全文获取类型
收费全文 | 17721篇 |
免费 | 2863篇 |
国内免费 | 5119篇 |
专业分类
测绘学 | 2281篇 |
大气科学 | 3467篇 |
地球物理 | 3853篇 |
地质学 | 7070篇 |
海洋学 | 3715篇 |
天文学 | 1415篇 |
综合类 | 1485篇 |
自然地理 | 2417篇 |
出版年
2024年 | 62篇 |
2023年 | 208篇 |
2022年 | 596篇 |
2021年 | 648篇 |
2020年 | 877篇 |
2019年 | 1035篇 |
2018年 | 764篇 |
2017年 | 892篇 |
2016年 | 923篇 |
2015年 | 1073篇 |
2014年 | 1042篇 |
2013年 | 1284篇 |
2012年 | 1155篇 |
2011年 | 1104篇 |
2010年 | 898篇 |
2009年 | 1067篇 |
2008年 | 1174篇 |
2007年 | 1395篇 |
2006年 | 1327篇 |
2005年 | 1172篇 |
2004年 | 967篇 |
2003年 | 783篇 |
2002年 | 751篇 |
2001年 | 555篇 |
2000年 | 687篇 |
1999年 | 650篇 |
1998年 | 494篇 |
1997年 | 382篇 |
1996年 | 316篇 |
1995年 | 254篇 |
1994年 | 236篇 |
1993年 | 205篇 |
1992年 | 180篇 |
1991年 | 125篇 |
1990年 | 73篇 |
1989年 | 95篇 |
1988年 | 59篇 |
1987年 | 43篇 |
1986年 | 45篇 |
1985年 | 27篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
根据作者导得的AfKdV方程,理论上确定了先锋孤立子生成问题的理论平均波阻,能量劈分及能量劈分比。本文的能量劈分是确定先锋孤立子生成参数的理论基础。同时,本理论确定了现有理论中的自由未知参数问题,从而使先锋孤立子生成参数得到理论预报。 相似文献
142.
研究流形上的聚类分析,针对基于密度的空间聚类引入了流形概念,提出1种基于流形的密度聚类算法,该方法将流形的概念与聚类相结合,可以适用于样本为复杂分布的聚类。文中通过实例证明此算法的有效性。 相似文献
143.
144.
Salt-water inflows into the Baltic Sea are important events for renewing the deep and bottom waters of the deep basins of the Baltic Sea. These events occur only at irregular intervals. The last strong event was in January 1993 followed by minor inflows in winter 1993/1994. As a result of these inflows, the deep water of the central Baltic basins was completely renewed.Based on extensive observations of polycyclic aromatic hydrocarbons (PAHs) in water, fluffy layer material and surface sediments between 1992 and 1998, the transformation of PAHs and the modification of their distribution in the Baltic deep water is discussed in connection with the spreading of the inflowing highly saline and oxygen-rich water along its pathway from the sills into the central basins. In the course of the inflows in 1993/1994, the PAH concentration in the deep water of the different basins increased significantly. The concentrations were elevated, at least by a factor of 2 and as much as seven to eight times (for the four-ring PAHs) compared to the previous and the following years. Two hypotheses for the causes were discussed: the inflowing salt water may have entrained more highly polluted surface water in the western Baltic Sea, or it may have entrained contaminated fluffy layer material or sediment particles along the route of transport. 相似文献
145.
146.
We collected surface water along the 142nd E meridian from Tasmania to Antarctica in December 1999. We measured temperature,
salinity and total chlorophyll a; additionally, we collected suspended particle size fractions and used fluorometric analysis to determine the quantity of
chlorophyll a in each of four cell size classes: picoplankton (<3 μm), two nanoplankton fractions (3–10 μm and 10–20 μm) and microplankton
(> 20 μm). Changes in temperature and salinity show that we crossed 6 water masses separated by 5 fronts. We found low abundance
(<0.2 mg m−3) of chlorophyll in all size classes, with the exception of higher values near the continent (0.2 to 0.4 mg m−3). Lowest chlorophyll values (<0.1 mg m−3) were found in the Polar Frontal Zone (51° to 54°S). Microplankton made up the largest portion of total chlorophyll throughout
most of the region. We conclude that biomass of all phytoplankton fractions, especially pico-and nanoplankton, was constrained
by limiting factors, most probably iron, throughout the region and that ecosystem dynamics within a zone are not circumpolar
but are regionalized within sectors. 相似文献
147.
148.
149.
Tide gauges distributed all over the world provide valuable information for monitoring mean sea level changes. The statistical models used in estimating sea level change from the tide gauge data assume implicitly that the random model components are stationary in variance. We show that for a large number of global tide gauge data this is not the case for the seasonal part using a variate-differencing algorithm. This finding is important for assessing the reliability of the present estimates of mean sea level changes because nonstationarity of the data may have marked impact on the sea level rate estimates, especially, for the data from short records. 相似文献
150.