全文获取类型
收费全文 | 3165篇 |
免费 | 453篇 |
国内免费 | 489篇 |
专业分类
测绘学 | 625篇 |
大气科学 | 205篇 |
地球物理 | 520篇 |
地质学 | 1283篇 |
海洋学 | 559篇 |
天文学 | 436篇 |
综合类 | 251篇 |
自然地理 | 228篇 |
出版年
2024年 | 6篇 |
2023年 | 24篇 |
2022年 | 109篇 |
2021年 | 131篇 |
2020年 | 135篇 |
2019年 | 177篇 |
2018年 | 111篇 |
2017年 | 149篇 |
2016年 | 153篇 |
2015年 | 163篇 |
2014年 | 194篇 |
2013年 | 205篇 |
2012年 | 192篇 |
2011年 | 213篇 |
2010年 | 147篇 |
2009年 | 207篇 |
2008年 | 188篇 |
2007年 | 203篇 |
2006年 | 158篇 |
2005年 | 163篇 |
2004年 | 169篇 |
2003年 | 151篇 |
2002年 | 125篇 |
2001年 | 84篇 |
2000年 | 101篇 |
1999年 | 61篇 |
1998年 | 57篇 |
1997年 | 75篇 |
1996年 | 43篇 |
1995年 | 41篇 |
1994年 | 39篇 |
1993年 | 26篇 |
1992年 | 25篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 19篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1978年 | 2篇 |
1954年 | 1篇 |
1921年 | 1篇 |
1905年 | 2篇 |
1900年 | 1篇 |
1897年 | 1篇 |
1882年 | 1篇 |
1880年 | 1篇 |
1877年 | 2篇 |
排序方式: 共有4107条查询结果,搜索用时 203 毫秒
991.
On 4 July 2005 at 5:52 UT the Deep Impact mission successfully completed its goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on the nucleus and ejecting material into the coma of the comet. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the 110-101 ortho-water ground-state rotational transition in Comet 9P/Tempel 1 before, during, and after the impact. No excess emission from the impact was detected by SWAS and we derive an upper limit of 1.8×107 kg on the water ice evaporated by the impact. However, the water production rate of the comet showed large natural variations of more than a factor of three during the weeks before and after the impact. Episodes of increased activity with alternated with periods with low outgassing (). We estimate that 9P/Tempel 1 vaporized a total of N∼4.5×1034 water molecules (∼1.3×109 kg) during June-September 2005. Our observations indicate that only a small fraction of the nucleus of Tempel 1 appears to be covered with active areas. Water vapor is expected to emanate predominantly from topographic features periodically facing the Sun as the comet rotates. We calculate that appreciable asymmetries of these features could lead to a spin-down or spin-up of the nucleus at observable rates. 相似文献
992.
Perihelion motion, i.e. a secular change of longitude of perihelion, of interplanetary dust particles is investigated under the action of solar gravity and solar electromagnetic radiation. As for spherical particle [Kla?ka, J., 2004. Electromagnetic radiation and motion of a particle. Cel. Mech. Dynam. Astron. 89, 1-61]: (i) perihelion motion is of the order ( is heliocentric velocity of the meteoroid and c is the speed of light in vacuum), if a component of electromagnetic radiation acceleration is considered as a part of central acceleration; (ii) perihelion motion is of the first order in if the total electromagnetic radiation force is considered as a disturbing force. The new facts presented in this paper concern irregular dust particles. Detailed numerical calculations were performed for the grains ejected at aphelion of comet Encke. Perihelion motion for irregular interplanetary dust particles exists already in the first order in for both cases of central accelerations. Moreover, perihelion motion of irregular particles exhibits both positive and negative directions during the particle orbital motion. Irregularity of the grains causes not only perihelion motion, but also dispersion of the dust in various directions, also normal to the orbital plane of the parent body. 相似文献
993.
Equilibrium trading of climate and weather risk and numerical simulation in a Markovian framework 总被引:3,自引:3,他引:0
Sébastien Chaumont Peter Imkeller Matthias Müller 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(3):184-205
We consider financial markets with agents exposed to external sources of risk caused, for example, by short-term climate events
such as the South Pacific sea surface temperature anomalies widely known by the name El Nino. Since such risks cannot be hedged
through investments on the capital market alone, we face a typical example of an incomplete financial market. In order to
make this risk tradable, we use a financial market model in which an additional insurance asset provides another possibility
of investment besides the usual capital market. Given one of the many possible market prices of risk, each agent can maximize
his individual exponential utility from his income obtained from trading in the capital market, the additional security, and
his risk-exposure function. Under the equilibrium market-clearing condition for the insurance security the market price of
risk is uniquely determined by a backward stochastic differential equation. We translate these stochastic equations via the
Feynman–Kac formalism into semi-linear parabolic partial differential equations. Numerical schemes are available by which
these semilinear pde can be simulated. We choose two simple qualitatively interesting models to describe sea surface temperature,
and with an ENSO risk exposed fisher and farmer and a climate risk neutral bank three model agents with simple risk exposure
functions. By simulating the expected appreciation price of risk trading, the optimal utility of the agents as a function
of temperature, and their optimal investment into the risk trading security we obtain first insight into the dynamics of such
a market in simple situations.
相似文献
Peter ImkellerEmail: |
994.
995.
996.
997.
998.
999.
1000.