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   48569篇
  免费   4141篇
  国内免费   8篇
  52718篇
  2023年   240篇
  2021年   385篇
  2020年   333篇
  2019年   330篇
  2018年   929篇
  2017年   956篇
  2016年   1066篇
  2015年   979篇
  2014年   1152篇
  2013年   1992篇
  2012年   3182篇
  2011年   3518篇
  2010年   1836篇
  2009年   1225篇
  2008年   2886篇
  2007年   2943篇
  2006年   2742篇
  2005年   2514篇
  2004年   2408篇
  2003年   2245篇
  2002年   2240篇
  2001年   1593篇
  2000年   1791篇
  1999年   1035篇
  1998年   495篇
  1997年   404篇
  1996年   467篇
  1995年   405篇
  1994年   430篇
  1993年   380篇
  1992年   524篇
  1991年   440篇
  1990年   425篇
  1989年   399篇
  1988年   370篇
  1987年   379篇
  1986年   337篇
  1985年   405篇
  1984年   456篇
  1983年   401篇
  1982年   366篇
  1981年   336篇
  1980年   303篇
  1979年   314篇
  1978年   303篇
  1977年   285篇
  1976年   279篇
  1975年   336篇
  1974年   273篇
  1973年   256篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
Biomechanics and Modeling in Mechanobiology - The load distribution among lumbar spinal structures—still an unanswered question—has been in the focus of this hybrid experimental and...  相似文献   
995.
996.
The interacting effects of global changes—including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes—are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient‐poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient‐poor Swedish lakes over 16 years (1998–2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon‐specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria.  相似文献   
997.
Ecosystems - Patterns of animal migration and the ecological forces that shape them have been studied for centuries. Yet ecological impacts caused by the migration, such as altered...  相似文献   
998.
Root-associated fungi (RAF) link nutrient fluxes between soil and roots and thus play important roles in ecosystem functioning. To enhance our understanding of the factors that control RAF, we fitted statistical models to explain variation in RAF community structure using data from 150 temperate forest sites covering a broad range of environmental conditions and chemical root traits. We found that variation in RAF communities was related to both root traits (e.g., cations, carbohydrates, NO3) and soil properties (pH, cations, moisture, C/N). The identified drivers were the combined result of distinct response patterns of fungal taxa (determined at the rank of orders) to biotic and abiotic factors. Our results support that RAF community variation is related to evolutionary adaptedness of fungal lineages and consequently, drivers of RAF communities are context-dependent.  相似文献   
999.
1000.
Vegetation History and Archaeobotany - Waldgirmes in Hesse (Germany) is one of the oldest Roman towns east of the Rhine River. It was founded in 3 bc and abandoned after ad 9, probably in ad 16,...  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