全文获取类型
收费全文 | 31869篇 |
免费 | 742篇 |
国内免费 | 292篇 |
专业分类
测绘学 | 734篇 |
大气科学 | 2435篇 |
地球物理 | 6641篇 |
地质学 | 11095篇 |
海洋学 | 2605篇 |
天文学 | 7055篇 |
综合类 | 74篇 |
自然地理 | 2264篇 |
出版年
2021年 | 231篇 |
2020年 | 279篇 |
2019年 | 330篇 |
2018年 | 673篇 |
2017年 | 621篇 |
2016年 | 787篇 |
2015年 | 603篇 |
2014年 | 790篇 |
2013年 | 1586篇 |
2012年 | 971篇 |
2011年 | 1333篇 |
2010年 | 1147篇 |
2009年 | 1570篇 |
2008年 | 1367篇 |
2007年 | 1316篇 |
2006年 | 1231篇 |
2005年 | 1057篇 |
2004年 | 1081篇 |
2003年 | 980篇 |
2002年 | 926篇 |
2001年 | 793篇 |
2000年 | 768篇 |
1999年 | 666篇 |
1998年 | 677篇 |
1997年 | 654篇 |
1996年 | 521篇 |
1995年 | 499篇 |
1994年 | 465篇 |
1993年 | 401篇 |
1992年 | 387篇 |
1991年 | 336篇 |
1990年 | 356篇 |
1989年 | 330篇 |
1988年 | 290篇 |
1987年 | 360篇 |
1986年 | 311篇 |
1985年 | 409篇 |
1984年 | 447篇 |
1983年 | 439篇 |
1982年 | 388篇 |
1981年 | 370篇 |
1980年 | 365篇 |
1979年 | 338篇 |
1978年 | 360篇 |
1977年 | 294篇 |
1976年 | 294篇 |
1975年 | 299篇 |
1974年 | 261篇 |
1973年 | 267篇 |
1972年 | 172篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
21.
The UBV photometric observations of RT Per, from Sanwal and Chaubey (1981), were analyzed by the Wilson and Devinney code (1971). The light curves include reflection effects that for the first time has been suggested by Dugan (1911). RT Per has a semi-detached configuration where the lower-mass component is in contact with its respective Roche surface. The higher-mass component very nearly fills its Roche lobe. It has the characteristic of an Algol type system. The absolute dimensions for the primary and secondary of this system were calculated from its spectral types and by combining the photometric solution with inferred component radial velocities (Lu, 1990). 相似文献
22.
23.
W. H. Jefferys G. F. Benedict P. D. Hemenway P. J. Shelus R. L. Duncombe 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):299-305
The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed. 相似文献
24.
Electron impact excitation rates for transitions in the S v ion, calculated with theR-matrix code, are used to derive the electron temperature sensitive emission line ratiosR
1 =I(854.8 Å)/I(786.9 Å),R
2 =I(852.2 Å)/I(786.9 Å),R
3 =I(849.2 Å)/I(786.9 Å), andR
4 =I(1199.1 Å)/I(786.9 Å), which are found to be significantly different from previous estimates. A comparison of the present results with observational data for a sunspot obtained with the Harvard S-055 spectrometer on boardSkylab reveals generally good agreement between theory and experiment, except in the case ofR
1, which is probably due to blending in the 854.8 Å feature. The possible effects of Lyman continuum absorption on the observed line ratios is briefly discussed. 相似文献
25.
M.S. Hanner E. Tedesco A.T. Tokunaga G.J. Veeder D.F. Lester F.C. Witteborn J.D. Bregman J. Gradie L. Lebofsky 《Icarus》1985,64(1):11-19
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm. 相似文献
26.
George Saklatvala Michael P. Hobson Stafford Withington 《Monthly notices of the Royal Astronomical Society》2006,367(3):1194-1200
We describe a procedure for the numerical modelling of astronomical interferometers, with particular relevance to far-infrared and submillimetre wavelengths. The scheme is based on identifying a set of modes that carry power from the sky to the detector. The procedure is extremely general, and can be used to model scalar or vector fields, in any state of coherence and polarization, the only limitation being that the propagation of a coherent field through the system be described by an integral transform, a constraint that is in practise always met.
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers. 相似文献
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers. 相似文献
27.
28.
In this paper we analyse error-removing techniques used without sufficient theoretical support in a previous paper, where Chandrasekhar's higher-order perturbation theories were developed for either uniformly or differentially-rotating polytropic stars. 相似文献
29.
30.