全文获取类型
收费全文 | 2125篇 |
免费 | 607篇 |
国内免费 | 1331篇 |
专业分类
测绘学 | 36篇 |
大气科学 | 2134篇 |
地球物理 | 816篇 |
地质学 | 593篇 |
海洋学 | 76篇 |
天文学 | 3篇 |
综合类 | 90篇 |
自然地理 | 315篇 |
出版年
2024年 | 18篇 |
2023年 | 63篇 |
2022年 | 86篇 |
2021年 | 129篇 |
2020年 | 125篇 |
2019年 | 157篇 |
2018年 | 146篇 |
2017年 | 152篇 |
2016年 | 129篇 |
2015年 | 168篇 |
2014年 | 179篇 |
2013年 | 354篇 |
2012年 | 188篇 |
2011年 | 175篇 |
2010年 | 139篇 |
2009年 | 178篇 |
2008年 | 166篇 |
2007年 | 232篇 |
2006年 | 225篇 |
2005年 | 190篇 |
2004年 | 135篇 |
2003年 | 112篇 |
2002年 | 98篇 |
2001年 | 73篇 |
2000年 | 71篇 |
1999年 | 58篇 |
1998年 | 56篇 |
1997年 | 50篇 |
1996年 | 42篇 |
1995年 | 39篇 |
1994年 | 36篇 |
1993年 | 23篇 |
1992年 | 13篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4063条查询结果,搜索用时 15 毫秒
991.
The occurrence of rapid movement of suspended sediment in subsurface stormflow on a large field plot in California is described. Concentrations of over 1000mgl?1 were recorded in storms of only low to moderate intensity. The observed sediment was composed of uniformly fine-sized particles 4 to 8 μm in diameter. The mode of transport seems different from processes previously reported. Differences in sediment concentrations in different events, levels of 137Cs on the sediment, and several other types of evidence indicate that the sediment was detached and entrained at the ground surface by raindrop impact and that the water and sediment flow occurred mainly through macropores in the soil. As conditions similar to those at the study site are not uncommon, it seems probable that the phenomenon may occur in many regions. 相似文献
992.
利用降水、大气环流和海表温度等多种再分析资料和偏相关方法,研究了1951—2007年南太平洋年代际振荡(SPDO)和北太平洋年代际振荡(即PDO,本文称为NPDO)分别与华北盛夏(7—8月)降水在年代际时间尺度上的关系及其可能物理机制.结果表明:在去除SPDO和NPDO的相关性之前,它们与华北盛夏降水的关系均偏弱;但在去除两者相关性之后,SPDO(NPDO)与华北盛夏降水存在显著正(负)相关关系.去除两者相关性之后,当SPDO处于正位相时,热带西北太平洋海温异常显著偏暖,这将在对流层中下层从热带西太平洋—东亚沿岸激发出"气旋-反气旋-气旋"的负位相东亚—太平洋型遥相关(EAP)波列,该波列导致东亚夏季风异常增强,有利于低纬地区水汽输送至华北地区,从而使得华北盛夏降水异常偏多,反之,当SPDO处于负位相时,华北盛夏降水异常将偏少;对NPDO来说,当其处于正位相时,不仅热带西北太平洋异常显著偏冷,而且印度洋大部分海温异常显著偏暖,在两者共同作用下,对流层中下层从热带西太平洋—东亚沿岸出现"反气旋-气旋-反气旋"的正位相EAP波列,这将引起东亚夏季风异常减弱,不利于低纬地区水汽输送至华北地区,华北盛夏降水异常因此减少,反之,当NPDO处于负位相时,华北盛夏降水异常将偏多. 相似文献
993.
The empirical orthogonal functions have been obtained for the individual summer monsoon (June through September) months using
the grid point values of monthly 700 mb geopotential heights over Indian region. The data for 21 summer monsoon months for
the years 1958 to 1978 have been used in the present computation.
The major variance reduction is due to the first three dominant functions accounting over 80% of the total variance in each
month. The variance reduction only due to the first function ranges from 45 to 65%.
The first function has in-pbase oscillation throughout the area indicating that the area under study is homogeneous and the
centre of the oscillation lies over northwest India. The amplitudes of the first function also show generally quasipers stence
in their sign within a season. The second function has two centres of action over the region of monsoon trough which are in
phase. The third function has also two centres oriented in the east-west direction but they are in the opposite phase.
Fairly large values of correlation coefficients between the patterns of the different monsoon months suggest that the patterns
for these months corresponding to the first and the second functions respectively are quite similar. The patterns for these
months also evolve with time in a related way. The spectrum analysis to the time series of amplitudes indicates the presence
of the quasi-periodicity of 3 years during these monsoon months. The amplitudes corresponding to the dominant functions are
found to be significantly related with the rainfall of central and western parts of India 相似文献
994.
ZHANG Ming-li WEN Zhi DONG Jian-hua WANG De-kai YUE Guo-dong WANG Bin GAO Qiang 《岩土力学》2020,41(5):1549-1559
In order to understand the hydrothermal activity mechanism of active layers to rainfall in permafrost regions caused by humidification of climate, the differences of ground surface energy balance and hydrothermal activity in different types of shallow soil with the consideration of rainfall were discussed. Based on the meteorological data in 2013 observed at Beiluhe observation station of Tibet Plateau, three types of shallow ground soil (i.e., sandy soil, sandy loam and silty clay) were selected to compare the differences in the water content and energy balance at the ground surface, dynamic processes of water and energy transport in active layers and coupling mechanism under rainfall condition in the plateau using a coupled water-vapor-heat transport model. The results show that the increase of soil particle size leads to the increase of surface net radiation and latent heat of evaporation, but the decrease of soil heat flux. The difference of surface energy balance, especially the sensible heat flux and latent heat of evaporation, are larger in the warm season but smaller in the cold season. The liquid water transport under hydraulic gradient and the water-vapor transport under thermal gradient are obvious as the particle size in soil increases. However, the water-vapor flux under thermal gradient increases but the liquid water flux under hydraulic potential gradient decreases. As a result, the water content in shallow soil decreases accordingly but it increases slightly at the depth of 25 ~75 cm. Moreover, with the increase of soil particle size, the thermal conductivity of soil, convective heat transfer under rainfall and surface evaporation increase, but the soil heat conduction flux and soil temperature gradient decrease. Thus, soil temperature in sandy soil is much higher than that of sandy loam and silty clay at the same depth. The permafrost table declines with the increase of the thickness of active layer, which is unfavourable to permafrost stability. The results can provide theoretical reference for stability prediction and protection of permafrost caused by humidification of climate. 相似文献
995.
Satellite rainfall estimate can provide rainfall information over large areas,and raingauge can provide point-based ground observations with high accuracy.With the combination of satellite and raingauge data together,the estimated rainfall fields are greatly improved.This combination method,called "fusing technique",is discussed in this paper,and the validation for this technique is accomplished with HUBEX IOP data. 相似文献
996.
利用滑动分区切比雪夫展开方法,求取高度场特征分布的展开系数及其时间变量,通过相关分析,从中提取物理意义明确和相关性好的预报因子集和消空因子集,再通过预报因子的多形态组合分析,提炼出物理图像清晰的福建省前汛期区域暴雨预报模型。研究结果表明:以高度场的滑动分区切比雪夫展开系数做为研制前汛期的区域性暴雨预报模型的信息源是合理且可行的。切比雪夫正交多项式能够对要素场的内在特征信息进行定量化提取,生成彼此相互独立的场量因子;滑动分区展开技术可对场信息做极限化的开发,产生多种尺度的特征信息,从而获得对预报对象成因更完备的认识。 相似文献
997.
998.
本文对2002年6月8日至9日发生在朔州市的一次强降雨过程从环流背景、物理量特征等方面进行了分析和探讨,进一步揭示了强降水在朔州市发生的天气演变形势和物理机制,为朔州市今后指导强降水预报提供理论依据。 相似文献
999.
1000.
SL3型翻斗雨量传感器的维护与调校方法 总被引:3,自引:1,他引:3
主要介绍了SL3型翻斗雨量传感器的结构、工作原理以及误差主要来源,并根据使用经验,较详尽地描述了该雨量传感器观测偏差值的调校及日常维护方法。 相似文献