全文获取类型
| 收费全文 | 194篇 |
| 免费 | 18篇 |
| 国内免费 | 1篇 |
专业分类
| 测绘学 | 3篇 |
| 大气科学 | 9篇 |
| 地球物理 | 45篇 |
| 地质学 | 75篇 |
| 海洋学 | 8篇 |
| 天文学 | 64篇 |
| 综合类 | 2篇 |
| 自然地理 | 7篇 |
出版年
| 2023年 | 3篇 |
| 2022年 | 3篇 |
| 2021年 | 6篇 |
| 2020年 | 6篇 |
| 2019年 | 8篇 |
| 2018年 | 12篇 |
| 2017年 | 17篇 |
| 2016年 | 12篇 |
| 2015年 | 11篇 |
| 2014年 | 12篇 |
| 2013年 | 4篇 |
| 2012年 | 22篇 |
| 2011年 | 17篇 |
| 2010年 | 14篇 |
| 2009年 | 10篇 |
| 2008年 | 12篇 |
| 2007年 | 11篇 |
| 2006年 | 6篇 |
| 2005年 | 7篇 |
| 2004年 | 7篇 |
| 2003年 | 5篇 |
| 2002年 | 1篇 |
| 2001年 | 1篇 |
| 2000年 | 3篇 |
| 1999年 | 2篇 |
| 1998年 | 1篇 |
排序方式： 共有213条查询结果，搜索用时 15 毫秒
101.
XMM-Newton is a major X-ray observatory of the European Space Agency (ESA). Its observing time is open to astronomers from the whole scientific community on a peer reviewed competitive basis. The Science Operations Centre, located at ESA’s premises in Villafranca del Castillo, Spain, is responsible for the instrument operations, as well as for all the tasks related to facilitating the scientific exploitation of the data which the mission has been producing since its launch in December 1999. Among them, one may list:
Everyone can be an XMM-Newton observer. So far, astronomers from 36 countries submitted observing programs. Public data can be accessed by every scientist in the world through the XMM-Newton Science Archive (XSA).Despite all these efforts, one can’t help noticing an asymmetric level of scientific exploitation in the realm of X-ray astronomy between developing and developed countries. The latter have traditionally enjoyed the comparative advantage of deeper know-how, deriving from direct experience in hardware and mission development. The XMM-Newton Science Operations Centre’s efforts act to alleviate this situation through, for example, increasing the usage of the web for data and information dissemination, as well as by supporting actively such initiatives as the COSPAR Capacity-Building Workshops, specifically designed to create long-lasting bridges between researchers in developing and developed countries. 相似文献
| • | distribution of scientific data in different formats, from raw telemetry, up to processed and calibrated high-level science products, such as images, spectra, source lists, etc; |
| • | development and distribution of dedicated science analysis software, as well as of continuously updated instrument calibration; |
| • | regular organisation of training workshops (free of cost), for potential users of XMM-Newton data, where the procedures and techniques to successfully reduce and analyze XMM-Newton data are introduced; |
| • | access to the data through state-of-the-art, in-house-developed archival facilities, either through the Internet or via CD-ROM; |
| • | continuously updated documentation on all aspects of spacecraft and instrument operations, data reduction and analysis; |
| • | maintenance of a comprehensive set of project web pages; |
| • | a competent and responsive HelpDesk, providing dedicated support to individual XMM-Newton users. |
102.
103.
Matteo Guainazzi 《Monthly notices of the Royal Astronomical Society》2002,329(1):L13-L17
In this paper, a BeppoSAX observation of the bright Seyfert 2 galaxy NGC 6300 is presented. The rapidly variable emission from the active nucleus is seen through a Compton-thin absorber. A Compton-reflection component with an unusually high reflection fraction , and the comparison with a reflection-dominated spectrum measured by RXTE two and half years earlier suggest that NGC 6300 belongs to the class of 'transient' active galactic nucleus, undergoing long and repeated periods of low activity. The spectral transition provides support to the idea that Compton-thick and Compton-thin X-ray absorbers in Seyfert 2 galaxies are decoupled, the former being most likely associated with the 'torus', whereas the latter is probably located at much larger distances. 相似文献
104.
Elisa Cenci Matteo PizzolonNicole Chimento Carlotta Mazzoldi 《Estuarine, Coastal and Shelf Science》2011
Deployed for diverse purposes, artificial substrata can, theoretically, act as fish attractors or as fish producers. We tested these hypotheses by comparing fish assemblages on two artificial hard substrata, the Ca’ Roman and Sottomarina jetties, before (1994 and 2003) and after (2005 and 2006) the deployment of a new breakwater in the area. Our results support the fish production hypothesis. A remarkable increase in richness and abundance of sedentary species was observed on the extant substrata with the presence of the new barrier. More mobile species showed less definite trends. The net result has been a total increase in abundance and richness in the area. While fish assemblage showed important temporal variation in composition before deployment (Ca’ Roman, comparison between 1994 and 2003), clear trends of increasing abundance were concurrent with the presence of the new barrier. This increase in abundance, particularly of sedentary species, may be attributed to enhanced connectivity and/or an improvement in larval retention due to the changes in water circulation connected with the new breakwater, or to an increase in juveniles and/or adults promoted by changes in environmental conditions. Indeed, changes in benthic cover were recorded, with an increase of uncovered rock and the appearance of previously unrecorded algae after breakwater deployment. 相似文献
105.
James S. Bolton Martin G. Haehnelt Matteo Viel Robert F. Carswell 《Monthly notices of the Royal Astronomical Society》2006,366(4):1378-1390
The low-density hydrogen and helium in the intergalactic medium (IGM) probed by quasi-stellar object (QSO) absorption lines is sensitive to the amplitude and spectral shape of the metagalactic ultraviolet (UV) background. We use realistic H i and He ii Lyα forest spectra, constructed from state-of-the-art hydrodynamical simulations of a Λ cold dark matter (ΛCDM) universe to confirm the reliability of using line profile fitting techniques to infer the ratio of the metagalactic H i and He ii ionization rates. We further show that the large spatial variations and the anticorrelation with H i absorber density observed in the ratio of the measured He ii to H i column densities can be explained in a model where the H i ionization rate is dominated by the combined UV emission from young star-forming galaxies and QSOs and the He ii ionization rate is dominated by emission from QSOs only. In such a model the large fluctuations in the column density ratio are due to the small number of QSOs expected to contribute at any given point to the He ii ionization rate. A significant contribution to UV emission at the He ii photoelectric edge from hot gas in galaxies and galaxy groups would decrease the expected fluctuations in the column density ratio. Consequently, this model appears difficult to reconcile with the large increase in He ii opacity fluctuations towards higher redshift. Our results further strengthen previous suggestions that observed He ii Lyα forest spectra at z ∼ 2–3.5 probe the tail end of the reionization of He ii by QSOs. 相似文献
106.
Sebastian Heinz Andrea Merloni Tiziana Di Matteo Rashid Sunyaev 《Astrophysics and Space Science》2005,300(1-3):15-21
The scale invariance model (Heinz, S. and Sunyaev, R.A.: 2003, MNRAS 343, L59) can be used to derive robust scaling relations between the radio luminosity from accreting black holes and the black
hole mass and accretion rate. These relations agree well with the recently found “fundamental plane” of black hole activity
(Merloni, A., Heinz, S. and Di Matteo, T.: 2003, MNRAS 345, 1057). This relation provides a new, powerful tool for the comparison of jets from black holes of different masses and accretion
rates. The regression coefficients of this relation contain information about the nature of the X-ray emission mechanism driving
the correlation. We argue that X-ray synchrotron emission from the base of the jets is unlikely to be the dominant contribution
to the X-ray spectrum in most of the sources. 相似文献
107.
108.
109.
John A. Regan Martin G. Haehnelt Matteo Viel 《Monthly notices of the Royal Astronomical Society》2007,374(1):196-205
We compare simulations of the Lyman α forest performed with two different hydrodynamical codes, gadget-2 and enzo . A comparison of the dark matter power spectrum for simulations run with identical initial conditions show differences of 1–3 per cent at the scales relevant for quantitative studies of the Lyman α forest. This allows a meaningful comparison of the effect of the different implementations of the hydrodynamic part of the two codes. Using the same cooling and heating algorithm in both codes, the differences in the temperature and the density probability distribution function are of the order of 10 per cent. The differences are comparable to the effects of box size and resolution on these statistics. When self-converged results for each code are taken into account, the differences in the flux power spectrum – the statistics most widely used for estimating the matter power spectrum and cosmological parameters from Lyman α forest data – are about 5 per cent. This is again comparable to the effects of box size and resolution. Numerical uncertainties due to a particular implementation of solving the hydrodynamic or gravitational equations appear therefore to contribute only moderately to the error budget in estimates of the flux power spectrum from numerical simulations. We further find that the differences in the flux power spectrum for enzo simulations run with and without adaptive mesh refinement are also of the order of 5 per cent or smaller. The latter require 10 times less CPU time making the CPU time requirement similar to that of a version of gadget-2 that is optimized for Lyman α forest simulations. 相似文献
110.