全文获取类型
收费全文 | 82431篇 |
免费 | 6251篇 |
国内免费 | 7595篇 |
专业分类
测绘学 | 2722篇 |
大气科学 | 10393篇 |
地球物理 | 17424篇 |
地质学 | 33877篇 |
海洋学 | 8332篇 |
天文学 | 14248篇 |
综合类 | 3450篇 |
自然地理 | 5831篇 |
出版年
2023年 | 613篇 |
2022年 | 1580篇 |
2021年 | 2088篇 |
2020年 | 1908篇 |
2019年 | 2002篇 |
2018年 | 3161篇 |
2017年 | 2947篇 |
2016年 | 3550篇 |
2015年 | 2271篇 |
2014年 | 3530篇 |
2013年 | 4394篇 |
2012年 | 3329篇 |
2011年 | 3884篇 |
2010年 | 3744篇 |
2009年 | 4327篇 |
2008年 | 3706篇 |
2007年 | 3717篇 |
2006年 | 3342篇 |
2005年 | 2668篇 |
2004年 | 2482篇 |
2003年 | 2394篇 |
2002年 | 2295篇 |
2001年 | 2087篇 |
2000年 | 2211篇 |
1999年 | 2439篇 |
1998年 | 2254篇 |
1997年 | 2239篇 |
1996年 | 1895篇 |
1995年 | 1774篇 |
1994年 | 1575篇 |
1993年 | 1384篇 |
1992年 | 1223篇 |
1991年 | 1054篇 |
1990年 | 936篇 |
1989年 | 837篇 |
1988年 | 791篇 |
1987年 | 727篇 |
1986年 | 650篇 |
1985年 | 731篇 |
1984年 | 770篇 |
1983年 | 666篇 |
1982年 | 634篇 |
1981年 | 552篇 |
1980年 | 519篇 |
1979年 | 508篇 |
1978年 | 472篇 |
1977年 | 375篇 |
1976年 | 351篇 |
1975年 | 360篇 |
1973年 | 345篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Peter S. Fiske 《Meteoritics & planetary science》1996,31(1):42-45
Abstract— The size, shape, composition, and vesicle content of 6 kg of layered tektite fragments, excavated near the town of Huai Sai, Thailand, place some constraints on the formation of layered tektites. The mass, shape, and distribution of the fragments are not consistent with an origin as a “puddle” of impact melt but suggest that they were derived from a single equant block. The presence of vesicles up to 7 mm in mean diameter within the tektite fragments suggests that the material was too viscous to allow for significant gravity-driven flow. These results suggest that layered tektites may be analogous to lava bombs, which may have been stretched and deformed in flight but underwent little flow after landing. Rather than being a product of “unusual circumstances,” such as multiple impacts, layered tektites may differ from splash-form tektites only in initial temperature of formation, speed of ejection, and small differences in initial composition. 相似文献
232.
233.
C. S. Crawford A. C. Fabian P. Gandhi R. J. Wilman R. M. Johnstone 《Monthly notices of the Royal Astronomical Society》2001,324(2):427-442
We present observations of a sample of optically faint, hard X-ray sources of the kind likely to be responsible for much of the hard X-ray background. We confirm that such sources are easily detected in the near-infrared, and find that they have a featureless continuum suggesting that the active nucleus is heavily obscured. The infrared colours of the majority of the targets observed are consistent with absorbed elliptical host galaxies at z =1–2. It is likely that we are observing some of the brighter members of the important new class of X-ray type II quasars. 相似文献
234.
The self-consistent dynamic pole tide in global oceans 总被引:1,自引:0,他引:1
S. R. Dickman 《Geophysical Journal International》1985,81(1):157-174
235.
236.
Observations of Comet P/Stephan-Oterma were made with an Intensified Dissector Scanner spectrograph on the McDonald Observatory 2.7-m telescope during the period from July 1980 to February 1981. These spectra cover a range of heliocentric distances from 2.3 AU preperihelion to 1.8 AU postperihelion. A small aperture was used to map the spatial distributions of the gases in the coma. Column densities of the observed cometary emissions (CN, C3, CH, and C2) were calculated and it is shown that Stephan-Oterma appeared nearly spherically symmetric. These date are used by Cochran (1985, Icarus62, 82–92) to constrain chemical models of Stephan-Oterma. 相似文献
237.
A regular perturbation analysis is presented for natural convection flow over an uniform flux vertical surface with temperature dependent viscosity. Numerical calculations are presented forP
r=6.7 which show that the first-order correction to the local temperature difference and to the local skin-fraction are negative whereas it is positive for the local Nusselt number. The effects of variable viscosity on the temperature, velocity profiles, the local temperature difference, the local Nusselt number and the local skin fraction are discussed. 相似文献
239.
240.