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   30520篇
  免费   350篇
  国内免费   458篇
安全科学   962篇
废物处理   1441篇
环保管理   3716篇
综合类   5079篇
基础理论   8005篇
环境理论   18篇
污染及防治   8075篇
评价与监测   2079篇
社会与环境   1773篇
灾害及防治   180篇
  2023年   141篇
  2022年   322篇
  2021年   316篇
  2020年   241篇
  2019年   289篇
  2018年   481篇
  2017年   482篇
  2016年   747篇
  2015年   569篇
  2014年   886篇
  2013年   2445篇
  2012年   1062篇
  2011年   1441篇
  2010年   1177篇
  2009年   1204篇
  2008年   1443篇
  2007年   1495篇
  2006年   1267篇
  2005年   1100篇
  2004年   985篇
  2003年   1080篇
  2002年   954篇
  2001年   1239篇
  2000年   865篇
  1999年   519篇
  1998年   348篇
  1997年   360篇
  1996年   357篇
  1995年   424篇
  1994年   452篇
  1993年   352篇
  1992年   377篇
  1991年   353篇
  1990年   387篇
  1989年   345篇
  1988年   301篇
  1987年   281篇
  1986年   225篇
  1985年   250篇
  1984年   268篇
  1983年   260篇
  1982年   241篇
  1981年   225篇
  1980年   177篇
  1979年   199篇
  1978年   176篇
  1975年   140篇
  1974年   117篇
  1972年   131篇
  1971年   131篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
272.
Wood-pastures are associated with high cultural and biodiversity values in Europe. However, due to their relatively low productivity, large areas of wood-pastures have been lost over the last century. In some areas, incentive schemes have been developed to revive wood-pastures. We investigated the effects of one such scheme in western Estonia. We compared the structure of grazed wood-pastures (old and restored) to those of abandoned wood-pastures and ungrazed forest stands to explore the effects of management, and conducted interviews with 24 farmers to investigate their motivations to carry out the management. We found a positive influence of active management on the semi-open structure of wood-pastures. Financial support was vital for management, but personal values related to tradition also played an important role. The interviewees differed widely in their range of motivations, suggesting that other strategies in addition to financial incentives would further improve the management of wood-pastures in the region.

Electronic supplementary material

The online version of this article (doi:10.1007/s13280-015-0719-8) contains supplementary material, which is available to authorized users.  相似文献   
273.
Concentrations of eight elements were measured in Chelonia mydas and Lepidochelys olivacea eggs collected along the Pacific coast of Panama. Manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), and mercury (Hg) concentrations were similar to previous reports of these species from around the world, while lead (Pb) was lower than previous reports. Cd posed the highest health risk to people who regularly eat the eggs, with average consumption rates leading to target hazard quotients (THQ) of up to 0.35 ± 0.15. Our conclusions indicate that current turtle egg consumption in isolated, coastal Pacific communities may pose a health concern for young children, and that youth and young adults should limit their consumption of turtle eggs to reduce their total intake of nonessential metals.  相似文献   
274.
275.
Dried leaves are a potential source of energy although these are not commonly used beside to satisfy daily energy demands in rural areas. This paper aims at preparing a leafy biomass feedstock in the form of briquettes which can be directly used for combustion or to extract the combustible gas using a gasifier. Teak (Tectona grandis) and rubber (Hevea brasiliensis) leaves are considered for the present study. A binder-assisted briquetting technique with tapioca starch as binder is adopted. Properties of these leafy biomass briquettes such as moisture content, calorific value, compressive strength, and shatter index are determined. From the study, briquettes with biomass-to-binder ratio of 3:5 are found to be stable. Higher mass percentage of binder is considered for preparation of briquettes due to the fact that leafy biomasses do not adhere well on densification with lower binder content. Ultimate analysis test is conducted to analyze the gasification potential of the briquettes. Results show that the leafy biomass prepared from teak and rubber leaves has calorific values of 17.5 and 17.8 MJ/kg, respectively, which are comparable with those of existing biomass feedstock made of sawdust, rice husk, and rice straw.  相似文献   
276.
277.
Environmental Science and Pollution Research - The objective of this study was to monitor a newly constructed wetland (CW) in north Wales, UK, to assess whether it contributes to an improvement in...  相似文献   
278.
The population of foxes in the central regions of Yakutia has grown by a factor of four to five during the period from 2000 to 2011–2012, following an increase in the abundance of voles from the genus Microtus. A total of 130 carcasses of foxes taken in 2007–2012 have been examined. Age- and sex-related variation in morphological features has been described. The demographic structure of the population has been studied by estimating animal age from annual layers in the recording structures. Changes in female fertility and involvement in reproduction depending on age and feeding conditions have been analyzed. Changes in the composition of fox diet caused by long-term population depression in the mountain hare and their effect on the dynamics of fox abundance have been revealed. Age- and sex-related characteristics of the condition factor in foxes and sex-related differences in their dietary preferences have been demonstrated.  相似文献   
279.
Communities of benthic macroinvertebrates in drainless Lake Chany, the largest lake in Western Siberia, have been analyzed to estimate the effects of basic abiotic ecological factors (hydrophysical and hydrochemical parameters of water and the type of bottom ground) on their composition, structure, and dynamics. It has been shown that the level of development of these communities depends mainly on the water regime of the lake and also on the type of bottom ground, lake depth, and water mineral content.  相似文献   
280.
The role of ecotones with different (sharp or smooth) spatial boundaries between forest and meadow in ant biodiversity preservation was studied at the right-of-way of a power line in the Voronezh Reserve. The ecotone with a sharp boundary between forest and meadow (transitional zone 2 m wide) had higher species richness of ants compared to the ecotones (also 2 m wide) with smooth boundary between forest and meadow.  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