全文获取类型
收费全文 | 267864篇 |
免费 | 7087篇 |
国内免费 | 6379篇 |
专业分类
测绘学 | 7706篇 |
大气科学 | 21316篇 |
地球物理 | 56157篇 |
地质学 | 94882篇 |
海洋学 | 23170篇 |
天文学 | 56874篇 |
综合类 | 1965篇 |
自然地理 | 19260篇 |
出版年
2021年 | 2974篇 |
2020年 | 3201篇 |
2019年 | 3497篇 |
2018年 | 4236篇 |
2017年 | 3974篇 |
2016年 | 6399篇 |
2015年 | 4838篇 |
2014年 | 7572篇 |
2013年 | 14816篇 |
2012年 | 7153篇 |
2011年 | 8570篇 |
2010年 | 7574篇 |
2009年 | 10137篇 |
2008年 | 8881篇 |
2007年 | 8345篇 |
2006年 | 10056篇 |
2005年 | 8028篇 |
2004年 | 7882篇 |
2003年 | 7415篇 |
2002年 | 7075篇 |
2001年 | 6338篇 |
2000年 | 6195篇 |
1999年 | 5531篇 |
1998年 | 5466篇 |
1997年 | 5279篇 |
1996年 | 4902篇 |
1995年 | 4630篇 |
1994年 | 4299篇 |
1993年 | 3998篇 |
1992年 | 3754篇 |
1991年 | 3665篇 |
1990年 | 3810篇 |
1989年 | 3588篇 |
1988年 | 3348篇 |
1987年 | 3884篇 |
1986年 | 3434篇 |
1985年 | 4241篇 |
1984年 | 4746篇 |
1983年 | 4412篇 |
1982年 | 4317篇 |
1981年 | 3929篇 |
1980年 | 3638篇 |
1979年 | 3509篇 |
1978年 | 3480篇 |
1977年 | 3281篇 |
1976年 | 3040篇 |
1975年 | 2954篇 |
1974年 | 2913篇 |
1973年 | 3082篇 |
1972年 | 2022篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase
of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for
by the field growth theories. 相似文献
992.
N. S. Chauhan 《Astrophysics and Space Science》1985,112(1):185-192
The treatment followed by Coxet al. (1973) for the estimation of the effects of thermal imbalance on the pulsational stability of stars is applied to Roche and point source (Chandrika Prashad) model. The calculations suggest that the eigenvalues obtained for the above model are correct to 0(t
ff/ts). The expressions for stability coefficients and corresponding eigenfunctions for the stars in thermal imbalance for the above models have also been derived. 相似文献
993.
P.S. Rainbow 《Estuarine, Coastal and Shelf Science》1985,21(5):669-686
The crab Carcinus maenas (L.) and the barnacle Elminius modestus Darwin were exposed to a range of dissolved concentrations of Zn, Cu and Cd for 21 days in artificial seawater. Accumulation of Zn and Cu by crabs has been interpreted in terms of the presence of a regulation mechanism to maintain constant body concentrations (83·2 ± 19·4 μg Zn g?1 dry wt.; 39·8 ± 9·8 μg Cu g?1 dry wt.) under varying external dissolved metal levels, until a threshold dissolved metal concentration (c. 400 μg Zn l?1; c. 170 μg Cu l?1) beyond which net accumulation of metal begins. Cadium appears to be accumulated by C. maenas at all exposures with no evidence for regulation of body cadmium concentrations. Exposure of E. modestus to Zn, Cu or Cd caused net accumulation of the respective metal in the bodies of the barnacles, with no evidence for regulation of body metal concentrations. 相似文献
994.
J.D. Pos 《Coastal Engineering》1985,9(2):101-123
An experimental technique and configuration has been developed by the author to simulate and measure (using short range photogrammetric techniques) the wave heights of waves diffracting into a model basin of infinite extent. The finite and infinite element program “WAVE” developed in the Department of Civil Engineering, University College of Swansea, Wales, has been modified to run on the UNIVAC 1100 at the University of Cape Town. The program is used to model the experimental configuration being tested mathematically. Two configurations, namely a symmetrical and an asymmetrical breakwater gap configuration, are analysed both experimentally and numerically. It is concluded that there is a good correlation between the finite element and experimental results and that the “WAVE” program is a very useful tool for the prediction of wave heights in large harbour basins. 相似文献
995.
996.
Sean J. McKenna 《Astrophysics and Space Science》1985,108(1):31-66
A general treatment of the transfer of polarized radiation in spectral lines assuming a Rayleigh phase function and a general law of frequency redistribution is derived. It is shown how nine families of coupled integral equations for the moments of the radiation field arise which are necessary to fully describe the state of polarization of the emergent radiation from a plane-parallel, semi-infinite atmosphere. The special case of angle independent redistribution functions is derived from the general formalism, and it is shown how the nine families of integral equations reduce to the six linearly independent integral equations derived by Collins (1972). To serve as a test of the formulation, solutions for isothermal atmospheres are given. 相似文献
997.
Attia A. Ashour 《Geophysical Journal International》1985,83(1):127-142
Summary. The electrical system of currents excited by a uniform electric field of arbitrary direction in an infinite plane sheet of uniform conductivity except for two non-overlapping circular areas is obtained analytically. Using the method introduced by Ashour, the magnetic field of the system is also obtained. The components of this additional field are expressed as line integrals which are suitable for computation. The results reduce, in the special case of one insertion, to those obtained earlier by Ashour & Chapman.
As an illustration, numerical results are obtained for the special case of two equal insertions of zero conductivity.
The analysis and results obtained are useful in estimating the modification of the currents flowing in an ocean and their magnetic field by two islands. 相似文献
As an illustration, numerical results are obtained for the special case of two equal insertions of zero conductivity.
The analysis and results obtained are useful in estimating the modification of the currents flowing in an ocean and their magnetic field by two islands. 相似文献
998.
Paul A. LaViolette 《Meteoritics & planetary science》1985,20(3):545-558
Dust filtered from the lower portion of the Camp Century ice core (77°10'N, 61°08'W) has been analyzed for the presence of the cosmic dust indicators iridium and nickel using the neutron activation analysis technique. This study was carried out to test the hypothesis that the climatic change toward the end of the Last Ice Age was triggered by an incursion of nebular material into the Solar System. The analytical results are consistent with this hypothesis. Concentrations of Ir and Ni in the ice were one to two orders of magnitude higher during the latter portion of the Last Ice Age (19,700-14,200 years BP) as compared with current levels. Ir and Ni levels in 6 out of 8 samples suggest a total cosmic dust influx rate of about 0.5?3 times 107 tons/yr to the Earth's surface as compared with about 1?7 x× 105 tons/yr for the current influx. Elemental concentrations in 6 of the 8 dust samples ranged from 6? 96 ppb for Ir and < 60 to 3200 ppm for Ni. It is concluded that a major fraction of this invading dust would have been of submicron size in which case the concentration of light scattering particles would have been sufficient to significantly alter the light transmission properties of the Solar System and substantially affect the Earth's climate. These results mark the first time that cosmic dust deposition rates have been estimated for prehistoric times using the polar ice record. 相似文献
999.
1000.