全文获取类型
收费全文 | 39337篇 |
免费 | 6735篇 |
国内免费 | 8905篇 |
专业分类
测绘学 | 3638篇 |
大气科学 | 6813篇 |
地球物理 | 6524篇 |
地质学 | 20344篇 |
海洋学 | 4527篇 |
天文学 | 3543篇 |
综合类 | 2694篇 |
自然地理 | 6894篇 |
出版年
2024年 | 218篇 |
2023年 | 532篇 |
2022年 | 1398篇 |
2021年 | 1580篇 |
2020年 | 1488篇 |
2019年 | 1928篇 |
2018年 | 1359篇 |
2017年 | 1551篇 |
2016年 | 1611篇 |
2015年 | 1786篇 |
2014年 | 2237篇 |
2013年 | 2237篇 |
2012年 | 2429篇 |
2011年 | 2519篇 |
2010年 | 2185篇 |
2009年 | 2716篇 |
2008年 | 2622篇 |
2007年 | 2771篇 |
2006年 | 2650篇 |
2005年 | 2520篇 |
2004年 | 2189篇 |
2003年 | 2083篇 |
2002年 | 1765篇 |
2001年 | 1606篇 |
2000年 | 1581篇 |
1999年 | 1373篇 |
1998年 | 1214篇 |
1997年 | 873篇 |
1996年 | 743篇 |
1995年 | 631篇 |
1994年 | 601篇 |
1993年 | 491篇 |
1992年 | 361篇 |
1991年 | 326篇 |
1990年 | 201篇 |
1989年 | 163篇 |
1988年 | 136篇 |
1987年 | 76篇 |
1986年 | 42篇 |
1985年 | 42篇 |
1984年 | 28篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 15篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
Wang Yanhui 《水文研究》1992,6(2):241-251
Black locust (Robina pseudoacacia) has become one of the most important shelter species in the loess area of northwest China. This paper summarizes recent research concerning its hydrological influence, including canopy interception, litter absorption capacity, its effect on rainfall kinetic energy, infiltration rates, surface runoff, soil moisture, and evapotranspiration, and its role in soil conservation. Several predictive models are listed. on the basis of existing results, optimum characteristics for an effective plantation are defined, and problems requiring further research are identified. 相似文献
144.
145.
C. Giraudi 《第四纪科学杂志》2004,19(6):537-545
The island of Lampedusa lies on the northern edge of the African continental shelf, but during some Quaternary marine lowstands it was joined to the African continent. The study and dating of the aeolian, alluvial, detrital sediments, calcareous crusts and speleothems have established that the climatic–environmental variations recorded on the island can be related chronologically to those known for northern Libya, Tunisia and the Italian peninsula. During the Last Glacial Maximum, phases of Saharan dust accumulation on Lampedusa occurred, and were coeval with dust accumulation in crater lakes and on high mountains in central‐southern Italy, and with phases of glacial advance in the Apennines and in the Alps. During the late Holocene, accumulation of Saharan dust on Lampedusa occurred but there was little accumulation of dust on the northern side of the Mediterranean Sea. With the new data from Lampedusa, it is possible to envisage two different scenarios of atmospheric circulation relating to the Last Glacial Maximum and to the late Holocene. During the Last Glacial Maximum, southerly atmospheric circulation brought rainfall to the southern slopes of the Alps and to the Apennines. During the late Holocene, a prevalent westerly atmospheric circulation became established in the northern Mediterranean. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
146.
Galileo系统及其在中国的应用 总被引:9,自引:0,他引:9
较详细地介绍了Galileo系统的全面体系结构、频率设计、服务内容及其广泛的应用范围,指出了它与GPS系统相比的优点,并对开发和增强Galileo系统在我国多层次、全方位的应用提出了建议。 相似文献
147.
148.
149.
Is Precipitation the Dominant Controlling Factor of High Inorganic Nitrogen Content in the Changjiang River and Its Mouth? 总被引:1,自引:1,他引:0
沈志良 《中国海洋湖沼学报》2003,21(4):368-376
The main reasons for the high content of inorganic N and its increase by several times in the Changjiang River and its mouth during the last 40 years were analysed in this work. The inorganic N in precipitation in the Changjiang River catchment mainly comes from gaseous loss of fertilizer N, N resulting from the increases of population and livestock, and from high temperature combustions of fossil fuels. N from precipitation is the first N source in the Changjiang River water and the only direct cause of high content of inorganic N in the Changjiang River and its mouth. The lost N in gaseous form and from agriculture non-point sources fertilizer comprised about 60% of annual consumption of fertilizer N in the Changjiang River catchment and were key factors controlling the high content of inorganic N in the Changjiang River mouth. The fate of the N in precipitation and other N sources in the Changjiang River catchment are also discussed in this paper. 相似文献
150.