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   913篇
  免费   15篇
  国内免费   20篇
安全科学   70篇
废物处理   25篇
环保管理   183篇
综合类   139篇
基础理论   275篇
环境理论   3篇
污染及防治   156篇
评价与监测   59篇
社会与环境   29篇
灾害及防治   9篇
  2023年   7篇
  2022年   7篇
  2021年   11篇
  2020年   10篇
  2019年   18篇
  2018年   13篇
  2017年   31篇
  2016年   36篇
  2015年   24篇
  2014年   25篇
  2013年   64篇
  2012年   28篇
  2011年   50篇
  2010年   31篇
  2009年   39篇
  2008年   56篇
  2007年   44篇
  2006年   47篇
  2005年   36篇
  2004年   25篇
  2003年   33篇
  2002年   28篇
  2001年   22篇
  2000年   19篇
  1999年   13篇
  1998年   15篇
  1997年   20篇
  1996年   11篇
  1995年   14篇
  1994年   14篇
  1993年   16篇
  1992年   12篇
  1991年   9篇
  1990年   5篇
  1989年   7篇
  1988年   10篇
  1987年   13篇
  1986年   4篇
  1985年   15篇
  1984年   9篇
  1983年   7篇
  1982年   10篇
  1981年   7篇
  1980年   7篇
  1979年   7篇
  1978年   5篇
  1977年   6篇
  1976年   2篇
  1974年   3篇
  1969年   1篇
排序方式: 共有948条查询结果,搜索用时 250 毫秒
881.
A review of wetland impacts authorized under the New Jersey Freshwater Wetlands Protection Act (FWPA) was conducted based on permitting data compiled for the period 1 July 1988 to 31 December 1993. Data regarding the acreage of wetlands impacted, location of impacts by drainage basin and watershed, and mitigation were analyzed. Wetland impacts authorized and mitigation under New Jersey's program were evaluated and compared with Section 404 information available for New Jersey and other regions of the United States.Under the FWPA, 3003 permits were issued authorizing impacts to 234.76 ha (602.27 acres) of wetlands and waters. Compensatory mitigation requirements for impacts associated with individual permits required the creation of 69.20 ha. (171.00 acres), and restoration of 16.49 ha (40.75 acres) of wetlands. Cumulative impacts by watershed were directly related to levels of development and population growth.The FWPA has resulted in an estimated 67% reduction [44.32 ha (109.47 acres) vs 136.26 ha (336.56 acres)] in annual wetland and water impacts when compared with Section 404 data for New Jersey. For mitigation, the slight increase in wetland acreage over acreage impacted is largely consistent with Section 404 data.Based on this evaluation, the FWPA has succeeded in reducing the level of wetland impacts in New Jersey. However, despite stringent regulation of activities in and around wetlands, New Jersey continues to experience approximately 32 ha (79 acres) of unmitigated wetland impacts annually. Our results suggest that additional efforts focusing on minimizing wetland impacts and increasing wetlands creation are needed to attain a goal of no net loss of freshwater wetlands.  相似文献   
882.
Based on intergroup theory, this study examined relationships among group characteristics (racioethnicity, gender, and level), contextual organizational unit characteristics (gender and racioethnic heterogeneity, resource support for women and racioethnic minorities) and perceptions of diversity climate by faculty at a large university. Compared to white men, white women and racioethnic minorities placed greater value on employer efforts to promote diversity, and held more favorable attitudes about the qualifications of women and racioethnic minorities. The study found that group rather than contextual organizational unit characteristics were more strongly related to diversity climate. However, the organizational unit characteristic, gender heterogeneity, was significantly related to valuing diversity. The greater the ratio of women in a unit, regardless of the respondents' gender, racioethnicity or level, the more favorable diversity activities were viewed. In addition, units whose allocation of resources to racioethnic minorities were perceived as insufficient by respondents were more likely to have members who valued diversity and held favorable perceptions toward the qualifications of racioethnic minorities. Implications for organizations and future research are offered.  相似文献   
883.
Many public programs have differential impacts on diverse parts of metropolitan areas. This fact has led analysts to use changes in land values as measures of the benefits of public programs. Using a model derived from theoretical urban economics, this paper demonstrates that changes in land values will only equal total benefits under very restrictive assumptions. Making concrete assumptions about consumer demand, the paper goes beyond previous work to consider the distributional impact of three different kinds of public programs: those which provide uniform benefits to every community, those which attempt to reduce intercommunity inequality, and those which generate improvements in only a subset of the region's towns.  相似文献   
884.
The National Oceanic Data Center (NODC) contains historical records from approximately 144,000 hydrographic stations in the North Atlantic. This data has been used by oceanographers to construct maps of point estimates of pressure, temperature, salinity and oxygen in the North Atlantic (Levitus (1994); Lozier et al. (1995)). Because data from any particular year are scarce, the previous maps have been for time-averaged values only. In addition, the maps have been reported without uncertainty estimates. This paper presents a Markov random field (MRF) analysis that can generate maps for specific time periods along with associated uncertainties. To estimate changes in oceanic properties over time previous oceanographic work has focused on differences between a few time periods each having many observations. Due to data scarcity this poses a severe restriction for both spatial and temporal coverage of climatic change. The MRF analysis provides a means for temporal modeling that does not require high data density at each time period. To demonstrate the usefulness of a MRF analysis of oceanic data we investigate the temporal variability along 24.5°N in the North Atlantic. Our results are compared to an earlier analysis (Parrilla et al. (1994)) where data from only three time periods was used. We obtain a more thorough understanding of the temperature change found by this previous study.  相似文献   
885.
886.
887.
888.
889.
890.
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