全文获取类型
收费全文 | 473篇 |
免费 | 110篇 |
国内免费 | 94篇 |
专业分类
测绘学 | 26篇 |
大气科学 | 133篇 |
地球物理 | 255篇 |
地质学 | 77篇 |
海洋学 | 94篇 |
天文学 | 20篇 |
综合类 | 35篇 |
自然地理 | 37篇 |
出版年
2024年 | 5篇 |
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 22篇 |
2016年 | 22篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 32篇 |
2012年 | 20篇 |
2011年 | 21篇 |
2010年 | 30篇 |
2009年 | 21篇 |
2008年 | 23篇 |
2007年 | 30篇 |
2006年 | 18篇 |
2005年 | 24篇 |
2004年 | 32篇 |
2003年 | 17篇 |
2002年 | 22篇 |
2001年 | 31篇 |
2000年 | 45篇 |
1999年 | 33篇 |
1998年 | 38篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有677条查询结果,搜索用时 31 毫秒
671.
The green–blue swing: plasticity of plankton food‐webs in response to coastal oceanographic dynamics
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Domenico D'Alelio Maria Grazia Mazzocchi Marina Montresor Diana Sarno Adriana Zingone Iole Di Capua Gayantonia Franzè Francesca Margiotta Vincenzo Saggiomo Maurizio Ribera d'Alcalà 《Marine Ecology》2015,36(4):1155-1170
The internal organization of plankton communities plays a key role in biogeochemical cycles and in the functioning of aquatic ecosystems. In this study, the structure of a marine plankton community (including both unicellular and multicellular organisms) was inferred by applying an ecological network approach to species abundances observed weekly at the long‐term ecological research station MareChiara (LTER‐MC) in the Gulf of Naples (Tyrrhenian Sea, Mediterranean Sea) in the summers of 2002–2009. Two distinct conditions, characterized by different combination of salinity and chlorophyll values, alternated at the site: one influenced by coastal waters, herein named ‘green’, and the other reflecting more offshore conditions, named ‘blue’. The green and blue ‘phases’ showed different keystone biological elements: namely, large diatoms and small‐sized flagellates, respectively. Several correlations amongst species belonging to different trophic groups were found in both phases (connectance ~0.30). In the green phase, several links between phytoplankton and mesozooplankton and within the latter were detected, suggesting matter flow from microbes up to carnivorous zooplankton. A microbial‐loop‐like sub‐web, including mixo‐ and heterotrophic dinoflagellates and ciliates, was present in the green phase, but it was relatively more important in the blue phase. The latter observation suggests a more intense cycling of matter at the microbial trophic level in the blue phase. These results show that different modes of ecological organization can emerge from relatively small changes in the composition of aquatic communities coping with environmental variability. This highlights a significant plasticity in the internal structure of plankton webs, which should be taken into account in predictions of the potential effects of climatic oscillations on aquatic ecosystems and biogeochemical cycles therein. 相似文献
672.
利用变分同化技术,将船舶报资料与海表面温度短期数值预报模式有机结合,实现了渤、黄、东海的海表面温度短期数值预报。本预报模式利用伴随方法实现了预报模式的全局优化,不但最大限度地利用了船舶报资料,而且初始温度场的调整由自动的数值迭代过程来实现。在渤、黄、东海海域,4个季节的典型月份的SST连续1个月的24h后报结果与船舶报资料均方差均降至0.8℃以下。同化后海表面温度初始场的绝均差较同化前有显著下降。与以前所用的客观分析方法比较的结果表明,伴随同化的预报精度明显高于客观分析方法。 相似文献
673.
The Influences of Thermodynamic Characteristics on Aerodynamic Roughness Length over Land Surface
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
It has previously been shown that aerodynamic roughness length changes significantly along with nearsurface atmospheric thermodynamic state; however, at present, this phenomenon remains poorly understood, and very little research concerning this topic has been conducted. In this paper, by using the data of different underlying surfaces provided by the Experimental Co-observation and Integral Research in Semi-arid and Arid Regions over North China, aerodynamic roughness length (z0) values in stable, neutral, and unstable atmospheric stratifications are compared with one another, and the relationship between z0 and atmospheric thermodynamic stability (ζ) is analyzed. It is found that z0 shows great differences among the stable, neutral, and unstable atmospheric thermodynamic states, with the difference in z0 values between the fully thermodynamic stable condition and the neutral condition reaching 60% of the mean z0. Furthermore, for the wind speed range in which the wind data are less sensitive to z0, the surface z0 changes more significantly with ζ, and is highly correlated with both the Monin-Obukhov stability (ζ0) and the overall Richardson number (Rib), with both of their correlation coefficients greater than 0.71 and 0.47 in the stable and unstable atmospheric stratification, respectively. The empirical relation fitted with the experimental observations is quite consistent with the Zilitinkevich theoretical relation in the stable atmosphere, but the two are quite distinct and even show opposite variation tendencies in the unstable atmosphere. In application, however, verification of the empirical fitted relations by using the experimental data finds that the fitted relation is slightly more applicable than the Zilitinkevich theoretical relation in stable atmospheric stratification, but it is much more suitable than the Zilitinkevich relation in unstable atmospheric stratification. 相似文献
674.
采用偏最小二乘回归建立了前汛期(4-6月)月降水量的预测模型,其中模型的输入因子是通过对3个前期月平均物理量场(海温场、500 hPa温度场和200 hPa高度场)大量的场相关因子采用系统降维的处理方法获得.为实现同时对多个站点的月降水量预测,将多站点的月降水量预测转换成多站点气候场的主分量预测,进一步利用气候场特征向量的近似不变性进行回算,从而得到多站点的逐站月降水量预测结果.对广西37个基本站的前汛期月降水量进行了6年独立样本检验,其预报结果显示该模型具有较好的预报能力. 相似文献
675.
风沙流和净风场中瞬时水平风速廓线特征比较 总被引:1,自引:1,他引:0
为进一步认识风沙流和净风场中瞬时水平风速廓线特征的异同,在风洞中分别对风沙流和净风场中瞬时水平风速廓线进行了测量,风速采集时间间隔缩短至0.01s,分析了风沙流和净风场中瞬时水平风速、瞬时摩阻风速和瞬时空气动力学粗糙度的变化特征。结果表明:相同来流条件下,风沙流中水平风速脉动强度高于净风场,风沙流中瞬时摩阻风速、瞬时空气动力学粗糙度以及它们的脉动幅度均大于净风场;风沙流和净风场中瞬时摩阻风速概率密度分布均可以表示为正态分布,但其正态分布的特征值却存在一定差别;净风场中瞬时空气动力学粗糙度的概率密度分布表现出单调递减分布,而风沙流中瞬时空气动力学粗糙度的概率密度分布呈现出单峰分布。因此,在相同主流风速下风沙流和净风场中瞬时水平风速廓线特征有明显差别。 相似文献
676.
677.