全文获取类型
收费全文 | 2064篇 |
免费 | 356篇 |
国内免费 | 692篇 |
专业分类
测绘学 | 207篇 |
大气科学 | 329篇 |
地球物理 | 459篇 |
地质学 | 1045篇 |
海洋学 | 458篇 |
天文学 | 46篇 |
综合类 | 194篇 |
自然地理 | 374篇 |
出版年
2024年 | 14篇 |
2023年 | 51篇 |
2022年 | 132篇 |
2021年 | 126篇 |
2020年 | 130篇 |
2019年 | 125篇 |
2018年 | 152篇 |
2017年 | 118篇 |
2016年 | 138篇 |
2015年 | 135篇 |
2014年 | 130篇 |
2013年 | 142篇 |
2012年 | 153篇 |
2011年 | 127篇 |
2010年 | 144篇 |
2009年 | 136篇 |
2008年 | 119篇 |
2007年 | 127篇 |
2006年 | 93篇 |
2005年 | 77篇 |
2004年 | 82篇 |
2003年 | 76篇 |
2002年 | 65篇 |
2001年 | 65篇 |
2000年 | 76篇 |
1999年 | 69篇 |
1998年 | 64篇 |
1997年 | 52篇 |
1996年 | 42篇 |
1995年 | 38篇 |
1994年 | 31篇 |
1993年 | 19篇 |
1992年 | 16篇 |
1991年 | 4篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有3112条查询结果,搜索用时 187 毫秒
51.
52.
一种基于向量序结构关系的多值形态变换 总被引:1,自引:0,他引:1
提出了一种向量型数据全序关系建立的一般方法,并以此为基础建立了多值形态变换的基本形式,并对其性质进行了讨论。多值形态变换作为数学形态学在多值图像空间中的扩展.具有与灰值形态变换类似的功能和作用,可有效地应用于多值图像的处理和目标形状特征的提取。 相似文献
53.
54.
55.
Introduction The research on the structure and physical property of ancient hidden hill, igneous rocks and basement is relatively difficult by using seismic data only. If we combine seismic data, magneto-telluric (MT) data and geophysical data together, better results can be obtained for the above problem. A number of geophysicists at home and abroad, such as CHEN and WANG (1990), Siri-punvarapor and Egbert (2000) have tried many methods to solve the problem by the inversion of seismic da… 相似文献
56.
CHAO Jiping LIU Lin & YU Weidong . Laboratory of Marine Science Numerical Modeling State Oceanic Administration Qingdao China . National Research Center for Marine Environmental Forecasts State Oceanic Administration Beijing China . Ocean University of China Qingdao China 《中国科学D辑(英文版)》2005,48(10)
Before the 1980s, El Ni?o was believed as the sea surface warming along the coast of Peru in South America. As the positive anomaly strengths, the warm water expands westward along the equator to form large area of anomalous high sea surface temperature. Rasmusson and Carpenter (1982) summarized the de-velopment process of the sea surface warm water and the corresponding wind field[1] during ENSO cylce. However, this canonical El Ni?o was questioned by 1982-1983 warm episode and later dat… 相似文献
57.
58.
Analysis of rock structure stability in coal mines 总被引:1,自引:0,他引:1
In this paper, the theory of limit point instability is used to analyse the stability of rock structures in coal mines. A general method of analysing stability of rock structures is put forward and a uniform instability condition of rock structures is set up. Some instability phenomena, such as rock bursts in circular roadways, pillars and long walls, and the outburst of coal and gas from circular roadways, are discussed analytically. At a later stage, the critical point of rock structure instability is determined. The influence of relative parameters (such as the mechanical properties of rock, coal, and the geometric sizes) on the stability of the rock structures is carefully analysed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
59.
60.
Exploring seasonal acidification in the Yellow Sea 总被引:1,自引:0,他引:1
Weidong ZHAI 《中国科学:地球科学(英文版)》2018,(6)
The Yellow Sea on the western continental margin of the North Pacific Ocean is of major ecological and economic importance. Four field surveys were conducted during May and November 2012, August 2015, and January 2016, investigating seasonal variations in dissolved oxygen and carbonate system parameters of this marginal sea. Results showed that the Yellow Sea cold water mass accumulated respiration-induced CO_2 in subsurface and bottom waters in summer and autumn, leading to acidified seawaters with critical carbonate saturation states of aragonite(Ω_(arag)) of less than 1.5. These seriously acidified seawaters occupied one third of surveyed areas in summer and autumn, likely affecting local calcified organisms and benthic communities. In a future scenario for the 2050 s, in which the atmospheric CO_2 mole fraction increases by 100 μmol mol-1, half of the Yellow Sea benthos would be seasonally covered by acidified seawater having a critical Ω_(arag) of less than 1.5. The corresponding bottom-water p H_T would be around 7.85 in summer, and 7.80 in autumn. Of the China seas, the Yellow Sea cold water mass represents one of the ecosystems most vulnerable to ocean acidification. 相似文献