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   675篇
  免费   59篇
  国内免费   191篇
安全科学   118篇
废物处理   13篇
环保管理   112篇
综合类   382篇
基础理论   92篇
污染及防治   92篇
评价与监测   54篇
社会与环境   36篇
灾害及防治   26篇
  2024年   4篇
  2023年   13篇
  2022年   26篇
  2021年   31篇
  2020年   31篇
  2019年   27篇
  2018年   22篇
  2017年   21篇
  2016年   34篇
  2015年   50篇
  2014年   40篇
  2013年   64篇
  2012年   56篇
  2011年   47篇
  2010年   40篇
  2009年   46篇
  2008年   45篇
  2007年   49篇
  2006年   28篇
  2005年   36篇
  2004年   29篇
  2003年   32篇
  2002年   27篇
  2001年   10篇
  2000年   10篇
  1999年   14篇
  1998年   10篇
  1997年   8篇
  1996年   2篇
  1995年   7篇
  1994年   9篇
  1993年   10篇
  1992年   5篇
  1991年   3篇
  1990年   7篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   5篇
  1984年   6篇
  1983年   3篇
  1982年   5篇
  1981年   1篇
  1979年   2篇
  1977年   2篇
  1974年   2篇
  1972年   1篇
  1969年   1篇
排序方式: 共有925条查询结果,搜索用时 585 毫秒
231.
The resource curse   总被引:7,自引:0,他引:7  
Countries that possess rich mineral deposits, it is widely assumed, are fortunate. Such deposits are assets, part of a country's natural capital. Mining is the key that converts dormant mineral wealth into schools, homes, ports, and other forms of capital that directly contribute to economic development. Over the past two decades, however, a more negative view of mining has emerged that questions the positive relationship between mineral extraction and economic development. The impetus for the alternative view came from empirical studies suggesting that countries where mining is important have not grown as rapidly as other countries. More recent studies have explored the possible reasons behind the disappointing performance of many mineral producing countries. While the central point of contention between the conventional and alternative views — namely, whether or not mining usually promotes economic development — remains unresolved, there is widespread agreement that rich mineral deposits provide developing countries with opportunities, which in some instances have been used wisely to promote development, and in other instances have been misused, hurting development. The consensus on this issue is important, for it means that one uniform policy toward all mining in the developing world is not desirable, despite the recent suggestions by some to the contrary. The appropriate public policy question is not should we or should we not promote mining in the developing countries, but rather where should we encourage it and how can we ensure that it contributes as much as possible to economic development and poverty alleviation.  相似文献   
232.
Much of the world's remaining mineral resources lie within the underdeveloped nations of the Third World. The current crisis of confidence characterized in international investment and trade in extractive resources has become detrimental to both the resource-rich developing countries and the resource-hungry industrialized countries. Japan is one nation that has developed a strategy to foster mutual trust and to restore confidence in the international extractive industries. This paper examines Japan's develop-for-import policy, ‘kaihatsu yunso’, and its design, implementation and effects on securing foreign resources supplies.  相似文献   
233.
Within the context of a case study of three Asia/Pacific countries' mineral taxation regimes, this article examines the impact of individual fiscal instrucments, and the total fiscal package, on investor risk perceptions, investor returns and government receipts. It shows that under conditions of uncertainty and risk aversion on the part of investors, significant gains in expected government revenues can be achieved without seriously affecting the investors' ex-ante assessments of projects by a judicious selection and mix of fiscal instruments.  相似文献   
234.
A novel technology for the removal of nitrogen from wastewater, autotrophic denitrification process with sulfur particle, has been developed. A respirometer was employed for the monitoring of nitrogen gas produced in the reactor. It was found that the autotrophic denitrification studied by gas production rate and nitrate depletion rate followed a first order reaction from the relationship. The reaction rate constant based on effective volume, kN was ranged from 2.67 to 3.07 h–1. The effective height was around 23.8 and 50% of the total height for 11.8 and 5.9 h of packed bed contact time, respectively. It was assumed that the reaction rate constants were similar in each experimental condition, PBCT = 11.9 and 5.9 h because there was little gradient of biomass concentration within 50% of the total height. The respirometry was found to be a simple and fast way to monitor the denitrification process. The method was especially useful for the determination of kinetic parameters.  相似文献   
235.
Long-term trends (i.e., 1985 through 1999; 14 1/2 yrs) of the phytoplankton community in Chesapeake Bay indicated patterns of increasing phytoplankton abundance and biomass associated with mainly diatoms and chlorophytes, and to a lesser degree dinoflagellates. Decreasing trends in productivity rates above the pycnocline were present over a shorter time period (10 1/2 yrs.), with evidence for increasing nitrogen limitation is indicated. Reduced light availability is inferred due to decreasing trends of Secchi depths and increased suspended solids trends, which were associated with decreasing trends in productivity rates.  相似文献   
236.
兰江流域水文动力参数变化与兰江防洪   总被引:2,自引:1,他引:2  
本文根据钱塘江重要干流兰江的地面蓄水累计曲线SPER、流域入渗曲线Holton公式参数(入渗率f、稳定入渗率fc、入渗比例系数k)、Maskingum指数(流水河段传播时间k、楔蓄系数x)、水位与水量等近30年的抽样数据,分析了兰江流域河槽导流环境、植被条件、土地性质、气象因素的变化,指出了该河段近年来洪水频发的原因,提出了治理建议.  相似文献   
237.
长江南通段江面风的观测分析   总被引:4,自引:0,他引:4  
通过在长江南通段江面、江岸建立风观测站,并在江岸建设80m高的风梯度观测塔,与邻近气象站开展了较长时间的风同步观测,获得了实地观测数据.利用同步风观测数据进行对比分析,揭示出长江南通段江面风的观测事实,并利用风梯度观测资料,分析给出了风随高度的变化规律.在此基础上,结合邻近气象站长年的风观测资料,推算了该处的设计基本风速及其他工程设计风参数.分析表明,该处江面风况明显有别于邻近气象站,风参数计算结果也明显高于风工程理论推算值.  相似文献   
238.
MapInfo是目前流行的地理信息系统 (GIS)应用软件之一 ,由于其强大的地图功能 ,在地震监测预报中得到了越来越广泛的应用。安徽省地震局合肥遥测台网不久前完成了台网自己的速报软件的开发研制工作 ,其中运用了MapInfo部分图形操作功能。本文介绍MapInfo技术在台肥遥测台网地震速报中的一些具体应用  相似文献   
239.
ABSTRACT: This paper presents the results of a statistical analysis performed for the watershed and stream corridor in the South Fork of the Clearwater River (SFCR) basin, in north central Idaho. The analysis was performed for 61 six‐field hydrological unit codes (HUCs) of the SFCR basin using an extensive record (up to 100 years) for 50 watershed and in‐stream parameters, including hydrologic, flow, fish, anthropogenic, and natural activity data. The objective of this research was twofold: first, the development of quantitative relations that describe the Index of Fish Density (IFD) of particular fish species as a function of watershed and instream parameters; and second, to provide a robust confirmation for the effects of some of these parameters, previously recorded by the fisheries profession, by using well established statistical techniques. The uniqueness of this work is the compilation and statistical analysis of large data sets to quantitatively describe the impacts of watershed and instream parameters on the IFD of all salmonids and specific fish species. Factor analysis was employed to regroup parameters that are highly correlated to each other into a set of single factors and to relate the IFD to these factors. Using factor extraction, 12 factors were developed from the 50 watershed and instream parameters. Multiple regression diagnostic tests indicated that only 7 of the 12 factors are strong predictors offish indicators. The strongest predictors are longitude, latitude, elevation, watershed gradient, and water temperature. The analysis indicated that the present model has reasonable predictive power, considering the uncertainty involved in estimating the interdependence of IFD with watershed parameters.  相似文献   
240.
粉煤灰静电脱炭技术研究   总被引:1,自引:0,他引:1  
本文介绍粉煤灰静电脱炭资源化利用技术的试验研究.利用YNDF-I型立式电场粉煤灰脱炭装置进行优化试验,提出电压、极板间距、摩擦分散器材料、粉尘浓度及气体流量等运行工艺特性参数与静电脱炭率的相关关系.试验结果表明,该立式电场脱炭装置在最优工艺参数条件下运行时,可使粉煤灰脱炭后的精灰含炭量降低到1.20%,脱炭率达86.74%,能够直接代替水泥用作建筑材料或修筑公路路面,具有较高的经济效益、社会效益和环境效益,为粉煤灰资源化利用提供了一种新的途径.  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