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   898篇
  免费   49篇
  国内免费   169篇
安全科学   120篇
废物处理   12篇
环保管理   150篇
综合类   503篇
基础理论   149篇
污染及防治   41篇
评价与监测   33篇
社会与环境   63篇
灾害及防治   45篇
  2024年   1篇
  2023年   3篇
  2022年   24篇
  2021年   33篇
  2020年   42篇
  2019年   33篇
  2018年   30篇
  2017年   34篇
  2016年   62篇
  2015年   40篇
  2014年   44篇
  2013年   47篇
  2012年   51篇
  2011年   63篇
  2010年   49篇
  2009年   58篇
  2008年   30篇
  2007年   63篇
  2006年   57篇
  2005年   48篇
  2004年   42篇
  2003年   34篇
  2002年   36篇
  2001年   25篇
  2000年   29篇
  1999年   20篇
  1998年   16篇
  1997年   11篇
  1996年   18篇
  1995年   15篇
  1994年   7篇
  1993年   6篇
  1992年   12篇
  1991年   8篇
  1990年   8篇
  1989年   6篇
  1988年   1篇
  1987年   2篇
  1986年   1篇
  1984年   1篇
  1983年   2篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
排序方式: 共有1116条查询结果,搜索用时 46 毫秒
41.
通过分析化学药品原料药制造业的基本情况、产品种类和生产工艺,以及自行监测技术指南编制的目的和基本要求,梳理出确定监测点位和对应多项污染物排放标准为目前该行业自行监测技术指南编制工作的难点。根据以上分析,提出将指南按工艺类型拆分、监测点位和废气监测指标的确定、监测频次的优化、生产记录内容的设定列为指南编制工作的重点。  相似文献   
42.
The ecosystem services (ES) concept is being increasingly incorporated into environmental policy formulation and management approaches. The Corporate Ecosystem Services Review (ESR) is a framework used to assess the dependence and impact that a business has on ES. The success of the corporate experience of ES assessment provides an opportunity for adaption for local authority decision making. In this paper, the ESR tool was adapted to the South African setting at a local government level, and tested at two sites in the Msunduzi Municipality, KwaZulu-Natal. In testing the tool and gathering feedback from key stakeholders, it was found that there are both opportunities and challenges to this approach. Overall, however, it provides an opportunity for the systematic inclusion of ES assessment into existing regulatory frameworks for land-use planning and Integrated Environmental Management, whether in a strategic application, at a broader spatial (municipal) scale or in a specific locale within the municipality.  相似文献   
43.
Climate and land-use/cover changes (LUCC) influence soil erosion vulnerability in the semi-arid region of Alqueva, threatening the reservoir storage capacity and sustainability of the landscape. Considering the effect of these changes in the future, the purpose of this study was to investigate soil erosion scenarios using the Revised Universal Soil Loss Equation (RUSLE) model. A multi-agent system combining Markov cellular automata with multi-criteria evaluation was used to investigate LUCC scenarios according to delineated regional strategies. Forecasting scenarios indicated that the intensive agricultural area as well as the sparse and xerophytic vegetation and rainfall-runoff erosivity would increase, consequently causing the soil erosion to rise from 1.78 Mg ha?1 to 3.65 Mg ha?1 by 2100. A backcasting scenario was investigated by considering the application of soil conservation practices that would decrease the soil erosion considerably to an average of 2.27 Mg ha?1. A decision support system can assist stakeholders in defining restrictive practices and developing conservation plans, contributing to control the reservoir's siltation.  相似文献   
44.
Urbanization increases directly connected impervious area (DCIA), the impervious area that is hydraulically connected to downstream drainage by closed pipelines. Although the benefits of low-impact development (LID) have been examined in other studies, its effect on alleviating DCIA levels has seldom been assessed. This study measured the DCIA of urban watersheds in Houston, TX, USA. Five land-use types were categorized and the contribution of LID facilities to reducing DCIA in each type was estimated by using Sutherland's equations. The results showed (1) DCIA in commercial areas was greater than that in residential areas, especially for big-box retailers; (2) the percentage of DCIA reduction by LID varied by land-use type; and (3) optimal combinations of LID application could maximize the effectiveness of DCIA reduction. The results contribute to prioritizing land-use type for implementing LID practices and providing local governments with a useful measure to estimate runoff volume.  相似文献   
45.
Understanding risks from the human-mediated spread of non-indigenous species (NIS) is a critical component of marine biosecurity management programmes. Recreational boating is well-recognised as a NIS pathway, especially at a regional scale. Assessment of risks from this pathway is therefore desirable for coastal environments where recreational boating occurs. However, formal or quantitative risk assessment for the recreational vessel pathway is often hampered by lack of data, hence often relies on expert opinion. The use of expert opinion itself is sometimes limited by its inherent vagueness, which can be an important source of uncertainty that reduces the validity and applicability of the assessment. Fuzzy logic, specifically interval type-2 fuzzy logic, is able to model and propagate this type of uncertainty, and is a useful technique in risk assessment where expert opinion is relied upon. The present paper describes the implementation of a NIS fuzzy expert system (FES) for assessing the risk of invasion in marine environments via recreational vessels. The FES was based on expert opinion gathered through systematic elicitation exercises, designed to acknowledge important uncertainty sources (e.g., underspecificity and ambiguity). The FES, using interval type-2 fuzzy logic, calculated an invasion risk value (integrating NIS infection and detection probabilities) for a range of invasion scenarios. These scenarios were defined by all possible combinations of two vessel types (moored and trailered), five vessel components (hull, deck, internal spaces, anchor, fishing gear), two infection modes (fouling, water/sediment retention) and six frequently visited marine habitats (marina, mooring, farm, ramp, wharf, anchorage). Although invasion risk values determined using the FES approach was scenario-specific, general patterns were identified. Moored vessels consistently showed higher invasion risk values than trailered vessels. Invasion risk values were higher for anchorages, moorings and wharves. Similarly, hull-fouling was revealed as the highest infection risk mode after pooling results across all habitats. The NIS fuzzy expert system presented here appears as a valuable prioritising and decision-making tool for NIS research, prevention and control activities. Its easy implementation and wide applicability should encourage the development and application of this type of system as an integral part of biosecurity, and other environmental management plans.  相似文献   
46.
介绍了一座80m烟囱由径向进气方式改为弧形切向进气的工程案例。列出了烟囱改造前后引风机运行一日的能耗数据,对比分析得出采用弧形烟道具有一定的节能效果,探讨了采用弧形烟道烟囱降低能耗的基本原因。  相似文献   
47.
缙云山土地利用方式对土壤轻组及颗粒态有机碳氮的影响   总被引:4,自引:0,他引:4  
雷利国  江长胜  郝庆菊 《环境科学》2015,36(7):2669-2677
选取缙云山阳坡同一海拔处亚热带常绿阔叶林(以下简称林地)、果园、坡耕地和撂荒地这4种不同土地利用类型,在0~60 cm深度内每隔10 cm采集一个土样,测定土壤轻组有机碳氮(LFOC、LFON)和颗粒态有机碳氮(POC、PON)含量,并计算其分配比例和碳氮比.结果表明,在0~60 cm土壤深度范围内,林地转变为坡耕地后,LFOC及LFON含量分别降低了71.42%和38.46%(P0.05),转变为果园后变化不明显,坡耕地撂荒后其含量分别升高了3.77倍和1.38倍(P0.05);林地转变为坡耕地或果园后,POC及PON含量均无明显变化,而坡耕地撂荒后其含量分别增加了4.12和1.25倍(P0.05).林地转变为坡耕地后土壤LFOC及LFON分配比例显著降低,转变为果园后则明显升高,而POC及PON分配比例变化均不明显;坡耕地撂荒后,LFOC、LFON、POC、PON分配比例均显著增加.土壤SOC/TN为撂荒地(12.93)林地(8.53)果园(7.52)坡耕地(4.40),LFOC/LFON为撂荒地(16.32)林地(14.29)果园(11.32)坡耕地(7.60),POC/PON为撂荒地(23.41)坡耕地(13.85)林地(10.30)果园(9.64).以上研究结果表明林地开垦为果园或坡耕地后容易导致土壤轻组有机碳氮的损失,而坡耕地撂荒则有利于土壤活性有机碳氮的积累;林地转变为坡耕地减弱了土壤有机碳氮的活性,而林地转变为果园以及坡耕地撂荒均使土壤有机碳氮活性增强;林地转变为坡耕地和果园加剧了土壤有机质的矿化,相对而言,坡耕地撂荒后有利于土壤有机质的固定.  相似文献   
48.
李栋  姚鹏  赵彬  王金鹏  潘慧慧 《环境科学》2015,36(8):2791-2799
利用高效液相色谱法分析了长江口-浙闽沿岸表层沉积物中的色素组成和含量,探讨了海洋初级生产力、浮游植物功能类群和浮游植物色素保存效率的空间分布特征及其影响因素.结果表明,沉积物中的色素类型主要为沉积绿素(chloropigments,Chlorins)[包括叶绿素a(chlorophyll-a,Chl-a)及其降解产物(pheopigments,Pheo-a),如脱镁叶绿素a(pheophytin-a,PHtin-a)、脱镁叶绿酸a(pheophorbide-a,PHide-a)、焦脱镁叶绿素a(p Pheophytin-a,p PHtin-a)、甾醇绿素酯(sterol chlorin esters,SCEs)和胡萝卜醇绿素酯(carotenol chlorin esters,CCEs)].Chlorins高值区呈南北两大斑块状分布,可能主要是受到长江冲淡水及浙闽沿岸泥质区上升流输运的营养盐的影响.研究区域内类胡萝卜素整体上无明显趋势性变化,在长江口以及浙闽沿岸各呈现一个高值区.基于沉积物中特征类胡萝卜素比例估算得到的浮游植物功能类群中硅藻、甲藻、定鞭藻、青绿藻、隐藻和蓝藻的相对贡献分别为48.8%±17.4%、10.7%±11.5%、8.1%±7.2%、18.6%±8.2%、9.4%±6.4%和4.3%±3.2%.对营养盐水平、水体盐度等外界环境的偏好导致硅藻和甲藻比例离岸降低,青绿藻、隐藻和蓝藻比例离岸增加.Chl-a/Pheo-a比值的分布表明,较高的沉积速率以及季节性的底层水体缺氧事件导致了近岸海域(长江口最大浑浊带外缘、杭州湾湾口以及浙闽沿岸上升流区)具有较高的沉积色素保存效率,这些沉积色素保存效率较高的区域可能是进行海洋生态环境历史重建的理想区域,而杭州湾水体通过舟山群岛与外部海水进行水体交换时造成的较差沉积环境可能是导致杭州湾外海具有较低沉积色素含量和较低保存效率的主要原因.  相似文献   
49.
陈成龙  高明  木志坚  倪九派  祁乐 《环境科学》2017,38(8):3254-3263
利用长期田间监测数据,分析了三峡库区典型农业小流域不同土地利用类型土壤、浅层地下水氮磷含量分异特征,剖析了坡面土壤氮磷含量与浅层地下水、坡面地表径流氮磷浓度的相互关系.结果表明梯田的土壤TN平均含量显著(P0.05)高于坡耕地,水田梯田平均含量1.49 g·kg~(-1)最高;旱地坡耕地和桑树套种坡耕地土壤TP平均含量显著高于其它地类;旱地梯田土壤NO_3~--N平均含量最高,离散程度最大.坡面土地利用类型对浅层地下水TN、NO_3~--N浓度影响较大,但对TP浓度影响较小;流域浅层地下水TN浓度与NO_3~--N浓度呈极显著正相关,不同坡面浅层地下水NO_3~--N对TN平均贡献率在67.82%~78.51%之间;浅层地下水TN、NO_3~--N月平均浓度变化规律基本一致,春秋两季农作物施肥后均呈现明显上升趋势.坡面土壤TN平均含量与浅层地下水TN浓度呈显著指数关系,坡面土壤NO_3~--N平均含量与浅层地下水NO_3~--N浓度呈对数关系,但与坡面地表径流TN、NO_3~--N浓度无显著相关性;当坡面地表径流TP浓度0.1 mg·L~(-1)时,坡面土壤TP平均含量与其呈显著线性相关;坡面地表径流与浅层地下水TN、NO_3~--N浓度均呈显著幂函数关系,且NO_3~--N相关性更好.  相似文献   
50.
利用浸渍法,将Fe3+负载在经酸碱改性后的粉状活性炭上,当浸渍液浓度为2.5%,固化温度为270℃时,制成的催化剂催化活性较高。用自制的非均相类benton试剂降解焦化废水,通过正交试验和极差分析得出,影响因素的主次顺序为催化剂用量〉初始pH值〉反应时间〉H:0:投加量。结果表明,在100ml水样中。室温条件下,初始pH值为4.0,催化剂使用量为1.5g,H20:投加量为5ml(分两次投加),反应时间为90min时,COD去除率可达99%。采用混凝+化学沉淀+非均相类Fenton试剂法处理焦化废水,各主要出水水质指标为:色度lO倍;COD浓度38.5mg/L;氨氮浓度8.4mg/L,达到国家一级排放标准。  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