全文获取类型
收费全文 | 56155篇 |
免费 | 2164篇 |
国内免费 | 3096篇 |
专业分类
测绘学 | 1918篇 |
大气科学 | 4964篇 |
地球物理 | 10143篇 |
地质学 | 25381篇 |
海洋学 | 5258篇 |
天文学 | 9643篇 |
综合类 | 1177篇 |
自然地理 | 2931篇 |
出版年
2023年 | 249篇 |
2022年 | 899篇 |
2021年 | 1229篇 |
2020年 | 1121篇 |
2019年 | 1230篇 |
2018年 | 4399篇 |
2017年 | 3999篇 |
2016年 | 3100篇 |
2015年 | 1189篇 |
2014年 | 1641篇 |
2013年 | 2182篇 |
2012年 | 2656篇 |
2011年 | 4391篇 |
2010年 | 3941篇 |
2009年 | 4163篇 |
2008年 | 3469篇 |
2007年 | 4124篇 |
2006年 | 1803篇 |
2005年 | 1313篇 |
2004年 | 1201篇 |
2003年 | 1332篇 |
2002年 | 1263篇 |
2001年 | 963篇 |
2000年 | 766篇 |
1999年 | 691篇 |
1998年 | 594篇 |
1997年 | 623篇 |
1996年 | 502篇 |
1995年 | 508篇 |
1994年 | 458篇 |
1993年 | 358篇 |
1992年 | 362篇 |
1991年 | 283篇 |
1990年 | 278篇 |
1989年 | 286篇 |
1988年 | 231篇 |
1987年 | 240篇 |
1986年 | 224篇 |
1985年 | 241篇 |
1984年 | 235篇 |
1983年 | 229篇 |
1982年 | 224篇 |
1981年 | 204篇 |
1980年 | 201篇 |
1979年 | 203篇 |
1978年 | 171篇 |
1977年 | 155篇 |
1976年 | 150篇 |
1975年 | 157篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Rodger I. Thompson 《Astrophysics and Space Science》2003,284(2):353-356
Tests and constraints on current theories of galaxy formation and evolution are presented. They are derived from observations
of the Northern Hubble Deep Field with WFPC2 and NICMOS. Photometric redshifts, extinctions and spectral energy distributions
are calculated for all objects in the field. The tests and constraints are derived from the output of this analysis. The tests
of the predictions from hierarchical and pure luminosity evolution galaxy evolution calculations favor the hierarchical model.
Constraints are provided by the current luminosity function and its evolution to a redshift of 6.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
142.
143.
A flare of OH maser emission was discovered in W75N in 2000. Its location was determined with the Very Long Baseline Array (VLBA) to be within 110 au from one of the ultracompact H ii regions, Very Large Array 2 (VLA2). The flare consisted of several maser spots. Four of the spots were found to form Zeeman pairs, all of them with a magnetic field strength of about 40 mG. This is the highest ever magnetic field strength found in OH masers, an order of magnitude higher than in typical OH masers. Three possible sources for the enhanced magnetic field are discussed: (i) the magnetic field of the exciting star dragged out by the stellar wind; (ii) the general interstellar field in the gas compressed by the magnetohydrodynamic shock; and (iii) the magnetic field of planets which orbit the exciting star and produce maser emission in gaseous envelopes. 相似文献
144.
145.
146.
147.
Churyumov K. I. Klesachonok V. V. Mussaev F. A. Bikmaev I. F. Galazutdinov G. H. 《Earth, Moon, and Planets》1997,78(1-3):105-110
We present the results of the preliminary study of the comet Hale-Bopp spectrum obtained April 17, 1997 by K. Churyumov and F. Mussayev with the help of the 1-meter Zeiss reflector and the echelle spectrometer (spectral resolutionλ/Δ λ ≈ 50000), CCD and the long slit, oriented along the radius-vector(“Sun-comet direction”). Energy distributions for three selected regions including the C3, C2 (0-0) and CN(Δ ν = 0) molecules emissions of the comet Hale-Bopp spectrum were built. The rotational lines of the CN(Δ ν = 0) band were identified. The nature of the high emission peak near λ 4020 Å in the C3 band is discussed. The presence of the cometary continuum of the nonsolar origin is assumed. 相似文献
148.
V. I. Ferronsky S. A. Denisik S. V. Ferronsky 《Celestial Mechanics and Dynamical Astronomy》1996,64(3):167-183
The physical meaning of the terms of the potential and kinetic energy expressions, expanded by means of the density variation function for a nonuniform self-gravitating sphere, is discussed. The terms of the expansions represent the energy and the moment of inertia of the uniform sphere, the energy and the moment of inertia of the nonuniformities interacting with the uniform sphere, and the energy of the nonuniformities interacting with each other. It follows from the physical meaning of the above components of the energy structure, and also from the observational fact of the expansion of the Universe that the phase transition, notably, fusion of particles and nuclei and condensation of liquid and solid phases of the expanded matter accompanied by release of energy, must be the physical cause of initial thermal and gravitational instability of the matter. The released kinetic energy being constrained by the general motion of the expansion, develops regional and local turbulent (cyclonic) motion of the matter, which should be the second physical effect responsible for the creation of celestial bodies and their rotation. 相似文献
149.
A. B. Pushkarev D. C. Gabuzda Yu. N. Vetukhnovskaya V. E. Yakimov 《Monthly notices of the Royal Astronomical Society》2005,356(3):859-871
We present the results of multifrequency (15 + 8 + 5 GHz) polarization Very Long Baseline Array (VLBA) observations of the three BL Lacertae objects 0745+241, 1418+546 and 1652+398 together with 5-GHz VLBI Space Observatory Programme (VSOP) observations of 1418+546 and 1.6- and 5-GHz VSOP observations of the blazar 1055+018. The jets of all these sources have polarization structure transverse to the jet axis, with the polarization E vectors aligned with the jet along the jet spine and 'sheaths' of orthogonal E vectors at one or both edges of the jet. The presence of polarization aligned with the jet near the 'spine' may indicate that the jets are associated with helical B fields that propogate outward with the jet flow; the presence of orthogonal polarization near the edges of the jet may likewise be a consequence of a helical jet B field, or may be owing to an interaction with the ambient medium on parsec scales. We have tentatively detected interknot polarization in 1055+018 with E aligned with the local jet direction, consistent with the possibility that the jet of this source is associated with a helical B field. 相似文献
150.