全文获取类型
收费全文 | 1738篇 |
免费 | 51篇 |
国内免费 | 22篇 |
专业分类
测绘学 | 58篇 |
大气科学 | 180篇 |
地球物理 | 304篇 |
地质学 | 650篇 |
海洋学 | 125篇 |
天文学 | 343篇 |
综合类 | 11篇 |
自然地理 | 140篇 |
出版年
2023年 | 10篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 19篇 |
2018年 | 38篇 |
2017年 | 32篇 |
2016年 | 45篇 |
2015年 | 26篇 |
2014年 | 45篇 |
2013年 | 74篇 |
2012年 | 58篇 |
2011年 | 78篇 |
2010年 | 81篇 |
2009年 | 120篇 |
2008年 | 82篇 |
2007年 | 105篇 |
2006年 | 87篇 |
2005年 | 89篇 |
2004年 | 62篇 |
2003年 | 52篇 |
2002年 | 55篇 |
2001年 | 44篇 |
2000年 | 45篇 |
1999年 | 33篇 |
1998年 | 29篇 |
1997年 | 25篇 |
1996年 | 25篇 |
1995年 | 21篇 |
1994年 | 22篇 |
1993年 | 18篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 23篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1976年 | 19篇 |
1975年 | 9篇 |
1973年 | 17篇 |
1972年 | 18篇 |
1971年 | 11篇 |
1970年 | 11篇 |
排序方式: 共有1811条查询结果,搜索用时 62 毫秒
991.
992.
Hamisai Hamandawana Frank Eckardt Raban Chanda 《International Journal of Applied Earth Observation and Geoinformation》2005,7(4):284-298
The broad objective of this paper is to illustrate how archival, historical and remotely sensed data can be used to complement each other for long-term environmental monitoring. One of the major constraints confronting scientific investigation in the area of long-term environmental monitoring is lack of data at the required temporal and spatial scales. While remotely sensed data have provided dependable change detection databases since 1972, long-term changes such as those associated with typical climate scenarios often require longer time series data. The lack of data in readily accessible and usable formats for periods predating commercial satellite products has for a long time restricted the scope of environmental studies to temporally brief, synoptic overviews covering short time scales, thereby compromising our understanding of complex environmental processes. One way to improve this understanding is by cross-linking different forms of data at different temporal scales. However, most remote sensing based change research has tended to marginalize the utility of archival and historical sources in environmental monitoring. While the accuracy of data from non-instrumental records is often source-specific and varies from place to place, carefully conducted searches can yield useful information that can be effectively used to extend the temporal coverage of projects dependant on time series data. This paper is based on an ongoing project on environmental monitoring in the world's largest Ramsar site, the Okavango Delta, located on the northeastern fringes of Southern Africa's Kalahari–Namib desert in northern Botswana. With a database covering over 150 years between 1849 and 2001, the primary objectives of this paper are to: (1) outline how modern remotely sensed data (i.e., CORONA and Landsat) can be complemented by historical in situ observations (i.e., travellers’ records and archival maps) to extend temporal coverage into the historical past, (2) illustrate that different forms of declassified Cold War intelligence data (i.e., CORONA) can be constructively exploited to further scientific understanding and (3) provide a conceptual framework for collating and disseminating data at regional and international levels through electronic media. 相似文献
993.
994.
Jeffrey L Bada Mark A Sephton Pascale Ehrenfreund Richard A Mathies Allison M Skelley Frank J Grunthaner Aaron P Zent Richard C Quinn Jean-Luc Josset François Robert Oliver Botta Daniel P Glavin 《Astronomy& Geophysics》2005,46(6):6.26-6.27
If we are to find unequivocal evidence for life on Mars, we will need new ways to search for it. Jeff L Bada and the MOD team describe the innovative strategy developed for the ExoMars mission. 相似文献
995.
996.
997.
Frank Wickert 《International Journal of Earth Sciences》1988,77(2):467-482
In the Beaujolais-Lyonnais area of the northeastern Massif Central accretion of continental and possibly oceanic crustal fragments occurred between Cambrian (?) and early Carboniferous time. Three distinct lithotectonic units (terranes?) have been recognized. The southern (Lyonnais-) Unit consists of medium- to high-grade metamorphics and includes eclogites; it formed in the early Paleozoic. The Brévenne-Unit to the north contains low- to medium-grade metamorphic mafic and felsic volcanics and subordinate sedimentary rocks which possibly originated during the early Paleozoic until Devonian time, in a sialic back-arc environment or along an active continental margin. The Beaujolais-Unit is represented by volcanics on the south and predominantly shallow marine clastics and carbonates on the north. It developed in a late Devonian or early Carboniferous ensialic marginal basin. The peak of metamorphism in the Lyonnais-unit (HP/HT) was reached in Silurian time. Subsequent NW-SE to E-W oriented convergence produced mylonitic foliation, structural imbrication of the Lyonnais basement rocks with the Brévenne-Unit and SE-vergent folds accompanied by low- to medium-grade metamorphism. Late Visean to Namurian N-S to NW-SE directed N-vergent thrusting produced tectonic imbrication of the metamorphic northern Brévenne-Unit with the nonmetamorphic Beaujolais-Unit. In the southern Brévenne-Unit and in the Lyonnais-Unit updoming along right-lateral high-angle normal faults was followed by emplacement of voluminous granitic plutons of crustal origin. Late Carboniferous to early Permian crustal thinning in the Beaujolais-Lyonnais area was associated with N-S trending left-lateral strike-slip faults and E-W to NE-SW trending right-lateral strike-slip faults. Basins that developed along these faults contain continental red beds. 相似文献
998.
Trace elements were determined in two well-documented Chinese Permian-Triassic (P/Tr) boundary sections (Meishan and Shangsi) and in a new section (Liangfenya). Iridium concentrations range from 3 to 87 pg/g, at or below levels in common sedimentary rocks. The results contrast with previous reports of high Ir concentration in the Meishan and Shangsi sections and offer no support to suggestions of a major meteoroid impact at the end of the Permian. A notable feature in each of these widely separated P/Tr sections (500–1500 km) is the existence of 2–5 light-colored clay layers at and near the boundary. These clay layers are strongly enriched in Cs, Zr, Hf, Ta, and Th and depleted in Cr, Co, and Ir, indicating that they are altered ash, apparently from the same massive silicic volcanic eruptions. We estimate the magnitude of these eruptions to be a few thousand km3 of magma, a volume comparable to the great Toba eruption. 相似文献
999.
1000.