全文获取类型
收费全文 | 1513篇 |
免费 | 234篇 |
国内免费 | 243篇 |
专业分类
测绘学 | 59篇 |
大气科学 | 259篇 |
地球物理 | 565篇 |
地质学 | 358篇 |
海洋学 | 381篇 |
天文学 | 38篇 |
综合类 | 89篇 |
自然地理 | 241篇 |
出版年
2024年 | 8篇 |
2023年 | 11篇 |
2022年 | 57篇 |
2021年 | 61篇 |
2020年 | 65篇 |
2019年 | 68篇 |
2018年 | 61篇 |
2017年 | 69篇 |
2016年 | 56篇 |
2015年 | 74篇 |
2014年 | 75篇 |
2013年 | 93篇 |
2012年 | 78篇 |
2011年 | 74篇 |
2010年 | 67篇 |
2009年 | 118篇 |
2008年 | 93篇 |
2007年 | 114篇 |
2006年 | 85篇 |
2005年 | 71篇 |
2004年 | 67篇 |
2003年 | 46篇 |
2002年 | 48篇 |
2001年 | 33篇 |
2000年 | 34篇 |
1999年 | 44篇 |
1998年 | 37篇 |
1997年 | 19篇 |
1996年 | 26篇 |
1995年 | 23篇 |
1994年 | 32篇 |
1993年 | 19篇 |
1992年 | 22篇 |
1991年 | 16篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有1990条查询结果,搜索用时 15 毫秒
971.
In this paper seven of the ten Water Control Zones (WCZs) in Hong Kong’s coastal waters with monthly or bi-weekly sampling
data of 17 parameters collected at 37 monitoring stations from 1988 to 1999 were selected to analyze the spatial and temporal
variations of chlorophyll-a and its influencing factors. Cluster analysis was employed to group the monitoring stations based
on the structure of the data set. Multiple step regression was employed to determine the significant influencing factors of
chlorophyll-a level. The results suggest that all the monitoring stations could be grouped into two clusters. Cluster I with
frequent red tide incidents comprises two WCZs which are semi-enclosed bays. Cluster II with less red tide occurrence comprises
the other five WCZs in an estuarine environment in the west. For both clusters, the organic contents indicator, BOD5, was
a common significant influencing factor of the chlorophyll-a level. Nitrogen and light penetration condition related to turbidity,
total volatile solids and suspended solids had more influence on the cholophyll-a level in Cluster I than in Cluster II, while
phosphorus and oceanographic conditions associated with salinity, temperature, dissolved oxygen and pH were more important
in Cluster II than in Cluster I. Generally, there was a higher average chlorophyll-a level in winter and autumn in a year.
The chlorophyll-a level was much higher in Cluster I than in Cluster II among all seasons. Although the chlorophyll-a concentration
had great variations from place to place in Hong Kong’s coastal waters, it seemed to have a common long term fluctuation period
of 8–10 years with a high-low-high variation in the period in the whole region, which might be influenced by other factors
of global scale. 相似文献
972.
973.
974.
根据上海台网观测记录到的上海及邻近地区1985年至1990年期间179次地震事件的资料,以虹桥台、南汇台的两口深井观测地震记录为例,探讨如何利用深井观测速度型记录的最大振幅来测定近震震级。对于400公里以内的地震,本文根据统计规律,提出:在已知系统速度灵敏度K,地震记录的最大振幅A和地震震中距Δ的前提下,速度型记录的近震震级可以表示为M_v=logA/K+blog(Δ)+c误差分析表明,M_v与M_L是比较接近的,结果是可用的。 相似文献
975.
977.
Fourier analysis of the monthly mean northern hemispheric geopotential heights for the levels 700 mb and 300 mb are undertaken for the months of April through to August. The wave to wave and wave to zonal mean flow kinetic energy interactions are computed for specified latitude bands of the northern hemisphere during the pre-monsoon period (April to May) and monsoon period (June through to August) for bad monsoon years (1972, 1974, 1979) and for years of good monsoon rainfall over India (1967, 1973, 1977). Planetary scale waves (waves 1 to 4) are the major kinetic energy source in the upper atmosphere during the monsoon months. Waves 1 and 2 in particular are a greater source of kinetic energy to other waves via both wave to wave interactions as well as wave to zonal mean flow interactions in good monsoon years than in bad monsoon years. The zonal mean flow shows significantly larger gains in the kinetic energy with a strengthening of zonal westerlies in good monsoon years than in bad monsoon years. 相似文献
978.
979.
In solar cycles 22–23, all solar indices showed maxima near 1990 and 2000 and minima in 1996. The maximum to minimum variation was only 1–2% in the UV range 240–350 nm. Dobson ozone intensities did not show any clear relationship with solar cycle and ozone variations were less than 10%. The UV-B (295–325 nm) observed at ground by Brewer spectrophotometers at some locations had variations of 50–100% for 295–300 nm, and 20–50% for 305–325 nm. The maxima were in different years at different locations (even with separations of only 300 km), did not match with the solar cycle, and were far too large to be explained on the basis of ozone changes (1% decrease of ozone is expected to cause 2% increase of UV-B). Thus, if the data are not bad, the UV-B changes do not match with solar activity or ozone changes and must be mostly due to other local effects (clouds, etc.?). When data are averaged over wide geographical regions, UV-B variation ranges are smaller (10–20%, probably because localised, highly varying cloud effects get filtered out), and are roughly as expected from ozone variations. 相似文献
980.