全文获取类型
收费全文 | 2261篇 |
免费 | 48篇 |
国内免费 | 26篇 |
专业分类
测绘学 | 48篇 |
大气科学 | 107篇 |
地球物理 | 576篇 |
地质学 | 771篇 |
海洋学 | 238篇 |
天文学 | 372篇 |
综合类 | 10篇 |
自然地理 | 213篇 |
出版年
2021年 | 21篇 |
2020年 | 31篇 |
2019年 | 28篇 |
2018年 | 42篇 |
2017年 | 32篇 |
2016年 | 63篇 |
2015年 | 44篇 |
2014年 | 55篇 |
2013年 | 120篇 |
2012年 | 64篇 |
2011年 | 114篇 |
2010年 | 78篇 |
2009年 | 95篇 |
2008年 | 82篇 |
2007年 | 92篇 |
2006年 | 85篇 |
2005年 | 90篇 |
2004年 | 76篇 |
2003年 | 53篇 |
2002年 | 74篇 |
2001年 | 40篇 |
2000年 | 38篇 |
1999年 | 43篇 |
1998年 | 28篇 |
1997年 | 30篇 |
1996年 | 32篇 |
1995年 | 41篇 |
1994年 | 33篇 |
1993年 | 26篇 |
1992年 | 25篇 |
1991年 | 32篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 35篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 35篇 |
1984年 | 38篇 |
1983年 | 41篇 |
1982年 | 32篇 |
1981年 | 30篇 |
1980年 | 27篇 |
1979年 | 32篇 |
1978年 | 24篇 |
1977年 | 33篇 |
1976年 | 31篇 |
1975年 | 25篇 |
1973年 | 19篇 |
1972年 | 22篇 |
1971年 | 18篇 |
排序方式: 共有2335条查询结果,搜索用时 46 毫秒
741.
The 2dF Galaxy Redshift Survey: the dependence of galaxy clustering on luminosity and spectral type 总被引:1,自引:0,他引:1
Peder Norberg Carlton M. Baugh Ed Hawkins Steve Maddox Darren Madgwick Ofer Lahav Shaun Cole Carlos S. Frenk Ivan Baldry Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Karl Glazebrook Carole Jackson Ian Lewis Stuart Lumsden John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,332(4):827-838
We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal-component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late types') and more quiescent galaxies ('early types'). We measure the clustering in real space, free from any distortion of the clustering pattern owing to peculiar velocities, for a series of volume-limited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range 2<( σ / h -1 Mpc)<15 , with a marginally steeper slope for early types than late types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of ∼2.5 between L * and 4 L *. At all luminosities, however, the correlation function amplitude for the early types is ∼50 per cent higher than that of the late types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity. 相似文献
742.
George E. Blanford 《Earth, Moon, and Planets》1984,31(3):221-227
Particle track measurements have been reported for 25 (5%) of the regolith breccias in the collection; they have been reported for 16 breccias (30%) in the reference suite. The most frequently reported measurement for these 25 breccias is the maximum surface exposure age of the compacted rock (48% of the published breccia measurements). Information on the nature of the precompaction regolith is given for 9 rocks (36%) and on the nature of the compaction event for 6 rocks (24%). Most of the breccias appear to have simple post-compaction surface exposure histories (89%). From the few track density frequency distributions (7) that are available and inferring from the low exposure ages of these rocks (75% < 106 yr), it appears that most of these breccias are amenable to studies which separate the contemporary surface exposure age from information about the precompaction regolith. If the number of immature-submature precompaction soils (6 out of 10 of the breccias for which appropriate data are available) represents many regolith breccias, then we can infer that regolith breccias may sample the deeper, less reworked materials in the lunar soil and compliment the samples available from the returned cores. 相似文献
743.
Karl Kehm George J. Flynn Charles M. Hohenberg 《Meteoritics & planetary science》2006,41(8):1199-1217
Abstract— The He, Ne, and Ar compositions of 32 individual interplanetary dust particles (IDPs) were measured using low‐blank laser probe gas extraction. These measurements reveal definitive evidence of space exposure. The Ne and Ar isotopic compositions in the IDPs are primarily a mixture between solar wind (SW) and an isotopically heavier component dubbed “fractionated solar” (FS), which could be implantation‐fractionated solar wind or a distinct component of the solar corpuscular radiation previously identified as solar energetic particles (SEP). Space exposure ages based on the Ar content of individual IDPs are estimated for a subset of the grains that appear to have escaped significant volatile losses during atmosphere entry. Although model‐dependent, most of the particles in this subset have ages that are roughly consistent with origin in the asteroid belt. A short (<1000 years) space exposure age is inferred for one particle, which is suggestive of cometary origin. Among the subset of grains that show some evidence for relatively high atmospheric entry heating, two possess elevated 21Ne/22Ne ratios generated by extended exposure to solar and galactic cosmic rays. The inferred cosmic ray exposure ages of these particles exceeds 107 years, which tends to rule out origin in the asteroid belt. A favorable possibility is that these 21Ne‐rich IDPs previously resided on a relatively stable regolith of an Edgeworth‐Kuiper belt or Oort cloud body and were introduced into the inner solar system by cometary activity. These results demonstrate the utility of noble gas measurements in constraining models for the origins of interplanetary dust particles. 相似文献
744.
745.
Nearly simultaneous photometry of the reflected and thermal infrared spectra of periodic comets Encke, Chernykh, Kearns-Kwee, Stephan-Oterma, and Tuttle are presented. The 10-μm, silicate emission feature has been detected for the first time in periodic comets and was observed in three of these objects. The albedo of the dust particles in the comae of these comets is calculted and compared to that of Comet Kohoutek. The peculiar behavior of the dust in Comet Encke is discussed. 相似文献
746.
747.
Sean C. Solomon Ralph L. McNutt Jr. Robert E. Gold Mario H. Acua Daniel N. Baker William V. Boynton Clark R. Chapman Andrew F. Cheng George Gloeckler James W. Head III Stamatios M. Krimigis William E. McClintock Scott L. Murchie Stanton J. Peale Roger J. Phillips Mark S. Robinson James A. Slavin David E. Smith Robert G. Strom Jacob I. Trombka Maria T. Zuber 《Planetary and Space Science》2001,49(14-15)
Mercury holds answers to several critical questions regarding the formation and evolution of the terrestrial planets. These questions include the origin of Mercury's anomalously high ratio of metal to silicate and its implications for planetary accretion processes, the nature of Mercury's geological evolution and interior cooling history, the mechanism of global magnetic field generation, the state of Mercury's core, and the processes controlling volatile species in Mercury's polar deposits, exosphere, and magnetosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to fly by and orbit Mercury to address all of these key questions. After launch by a Delta 2925H-9.5, two flybys of Venus, and two flybys of Mercury, orbit insertion is accomplished at the third Mercury encounter. The instrument payload includes a dual imaging system for wide and narrow fields-of-view, monochrome and color imaging, and stereo; X-ray and combined gamma-ray and neutron spectrometers for surface chemical mapping; a magnetometer; a laser altimeter; a combined ultraviolet–visible and visible-near-infrared spectrometer to survey both exospheric species and surface mineralogy; and an energetic particle and plasma spectrometer to sample charged species in the magnetosphere. During the flybys of Mercury, regions unexplored by Mariner 10 will be seen for the first time, and new data will be gathered on Mercury's exosphere, magnetosphere, and surface composition. During the orbital phase of the mission, one Earth year in duration, MESSENGER will complete global mapping and the detailed characterization of the exosphere, magnetosphere, surface, and interior. 相似文献
748.
749.
750.
George Bozis 《Celestial Mechanics and Dynamical Astronomy》1983,31(1):43-51
Any two of the componentsX, Y, andZ of an autonomous force field which gives rise to the space orbitsF(x, y, z)=c 1,G(x, y, z)=c 2 are related by a partial differential equation with coefficients depending on the functionsF andG. This is a generalization of the corresponding equation for planar orbits (Bozis, 1983). The above partial differential equation is accompanied by the algebraic linear equation inX, Y, andZ expressing the fact that the force vector is lying in the osculating plane at each point of the orbit. The two equations constitute a generalization of the corresponding Szebehely's equations in the three dimensional space (Érdi, 1982). The generalization is meant in the sense that the dynamical system is not necessarily assumed to be conservative. 相似文献