全文获取类型
收费全文 | 1442篇 |
免费 | 235篇 |
国内免费 | 149篇 |
专业分类
测绘学 | 134篇 |
大气科学 | 386篇 |
地球物理 | 666篇 |
地质学 | 364篇 |
海洋学 | 60篇 |
天文学 | 119篇 |
综合类 | 55篇 |
自然地理 | 42篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 15篇 |
2021年 | 27篇 |
2020年 | 41篇 |
2019年 | 52篇 |
2018年 | 44篇 |
2017年 | 40篇 |
2016年 | 49篇 |
2015年 | 60篇 |
2014年 | 80篇 |
2013年 | 75篇 |
2012年 | 61篇 |
2011年 | 107篇 |
2010年 | 75篇 |
2009年 | 105篇 |
2008年 | 108篇 |
2007年 | 115篇 |
2006年 | 101篇 |
2005年 | 87篇 |
2004年 | 78篇 |
2003年 | 47篇 |
2002年 | 67篇 |
2001年 | 43篇 |
2000年 | 46篇 |
1999年 | 41篇 |
1998年 | 43篇 |
1997年 | 36篇 |
1996年 | 37篇 |
1995年 | 26篇 |
1994年 | 24篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1826条查询结果,搜索用时 15 毫秒
101.
102.
西影井水位自1974-1978年三次井溢后,1989年9月以来又出现了一次大起大落的特异变化。很多学者都十分关注这罕见的现象,并认为是区域应力增强所致的。经过多年的调查与分析,笔者认为是大量抽取地下水引起的地面沉降与地裂并由此导致地下岩层的层间错动与井管变形破坏的结果。 相似文献
103.
本文利用主应变比异常理论分析了祁连建站以来地应变观测资料,认为肃南──祁连断裂段上及附近发生的地震是由于构造应力场的变化,在引张应力状态下,正断层或走滑断层易于活动而导致的。 相似文献
104.
105.
106.
A large sample of summertime data from the McGill Radar Weather Observatory was analyzed to determine the variation with altitude
of the horizontal extent of individual rainshowers. For echoes defined by a reflectivity factor of 39 dBz (equivalent to a
rainfall rate of about 10 mm/h) it was found that the mean area of the total population of echoes decreases linearly with
altitude from approximately 20 km2 at 2 km to 11 km2 at 8 km. Subsets of the total population were investigated, consisting of only the echoes penetrating the altitudes of 6,
7, and 8 km. On the average these relatively tall echoes are much greater in horizontal extent than the total population.
Whereas the sizes of the total population of echoes at any altitude are distributed approximately exponentially in terms of
the square root of area, the sizes of the “survivors” that extend to high altitudes may be described by the gamma distribution
with a mean value decreasing approximately linearly with height above 3 km and a dispersion of 0.55. Some characteristics
are also reported for echoes defined by reflectivities of 31 dBz and 47 dBz. Estimates are given of the fraction of the total
area in a horizontal plane that contains echoes in each of these categories. 相似文献
107.
A large sample of radar reflectivity data from essentially a full summer of operation was analyzed to determine the horizontal
extents and internal structure of rain areas observed at altitude levels from 2 to 10 km. Results are given on the size distributions
of individual cells or patches defined by reflectivity thresholds approximately 4 dBz apart, on the dependence of mean size
on altitude and reflectivity threshold, and on the interior structure of the patches as characterized by the number and sizes
of higher-threshold patches contained in each echo. In a more detailed analysis of internal structure, the data were restricted
to convective echoes in which certain prescribed reflectivities, ranging from about 30 to 50 dBz, were exceeded. It was found
that the dependence of mean quantities, such as patch area, on reflectivity and altitude could be approximately described
by simple functions, but that the scatter of observations about the mean was usually large. 相似文献
108.
109.
110.
Short-term risk forecasts of point precipitation are obtained with COTREC/RainCast, a technique for extrapolation of radar images. The risk forecasts are updated every 5 min for the next 0–2 h. Risk levels are defined for moderate, heavy and extreme precipitation. Warning messages are generated if, at the locations of 23 rain gauges, these risk levels are reached or exceeded. The time-resolved gauge data are used to judge if the warning messages are in time, early or late.Data over a period of 4 months (summer 2002) are used for verification. The largest number of warnings (1790) was obtained for moderate precipitation. About 55% of these warnings were in time, 23% were early and 22% were late. This finding is in a good agreement with the defined risk level for warnings (50%), indicating that the model for calculating the risk factors is reliable. Less warnings in time, and more late warnings were found for heavy and extreme precipitation. Hence, the risk levels need to be lowered for heavy and extreme precipitation, in order to reduce the number of late warnings. 相似文献