全文获取类型
收费全文 | 106702篇 |
免费 | 1591篇 |
国内免费 | 926篇 |
专业分类
测绘学 | 2915篇 |
大气科学 | 7463篇 |
地球物理 | 20470篇 |
地质学 | 39703篇 |
海洋学 | 9016篇 |
天文学 | 23879篇 |
综合类 | 400篇 |
自然地理 | 5373篇 |
出版年
2022年 | 538篇 |
2021年 | 939篇 |
2020年 | 1031篇 |
2019年 | 1111篇 |
2018年 | 4373篇 |
2017年 | 4038篇 |
2016年 | 3869篇 |
2015年 | 1667篇 |
2014年 | 2722篇 |
2013年 | 4855篇 |
2012年 | 3671篇 |
2011年 | 5666篇 |
2010年 | 5014篇 |
2009年 | 6171篇 |
2008年 | 5169篇 |
2007年 | 5646篇 |
2006年 | 3628篇 |
2005年 | 3074篇 |
2004年 | 3050篇 |
2003年 | 2866篇 |
2002年 | 2689篇 |
2001年 | 2173篇 |
2000年 | 2081篇 |
1999年 | 1721篇 |
1998年 | 1786篇 |
1997年 | 1632篇 |
1996年 | 1439篇 |
1995年 | 1396篇 |
1994年 | 1253篇 |
1993年 | 1103篇 |
1992年 | 1076篇 |
1991年 | 1076篇 |
1990年 | 1147篇 |
1989年 | 949篇 |
1988年 | 931篇 |
1987年 | 1061篇 |
1986年 | 937篇 |
1985年 | 1188篇 |
1984年 | 1310篇 |
1983年 | 1213篇 |
1982年 | 1116篇 |
1981年 | 1097篇 |
1980年 | 977篇 |
1979年 | 934篇 |
1978年 | 895篇 |
1977年 | 756篇 |
1976年 | 714篇 |
1975年 | 719篇 |
1974年 | 667篇 |
1973年 | 738篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
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
52.
Similarity solutions, describing the flow of a perfect gas behind spherical shock waves, are investigated including the radiation heat flux. The shock is assumed to be propagating in a medium at rest. Shock radius varies exponentially with time and density is inversely proportional to fifth power of the shock radius immediately ahead of the shock front. 相似文献
53.
54.
55.
56.
Rostov State Pedagogical Institute; All-Union Scientific Research Institute Gradient. Translated from Astrofizika, Vol. 33, No. 3, pp. 379–393, November–December, 1990. 相似文献
57.
It is shown that the kinematical parameters associated with the congruence formed by tachyonic motion can be defined in the manner of Greenberg, but not that of Ehlers. The space-like counterpart of Raychaudhuri's equation has also been obtained. 相似文献
58.
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
59.
The Raychaudhuri equation is written in terms of atomic units in the scale-covariant theory of Canutoet al. (1977) and it is pointed out that even dust-filled nonrotating cosmological models may not have an observable singularity of infinite density in the beginning. Simple explicit solutions of Einstein's equations are also constructed in terms of atomic units and its is shown that the Einstein-de Sitter solution in gravitational units may appear to be a static or an oscillating universe in atomic units. 相似文献
60.
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