全文获取类型
收费全文 | 10255篇 |
免费 | 1887篇 |
国内免费 | 2733篇 |
专业分类
测绘学 | 122篇 |
大气科学 | 204篇 |
地球物理 | 1525篇 |
地质学 | 8276篇 |
海洋学 | 715篇 |
天文学 | 2137篇 |
综合类 | 595篇 |
自然地理 | 1301篇 |
出版年
2024年 | 50篇 |
2023年 | 147篇 |
2022年 | 423篇 |
2021年 | 449篇 |
2020年 | 419篇 |
2019年 | 461篇 |
2018年 | 419篇 |
2017年 | 421篇 |
2016年 | 433篇 |
2015年 | 495篇 |
2014年 | 535篇 |
2013年 | 541篇 |
2012年 | 580篇 |
2011年 | 554篇 |
2010年 | 459篇 |
2009年 | 755篇 |
2008年 | 612篇 |
2007年 | 682篇 |
2006年 | 777篇 |
2005年 | 577篇 |
2004年 | 592篇 |
2003年 | 632篇 |
2002年 | 503篇 |
2001年 | 466篇 |
2000年 | 490篇 |
1999年 | 399篇 |
1998年 | 429篇 |
1997年 | 303篇 |
1996年 | 237篇 |
1995年 | 233篇 |
1994年 | 185篇 |
1993年 | 153篇 |
1992年 | 132篇 |
1991年 | 76篇 |
1990年 | 81篇 |
1989年 | 51篇 |
1988年 | 31篇 |
1987年 | 39篇 |
1986年 | 20篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 7篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
21.
22.
Massimo Dotti Monica Colpi Francesco Haardt 《Monthly notices of the Royal Astronomical Society》2006,367(1):103-112
We study the inspiral of double black holes, with masses in the Laser Interferometer Space Antenna ( LISA ) window of detectability, orbiting inside a massive circumnuclear, rotationally supported gaseous disc. Using high-resolution smoothed particle hydrodynamics simulations, we follow the black hole dynamics in the early phase when gas-dynamical friction acts on the black holes individually, and continue our simulation until they form a close binary. We find that in the early sinking the black holes lose memory of their initial orbital eccentricity if they corotate with the gaseous disc. As a consequence, the massive black holes bind forming a binary with a low eccentricity, consistent with zero within our numerical resolution limit. The cause of circularization resides in the rotation present in the gaseous background where dynamical friction operates. Circularization may hinder gravitational waves from taking over and leading the binary to coalescence. In the case of counter-rotating orbits, the initial eccentricity (if present) does not decrease, and the black holes may bind forming an eccentric binary. When dynamical friction has subsided, for equal mass black holes and regardless their initial eccentricity, angular momentum loss, driven by the gravitational torque exerted on the binary by surrounding gas, is nevertheless observable down to the smallest scale probed (≃1 pc). In the case of unequal masses, dynamical friction remains efficient down to our resolution limit, and there is no sign of formation of any ellipsoidal gas distribution that may further harden the binary. During inspiral, gravitational capture of gas by the black holes occurs mainly along circular orbits; eccentric orbits imply high relative velocities and weak gravitational focusing. Thus, the active galactic nucleus activity may be excited during the black hole pairing process and double active nuclei may form when circularization is completed, on distance scales of tens of parsecs. 相似文献
23.
24.
25.
26.
27.
杨吉 《地球科学与环境学报》2003,25(3):16-20
北秦岭侵入岩带中的中酸性侵入岩主要形成于晋宁旋回的中晚期阶段。主要岩石类型包括辉石闪长岩、闪长岩、石英闪长岩、英云闪长岩、花岗闪长岩、斜长花岗岩、花岗岩和钾长花岗岩。岩石化学、稀土元素和微量元素地球化学研究证明,这些岩石主要形成于B型俯冲和碰撞造山的构造环境中,而钾长花岗岩形成于后造山的伸展阶段。据此,该侵入岩带揭示了北秦岭褶皱带在晋宁旋回中晚期阶段的演化过程。 相似文献
28.
29.
The steady-state population of bodies resulting from a collisional cascade depends on how material strength varies with size. We find a simple expression for the power-law index of the population, given a power law that describes how material strength varies with size. This result is extended to the case relevant for the asteroid belt and Kuiper belt, in which the material strength is described by 2 separate power laws—one for small bodies and one for larger bodies. We find that the power-law index of the small body population is unaffected by the strength law for the large bodies, and vice versa. Simple analytical expressions describe a wave that is superimposed on the large body population because of the transition between the two power laws describing the strength. These analytical results yield excellent agreement with a numerical simulation of collisional evolution. These results will help to interpret observations of the asteroids and KBOs, and constrain the strength properties of those objects. 相似文献
30.
疏散星团在天文学和天体物理学研究中有着多方面的重要性。近年来在观测和理论工作上都取得了显著的进展。综述了疏散星团的研究现状,对成员判别、基本参数确定、团与恒星的演化、团的结构和动力学进行了详细评述。 相似文献