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   25527篇
  免费   162篇
  国内免费   191篇
安全科学   641篇
废物处理   991篇
环保管理   2791篇
综合类   6780篇
基础理论   5710篇
环境理论   15篇
污染及防治   6146篇
评价与监测   1576篇
社会与环境   1122篇
灾害及防治   108篇
  2022年   208篇
  2019年   211篇
  2018年   328篇
  2017年   349篇
  2016年   529篇
  2015年   398篇
  2014年   606篇
  2013年   1758篇
  2012年   660篇
  2011年   930篇
  2010年   773篇
  2009年   844篇
  2008年   982篇
  2007年   953篇
  2006年   865篇
  2005年   776篇
  2004年   759篇
  2003年   726篇
  2002年   700篇
  2001年   909篇
  2000年   591篇
  1999年   417篇
  1998年   278篇
  1997年   285篇
  1996年   285篇
  1995年   323篇
  1994年   324篇
  1993年   274篇
  1992年   292篇
  1991年   319篇
  1990年   324篇
  1989年   288篇
  1988年   251篇
  1987年   209篇
  1986年   234篇
  1985年   235篇
  1984年   243篇
  1983年   231篇
  1982年   242篇
  1981年   249篇
  1980年   204篇
  1979年   214篇
  1978年   193篇
  1976年   178篇
  1973年   181篇
  1967年   215篇
  1966年   175篇
  1965年   189篇
  1964年   192篇
  1963年   177篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
Implementing the UNCCD: Participatory challenges   总被引:1,自引:0,他引:1  
The United Nations Convention to Combat Desertification (UNCCD) emphasizes the need for public participation in land degradation assessment and rehabilitation. While participatory approaches are supported by a growing body of research and practice, meaningfully involving the people affected by land degradation is far from straightforward. This paper investigates the challenge of using the UNCCD as a guide to influence community participation in policy‐making and practice at national and local levels by analyzing experiences from three southern African countries. We show that the UNCCD represents a useful normative framework for addressing degradation problems, but that the participatory ethos is difficult to enact at the national level. Whilst there is increasing evidence that combining local and scientific knowledge using participatory mechanisms can deliver the benefits that the Convention strives to achieve, communication between researchers and practitioners, and those involved in implementing the UNCCD at the national level needs to be strengthened. Broad lessons and best practices in incorporating participatory practices into policy development are elucidated. Our case studies show that a range of mixed‐method, interdisciplinary approaches can enable policy‐makers and practitioners to meaningfully engage those who are affected by land degradation in its definition, assessment and rehabilitation.  相似文献   
222.
Current methods for large-scale vegetation monitoring rely on multispectral remote sensing, which has serious limitation for the detection of vegetation stress. To contribute to the establishment of a generalized spectral approach for vegetation stress detection, this study compares the ability of high-spectral-resolution reflectance (R) and fluorescence (F) foliar measurements to detect vegetation changes associated with common environmental factors affecting plant growth and productivity. To obtain a spectral dataset from a broad range of species and stress conditions, plant material from three experiments was examined, including (i) corn, nitrogen (N) deficiency/excess; (ii) soybean, elevated carbon dioxide, and ozone levels; and (iii) red maple, augmented ultraviolet irradiation. Fluorescence and R spectra (400-800 nm) were measured on the same foliar samples in conjunction with photosynthetic pigments, carbon, and N content. For separation of a wide range of treatment levels, hyperspectral (5-10 nm) R indices were superior compared with F or broadband R indices, with the derivative parameters providing optimal results. For the detection of changes in vegetation physiology, hyperspectral indices can provide a significant improvement over broadband indices. The relationship of treatment levels to R was linear, whereas that to F was curvilinear. Using reflectance measurements, it was not possible to identify the unstressed vegetation condition, which was accomplished in all three experiments using F indices. Large-scale monitoring of vegetation condition and the detection of vegetation stress could be improved by using hyperspectral R and F information, a possible strategy for future remote sensing missions.  相似文献   
223.
The introduction of potentially invasive species is a concern to the public and the aquaculture industry. Used to protect channel catfish from infectious trematode infestations, the non-indigenous black carp has been evaluated by the US Fish and Wildlife Service (USFWS) and deemed potentially ‘injurious’ under the terms of the Lacey Act. Consequently, the black carp may be restricted from interstate commerce and eventually removed from US waters. An alternative approach to evaluating the risks posed by invasive species is considered and compared to that used by the USFWS. Short of outright restriction, reasonable options for management of such invasive species probably exist, including better use of environmental assurance bonds and return-deposit models.  相似文献   
224.
225.
226.
227.
Summary In Kumaun Himalaya, India, 60 percent of the rural population is dependent on natural springs for water supply. The authors claim that substantial reductions in spring water discharges are due to losses in the indigenous oak forest coverage and its partial replacement by pine. Other factors, such as overall forest cover depletion and construction activities, combine to produce severe reductions in spring discharge rates.Drs Anil Singh and Ravindra Pande are members of academic staff at Kumaun University working in the Laboratory for Hydrological and Geomorphological Investigations in the Department of Geography.  相似文献   
228.
This article addresses the development of an agricultural productivity equation for predicting new soil (neo-sol) plant growth potential in Clay County, Minnesota, USA. Soil factors examined in the study include percent organic matter, percent slope, percent rock fragments, hydraulic conductivity, electrical conductivity, pH, topographic position, available water-holding capacity, bulk density, and percent clay. Squared terms and two-factor interaction terms were also examined as possible regressors. A best equation was selected that had a multiple coefficient of determination of 0.7399 and has five significant regressors and intercept withP.0001. The regressors are hydraulic conductivity, percent slope squared, bulk density times percent rock fragments, electrical conductivity times percent rock fragments, and electrical conductivity times percent organic matter. The regressors predict soil suitability for a general crop model. The crops included in the model are wheat, oats, barley, soybeans, sugar beets, sunflowers, and grasses/legumes.  相似文献   
229.
230.
Summary Plants and animals were investigated to ascertain their- radioactivity values on both dune sites (machair) and inter-tidal sites on the western coast of Barra, Outer Hebrides, UK. Material in both habitats was clearly contaminated. The accumulation of-radioactivity through food webs to organisms such asNucella lapillus (dog whelk) in the inter-tidal sites and in sheep and cattle in terrestrial sites is described.Dr F.B. Pyatt is the Section Leader and Principal Lecturer in Ecology in the Department of Life Sciences at Trent Polytechnic. Dr E.H. Beaumont was previously Lecturer in Zoology at St Hugh's College, University of Oxford, Oxford, UK.  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