全文获取类型
收费全文 | 70297篇 |
免费 | 928篇 |
国内免费 | 573篇 |
专业分类
测绘学 | 1686篇 |
大气科学 | 4926篇 |
地球物理 | 12869篇 |
地质学 | 28130篇 |
海洋学 | 5843篇 |
天文学 | 14783篇 |
综合类 | 254篇 |
自然地理 | 3307篇 |
出版年
2022年 | 371篇 |
2021年 | 575篇 |
2020年 | 665篇 |
2019年 | 729篇 |
2018年 | 3939篇 |
2017年 | 3602篇 |
2016年 | 2940篇 |
2015年 | 1041篇 |
2014年 | 1602篇 |
2013年 | 2744篇 |
2012年 | 2636篇 |
2011年 | 4540篇 |
2010年 | 3992篇 |
2009年 | 4640篇 |
2008年 | 3816篇 |
2007年 | 4423篇 |
2006年 | 2186篇 |
2005年 | 1877篇 |
2004年 | 1768篇 |
2003年 | 1753篇 |
2002年 | 1562篇 |
2001年 | 1266篇 |
2000年 | 1173篇 |
1999年 | 948篇 |
1998年 | 995篇 |
1997年 | 968篇 |
1996年 | 801篇 |
1995年 | 741篇 |
1994年 | 725篇 |
1993年 | 591篇 |
1992年 | 566篇 |
1991年 | 525篇 |
1990年 | 584篇 |
1989年 | 463篇 |
1988年 | 433篇 |
1987年 | 548篇 |
1986年 | 439篇 |
1985年 | 627篇 |
1984年 | 622篇 |
1983年 | 607篇 |
1982年 | 577篇 |
1981年 | 497篇 |
1980年 | 542篇 |
1979年 | 450篇 |
1978年 | 495篇 |
1977年 | 412篇 |
1976年 | 415篇 |
1975年 | 436篇 |
1974年 | 383篇 |
1973年 | 392篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
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
82.
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
83.
N. I. Kobanov 《Solar physics》1990,125(1):25-30
Using a differential method we have carried out observations of oscillations in six sunspots. Spectral lines Fe i 5434 Å and Fe i 5576 Å were used. Horizontal waves are not observed in the sunspot umbra photosphere. Results obtained indicate that, at least, the sunspot umbra oscillates as a single whole. 相似文献
84.
An algorithm for considering time-correlated errors in a Kalman filter is presented. The algorithm differs from previous implementations
in that it does not suffer from numerical problems; does not contain inherent time latency or require reinterpretation of
Kalman filter parameters, and gives full consideration to additive white noise that is often still present but ignored in
previous implementations. Simulation results indicate that the application of the new algorithm yields more realistic and
therefore useful state and covariance information than the standard implementation. Results from a field test of the algorithm
applied to the problem of kinematic differential GPS demonstrate that the algorithm provides slightly pessimistic covariance
estimates whereas the standard Kalman filter provides optimistic covariance estimates. 相似文献
85.
N. N. Chugai 《Astronomy Letters》2006,32(11):739-746
I study the question of whether the asymmetry of 56Ni ejecta that results in the asymmetry of the Hα emission line at the nebular epoch of the type-IIP supernova SN 2004dj can account for the recently detected polarization of the supernova radiation. I have developed a model of the Hα profile and luminosity with nonthermal ionization and excitation in a spherically symmetric envelope for an asymmetric bipolar 56Ni distribution. I have calculated the polarized radiation transfer against the background of the recovered electron density distribution. The observed polarization is shown to be reproduced at the nebular epoch around day 140 for the same parameters of the envelope, and the 56Ni distribution for which the evolution of the Hα luminosity and profile is explained. Yet the model polarization decreases with time more slowly than is observed. The origin of the additional component responsible for the early polarization on day 107 is discussed. 相似文献
86.
87.
This paper describes a wide-field survey made at 34.5 MHz using GEETEE,1 the low frequency telescope at Gauribidanur (latitude
13°36′12′′N). This telescope was used in the transit mode and by per forming 1-D synthesis along the north-south direction
the entire observable sky was mapped in a single day. This minimized the problems that hinder wide-field low-frequency mapping.
This survey covers the declination range of-50° to + 70° (- 33° to +61° without aliasing) and the complete 24 hours of right
ascension. The synthesized beam has a resolution of 26′ x 42′ sec (δ- 14°. 1). The sensitivity of the survey is 5 Jy/beam (1σ). Special care has been taken to ensure that the antenna responds
to all angular scale structures and is suitable for studies of both point sources and extended objects
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Roman Research Institute, Bangalore. 相似文献
88.
89.
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
90.