全文获取类型
收费全文 | 16316篇 |
免费 | 3689篇 |
国内免费 | 1708篇 |
专业分类
测绘学 | 307篇 |
大气科学 | 509篇 |
地球物理 | 12400篇 |
地质学 | 5023篇 |
海洋学 | 507篇 |
天文学 | 827篇 |
综合类 | 1214篇 |
自然地理 | 926篇 |
出版年
2024年 | 52篇 |
2023年 | 189篇 |
2022年 | 455篇 |
2021年 | 614篇 |
2020年 | 544篇 |
2019年 | 657篇 |
2018年 | 609篇 |
2017年 | 605篇 |
2016年 | 482篇 |
2015年 | 711篇 |
2014年 | 854篇 |
2013年 | 853篇 |
2012年 | 876篇 |
2011年 | 949篇 |
2010年 | 836篇 |
2009年 | 1166篇 |
2008年 | 921篇 |
2007年 | 1047篇 |
2006年 | 1021篇 |
2005年 | 928篇 |
2004年 | 885篇 |
2003年 | 817篇 |
2002年 | 640篇 |
2001年 | 590篇 |
2000年 | 611篇 |
1999年 | 539篇 |
1998年 | 556篇 |
1997年 | 470篇 |
1996年 | 451篇 |
1995年 | 386篇 |
1994年 | 354篇 |
1993年 | 278篇 |
1992年 | 239篇 |
1991年 | 135篇 |
1990年 | 111篇 |
1989年 | 89篇 |
1988年 | 71篇 |
1987年 | 26篇 |
1986年 | 33篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 16篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1954年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
21.
22.
Piero F. Spinnato Michael Fellhauer Simon F. Portegies Zwart 《Monthly notices of the Royal Astronomical Society》2003,344(1):22-32
We study the efficiency at which a black hole or dense star cluster spirals in to the Galactic Centre. This process takes place on a dynamical friction time-scale, which depends on the value of the Coulomb logarithm (ln Λ). We determine the accurate value of this parameter using the direct N -body method, a tree algorithm and a particle-mesh technique with up to two million plus one particles. The three different techniques are in excellent agreement. Our measurement for the Coulomb logarithm appears to be independent of the number of particles. We conclude that ln Λ= 6.6 ± 0.6 for a massive point particle in the inner few parsec of the Galactic bulge. For an extended object, such as a dense star cluster, ln Λ is smaller, with a value of the logarithm argument Λ inversely proportional to the object size. 相似文献
23.
The lensing properties of the Plummer model with a central point mass and external shear are derived, including the image multiplicities, critical curves and caustics. This provides a simple model for a flattened galaxy with a central supermassive black hole. For the Plummer model with black hole, the maximum number of images is four, provided the black hole mass is less than an upper bound which is calculated analytically. This introduces a method to constrain black hole masses by counting images, thus applicable at cosmological distance. With shear, the maximum number of images is six and we illustrate the occurrence of an astroid caustic and two metamorphoses. 相似文献
24.
形变大地测量学的进展、问题与地震预报 总被引:12,自引:7,他引:5
简要概括了形变大地测量学的革命性进展,研讨了它的科学特色、功能和定义以及对地球科学和防灾减灾的推动。形变大地测量学有助于从根本上击破多年来制约地震预报的“瓶颈”,但也存在不少急待解决的问题。着重研讨了在21世纪前10年,形变大地测量学如何依托多年的学科积累并充分受益于人造卫星和数字化等新技术,开展创新性研究和试验以推进地震预报。为此,对当前的研究工作提出了12条科学技术途径。最后对学科名称提出了建议。 相似文献
25.
Pittichovâ J. Sekenina Z. Birkle K. Boehnhardt J. Engels D. Keller P. 《Earth, Moon, and Planets》1997,78(1-3):329-338
The Sekanina-Farrell particle fragmentation model for the striated tails of dust comets is successfully applied to two images
of comet Hale-Bopp to study the motions of 12 striae in a time span of March 12–15, 1997. There is evidence for recurring
outbursts with a periodicity of 11h21m, consistent with results based on analysis of dust jets. The ejecta in all the striae appear to have been released from one
source on the nucleus between the end of January and the second half of February 1997, some 60 to 40 days before perihelion.
The parent particles were subjected to a radiation pressure acceleration of βp ≃ 0.55 and their fragmentation lifetimes in 11 of the 12 striae were practically constant and equal to 13–15 days, when normalized
to 1 AU from the Sun. Brief analysis of Watanabe et al.'s measurements of striae on their images from March 5–9, 1997 shows
even shorter fragmentation lifetimes for the parent particles, mostly about 7–11 days at1 AU.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
26.
We have recently put forward a ‘unified’ semi-empirical model for the coupling between accretion and jet production in galactic
black hole X-ray binaries. In this paper, we summarise this model and briefly discuss relevant considerations that have arisen
since its publication. 相似文献
27.
Kenai, located on the west coast of the Kenai Peninsula, Alaska, subsided during the great earthquake of AD 1964. Regional land subsidence is recorded within the estuarine stratigraphy as peat overlain by tidal silt and clay. Reconstructions using quantitative diatom transfer functions estimate co‐seismic subsidence (relative sea‐level rise) between 0.28±0.28 m and 0.70±0.28 m followed by rapid post‐seismic recovery. Stratigraphy records an earlier co‐seismic event as a second peat‐silt couplet, dated to ~1500–1400 cal. yr BP with 1.14±0.28 m subsidence. Two decimetre‐scale relative sea‐level rises are more likely the result of glacio‐isostatic responses to late Holocene and Little Ice Age glacier expansions rather than to co‐seismic subsidence during great earthquakes. Comparison with other sites around Cook Inlet, at Girdwood and Ocean View, helps in constructing regional patterns of land‐level change associated with three great earthquakes, AD 1964, ~950–850 cal. yr BP and ~1500–1400 cal. yr BP. Each earthquake has a different spatial pattern of co‐seismic subsidence which indicates that assessment of seismic hazard in southern Alaska requires an understanding of multiple great earthquakes, not only the most recent. All three earthquakes show a pre‐seismic phase of gradual land subsidence that marked the end of relative land uplift caused by inter‐seismic strain accumulation. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
28.
Yehuda Ben-Zion 《Geophysical Journal International》1990,101(3):507-528
29.
30.
秦岭凤太矿田层控铅锌(铜)矿床的金属物质、硫和成矿溶液主要来自深部基底的岩石,属海底喷流—沉积成因矿床。从这一理论认识出发可进一步分析控矿地质条件及今后在该区有效地寻找同类矿床。 相似文献