全文获取类型
收费全文 | 621篇 |
免费 | 4篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 47篇 |
地球物理 | 135篇 |
地质学 | 203篇 |
海洋学 | 22篇 |
天文学 | 199篇 |
自然地理 | 14篇 |
出版年
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 14篇 |
2013年 | 12篇 |
2012年 | 20篇 |
2011年 | 11篇 |
2010年 | 11篇 |
2009年 | 24篇 |
2008年 | 15篇 |
2007年 | 28篇 |
2006年 | 25篇 |
2005年 | 26篇 |
2004年 | 29篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 21篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1964年 | 4篇 |
1962年 | 4篇 |
1958年 | 4篇 |
1955年 | 5篇 |
1954年 | 4篇 |
排序方式: 共有629条查询结果,搜索用时 10 毫秒
251.
Starting from the argument that the density wave theory of spiral structure is incompatible with the existence of a stationary very hot extended component of the interstellar gas, we develop a cyclic model, in which an interstellar gas of a temperature around 104 K is heated to roughly 106 K by type II supernovae resulting from the enhanced star formation triggered by the density wave, and cools down again to 104 K after the supernova activity subsides to be ready for shock compression in the next sweep of the density wave pattern. The time scales for heating by supernovae and subsequent cooling turn out to be consistent with current density wave theory. The scenario proposed is corroborated by recent results on cosmic ray composition and -ray observations. 相似文献
252.
Th. Roatsch M. Wählisch A. Hoffmeister T. Denk P. Thomas C. Porco 《Planetary and Space Science》2006,54(12):1137-1145
Images of the icy Saturnian satellites Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus, and Phoebe, derived by the Voyager and Cassini cameras are used to produce new local high-resolution image mosaics as well as global mosaics [http://ciclops.org, http://photojournal.jpl.nasa.gov]. These global mosaics are valuable both for scientific interpretation and for the planning of future flybys later in the ongoing Cassini orbital tour. Furthermore, these global mosaics can be extended to standard cartographic products. 相似文献
253.
The presence of flux tubes, visible as Network Bright Points (NBP) at the surface of the Sun outside active regions, disturbs the granular pattern in a similar way as it can be observed in laboratory convection experiments. Around an NBP, granules are smaller, more numerous than around a normal intergranular space without NBP; they are elongated and pointing towards it. Such a perturbation is visible several minutes before the appearance of the NBP, indicating that the magnetic flux, although not yet visible as a bright point, is already interacting with the convection pattern. The perturbation reaches its maximum within one minute after the NBP appearance; and the granular pattern returns to normal just after the NBP disappearance. 相似文献
254.
Our intention in this paper is to present the results obtained from a systematic comparative study of several high-order Runge-Kutta methods as applied in a composite problem of celestial dynamics, namely the magnetic-binary problem. 相似文献
255.
We present archival and recent IUE high dispersion spectra of late B stars which reveal the presence of accreting gas with velocities as high as 350 km s–1, collisional ionization of the accreting gas to temperatures above the stellar Teff, and column densities intermediate between those observed toward classical Herbig Ae/Be stars and the nearby proto-planetary system Pictoris. One of the stars, HD 176386, while lacking obvious optical signatures of youth, is a member of the R CrA star formation region, and with an inferred age of 2.8 Myr has not yet arrived on the zero-age main sequence (ZAMS). The other object, an isolated, field B star with pronounced IR excess due to warm, circumstellar dust, 51 Oph, exhibits only modest h emission. The combination of high velocity, accreting gas in systems with IR excesses due to circumstellar dust suggests that not only are these objects candidate proto-planetary systems, but that they may represent an extension to higher stellar masses of the weak-emission pre-main sequence (PMS) stars.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
256.
We analyze a time series of high resolution observations near the solar limb, obtained in H and the Mg b1 line. We identified arch-shaped dark mottles, which are thin, faint H structures observable under very good seeing conditions, best seen in H +0.75 Å. Their mean length is about 15, their mean height about 6 and indicative lifetimes is of the order of 5 min. They show negative (away from the observer) line-of-sight velocities. A possible interpretation is that material flows from the apex towards the feet of the arches. 相似文献
257.
Th. Roatsch M. Wählisch K.-D. Matz E. Kersten T. Denk C. Porco 《Planetary and Space Science》2008,56(11):1499-1505
The Cassini imaging science subsystem (ISS) acquired 449 high-resolution images (<800 m/pixel) during one close flyby of Dione in 2005 and three non-targeted flybys in 2004, 2006, and 2007. We combined these images with lower-resolution Cassini images and one other taken by Voyager cameras to produce a high-resolution semi-controlled mosaic of Dione. This global mosaic is the baseline for a high-resolution Dione atlas that consists of 15 tiles mapped at a scale of 1:1,000,000. The nomenclature used in this atlas was proposed by the Cassini imaging team and was approved by the International Astronomical Union (IAU). The whole atlas is available to the public through the Imaging Team's website [http://ciclops.org/maps]. 相似文献
258.
R. Scuflaire S. Théado J. Montalbán A. Miglio P.-O. Bourge M. Godart A. Thoul A. Noels 《Astrophysics and Space Science》2008,316(1-4):83-91
CLÉS is an evolution code recently developed to produce stellar models meeting the specific requirements of studies in asteroseismology. It offers the users a lot of choices in the input physics they want in their models and its versatility allows them to tailor the code to their needs and implement easily new features. We describe the features implemented in the current version of the code and the techniques used to solve the equations of stellar structure and evolution. A brief account is given of the use of the program and of a solar calibration realized with it. 相似文献
259.
The bounds for the energy change rate of a Maxwell field in the outer space of a rotating black hole, calculated by de Vries (1994) and de Vries (1995), enable us to deduce limits for the rotation and the mass of black holes. For this purpose we assume that a certain part of the anisotropies of the cosmic background radiation is due to absorption or superradiance of black holes (Teukolsky, 1973, Starobinskii and Churilov, 1973). The knowledge of these anisotropies yields bounds for rotation and mass of the black holes in the observable universe. 相似文献
260.
D. Soltau Th. Berkefeld A. Hofmann O. v. d. Lühe W. Schmidt R. Volkmer E. Wiehr 《Astronomische Nachrichten》2003,324(4):292-295
After many years of successful work the Gregory Coudé Telescope (GCT) is going to be replaced by GREGOR. This new 1.5 m telescope is the result of design considerations which to a wide extent are based on new technologies. Special aspects of the design are presented, including measures to compensate for optical aberrations caused by instrumental and atmospheric effects (Adaptive Optics). First light is expected for the end of 2004. 相似文献