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   37736篇
  免费   387篇
  国内免费   287篇
安全科学   1056篇
废物处理   1452篇
环保管理   5156篇
综合类   6522篇
基础理论   10337篇
环境理论   26篇
污染及防治   9763篇
评价与监测   2200篇
社会与环境   1654篇
灾害及防治   244篇
  2022年   251篇
  2021年   252篇
  2019年   269篇
  2018年   491篇
  2017年   479篇
  2016年   718篇
  2015年   612篇
  2014年   849篇
  2013年   2767篇
  2012年   1061篇
  2011年   1553篇
  2010年   1265篇
  2009年   1325篇
  2008年   1553篇
  2007年   1686篇
  2006年   1485篇
  2005年   1247篇
  2004年   1262篇
  2003年   1208篇
  2002年   1173篇
  2001年   1496篇
  2000年   1076篇
  1999年   691篇
  1998年   501篇
  1997年   519篇
  1996年   525篇
  1995年   585篇
  1994年   536篇
  1993年   486篇
  1992年   503篇
  1991年   476篇
  1990年   460篇
  1989年   493篇
  1988年   441篇
  1987年   389篇
  1986年   342篇
  1985年   372篇
  1984年   385篇
  1983年   405篇
  1982年   415篇
  1981年   346篇
  1980年   315篇
  1979年   348篇
  1978年   289篇
  1977年   251篇
  1976年   259篇
  1975年   255篇
  1974年   247篇
  1973年   221篇
  1972年   250篇
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
471.
The restoration of surface mining landscapes requires the (re)creation of ecosystems. In Lusatia (eastern Germany), large-scale open-cast lignite mining operations generated spoil dumps widely consisting of acidified, phytotoxic substrates. Amelioration and rehabilitation measures have been developed and applied to these substrates since the 1950s. However, it is still not clear whether these approaches are sustainable. This paper reports on collaborative research work into the ecological potential of forest ecosystem development on typical minesites in the Lusatian lignite district. At first sight, pine stands on minesites along a chronosequence comprising about 35 years did not show differences when compared with stands on non-mined sites of the general region. Furthermore, with some modification, conceptual models for flora and fauna succession in forest stands on non-mined sites seem to be applicable, at least for the early stages of forest ecosystem development. For example, soil organism abundance and activity at minesites had already reached levels typical of non-mined sites after about 20-30 years. In contrast, mine soils are very different from non-mined soils of the test region. Chemically, mine soil development is dominated by processes originating from pyrite oxidation. Geogenic, i.e. lignitic, soil organic carbon was shown to substitute for some functions of pedogenic soil organic matter. Rooting was hampered but not completely impeded in strongly acidified soil compartments. Roots and mycorrhizae are apparently able to make use of the characteristic heterogeneity of young mine soils. Considering these recent results and the knowledge accumulated during more than 30 years of research on minesite rehabilitation internationally, it can be stated that minesite restoration might be used as an ideal case study for forest ecosystem development starting at "point zero" on "terra nova".  相似文献   
472.
We have determined the activity of alkaline phosphatase in chorionic villous tissue obtained in the first trimester of pregnancy, in order to obtain the normal range of values as a prerequisite for application to the prenatal diagnosis of the rare bone disease hypophosphatasia. The activities found were a combination of intestinal and liver/bone/kidney types; traces of placental type were present in only one sample.  相似文献   
473.
Prenatal counselling for fetal agenesis of the corpus callosum is difficult as the prognosis until now has been so uncertain. We have reviewed the current world English literature to provide the best probabilistic information for prospective parents. In total, there are 70 cases where the diagnosis was made prenatally. The diagnosis of apparently isolated agenesis of the corpus callosum (in the absence of other sonographically detectable anomalies) appears to carry an excellent prognosis, with an 85 per cent chance of a normal developmental outcome and a 15 per cent risk of handicap. Fetal karyotyping is recommended as there is a 1 in 10 risk of aneuploidy. If other anomalies are detected prenatally, the outcome is very poor. Termination of pregnancy is advised in these circumstances.  相似文献   
474.
475.
476.
477.
478.
479.
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   
480.
The rate of carbon accumulation in the atmosphere can be reduced by decreasing emissions from the burning of fossil fuels and by increasing the net uptake (or reducing the net loss) of carbon in terrestrial (and aquatic) ecosystems. The Kyoto Protocol addresses both the release and uptake of carbon. Canada is developing a National Forest Carbon Monitoring, Accounting and Reporting System in support of its international obligations to report greenhouse gas sources and sinks. This system employs forest-inventory data, growth and yield information, and statistics on natural disturbances, management actions and land-use change to estimate forest carbon stocks, changes in carbon stocks, and emissions of non-CO2 greenhouse gases. A key component of the system is the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS). The model is undergoing extensive revisions to enable analyses at four spatial scales (national, provincial, forest management unit and stand) and in annual time steps. The model and the supporting databases can be used to assess carbon-stock changes between 1990 and the present, and to predict future carbon-stock changes based on scenarios of future disturbance rates and management actions.  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