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   101051篇
  免费   1237篇
  国内免费   1160篇
安全科学   3956篇
废物处理   3726篇
环保管理   15263篇
综合类   21615篇
基础理论   27887篇
环境理论   75篇
污染及防治   19813篇
评价与监测   6039篇
社会与环境   4396篇
灾害及防治   678篇
  2022年   831篇
  2021年   838篇
  2020年   671篇
  2019年   895篇
  2018年   1312篇
  2017年   1350篇
  2016年   2301篇
  2015年   1878篇
  2014年   2639篇
  2013年   9328篇
  2012年   2658篇
  2011年   3327篇
  2010年   3493篇
  2009年   3648篇
  2008年   2974篇
  2007年   2905篇
  2006年   3016篇
  2005年   2813篇
  2004年   3114篇
  2003年   2984篇
  2002年   2545篇
  2001年   3044篇
  2000年   2396篇
  1999年   1662篇
  1998年   1429篇
  1997年   1418篇
  1996年   1546篇
  1995年   1650篇
  1994年   1536篇
  1993年   1389篇
  1992年   1386篇
  1991年   1362篇
  1990年   1305篇
  1989年   1268篇
  1988年   1113篇
  1987年   1033篇
  1986年   1011篇
  1985年   1095篇
  1984年   1190篇
  1983年   1194篇
  1982年   1187篇
  1981年   1119篇
  1980年   962篇
  1979年   964篇
  1978年   840篇
  1977年   742篇
  1976年   669篇
  1974年   656篇
  1973年   682篇
  1972年   695篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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   
72.
73.
74.
75.
工业革命以来,全球环境发生了前所未有的变化,将可能给地球系统带来灾难性后果,究其原因主要是由于人类活动造成的。人的行为深受意识的影响和制约,环境意识对于环境问题的产生和解决至关重要。本文选取上海、香港两个地区来分析公民对环境的关注度、公民的环保意识、环保行为以及公民对政府环境工作的看法和评价,研究公民对全球环境变化反应的区域差异,为政府制定相关环境保护政策提供理论依据。调查结果显示,上海、香港两地公民在很多环境闷题上具有共识。但是。在对手环境状况好转的期待值、参与环境保护活动的积极性、对人为因素主导力量的认识、环境保护与日常生活的切实关系、为环境保护的支付意愿、对于环境教育内容的认可度等方面存在着一定的差异。  相似文献   
76.
77.
A statistical analysis of interannual variation in a set of vegetative and generative characters over 13 years has been performed to characterize the growth and seed production dynamics of the Siberian stone pine (Pinus sibirica Du Tour) in the southeast of the forest zone in western Siberia. The results have shown that the range of fluctuations in most of vegetative characters is ordinary and their distribution is close to normal. The range of fluctuations in many generative characters is enormous (from 0 to +∞), and the distribution of their values is usually skewed, with low values being recorded several times more frequently than high values. Most variable are the proportion of abortive cones and other characters that are determined mainly in the spring of the pollination year. These characters account for a very high level of variation in the total seed production.  相似文献   
78.
79.
While the world is going into different tourism expectations, the tourism understanding in Turkey is defined as tourism in the sea-sand-sun triangle. However, it is possible to contribute to the income and local development of the indigenous people by developing nature-based tourism. Besides, with the sustainable use and preservation of the natural-cultural assets, the damage of the traditional tourism industry on the natural and cultural environment could be reduced. In this study, it is aimed to bring up the nature-based tourism concept in Çanakkale by evaluating the nature-based tourism industry in the general of Turkey and assessing the natural-cultural resources that Çanakkale comprehends. The most important areas that have a nature-based tourism potential in Çanakkale and the tourism activities that are most suitable for these areas have been determined.  相似文献   
80.
Phylogenetic relationships and genetic population structures were analyzed for tideland gastropods in the genus Cerithidea around Japan on the basis of partial sequence of the mitochondrial COI gene. Large genetic divergence was shown between individuals of Cerithidea cingulata in the southern Ryukyus and those in the central Ryukyus and the Japanese Islands. Haplotypes of C. cingulata from the Japanese Islands were paraphyletic with the exclusion of a monophyletic group from the central Ryukyus. Genetic differentiation of C. cingulata was also detected between Amami-Oshima Island and Okinawajima Island. No genetic divergence was found between Cerithidea rhizophorarum in the Japanese Islands and its subspecies C. rhizophorarum morchii in the Ryukyu Islands. The lack of genetic divergence of Cerithidea largillierti between continental China and Japan suggests relatively recent migration between the Japanese Islands and the Asian continent. For all three Cerithidea species distributed in both the Japanese Islands and the Ryukyu Islands, the Tokara Gap and the Kerama Gap were shown to have acted as barriers to the dispersal.  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