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   3515篇
  免费   82篇
  国内免费   42篇
安全科学   178篇
废物处理   138篇
环保管理   953篇
综合类   308篇
基础理论   845篇
环境理论   2篇
污染及防治   846篇
评价与监测   208篇
社会与环境   132篇
灾害及防治   29篇
  2023年   17篇
  2022年   30篇
  2021年   39篇
  2020年   36篇
  2019年   45篇
  2018年   72篇
  2017年   68篇
  2016年   115篇
  2015年   75篇
  2014年   88篇
  2013年   386篇
  2012年   130篇
  2011年   192篇
  2010年   156篇
  2009年   159篇
  2008年   176篇
  2007年   182篇
  2006年   162篇
  2005年   98篇
  2004年   130篇
  2003年   128篇
  2002年   110篇
  2001年   66篇
  2000年   57篇
  1999年   56篇
  1998年   44篇
  1997年   50篇
  1996年   55篇
  1995年   60篇
  1994年   47篇
  1993年   47篇
  1992年   34篇
  1991年   37篇
  1990年   39篇
  1989年   32篇
  1988年   34篇
  1987年   31篇
  1986年   42篇
  1985年   28篇
  1984年   42篇
  1983年   33篇
  1982年   38篇
  1981年   34篇
  1980年   22篇
  1979年   20篇
  1978年   16篇
  1977年   15篇
  1976年   15篇
  1974年   11篇
  1972年   10篇
排序方式: 共有3639条查询结果,搜索用时 15 毫秒
21.
The design of environmental monitoring programs is frequently hampered by a lack of objective, quantitative criteria for evaluating alternative monitoring variables. In this paper we describe two such criteria, which we call samples required — the number of samples required to detect a given change in value — and information imparted — the amount of environmental information revealed by the monitoring variable. We then use these criteria to evaluate fin erosion in winter flounder (Pleuronectes americanus) and Dover sole (Microstomus pacificus) as marine environmental monitoring variables. Two methods for determining the samples required use contaminated and reference areas to estimate the sample statistics of a hypothetical impacted population. The first method is based on the overall difference in the proportions of diseased fish in the reference and hypothetical populations. The second treats the proportion of diseased fish in individual trawls as the variate and determines the samples required based on the mean and variance of the reference and contaminated populations. We use both methods to predict the number of trawls needed to detect an increase of 200% in fin erosion in the reference population. The first method had greater statistical power but assumes spatially homogeneous populations. The second method accounts for environmental patchiness. For Dover sole it predicted 1661 trawls would be needed to detect the 200% increase. An estuarine winter flounder population would require 74 trawls, and an oceanic winter flounder population would require 142.5 trawls. It appears that fin erosion in winter flounder may be a useful indicator of environmental contamination, but several stipulations apply. Migration may inflate the number of diseased fish observed in the reference population, and a more detailed etiology of the disease is required, including an understanding of what contaminants are responsible for manifestation of the disease.  相似文献   
22.
Large, complex energy models present considerable challenges to develop and test. Uncertainty assessments of such models provide only partial guidance on the quality of the results. We have developed a model quality assistance checklist to aid in this purpose. The model checklist provides diagnostic output in the form of a set of pitfalls for the model application. The checklist is applied here to an energy model for the problem of assessing energy use and greenhouse gas emissions. Use of the checklist suggests that results on this issue are contingent on a number of assumptions that are highly value-laden. When these assumptions are held fixed, the model is deemed capable of producing moderately robust results of relevance to climate policy over the longer term. Checklist responses also indicate that a number of details critical to policy choices or outcomes on this issue are not captured in the model, and model results should therefore be supplemented with alternative analyses.  相似文献   
23.
本文研究了米达河(南纬3°20',东经40°00')两个红树林森林地区(乌永博和基雷普维)带状横断面的红树林植被的结构和恢复型式.  相似文献   
24.
25.
A case is presented in which percutaneous umbilical sampling (PUBS) was utilized in the second and third trimesters for the diagnosis and management of a pregnancy at risk for neonatal alloimmune thrombocytopenia (NAIT).  相似文献   
26.
A national interregional linear programming model of U.S. agriculture is used to evaluate and compare two conventional and three organic production alternatives. The objective is to estimate the effects on production, supply prices, land use, farm income, and export potential, of a complete transformation of U.S. agriculture to organic practices. Crop yields and production costs are estimated for 150 producing regions for seven crops under both conventional and organic methods. Results indicate that compared with conventional methods, widespread organic farming leads to a decrease in total production, lower export potential, higher supply prices, higher value of production, lower costs of production, and higher net farm income. The United States domestic crop demand can be met with organic methods, but would be more expensive. Some interregional shifts in crop production would also occur.  相似文献   
27.
The long time scale of the climate change problem and the inherent nature of the carbon cycle bring important implications for present technology development efforts. Even if major technology improvements are achieved for non-carbon-emitting technologies such as energy-intensity improvements, wind, solar, biomass, and nuclear over the course of the 21st century, most examinations of potential future greenhouse emissions conclude that additional technology development will be required to stabilize greenhouse gas concentrations. The evelopment of an expanded suite of technologies including carbon capture and disposal, hydrogen systems and biotechnology hold the potential to dramatically reduce the cost of stabilizing greenhouse gas concentrations. This paper examines these technologies in the context of a global integrated assessment model of energy, agriculture, land-use, economics, and carbon cycle processes.  相似文献   
28.
This paper considers relationships between sustainability objectives, transport, spatial design of the built environment and rational use of energy. Conventional transport modelling, housing supply and energy assessment tools are drawn together to provide a common platform for appraisal of city-wide energy use by stationary and mobile sources. The paper outlines methodologies developed for the city of Belfast, Northern Ireland. The paper concludes by briefly reviewing the effect in terms of mobile and stationary energy consumption and travel behaviour of implementing sustainable policy measures in current and future years within the study area.  相似文献   
29.
This work presents a framework for viewing agricultural adaptation, emphasizing the multiple spatial and temporal scales on which individuals and institutions process information on changes in their environment. The framework is offered as a means to gain perspective on the role of climate variability and change in agricultural adaptation, and developed for a case study of Australian agriculture. To study adaptation issues at the scale of individual farms we developed a simple modelling framework. The model highlights the decision making element of adaptation in light of uncertainty, and underscores the importance of decision information related to climate variability. Model results show that the assumption of perfect information for farmers systematically overpredicts adaptive performance. The results also suggest that farmers who make tactical planting decisions on the basis of historical climate information are outperformed by those who use even moderately successful seasonal forecast information. Analysis at continental scales highlights the prominent role of the decline in economic operating conditions on Australian agriculture. Examples from segments of the agricultural industry in Australia are given to illustrate the importance of appropriate scale attribution in adapting to environmental changes. In particular, adaptations oriented toward short time scale changes in the farming environment (droughts, market fluctuations) can be limited in their efficacy by constraints imposed by broad changes in the soil/water base and economic environment occuring over longer time scales. The case study also makes the point that adaptation must be defined in reference to some goal, which is ultimately a social and political exercise. Overall, this study highlights the importance of allowing more complexity (limited information, risk aversion, cross-scale interactions, mis-attribution of cause and effect, background context, identification of goals) in representing adaptation processes in climate change studies.  相似文献   
30.
While true mosaicism occurs in only 0–25 per cent of genetic amniocenteses, nearly 2–5 per cent of amniotic fluid cell cultures contain a second cell line. In the common practice of prenatal diagnosis, an aberrant cell line confined to a single colony is usually disregarded. We present a case of mosaic trisomy 14 which was not detected on initial chromosome analysis. At birth, multiple malformations were apparent. Newborn cytogenetic studies revealed mosaicism [46,XX/46,XX,-14,+i(14q)] with an isochromosome 14 in 37 per cent of lymphocytes. Additional cells from the initial amniotic fluid culture were analysed post-delivery and the isochromosome 14 identified in only one of 12 total colonies. This case illustrates two important lessons in prenatal diagnosis. First, amniotic fluid cell cultures may not accurately reflect the relative distribution of the normal and abnormal cell lines within a mosaic fetus. Second, while it is generally reasonable to disregard mosaicism confined to a single colony, this policy will, on rare occasion, result in diagnostic error. This should be taken into consideration, particularly when dealing with autosomal trisomies potentially compatible with livebirth.  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