全文获取类型
收费全文 | 10355篇 |
免费 | 2241篇 |
国内免费 | 1533篇 |
出版年
2024年 | 14篇 |
2023年 | 496篇 |
2022年 | 255篇 |
2021年 | 431篇 |
2020年 | 819篇 |
2019年 | 797篇 |
2018年 | 732篇 |
2017年 | 785篇 |
2016年 | 745篇 |
2015年 | 723篇 |
2014年 | 745篇 |
2013年 | 800篇 |
2012年 | 568篇 |
2011年 | 523篇 |
2010年 | 510篇 |
2009年 | 645篇 |
2008年 | 613篇 |
2007年 | 551篇 |
2006年 | 476篇 |
2005年 | 431篇 |
2004年 | 355篇 |
2003年 | 263篇 |
2002年 | 232篇 |
2001年 | 203篇 |
2000年 | 214篇 |
1999年 | 142篇 |
1998年 | 143篇 |
1997年 | 95篇 |
1996年 | 103篇 |
1995年 | 115篇 |
1994年 | 89篇 |
1993年 | 66篇 |
1992年 | 46篇 |
1991年 | 43篇 |
1990年 | 36篇 |
1989年 | 25篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 28篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 24篇 |
1982年 | 38篇 |
1981年 | 19篇 |
1980年 | 29篇 |
1979年 | 27篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1958年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
《农业工程》2014,34(2):106-109
Nature reserve has been served as the important pathway for biodiversity conservation and carbon storage. Global climate change is an indisputable fact and impacted the biodiversity and nature reserve. How nature reserves adapt to climate change has drawn more and more concerns. This research conducted questionnaires of 68 national nature reserves from 24 provincial regions, and the questionnaires showed that all surveyed nature reserves experienced climate change, and 68.57%, 61.43% and 68.57% of nature reserves, respectively, considered warming temperature, precipitation change, and occurrence of extreme climate events as new threats to them. These new factors directly threat the distribution range and survival of endangered species, change of ecosystem function, enhance of pest and disease damages, and directed damage the infrastructures. However, most of the surveyed nature reserves did not consider the systematic monitoring the facts of climate change, and lack actions and strategies of initiative adaptation to climate change. At last, we proposed the strategies for nature reserves to adapt to climate change, including enhancing the monitoring on the impact of climate change, making scientific planning and designing for development of nature reserves, decreasing the pressure through sustainable development, and enhancing the scientific research and the investment to improve the ability of nature reserves to adapt to climate change. 相似文献
102.
103.
Metabolic approaches to understanding climate change impacts on seasonal host‐macroparasite dynamics
Climate change is expected to alter the dynamics of infectious diseases around the globe. Predictive models remain elusive due to the complexity of host–parasite systems and insufficient data describing how environmental conditions affect various system components. Here, we link host–macroparasite models with the Metabolic Theory of Ecology, providing a mechanistic framework that allows integrating multiple nonlinear environmental effects to estimate parasite fitness under novel conditions. The models allow determining the fundamental thermal niche of a parasite, and thus, whether climate change leads to range contraction or may permit a range expansion. Applying the models to seasonal environments, and using an arctic nematode with an endotherm host for illustration, we show that climate warming can split a continuous spring‐to‐fall transmission season into two separate transmission seasons with altered timings. Although the models are strategic and most suitable to evaluate broad‐scale patterns of climate change impacts, close correspondence between model predictions and empirical data indicates model applicability also at the species level. As the application of Metabolic Theory considerably aids the a priori estimation of model parameters, even in data‐sparse systems, we suggest that the presented approach could provide a framework for understanding and predicting climatic impacts for many host–parasite systems worldwide. 相似文献
104.
冰川景观变化是全球环境和气候变化的共同"指示器"。随着全球气候变化加剧,干旱和半干旱地区的冰川景观将进一步变化。科学评估冰川景观格局时空演变特征,为应对冰川景观变化及其影响提供科学参考。基于1991-2017年Landsat TM/ETM+/OLI遥感影像,采用监督分类方法获取叶尔羌河流域冰川景观时空格局及变化数据,利用景观格局指数、质心迁移模型、分形维数等方法分析近26年叶尔羌河流域冰川景观格局时空演变特征。结果表明:(1)1991-2017年叶尔羌河流域冰川斑块面积呈消减趋势,但有所减缓,共减少799.50 km2(-13.09%)。冰川斑块面积消减主要集中在海拔5400-5800 m之间,相较之下,海拔4400 m以下的区域冰川斑块面积消减率最高,达63.68%;不同坡度冰川景观消减率存在差异,陡坡冰川斑块面积消减率最高(15.98%),急陡坡消减率最低(2.87%);阴阳两坡冰川景观均呈消减趋势,阳坡冰川斑块面积消减速率显著高于阴坡。(2)近26年来,叶尔羌河流域冰川斑块数量、最大斑块指数均减小,而平均形状指数、平均周长面积比、分裂指数均增加,表明冰川景观不断消减,破碎化程度增加。(3)研究期间,叶尔羌河流域冰川景观质心发生迁移,整体呈现东北偏移趋势。(4)通过分形理论对叶尔羌河流域冰川景观空间结构特征进行分析表明,该流域冰川景观消减率略微降低,但仍然处于持续消融状态。 相似文献
105.
基于MODIS NDVI的长江中游区域植被动态及与气候因子的关系 总被引:1,自引:0,他引:1
基于1999-2015年的MODIS NDVI时间序列遥感数据,应用趋势分析、变异系数、重标极差分析和偏相关分析等方法,分析了长江中游的植被时空变化特征及其与气象因子的关系。结果表明,长江中游地区NDVI均值总体上呈上升趋势(从0.72增加到0.80)。从空间分布来看,NDVI低值区域(0.1-0.5)占1.40%,高值区域(>0.7)占87.15%;NDVI空间格局呈"西高东低、北高南低"的分布特征,低值区域表现为以三省省会城市为中心向外辐射。Hurst指数显示,研究区大部分区域(60.54%)的NDVI变化趋势具有不确定性,持续性改善区域(34.78%)主要分布在西部山地区,持续性退化区域(3.26%)主要分布在人类活动频繁的较发达城市区域。在年际尺度上,研究区NDVI与各气象因子关系均不显著;月际尺度上,NDVI与降水、相对湿度和日照时数显著相关,降水和日照时数有明显的时滞性。区域内NDVI动态趋势以不确定性发展为主,城市群周边NDVI呈现持续退化的区域应该引起关注。 相似文献
106.
107.
108.
109.
R. Pampanini 《Plant biosystems》2013,147(1):199-219
Abstract Bryophytes are excellent indicator organisms for monitoring environmental changes to which they could be more sensitive than vascular plants but our knowledge on their adaptation to alpine conditions is still very poor. Research programmes were set up to establish the ecological parameters for bryophyte distribution along the altitudinal gradient as well as for a better understanding of the population biology of alpine bryophytes. 相似文献
110.
《Current biology : CB》2021,31(23):5385-5392.e4