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   2045篇
  免费   239篇
  国内免费   46篇
安全科学   46篇
废物处理   16篇
环保管理   567篇
综合类   360篇
基础理论   1068篇
环境理论   5篇
污染及防治   58篇
评价与监测   43篇
社会与环境   148篇
灾害及防治   19篇
  2023年   66篇
  2022年   55篇
  2021年   80篇
  2020年   84篇
  2019年   82篇
  2018年   75篇
  2017年   87篇
  2016年   90篇
  2015年   103篇
  2014年   92篇
  2013年   133篇
  2012年   80篇
  2011年   106篇
  2010年   119篇
  2009年   123篇
  2008年   112篇
  2007年   136篇
  2006年   99篇
  2005年   87篇
  2004年   76篇
  2003年   39篇
  2002年   41篇
  2001年   57篇
  2000年   43篇
  1999年   25篇
  1998年   22篇
  1997年   22篇
  1996年   20篇
  1995年   24篇
  1994年   18篇
  1993年   19篇
  1992年   16篇
  1991年   11篇
  1990年   9篇
  1989年   6篇
  1988年   5篇
  1987年   10篇
  1986年   4篇
  1985年   4篇
  1984年   3篇
  1983年   7篇
  1982年   7篇
  1981年   8篇
  1980年   7篇
  1979年   4篇
  1978年   4篇
  1973年   1篇
  1972年   1篇
  1971年   4篇
  1968年   1篇
排序方式: 共有2330条查询结果,搜索用时 31 毫秒
921.
省级区域耕地保有量测算研究——以江苏省为例   总被引:1,自引:0,他引:1  
预测了江苏省耕地供给变化趋势和耕地需求量。根据预测结果,对耕地供需平衡情况进行了判断,分析了不同的耕地集约利用水平、耕地种植结构对耕地供需平衡的影响耕地的供需状况。以此为依据,确定了区域粮食供应的优选策略。在此基础上,从区间估计的角度,探讨了耕地保有量的确定思路与方法,确定了江苏省规划期内不同时间阶段的耕地保有量区间,即到2010年耕地保有量应维持439.7-473.0万hm^2,2020年耕地保有量应维持420.8-458.4万hm^2。  相似文献   
922.
水土保持对维持良好的水库水生态环境具有重要的影响.生态修复技术作为一种新的水土保持措施,可实现受损水库生态环境的修复.围绕水库消落带、水库涵养林、库区耕地和水库水环境等方面来研究生态修复技术在水库水土保持中的应用情况.  相似文献   
923.
多晶硅片制造是光伏产品生命周期过程中能耗及环境影响较大的环节之一.以四川某硅片企业一期(国内普遍水平)和二期(国内较先进水平)的实际生产数据为例,运用生命周期评价方法的分类、特征化、量化处理方法,定量计算单位多晶硅片生产的环境影响,计算结果显示:国内较先进水平比普遍水平提高了资源、能源的利用率,减少了污染物的环境排放,尤其表现在粉尘排放量、酸化潜值、全球变暖值和臭氧消耗潜值方面;并提出国内多晶硅片企业节能减排方法技术方法为利用清洁能源,提高循环水利用率,改进铸锭工艺,增大晶锭中晶粒的尺寸,改用环境污染物排放较少的硅片清洗原料.  相似文献   
924.
ABSTRACT: In areas where water is scarce, drip irrigation provides the most efficient way to conserve irrigation water, but its cost of £1000 an acre is prohibitive for most small farmers in developing countries. The cost was reduced by 90 percent by (1) making dripper lines moveable, so that each line reaches ten rows instead of one; (2) replacing 25-cent emitters with simple 0.70 mm holes punched by a heated needle; and (3) using £3.00 off-the-shelf 20 liter containers with cloth filters in place of expensive filter systems. This reduced the cost of a half-acre system to £50. The low cost system was field tested in the hill areas of Nepal, and in mulberry cultivation in Andhra Pradesh, India. Uniformity of flow from emitters was 73–84 percent. Small farmers reported that the low cost trickle irrigation system cut labor requirements in half, and doubled the area irrigated by the same amount of water. The low cost drip system is likely to be widely adopted by small farmers in semi-arid and hilly regions.  相似文献   
925.
清河是辽河主要支流,清河水库上游山区森林植被也是保护辽河平原的绿色屏障。受自然条件和人为因素的影响,清河水库生态环境逐渐退化,因而清河水源涵养区生态功能保护势在必行。按照自然环境的现状特点、社会发展的需求及生态功能保护与恢复的基本要求,在生态功能分区的基础上,制定分区保护措施,并提出清河水源涵养区生态功能保护建设的具体方案。通过实施保护和修复,防止生态环境的破坏和生态功能的进一步退化,对地区可持续发展起到积极的推动作用。  相似文献   
926.
从2001年8月到2002年8月对藏东南察隅河上游流域内的大中型兽类动物资源现状进行了野外调查,对其捕猎状况进行了社区调查。主要调查了灵长目、食肉目和偶蹄目共21种动物,确认了一物种分布新记录。调查发现,数量最多的是羚牛、鬣羚等偶蹄类动物,种类数量最多的是食肉类动物,但其数量稀少,有的可能已经灭绝。调查发现,捕猎是威胁当地野生大中型动物生存的最直接和最大的因素,另外,它们还受到林区人为活动和栖息地破坏等不利因素的威胁。论文把保护当地野生动物与发展当地经济结合起来考虑,并提出了6点保护建议。  相似文献   
927.
林锡奎  刘平  程炯 《生态环境》2006,15(2):439-442
互联网上有大量的水土保持信息资源,其内容极为丰富,但要从这大量的信息中快速获得所需要的信息却很困难。文章介绍了国内外主要水土保持信息资源的网址及有关水土保持电子论坛、水土保持专利等方面的信息交流与检索途径,并在此基础上对水土保持信息资源的应用及发展前景提出建议。  相似文献   
928.
Marine protected areas (MPAs) are the cornerstone of most marine conservation strategies, but the effectiveness of each one partly depends on its size and distance to other MPAs in a network. Despite this, current recommendations on ideal MPA size and spacing vary widely, and data are lacking on how these constraints might influence the overall spatial characteristics, socio‐economic impacts, and connectivity of the resultant MPA networks. To address this problem, we tested the impact of applying different MPA size constraints in English waters. We used the Marxan spatial prioritization software to identify a network of MPAs that met conservation feature targets, whilst minimizing impacts on fisheries; modified the Marxan outputs with the MinPatch software to ensure each MPA met a minimum size; and used existing data on the dispersal distances of a range of species found in English waters to investigate the likely impacts of such spatial constraints on the region's biodiversity. Increasing MPA size had little effect on total network area or the location of priority areas, but as MPA size increased, fishing opportunity cost to stakeholders increased. In addition, as MPA size increased, the number of closely connected sets of MPAs in networks and the average distance between neighboring MPAs decreased, which consequently increased the proportion of the planning region that was isolated from all MPAs. These results suggest networks containing large MPAs would be more viable for the majority of the region's species that have small dispersal distances, but dispersal between MPA sets and spill‐over of individuals into unprotected areas would be reduced. These findings highlight the importance of testing the impact of applying different MPA size constraints because there are clear trade‐offs that result from the interaction of size, number, and distribution of MPAs in a network.  相似文献   
929.
Systematic conservation planning aims to design networks of protected areas that meet conservation goals across large landscapes. The optimal design of these conservation networks is most frequently based on the modeled habitat suitability or probability of occurrence of species, despite evidence that model predictions may not be highly correlated with species density. We hypothesized that conservation networks designed using species density distributions more efficiently conserve populations of all species considered than networks designed using probability of occurrence models. To test this hypothesis, we used the Zonation conservation prioritization algorithm to evaluate conservation network designs based on probability of occurrence versus density models for 26 land bird species in the U.S. Pacific Northwest. We assessed the efficacy of each conservation network based on predicted species densities and predicted species diversity. High‐density model Zonation rankings protected more individuals per species when networks protected the highest priority 10‐40% of the landscape. Compared with density‐based models, the occurrence‐based models protected more individuals in the lowest 50% priority areas of the landscape. The 2 approaches conserved species diversity in similar ways: predicted diversity was higher in higher priority locations in both conservation networks. We conclude that both density and probability of occurrence models can be useful for setting conservation priorities but that density‐based models are best suited for identifying the highest priority areas. Developing methods to aggregate species count data from unrelated monitoring efforts and making these data widely available through ecoinformatics portals such as the Avian Knowledge Network will enable species count data to be more widely incorporated into systematic conservation planning efforts.  相似文献   
930.
Sustainability standards and certification serve to differentiate and provide market recognition to goods produced in accordance with social and environmental good practices, typically including practices to protect biodiversity. Such standards have seen rapid growth, including in tropical agricultural commodities such as cocoa, coffee, palm oil, soybeans, and tea. Given the role of sustainability standards in influencing land use in hotspots of biodiversity, deforestation, and agricultural intensification, much could be gained from efforts to evaluate and increase the conservation payoff of these schemes. To this end, we devised a systematic approach for monitoring and evaluating the conservation impacts of agricultural sustainability standards and for using the resulting evidence to improve the effectiveness of such standards over time. The approach is oriented around a set of hypotheses and corresponding research questions about how sustainability standards are predicted to deliver conservation benefits. These questions are addressed through data from multiple sources, including basic common information from certification audits; field monitoring of environmental outcomes at a sample of certified sites; and rigorous impact assessment research based on experimental or quasi‐experimental methods. Integration of these sources can generate time‐series data that are comparable across sites and regions and provide detailed portraits of the effects of sustainability standards. To implement this approach, we propose new collaborations between the conservation research community and the sustainability standards community to develop common indicators and monitoring protocols, foster data sharing and synthesis, and link research and practice more effectively. As the role of sustainability standards in tropical land‐use governance continues to evolve, robust evidence on the factors contributing to effectiveness can help to ensure that such standards are designed and implemented to maximize benefits for biodiversity conservation.  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