全文获取类型
收费全文 | 133493篇 |
免费 | 1731篇 |
国内免费 | 1700篇 |
专业分类
测绘学 | 3790篇 |
大气科学 | 9297篇 |
地球物理 | 25760篇 |
地质学 | 49794篇 |
海洋学 | 11232篇 |
天文学 | 26987篇 |
综合类 | 2393篇 |
自然地理 | 7671篇 |
出版年
2022年 | 680篇 |
2021年 | 1228篇 |
2020年 | 1306篇 |
2019年 | 1475篇 |
2018年 | 7297篇 |
2017年 | 6399篇 |
2016年 | 5650篇 |
2015年 | 1941篇 |
2014年 | 3234篇 |
2013年 | 5802篇 |
2012年 | 4344篇 |
2011年 | 6979篇 |
2010年 | 6008篇 |
2009年 | 7471篇 |
2008年 | 6381篇 |
2007年 | 6888篇 |
2006年 | 4535篇 |
2005年 | 3526篇 |
2004年 | 3640篇 |
2003年 | 3437篇 |
2002年 | 3260篇 |
2001年 | 2705篇 |
2000年 | 2610篇 |
1999年 | 2085篇 |
1998年 | 2153篇 |
1997年 | 2011篇 |
1996年 | 1700篇 |
1995年 | 1691篇 |
1994年 | 1467篇 |
1993年 | 1429篇 |
1992年 | 1317篇 |
1991年 | 1314篇 |
1990年 | 1295篇 |
1989年 | 1194篇 |
1988年 | 1108篇 |
1987年 | 1290篇 |
1986年 | 1135篇 |
1985年 | 1386篇 |
1984年 | 1563篇 |
1983年 | 1478篇 |
1982年 | 1350篇 |
1981年 | 1333篇 |
1980年 | 1143篇 |
1979年 | 1096篇 |
1978年 | 1052篇 |
1977年 | 967篇 |
1976年 | 926篇 |
1975年 | 903篇 |
1974年 | 887篇 |
1973年 | 961篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Persistent 22-year cycle in sunspot activity: Evidence for a relic solar magnetic field 总被引:1,自引:0,他引:1
We use the recently presented group sunspot number series to show that a persistent 22-year cyclicity exists in sunspot activity throughout the entire period of about 400 years of direct sunspot observations. The amplitude of this cyclicity is about 10% of the present sunspot activity level. A 22-year cyclicity in sunspot activity is naturally produced by the 22-year magnetic polarity cycle in the presence of a relic dipole magnetic field. Accordingly, a persistent 22-year cyclicity in sunspot activity gives an evidence for the existence of such a relic magnetic field in the Sun. The stable phase and the roughly constant amplitude of this cyclicity during times of very different sunspot activity level strongly support this interpretation. 相似文献
942.
A. T. Kalloghlian R. A. Kandalyan H. M. K. Al-Naimiy A. M. Khassawneh 《Astrophysics》2001,44(3):292-304
The near and mid-IR properties of barred and unbarred spiral galaxies are discussed on the basis of complete samples that were compiled earlier. The two types of spirals are shown not to differ from one another in emission power in the near and mid-IR ranges. Multiple regression and principal component analysis have been applied to investigate near and mid-IR properties of SB and SA galaxies, particularly their relation to X-ray and radio continuum emissions. There are definite differences between SB and SA spirals in the near and mid-IR. In the case of SB galaxies, the compactness of 10 m emission is closely related to the J - H color index, and the redder J - H color corresponds to relatively more extended emission at 10 m. It is assumed that these are caused by the bar itself, which stimulates enhanced star formation in a barred galaxy with respect to unbarred spiral. 相似文献
943.
944.
945.
Using a sample of 57 VLT FORS spectra in the redshift range 1.37< z < 3.40 and a comparison sample with 36 IUE spectra of local (
) starburst galaxies we derive CIV equivalent width values and estimate metallicities of starburst galaxies as a function
of redshift. Assuming that a calibration of the CIV equivalent widths in terms of the metallicity based on the local sample
of starburst galaxies is applicable to high-z objects, we find a significant increase of the average metallicities from about 0.16 Z
⊙ at the cosmic epoch corresponding to z ≈ 3.2 to about 0.42 Z
⊙ at z ≈ 2.3. A significant further increase in metallicity during later epochs cannot be detected in our data. Compared to the
local starburst galaxies our high-redshift objects tend to be overluminous for a given metallicity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
946.
Hypothesis of possible superconductivity of the iced matter of the rings of Saturn (based on the data of Voyager and Pioneer
space missions) allow us to explain many phenomena which have not been adequately understood earlier. Introducing into planetary
physics force of magnetic levitation of the superconducting iced particle of the rings, which interact with magnetosphere
of the planet, becomes to be possible to explain origin, evolution, and dynamics of the rings; to show how the consequent
precipitation of the rings’ matter upon the planet was concluded; how the rings began their rotation; how they were compressed
by the magnetic field into the thin disc, and how this disc was fractured into hundreds of thousands of separated rings; why
in the ring B do exist “spokes”; why magnetic field lines have distortion near by ring F; why there is a variable azimuth brightness of the ring A; why the rings reflected radio waves so efficiently; why exists strong electromagnetic radiation of the rings in the 20.4
kHz–40.2 MHz range and Saturnian kilometric radiation; why there is anomalous reflection of circularly polarized microwaves;
why there are spectral anomalies of the thermal radiation of the rings; why the matter of the various rings does not mix but
preserves its small-scale color differences; why there is an atmosphere of unknown origin nearby the rings of Saturn; why
there are waves of density and bending waves within Saturn’s rings; why planetary rings in the solar system appear only after
the Belt of Asteroids (and may be the Belt of Asteroids itself is a ring for the Sun); why our planet Earth has no rings of
its own. 相似文献
947.
948.
949.
We have made near-infrared photometric observations of nine β-Cephei and eight δ-Scuti stars inJ, H, andK bands. The observed fluxes are in good agreement with those expected according to their spectral types. We conclude that these stars do not have any anomalous emission in these near-infrared bands. 相似文献
950.
Excitation of electron cyclotron waves and whistlers by reflected auroral electrons which possess a loss-cone distribution is investigated. Based on a given magnetic field and density model, the instability problem is studied over a broad region along the auroral field lines. This region covers altitudes ranging from one quarter of an Earth radius to five Earth radii. It is found that the growth rate is significant only in the region of low altitude, say below the source region of the auroral kilometric radiation. In the high altitude region the instability is insignificant either because of low refractive indices or because of small loss cone angles. 相似文献