全文获取类型
收费全文 | 91304篇 |
免费 | 1366篇 |
国内免费 | 2144篇 |
专业分类
测绘学 | 2925篇 |
大气科学 | 6200篇 |
地球物理 | 17961篇 |
地质学 | 36591篇 |
海洋学 | 7272篇 |
天文学 | 16954篇 |
综合类 | 2441篇 |
自然地理 | 4470篇 |
出版年
2022年 | 708篇 |
2021年 | 1071篇 |
2020年 | 1100篇 |
2019年 | 1179篇 |
2018年 | 6832篇 |
2017年 | 5968篇 |
2016年 | 4875篇 |
2015年 | 1472篇 |
2014年 | 2310篇 |
2013年 | 3582篇 |
2012年 | 3581篇 |
2011年 | 5864篇 |
2010年 | 4908篇 |
2009年 | 5768篇 |
2008年 | 4921篇 |
2007年 | 5553篇 |
2006年 | 3179篇 |
2005年 | 2157篇 |
2004年 | 2196篇 |
2003年 | 2090篇 |
2002年 | 1867篇 |
2001年 | 1552篇 |
2000年 | 1407篇 |
1999年 | 1040篇 |
1998年 | 1104篇 |
1997年 | 1095篇 |
1996年 | 869篇 |
1995年 | 863篇 |
1994年 | 775篇 |
1993年 | 674篇 |
1992年 | 660篇 |
1991年 | 630篇 |
1990年 | 730篇 |
1989年 | 622篇 |
1988年 | 581篇 |
1987年 | 666篇 |
1986年 | 519篇 |
1985年 | 686篇 |
1984年 | 789篇 |
1983年 | 706篇 |
1982年 | 689篇 |
1981年 | 637篇 |
1980年 | 647篇 |
1979年 | 527篇 |
1978年 | 567篇 |
1977年 | 517篇 |
1976年 | 470篇 |
1975年 | 457篇 |
1974年 | 457篇 |
1973年 | 526篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
L. Kahl Kristensen 《Astronomische Nachrichten》1995,316(4):261-266
An elliptic orbit is determined from two short-arc pairs of observations at different oppositions by the angular momentum integral. Other methods for initial orbit determination than the classical do exist. 相似文献
962.
963.
E. V. Ruban G. A. Alekseeva A. A. Arkharov E. I. Hagen-Thorn V. D. Galkin I. N. Nikanorova V. V. Novikov V. P. Pakhomov T. Yu. Puzakova 《Astronomy Letters》2006,32(9):604-607
We present the results of our visual and near-infrared spectrophotometric observations for 77 variable stars obtained during 1971–1991 in Chile, Armenia, and Bolivia. The quasi-monochromatic, extraatmospheric fluxes from the stars are given in absolute energy units (W m?2 m?1) at all wavelengths of the spectral range at 2.5-nm intervals. 相似文献
964.
We analyze the role of weak photospheric flux concentrations that evolve in a filament channel, in the triggering of dynamic
changes in the shape of a filament. The high polarimetric sensitivity of THEMIS allowed us to detect weak flux concentrations
(few Gauss) associated with the filament development. The synoptic instruments (MDI, SOLIS) even if their sensitivity is much
less than THEMIS were useful to follow any subsequent strengthening of these flux concentrations after their identification
in the THEMIS magnetograms. We found that (1) the northern part of the filament develops an Hα barb at the same time that
weak minority polarity elements develop near a plage; (2) a section in the southern part of the Hα filament gradually disappears
and later reforms at the same time that several mixed-polarity magnetic elements appear, then subsequently cancel or spread
away from each other. These changes correspond to increases in EUV emission, as observed by TRACE, EIT, and CDS. This suggests
that the plasma is temporarily heated along the filament spine. An idealized sequence of force-free models of this filament
channel, based on plasma-supporting magnetic dips occurring in the windings of a very weakly twisted flux tube, naturally
explains the evolution of its southern part as being due to changes in the topology of the coronal magnetic field as the photospheric
flux concentrations evolve. 相似文献
965.
Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington Rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 R⊙ using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron-density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 Å band obtained by tomography for the same CR. A global 3D MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic-field structures. We show that the density-maximum locations can serve as an indicator of current-sheet position, while the locations of the density-gradient maximum can be a reliable indicator of coronal-hole boundaries. We find that the magnetic-field configuration during CR 2066 has a tendency to become radially open at heliocentric distances greater than 2.5 R⊙. We also find that the potential-field model with a fixed source surface is inconsistent with the boundaries between the regions with open and closed magnetic-field structures. This indicates that the assumption of the potential nature of the coronal global magnetic field is not satisfied even during the deep solar minimum. Results of our 3D density reconstruction will help to constrain solar coronal-field models and test the accuracy of the magnetic-field approximations for coronal modeling. 相似文献
966.
Klochkova V. G. Panchuk V. E. Tavolzhanskaya N. S. Yushkin M. V. 《Astronomy Letters》2020,46(8):528-540
Astronomy Letters - Evidence of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser ( $${=}$$ IRAS 17279 $$-$$ 1119)... 相似文献
967.
968.
969.
970.
The seasonal variation of the nocturnal average intensity, and the typical variation of the sodium airglow intensity during the night have been deduced, using a data set that has been accumulated over a period of 5 years. The maximum intensity, which occurs at the equinoxes, is about 2–3 times as large as the intensity during winter, when the intensity of the D2 line is about 30 R. The nocturnal variation is symmetrical about midnight, where the intensity is some 30% less than just after (before) dusk (dawn) values. 相似文献