a waste product from coir industry, was investigated in this study for the removal of metallic pollutants such as Ni, Cu and Zn from aqueous solutions. The disposal of coir pith is a major problem associated with the coir industries, especially working in the small-scale sector. The present study explores the effectiveness of utilization of coir pith, an accumulating waste, as a biosorbent for heavy metal removal. Batch mode studies were done to evaluate the efficiency of removal of metals under varying adsorption conditions of pH, metal concentration and contact time. Characterization studies of the biosorbent and SEM analysis were done. Kinetic modelling studies were tried using Lagergren pseudo-first-order and second-order models. Equilibrium studies were done using well-known Freundlich, Langmuir and D–R isotherm models. It was found that all isotherms are fitting well indicating the efficiency of coir pith as an adsorbent of heavy metals. The applicability of all the three isotherms to the sorption processes shows that both monolayer adsorption and heterogeneous energetic distribution of active sites on the surface of the adsorbent are possible. Due to the abundance and low cost of these materials, adsorption technologies developed can act as good sustainable options for the future in heavy metal removal from industrial effluents. 相似文献
143.
144.
This research article demonstrates biodiesel synthesis through the methanolysis of the oily contents (4.02 ± 0.27% w/w on dried basis) of Dictyota dichotoma collected from the coast of Hawksbay, Pakistan. The metal oxides (CaO, MgO, ZnO, and TiO2) used as nanocatalysts were refluxed (5% K2SO4), calcinated (850 °C) and characterized by Atomic Force Microscopy (AFM) which produced 93.2% w/w FAME (biodiesel) at relatively mild condition (5% catalyst, 65 °C, 3 h, 18:1 molar ratio) using CaO. Whereas, MgO, ZnO, and TiO2 produced 92.4%, 72.5%, and 31.8% w/w FAME, respectively at elevated condition (225 °C). Thus, CaO was considered to be the best catalyst among the others. This tri-phase reaction require continuous fast mixing and the yield depends on the reaction parameters like catalyst amount, temperature, reaction time and molar ratio (methanol: oil). The reusability of these heterogeneous catalysts simplified the purification step, reduced the waste generation and make the final product technically and economically viable. 相似文献
145.
SGA对垃圾焚烧飞灰中重金属的固化性能研究 总被引:1,自引:0,他引:1
根据EPA1311、HJ/T299—2007、HJ/T300—2007和HJ557—2009等国内外不同标准,研究了深圳某垃圾焚烧发电厂垃圾焚烧飞灰的浸出毒性,探讨了六硫代胍基甲酸(sixthioguanidineacid,SGA)、二甲基二硫代氨基甲酸盐(sodiumdimethyldithiocarbamate,SDD)和Ca(OH)2浓度对垃圾焚烧飞灰中重金属的固定性能的影响。研究结果表明,随着浸提液pH的降低,该厂焚烧飞灰中大部分金属元素的浸出量增大,焚烧飞灰浸出液中的cd、Ni、Ph和zn浓度分别超过国家危险废物鉴别标准(GB5085.3—2007)规定值的4.75倍、1.47倍、6.72倍和2.20倍,属于危险废弃物,必须进行稳定化处理。当固化剂SGA加入量为0.1mol/kg时,稳定化后的重金属浸出浓度已经低于危险废物鉴别标准,且对Cd、Cr、Cu和Pb的固化性能优于SDD和Ca(OH)2;当固化剂SGA、SDD和Ca(OH)2加入量为0.5mol/kg时,稳定化后的焚烧飞灰重金属浸出浓度均低于国家危险废物鉴别标准(GB5085.3-2007)中的规定值。与SDD和Ca(OH):相比,SGA对垃圾焚烧飞灰中重金属的固化处理更具有优势。 相似文献
146.
为探究草坪除草剂与重金属复合污染对高等植物的生态毒性效应,以小麦与黄瓜为敏感受试植物,采用滤纸发芽试验法,研究了典型草坪除草剂环草隆与4种重金属(Cu/Zn/Pb/Cd)单一及复合污染条件下,对2种植物种子萌发与幼苗生长的毒性效应并进行评估。在此基础上采用评估因子法外推环草隆在土壤中的预测无效应浓度(PNECsoil)。结果表明,2种植物的根长及小麦的芽长对环草隆与重金属非常敏感(P<0.01),且存在明显的剂量-效应关系。黄瓜根长对环草隆最敏感,根长半抑制浓度(RI50)为0.281 mg·L-1。小麦根长对Cu、Pb、Cd比黄瓜根长更敏感。环草隆与重金属复合污染时,黄瓜根长表现得最为敏感,可作为敏感生物标记物。环草隆与重金属复合污染对小麦及黄瓜根长抑制具有协同作用,并且随着重金属浓度的增大,黄瓜和小麦根生长对环草隆的敏感性增加。环草隆与重金属复合污染对小麦芽长的联合效应主要与重金属种类及其暴露浓度有关。以黄瓜的根伸长抑制率为急性毒性终点,利用外推法计算得环草隆在土壤中的PNECsoil为1.90μg·kg~(-1),远远低于环草隆田间推荐使用量1.5~9 mg·kg~(-1)。与重金属复合污染时,环草隆的PNECsoil明显降低,导致其生态风险提高。上述研究结果能够为草坪除草剂环草隆与重金属复合污染的生态风险评价提供数据支持。 相似文献
147.
148.
İsmail Hilali 《International Journal of Green Energy》2016,13(9):911-917
This study presents a comparative analysis of sizing of metal hydride tank filled with different alloys. Alloys include solid solutions and intermetallic compounds of the generic families AB5, AB2, AB, A2B. The effects of the different alloys on the sizing of metal hydride hydrogen storage tanks are complicated and depend on many factors. In this paper, a thermoeconomic optimization analysis with a simple algebraic formula was presented for the estimation of optimum metal hydride tank surface area for heat transfer enhancement. The optimum area of the metal hydride tank filled with commercially available different alloys (LaN5, Ti0,98Zr0,02V0,43Fe0,09Cr0,05Mn1,5, TiFe, Mg2NiH4) was evaluated and compared by the developed method. The optimum net savings and the value of payback were determined for four alloys. It is found that mathematical model can be employed for the determination of optimum metal hydride tank design and increasing net savings according to alloy types. The optimum areas of the tanks filled with four alloys (LaN5, Ti0,98Zr0,02V0,43Fe0,09Cr0,05Mn1,5, TiFe, Mg2NiH4) were calculated as 0.136, 0.130, 0.133, and 0.173 m2, respectively. The optimum net savings for tanks filled with four alloys (LaN5, Ti0,98Zr0,02V0,43Fe0,09Cr0,05Mn1,5, TiFe, Mg2NiH4) are about 461.0, 409.3, 419.6, and 979.6 $ and the values of payback are about 1.98, 2.1, 2.17, and 1.37 years, respectively. Excessive area of the metal hydride tank would not be as economical as the optimum tank area. Thermal management of metal hydride tank must be designed for optimum points calculated at which maximum savings occur. 相似文献
149.
随着环境问题日渐突出,地表灰尘重金属污染日益成为研究热点。单纯采用化学方法监测重金属污染具有一定局限性,环境磁学方法以其简便、快捷、经济且无害化的特点在城市重金属污染研究中广为应用。通过文献调研,综述环境磁学在城市地表灰尘重金属污染研究中的应用与研究进展,阐明重金属的主要来源,简述环境磁学的诸多参数,分析磁学参数与重金属的关系,并通过对比不同的磁学分析方法,探讨环境磁学方法在城市地表灰尘重金属污染研究中存在的问题及其发展趋势。 相似文献
150.
采用聚合物前驱体法制备了Ti/SnO2-Sb2O3电极,再通过恒电流电沉积法制备了 Ti/SnO2-Sb2O3/PbO2和Ti/SnO2-Sb2O3/MnO2电极。采用SEM技术对3种金属氧化物电极表面的形貌进行了表征,并分别以3种电极为阳极进行了苯酚的电催化氧化实验。实验结果表明:电解时间为2.5 h时,Ti/SnO2-Sb2O3电极、Ti/SnO2-Sb2O3/PbO2电极和Ti/SnO2-Sb2O3/MnO2电极对苯酚的降解率分别为85.9%,83.2%,44.6%;苯酚在3种电极上的电催化氧化反应均遵循一级反应动力学方程;苯酚在Ti/SnO2-Sb2O3 电极和Ti/SnO2-Sb2O3/PbO2电极上的反应速率较快,并具有较高的析氧电位;Ti/SnO2-Sb2O3/PbO2电极具有更好的耐腐蚀性和更长的使用寿命。 相似文献