全文获取类型
收费全文 | 29661篇 |
免费 | 403篇 |
国内免费 | 225篇 |
专业分类
测绘学 | 735篇 |
大气科学 | 2258篇 |
地球物理 | 5767篇 |
地质学 | 10861篇 |
海洋学 | 2559篇 |
天文学 | 6291篇 |
综合类 | 65篇 |
自然地理 | 1753篇 |
出版年
2021年 | 275篇 |
2020年 | 298篇 |
2019年 | 302篇 |
2018年 | 727篇 |
2017年 | 725篇 |
2016年 | 839篇 |
2015年 | 467篇 |
2014年 | 803篇 |
2013年 | 1558篇 |
2012年 | 925篇 |
2011年 | 1224篇 |
2010年 | 1053篇 |
2009年 | 1365篇 |
2008年 | 1184篇 |
2007年 | 1172篇 |
2006年 | 1160篇 |
2005年 | 840篇 |
2004年 | 839篇 |
2003年 | 767篇 |
2002年 | 768篇 |
2001年 | 713篇 |
2000年 | 702篇 |
1999年 | 550篇 |
1998年 | 519篇 |
1997年 | 599篇 |
1996年 | 469篇 |
1995年 | 474篇 |
1994年 | 471篇 |
1993年 | 381篇 |
1992年 | 387篇 |
1991年 | 358篇 |
1990年 | 373篇 |
1989年 | 342篇 |
1988年 | 344篇 |
1987年 | 368篇 |
1986年 | 325篇 |
1985年 | 425篇 |
1984年 | 414篇 |
1983年 | 446篇 |
1982年 | 415篇 |
1981年 | 365篇 |
1980年 | 402篇 |
1979年 | 324篇 |
1978年 | 302篇 |
1977年 | 294篇 |
1976年 | 266篇 |
1975年 | 264篇 |
1974年 | 269篇 |
1973年 | 254篇 |
1971年 | 173篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
942.
B. L. Jakeman 《Mathematical Geology》1980,12(3):185-212
Using trend-surface analysis, the patterns of formation structure and thickness variation in the Permo-Triassic succession of the Southern Coalfield, Sydney Basin, are resolved into geologically meaningful large- and small-scale features. The structural trends correspond to the regional syncline of the southern Sydney Basin and the negative and positive residual domains to smaller-scale structures including the South Bulli and Douglas Park Synclines and the Bulli and Kemira Anticlines. The results of trend-surface analysis and simple linear regression reveal an inverse relationship between structural elevation (relative to sea level) and formation thickness on both a regional and a local scale. This relationship is strongest for the Bulli Coal and the Bald Hill Claystone. In the case of the Bulli Coal, the present-day structural trends and formation thickness trends show a strong inverse correlation and the residuals show a moderate inverse correlation; the correlations between the inferred Middle Triassic structure of the Bulli Coal and formation thickness are even stronger than those involving the present-day structure. These results indicate that structures which were active during the Permo-Triassic and which influenced sedimentation have been preserved in the present-day structure. The persistence of the patterns of structure and thickness variation upward through the Permo-Triassic sequence suggests that sedimentation was controlled by contemporaneous basement subsidence, rather than by short-lived compaction-induced subsidence patterns. 相似文献
943.
944.
P.B. Robertson L.C. Coleman E.J. Olsen S.A. Kissin 《Meteoritics & planetary science》1982,17(3):163-170
The recovery of several thousand meteorite fragments from Antarctica has led to speculation that accumulations may occur on the Earth's other major ice caps. Meteorites falling over the past 80,000 years on the Devon Island ice cap in the Canadian Arctic may be exposed at the surface near the ice cap margin. From the terrestrial meteorite flux, ice movement rates, and fragmentation factors it is calculated that 12,560 samples of 150 g mass are potentially concentrated in a 65 km2 zone along the northwest margin. A search of this region on foot and by helicopter in July, 1981, failed to recover any specimens. Although metre-sized gneissic boulders, plucked from the underlying Precambrian basement, were concentrated in this zone it is postulated that the unseasonal 30 cm snow cover on the ice prohibited the recognition of possible meteorite specimens, which may average only 5 cm in diameter. 相似文献
945.
946.
947.
948.
Palaeomagnetism of the Roraima Dolerites 总被引:1,自引:0,他引:1
R. B. Hargraves 《Geophysical Journal International》1968,16(2):147-160
949.
Atomic self consistent field calculations are applied to identify Fe VI and Fe VII spectra belonging to the 3p
6 3d
n — 3p
5 3d
n + 1 transition arrays. Their presence in vacuum spark spectra and absence in solar spectrograms is discussed. 相似文献
950.