全文获取类型
收费全文 | 30033篇 |
免费 | 488篇 |
国内免费 | 326篇 |
专业分类
测绘学 | 668篇 |
大气科学 | 1885篇 |
地球物理 | 5449篇 |
地质学 | 11472篇 |
海洋学 | 3081篇 |
天文学 | 6953篇 |
综合类 | 71篇 |
自然地理 | 1268篇 |
出版年
2022年 | 302篇 |
2021年 | 464篇 |
2020年 | 524篇 |
2019年 | 566篇 |
2018年 | 1107篇 |
2017年 | 1061篇 |
2016年 | 1172篇 |
2015年 | 566篇 |
2014年 | 1071篇 |
2013年 | 1739篇 |
2012年 | 1180篇 |
2011年 | 1474篇 |
2010年 | 1322篇 |
2009年 | 1615篇 |
2008年 | 1355篇 |
2007年 | 1437篇 |
2006年 | 1346篇 |
2005年 | 780篇 |
2004年 | 729篇 |
2003年 | 690篇 |
2002年 | 708篇 |
2001年 | 640篇 |
2000年 | 585篇 |
1999年 | 476篇 |
1998年 | 488篇 |
1997年 | 465篇 |
1996年 | 404篇 |
1995年 | 362篇 |
1994年 | 389篇 |
1993年 | 304篇 |
1992年 | 310篇 |
1991年 | 293篇 |
1990年 | 327篇 |
1989年 | 225篇 |
1988年 | 233篇 |
1987年 | 272篇 |
1986年 | 210篇 |
1985年 | 317篇 |
1984年 | 281篇 |
1983年 | 261篇 |
1982年 | 280篇 |
1981年 | 207篇 |
1980年 | 246篇 |
1979年 | 202篇 |
1978年 | 216篇 |
1977年 | 169篇 |
1976年 | 163篇 |
1975年 | 175篇 |
1974年 | 169篇 |
1973年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
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
73.
74.
Eight-year-old Loblolly pine (Pinus taeda) plots located in South Carolina were evaluated using high resolution aircraft multispectral scanner data to determine if biomass could be accurately measured. Sixteen pine plots located on both sandy and clay soils were treated with 0, 180, or 360 kg. (approximately 0, 400, or 800 lb.) of nitrogen per plot. Indices of biomass from remote sensing data were significantly correlated with in situ biomass measurements made in each plot. A ratio of infrared (.9–1.1 μm) and red (.65–.70 μm) channels yielded the best correlation. The indices were not sensitive to differences in soil type (sandy or clay). 相似文献
75.
Sunetra Giridhar N. Kameswara Rao David L. Lambert 《Journal of Astrophysics and Astronomy》1996,17(1-2):23-40
Two high resolution spectra of the hot RCrB star DY Cen in the red region are compared. The photospheric absorption lines
show a radial velocity variation of 12 kms-1 between 1989 July and 1992 May. Emission components to some CII lines present
in 1989 are almost entirely absent in 1992. Nebular forbidden lines of [OI], [NII] and [SII] appear unchanged from 1989 to
1992 相似文献
76.
The main analytical properties of the generalized Shkarofsky function and a numerical code for its computation are discussed. The results of a numerical analysis are compared with the results of an asymptotic analysis for parameter values relevant to the problem of whistler-mode propagation in the Earth's magnetosphere. This comparison allows us to specify the range of applicability of different approximations to the generalized Shkarofsky function, which have been used for the analysis of relativistic effects on whistler-mode propagation and instability. 相似文献
77.
78.
Axial surveys were performed in the two river tributaries of the Cochin estuary, SW India during November 1988. Surficial sediments were subjected to sequential chemical extractions to delineate five metal fractions, namely, exchangeable, carbonate bound, easily reducible, organic/sulfide bound, and residual. The results indicated selective accumulation of Mn and Ni in carbonate bound and organic/sulfide forms, along with marginal amounts of Co in the exchangeable fraction. Large portions of Fe and Cr occurred in the residual fraction, whereas composite fractionation of Zn species was noticed. The exchangeable fractions of Fe and Cr as well as of easily reducible cobalt were below detection limits. The levels of Cr and Zn indicate anthropogenic inputs in this estuary, whereas Co and Ni show regional contamination exceeding natural levels. The analytical speciation procedure helps to deduce the sedimental diagenetic processes in the estuarine environment. 相似文献
79.
80.
Translated fromAstrofizika, Vol. 37, No. 4, 1994. 相似文献