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   30379篇
  免费   270篇
  国内免费   201篇
安全科学   637篇
废物处理   1623篇
环保管理   4524篇
综合类   4401篇
基础理论   8205篇
环境理论   14篇
污染及防治   6579篇
评价与监测   2284篇
社会与环境   2411篇
灾害及防治   172篇
  2022年   139篇
  2021年   169篇
  2020年   136篇
  2019年   188篇
  2018年   1787篇
  2017年   1728篇
  2016年   1638篇
  2015年   486篇
  2014年   476篇
  2013年   1819篇
  2012年   1089篇
  2011年   2207篇
  2010年   1442篇
  2009年   1352篇
  2008年   1813篇
  2007年   2205篇
  2006年   814篇
  2005年   715篇
  2004年   690篇
  2003年   793篇
  2002年   748篇
  2001年   639篇
  2000年   530篇
  1999年   336篇
  1998年   286篇
  1997年   249篇
  1996年   277篇
  1995年   281篇
  1994年   266篇
  1993年   270篇
  1992年   284篇
  1991年   242篇
  1990年   251篇
  1989年   215篇
  1988年   183篇
  1987年   168篇
  1986年   196篇
  1985年   197篇
  1984年   220篇
  1983年   215篇
  1982年   192篇
  1981年   206篇
  1980年   193篇
  1979年   167篇
  1978年   128篇
  1977年   137篇
  1974年   116篇
  1973年   98篇
  1972年   113篇
  1971年   97篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
291.
This paper describes a method for determining reductions of SO2 emissions from coal- and oil-fired power stations, oil refineries and large industrial units in the UK taking into account their pollution potential. The method is based on the use of two gridded data sets: critical loads, which represent the sensitivity of the environment to acid deposition and modelled estimates of total (wet + dry) sulphur deposition for 646 point sources within the UK. An iterative method is used to identify and subsequently reduce emissions from point sources that contribute most to areas of critical loads exceedance. This paper demonstrates how the method may be used to determine an optimal allocation of emissions across the UK which yields the maximum amount of environmental protection per unit of emission.The paper then goes on to consider the changes that will have to take place within the UK power generation industry in order to meet the revised EC Large Combustion Plant Directive which comes into force on 1 January 2008. Particular emphasis is placed upon proposed emissions trading schemes and the environmental implications of allowing trading between stations with high and low pollution potentials. The paper concludes by suggesting that the emissions trading process should take into account the pollution potential of each source, irrespective of whether the proposed emission is within the plant's agreed emission limit. An approach based entirely on minimizing environmental damage rather than one which takes cost into account, as in current integrated assessment modelling, could provide an interesting approach across the rest of Europe.  相似文献   
292.
A United Nations Framework Convention on Climate Change (UNFCCC) Joint Implementation (JI) host country has to make sure that JI projects are additional to avoid extra costs to generate the reductions necessary to cover the deduction of Emission Reduction Units (ERUs) from the country’s Kyoto Protocol emissions budget. A tender of ERUs by the government allows to generate additional reductions beyond the ERUs issued if it thoroughly checks project additionality. The government of New Zealand is running a tender for JI projects under the title “Projects to Reduce Emissions” since 2003. In two rounds, 10 million ERUs have been awarded and several projects have already entered into contracts with European buyers. The ratio of ERUs awarded to reductions achieved was 0.8 in the second tender. However it remains to be seen whether the additionality test of this tender is sufficient to exclude clearly non-additional projects.  相似文献   
293.
Sustainable resource management is the critical agricultural research and development challenge in sub-Saharan Africa. The accumulated knowledge on soil management gathered over the last 10 years, combined with solid crop improvement and plant health research at farmers’ level, has brought us to a stage where we can now address with confidence the intensification of cereal–grain–legume-based cropping systems in the dry savanna of West Africa in a sustainable and environmentally positive manner.Two sustainable farming systems that greatly enhance the productivity and sustainability of integrated livestock systems have been developed and implemented in the dry savanna of Nigeria. These are: (i) maize (Zea mays L.)–promiscuous soybean [Glycine max (L.) Merr.] rotations that combine high nitrogen fixation and the ability to kill large numbers of Striga hermonthica seeds in the soil; and (ii) miflet [Eleusine coracana (L.) Gaerth] and dual-purpose cowpea [Vigna unguiculata (L.) Walp.]. Improvement of the cropping systems in the dry savanna has been driven by the adoption of promiscuously nodulating soybean varieties (in particular TGx 1448-2E) and dual-purpose cowpea. The rate of adoption is very high, even in the absence of an efficient seed distribution system. The number of farmers cultivating the improved varieties increased by 228% during the last 3 years. Increased production of promiscuous soybean has been stimulated by increased demand from industries and home utilization. Production in Nigeria was estimated at 405,000 t in 1999 compared to less than 60,000 t in 1984. Economic analysis of these systems shows already an increase of 50–70% in the gross incomes of adopting farmers compared to those still following the current practices, mainly continuous maize cultivation. Furthermore, increases in legume areas of 10% in Nigeria (about 30,000 ha in the northern Guinea savanna) and increases of 20% in yield have translated into additional fixed nitrogen valued annually at US$ 44 million. This reflects, at the same time, an equivalent increase in land-use productivity, and with further spread of the improved crops, there are excellent prospects for additional economic and environmental benefits from a very large recommendation domain across West Africa.  相似文献   
294.
295.
296.
297.
298.
299.
300.
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