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   96430篇
  免费   1751篇
  国内免费   3397篇
安全科学   4286篇
废物处理   3552篇
环保管理   14426篇
综合类   25225篇
基础理论   27219篇
环境理论   78篇
污染及防治   16178篇
评价与监测   5736篇
社会与环境   4116篇
灾害及防治   762篇
  2023年   606篇
  2022年   1233篇
  2021年   1197篇
  2020年   1071篇
  2019年   1164篇
  2018年   1434篇
  2017年   1546篇
  2016年   2576篇
  2015年   2266篇
  2014年   3062篇
  2013年   9831篇
  2012年   2764篇
  2011年   3062篇
  2010年   3722篇
  2009年   3838篇
  2008年   2456篇
  2007年   2215篇
  2006年   2576篇
  2005年   2442篇
  2004年   2722篇
  2003年   2548篇
  2002年   2096篇
  2001年   2316篇
  2000年   2121篇
  1999年   1593篇
  1998年   1468篇
  1997年   1430篇
  1996年   1542篇
  1995年   1621篇
  1994年   1511篇
  1993年   1363篇
  1992年   1338篇
  1991年   1296篇
  1990年   1249篇
  1989年   1198篇
  1988年   1044篇
  1987年   972篇
  1986年   991篇
  1985年   1067篇
  1984年   1165篇
  1983年   1160篇
  1982年   1175篇
  1981年   1097篇
  1980年   942篇
  1979年   925篇
  1978年   817篇
  1977年   716篇
  1976年   637篇
  1973年   632篇
  1972年   636篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
7.
Abstract:  Introduction of artificial light into wildlife habitat represents a rapidly expanding form of human encroachment, particularly in coastal systems. Light pollution alters the behavior of sea turtles during nesting; therefore, long-wavelength lights—low-pressure sodium vapor and bug lights—that minimize impacts on turtles are required for beach lighting in Florida (U.S.A.). We investigated the effects of these two kinds of lights on the foraging behavior of Santa Rosa beach mice (  Peromyscus polionotus leucocephalus ). We compared patch use and giving-up densities of mice for experimental food patches established along a gradient of artificial light in the field. Mice exploited fewer food patches near both types of artificial light than in areas with little light and harvested fewer seeds within patches near bug lights. Our results show that artificial light affects the behavior of terrestrial species in coastal areas and that light pollution deserves greater consideration in conservation planning.  相似文献   
8.
The genetic polymorphism of natural populations of Lepilemur mustelinus ruficaudatus was studied by protein electrophoresis. We sampled blood from 72 individuals from four populations separated by geographic or anthropogenic barriers from southwestern Madagascar. Six out of 22 enzyme loci showed genetic variation with a degree of polymorphism of 0.273. The expected and observed degree of genetic heterozygosity over all loci is similar to that of other primates (He = 0.058, Ho = 0.036). The F-statistics revealed that the four subpopulations were similar with respect to gene structure (FST = 0.065, p = 0.016), but the genotypic structures within subpopulations were inconsistent with random mating. For the total of the four subpopulations the proportion of heterozygous individuals was significantly smaller than expected under random mating (FIS = 0.373, FIT = 0.414, p < 0.01). These results correspond closely to what is expected considering the low migration ability of individuals of L. m ruficaudatus leading to small and rather isolated inbred populations.  相似文献   
9.
10.
Abstract: Coffee farms can support significant biodiversity, yet intensification of farming practices is degrading agricultural habitats and compromising ecosystem services such as biological pest control. The coffee berry borer (Hypothenemus hampei) is the world's primary coffee pest. Researchers have demonstrated that birds reduce insect abundance on coffee farms but have not documented avian control of the berry borer or quantified avian benefits to crop yield or farm income. We conducted a bird‐exclosure experiment on coffee farms in the Blue Mountains, Jamaica, to measure avian pest control of berry borers, identify potential predator species, associate predator abundance and borer reductions with vegetation complexity, and quantify resulting increases in coffee yield. Coffee plants excluded from foraging birds had significantly higher borer infestation, more borer broods, and greater berry damage than control plants. We identified 17 potential predator species (73% were wintering Neotropical migrants), and 3 primary species composed 67% of migrant detections. Average relative bird abundance and diversity and relative resident predator abundance increased with greater shade‐tree cover. Although migrant predators overall did not respond to vegetation complexity variables, the 3 primary species increased with proximity to noncoffee habitat patches. Lower infestation on control plants was correlated with higher total bird abundance, but not with predator abundance or vegetation complexity. Infestation of fruit was 1–14% lower on control plants, resulting in a greater quantity of saleable fruits that had a market value of US$44–$105/ha in 2005/2006. Landscape heterogeneity in this region may allow mobile predators to provide pest control broadly, despite localized farming intensities. These results provide the first evidence that birds control coffee berry borers and thus increase coffee yield and farm income, a potentially important conservation incentive for producers.  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