全文获取类型
收费全文 | 4775篇 |
免费 | 806篇 |
国内免费 | 646篇 |
专业分类
测绘学 | 745篇 |
大气科学 | 588篇 |
地球物理 | 1629篇 |
地质学 | 1119篇 |
海洋学 | 574篇 |
天文学 | 414篇 |
综合类 | 425篇 |
自然地理 | 733篇 |
出版年
2024年 | 13篇 |
2023年 | 57篇 |
2022年 | 119篇 |
2021年 | 150篇 |
2020年 | 158篇 |
2019年 | 209篇 |
2018年 | 152篇 |
2017年 | 190篇 |
2016年 | 194篇 |
2015年 | 201篇 |
2014年 | 236篇 |
2013年 | 260篇 |
2012年 | 279篇 |
2011年 | 284篇 |
2010年 | 230篇 |
2009年 | 305篇 |
2008年 | 260篇 |
2007年 | 338篇 |
2006年 | 329篇 |
2005年 | 256篇 |
2004年 | 235篇 |
2003年 | 223篇 |
2002年 | 177篇 |
2001年 | 181篇 |
2000年 | 147篇 |
1999年 | 142篇 |
1998年 | 172篇 |
1997年 | 96篇 |
1996年 | 94篇 |
1995年 | 97篇 |
1994年 | 100篇 |
1993年 | 85篇 |
1992年 | 57篇 |
1991年 | 41篇 |
1990年 | 26篇 |
1989年 | 48篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有6227条查询结果,搜索用时 15 毫秒
141.
142.
应用经验模式分解(EMD)将恒电量瞬态响应信号分解为不同时间尺度的内在模函数(IMF)分量。去除其中的小时间尺度的干扰噪声分量。然后经过拉普拉斯变换获得恒电量频谱以研究电化学腐蚀过程。 相似文献
143.
144.
145.
146.
147.
Statistical analysis and forecasts of long-term sandbank evolution at Great Yarmouth, UK 总被引:3,自引:1,他引:3
Dominic E. Reeve Jos M. Horrillo-Caraballo Vanesa Magar 《Estuarine, Coastal and Shelf Science》2008,79(3):387-399
A data-driven model has been developed to analyse the long-term evolution of a sandbank system and to make ensemble predictions in a period of 8 years. The method uses a combination of empirical orthogonal function (EOF) analysis, (to define spatial and temporal patterns of variability), jack-knife resampling, (to generate an ensemble of EOFs), a causal auto-regression technique, (to extrapolate the temporal eigenfunctions), and straightforward statistical analysis of the resulting ensemble of predictions to determine a ‘forecast’ and associated uncertainty. The methodology has been applied to a very demanding site which includes a curved shoreline and a group of mobile nearshore sandbanks. The site is on the eastern coast of the UK and includes the Great Yarmouth sandbanks and neighbouring shoreline. A sequence of 33 high quality historical survey charts reaching back to 1848 have been used to analyse the patterns and to predict morphological evolution of the sandbank system. The forecasts demonstrate an improved skill relative to an assumption of persistence, but suffer in locations where there are propagating features in the morphology that are not well-described by EOFs. 相似文献
148.
Robert E. Reed David A. Dickey JoAnn M. Burkholder Carol A. Kinder Cavell Brownie 《Estuarine, Coastal and Shelf Science》2008
Water level time series records from the Neuse and Pamlico River Estuaries were statistically compared to local and distant wind field data, water level records within the Pamlico Sound and also coastal ocean sites to determine the relative contribution of each time series to water levels in the Neuse and Pamlico Estuaries. The objectives of this study were to examine these time series data using various statistical methods (i.e. autoregressive, empirical orthogonal function analysis (EOF), exploratory data analysis (EDA)) to determine short- and long-time-scale variability, and to develop predictive statistical models that can be used to estimate past water level fluctuations in both the Neuse Estuary (NE) and Pamlico Estuary (PE). Short- and long-time-scale similarities were observed in all time series of estuarine, Pamlico Sound and subtidal coastal ocean water level and wind component data, due to events (nor'easters, fronts and tropical systems) and seasonality. Empirical orthogonal function analyses revealed a strong coastal ocean and wind field contribution to water level in the NE and PE. Approximately 95% of the variation was captured in the first two EOF components for water level data from the NE, sound and coastal ocean, and 70% for the PE, sound and coastal ocean. Spectral density plots revealed strong diurnal signals in both wind and water level data, and a strong cross correlation and coherency between the NE water level and the North/South wind component. There was good agreement between data and predictions using autoregressive statistical models for the NE (R2 = 0.92) and PE (R2 = 0.76). These methods also revealed significant autoregressive lags for the NE (days 1 and 3) and for the PE (days 1, 2 and 3). Significant departures from predictions are attributed to local meteorological and hydrological events. The autoregressive techniques showed significant predictive improvement over ordinary least squares methods. The results are considered within the context of providing long time-scale hindcast data for the two estuaries, and the importance of these data for multidisciplinary researchers and managers. 相似文献
149.
讨论了一类离散非线性系统降维观测器的存在性。对给定的Lyapunov函数,在保证观测误差渐近稳定的条件下,给出了该离散非线性系统降维观测器的设计方法。用数值例子说明了该设计方法的有效性。 相似文献
150.