全文获取类型
收费全文 | 13190篇 |
免费 | 2266篇 |
国内免费 | 3338篇 |
专业分类
测绘学 | 1061篇 |
大气科学 | 899篇 |
地球物理 | 2878篇 |
地质学 | 7277篇 |
海洋学 | 1554篇 |
天文学 | 2192篇 |
综合类 | 868篇 |
自然地理 | 2065篇 |
出版年
2024年 | 62篇 |
2023年 | 185篇 |
2022年 | 503篇 |
2021年 | 580篇 |
2020年 | 619篇 |
2019年 | 656篇 |
2018年 | 560篇 |
2017年 | 560篇 |
2016年 | 603篇 |
2015年 | 675篇 |
2014年 | 738篇 |
2013年 | 766篇 |
2012年 | 791篇 |
2011年 | 831篇 |
2010年 | 712篇 |
2009年 | 999篇 |
2008年 | 856篇 |
2007年 | 918篇 |
2006年 | 971篇 |
2005年 | 752篇 |
2004年 | 782篇 |
2003年 | 747篇 |
2002年 | 590篇 |
2001年 | 501篇 |
2000年 | 474篇 |
1999年 | 412篇 |
1998年 | 418篇 |
1997年 | 310篇 |
1996年 | 242篇 |
1995年 | 204篇 |
1994年 | 187篇 |
1993年 | 149篇 |
1992年 | 126篇 |
1991年 | 73篇 |
1990年 | 65篇 |
1989年 | 52篇 |
1988年 | 34篇 |
1987年 | 33篇 |
1986年 | 18篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
81.
82.
E. García L. De Haro C. O'Sullivan G. Cahill J. A. López Fernández F. Tercero B. Galocha J. L. Besada 《Experimental Astronomy》2003,15(3):173-193
A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower
the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes
modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the
horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on
the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME).
Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical
Optics (GO) with a Kirchoff–Huygens integration to get the far-field pattern, have been compared with measurements. As a direct
application, a full focusing system for the new 40-m radiotelescope at the “Centro Astronómico de Yebes” is presented for
the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
83.
Miguel Cerviño 《Astrophysics and Space Science》2003,284(2):897-900
Evolutionary synthesis models have been used to study the physical properties of unresolved populations in a wide range of
scenarios. Unfortunately, their self-consistency is difficult to test and there are some theoretical open questions without
an answer: (1) The change of the homology relations assumed in the computation of isochrones due to the effect of stellar
winds (or rotation) and the discontinuities in the stellar evolution are not considered. (2) There is no consensus about how
the isochrones must be integrated. (3) The discreteness of the stellar populations (that produce an intrinsic statistical
dispersion) usually are not taken into account, and model results are interpreted in a deterministic way instead of a statistical
one. The objective of this contribution is to present some inconsistencies in the computation and some cautions in the application
of the results of such codes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
84.
1IntroductionOne of the key factors related to basin geody-namics is deep process controlling formation and evolution of sedimentary basin. Depth and tempera-ture of asthenosphere,existence of mantle plume,occurrence of mantle melting,and amounts of melts under depressurization during thinning of lithosphere are controlling factors influenced formation and characteristics of extensional basin directly (Li,1994). Rifting is probably governed by frictional forces exerted on the base of litho… 相似文献
85.
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
86.
87.
88.
89.
90.