全文获取类型
收费全文 | 47352篇 |
免费 | 7949篇 |
国内免费 | 10567篇 |
专业分类
测绘学 | 4087篇 |
大气科学 | 5246篇 |
地球物理 | 9297篇 |
地质学 | 27740篇 |
海洋学 | 4898篇 |
天文学 | 3875篇 |
综合类 | 3275篇 |
自然地理 | 7450篇 |
出版年
2024年 | 168篇 |
2023年 | 432篇 |
2022年 | 1186篇 |
2021年 | 1365篇 |
2020年 | 1439篇 |
2019年 | 1783篇 |
2018年 | 1388篇 |
2017年 | 1582篇 |
2016年 | 1737篇 |
2015年 | 1904篇 |
2014年 | 2379篇 |
2013年 | 2364篇 |
2012年 | 2667篇 |
2011年 | 2939篇 |
2010年 | 2496篇 |
2009年 | 3102篇 |
2008年 | 3044篇 |
2007年 | 3427篇 |
2006年 | 3323篇 |
2005年 | 2955篇 |
2004年 | 2834篇 |
2003年 | 2679篇 |
2002年 | 2361篇 |
2001年 | 2104篇 |
2000年 | 1955篇 |
1999年 | 1833篇 |
1998年 | 1607篇 |
1997年 | 1396篇 |
1996年 | 1272篇 |
1995年 | 1090篇 |
1994年 | 1114篇 |
1993年 | 925篇 |
1992年 | 732篇 |
1991年 | 519篇 |
1990年 | 459篇 |
1989年 | 363篇 |
1988年 | 277篇 |
1987年 | 177篇 |
1986年 | 127篇 |
1985年 | 84篇 |
1984年 | 43篇 |
1983年 | 32篇 |
1982年 | 37篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 29篇 |
1978年 | 36篇 |
1977年 | 24篇 |
1975年 | 4篇 |
1954年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
112.
随着河南区域化探扫面工作的结束,异常评价是摆在我们面前的当务之急。近年来,随着地质工作的不断深入,我们在异常评价程序及方法上作了一些探索,下面以桐柏县固庙—新集1:20万金银异常评价方法及效果为例,重点加以讨论。 相似文献
113.
114.
115.
C. Tadhunter K. Wills R. Morganti T. Oosterloo R. Dickson 《Monthly notices of the Royal Astronomical Society》2001,327(1):227-232
We present new spectroscopic observations of the southern radio galaxy . Despite the flat-spectrum character of the radio emission from this source, our optical spectra show no sign of the broad permitted lines and non-stellar continuum characteristic of quasar nuclei and broad-line radio galaxies. However, the high-ionization forbidden lines, including [O iii ] λλ 5007, 4959, are unusually broad for a narrow-line radio galaxy , and are blueshifted by 600 km s−1 relative to the low-ionization lines such as [O ii ] λλ 3726,3729. The [O ii ] lines are also considerably narrower than the [O iii ] lines, and have a redshift consistent with that of the recently detected H i 21-cm absorption-line system. Whereas the kinematics of the [O iii ] emission lines are consistent with outflow in an inner narrow-line region, the properties of the [O ii ] emission lines suggest that they are emitted by a more extended and quiescent gaseous component. We argue that, given the radio properties of the source, our line of sight is likely to be lying close to the direction of bulk outflow of the radio jets. In this case it is probable that the quasar nucleus is entirely obscured at optical wavelengths by the material responsible for the H i absorption-line system. The unusually broad [O iii ] emission lines suggest that the radio source is intrinsically compact. Overall, our data are consistent the idea that is a radio source in an early stage of evolution. 相似文献
116.
企鹅珍珠贝人工苗生长的初步观察 总被引:3,自引:0,他引:3
为了解企鹅珍珠贝生长规律,观察了壳高2.5~5.0mm的出池幼苗,按月测量其生长参数和成活率,以及环境因子。结果表明,企鹅珍珠贝生长最快的月份为7~11月和次年4~6月,壳长,壳高和壳宽月均增加量分别为3.8~13.0mm、4.7~11.2mm、2.3~3.8mm,月成活率97.8%~98.6%。企鹅珍珠贝生长最慢月份是11月至次年3月。 相似文献
117.
N. Yoshida J. Colberg S.D.M. White A.E. Evrard T.J. MacFarland † H.M.P. Couchman A. Jenkins C.S. Frenk F.R. Pearce G. Efstathiou J.A. Peacock P.A. Thomas 《Monthly notices of the Royal Astronomical Society》2001,325(2):803-816
We create mock pencil-beam redshift surveys from very large cosmological N -body simulations of two cold dark matter (CDM) cosmogonies, an Einstein–de Sitter model ( τ CDM) and a flat model with Ω0 =0.3 and a cosmological constant (ΛCDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et al. Simulation particles are tagged as 'galaxies' so as to reproduce observed present-day correlations. They are then identified along the past light-cones of hypothetical observers to create mock catalogues with the geometry and the distance distribution of the Broadhurst et al. data. We produce 1936 (2625) quasi-independent catalogues from our τ CDM (ΛCDM) simulation. A couple of large clumps in a catalogue can produce a high peak at low wavenumbers in the corresponding one-dimensional power spectrum, without any apparent large-scale periodicity in the original redshift histogram. Although the simulated redshift histograms frequently display regularly spaced clumps, the spacing of these clumps varies between catalogues and there is no 'preferred' period over our many realizations. We find only a 0.72 (0.49) per cent chance that the highest peak in the power spectrum of a τ CDM (ΛCDM) catalogue has a peak-to-noise ratio higher than that in the Broadhurst et al. data. None of the simulated catalogues with such high peaks shows coherently spaced clumps with a significance as high as that of the real data. We conclude that in CDM universes, the regularity on a scale of ∼130 h −1 Mpc observed by Broadhurst et al. has a priori probability well below 10−3 . 相似文献
118.
119.
We present the results of a three-year observational program of long-slit spectroscopy and UBVRI photometry of Triton. We find evidence for short-lived albedo variations at wavelengths less than 0.5 μm with the most notable reddening event measured in October 1997 and “normal” colors returning by May 1998. We report a possible variation in the relative 0.73/0.89 μm methane absorption band strengths, suggesting that the transport or denudation of this species may play a major role in the reddening events. 相似文献
120.
L. K. Erastova 《Astrophysics》2004,47(4):547-554
Some features of a sample of galaxies from the Second Byurakan Survey are discussed. Most of them are small galaxies with star formation. It is shown that different types of galaxies are in the Survey, with high, medium, and low levels of excitation and continua ranging from blue to relatively red. Many of the galaxies have absorption lines in their spectra; their continua are formed by stars in later spectral classes. 相似文献