全文获取类型
收费全文 | 87585篇 |
免费 | 1412篇 |
国内免费 | 681篇 |
专业分类
测绘学 | 2223篇 |
大气科学 | 6813篇 |
地球物理 | 18006篇 |
地质学 | 29758篇 |
海洋学 | 7528篇 |
天文学 | 19219篇 |
综合类 | 188篇 |
自然地理 | 5943篇 |
出版年
2021年 | 577篇 |
2020年 | 730篇 |
2019年 | 757篇 |
2018年 | 1539篇 |
2017年 | 1537篇 |
2016年 | 2025篇 |
2015年 | 1354篇 |
2014年 | 2034篇 |
2013年 | 4394篇 |
2012年 | 2210篇 |
2011年 | 3170篇 |
2010年 | 2767篇 |
2009年 | 3857篇 |
2008年 | 3477篇 |
2007年 | 3218篇 |
2006年 | 3250篇 |
2005年 | 2688篇 |
2004年 | 2764篇 |
2003年 | 2570篇 |
2002年 | 2460篇 |
2001年 | 2242篇 |
2000年 | 2204篇 |
1999年 | 1848篇 |
1998年 | 1825篇 |
1997年 | 1856篇 |
1996年 | 1587篇 |
1995年 | 1528篇 |
1994年 | 1407篇 |
1993年 | 1262篇 |
1992年 | 1219篇 |
1991年 | 1065篇 |
1990年 | 1256篇 |
1989年 | 1103篇 |
1988年 | 1007篇 |
1987年 | 1203篇 |
1986年 | 1046篇 |
1985年 | 1346篇 |
1984年 | 1480篇 |
1983年 | 1430篇 |
1982年 | 1314篇 |
1981年 | 1230篇 |
1980年 | 1126篇 |
1979年 | 1054篇 |
1978年 | 1084篇 |
1977年 | 1005篇 |
1976年 | 937篇 |
1975年 | 889篇 |
1974年 | 893篇 |
1973年 | 897篇 |
1972年 | 567篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
The eclipsing binary AV Hya has been observed photoelectrically inU, B andV filters on 15 nights. The primary eclipse appeared to be total with a totality of 23 min duration. A modified period of 0d.6 834 062 has been obtained. Geometrical elements could only be determined for partial transit case. 相似文献
954.
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
955.
956.
Falconer David A. Jordan Stuart D. Brosius Jeffrey W. Davila Joseph M. Thomas Roger J. Andreatta Vicenzo Hara Hirohisa 《Solar physics》1998,180(1-2):179-191
We investigate the possibility that strong EUV lines observed with the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) provide good proxies for estimating the total coronal flux over shorter wavelength ranges. We use coordinated SERTS and Yohkoh observations to obtain both polynomial and power-law fits relating the broad-band soft X-ray fluxes to the intensities of Fexvi 335 Ú and 361 Ú, Fexv 284 Ú and 417 Ú, and Mgix 368 Ú measured with SERTS. We found that the power-law fits best cover the full range of solar conditions from quiet Sun through active region, though not surprisingly the cooler Mgix 368 Ú line proves to be a poor proxy. The quadratic polynomial fits yield fair agreement over a large range for all but the Mgix line. However, the linear fits fail conspicuously when extrapolated into the quiet-Sun regime. The implications of this work for the Heii 304 Ú line formation problem are also briefly considered. 相似文献
957.
Mouradian Z. Soru-Escaut I. Hiei E. McALLISTER A. H. Shibasaki K. Ohyama M. Khan J. I. Uchida Y. 《Solar physics》1998,180(1-2):313-329
The 7 May 1992 filament disappearance in the low corona is analyzed. The cool and hot components of this event are studied, using H, soft X-ray and radio data. We first show the general effect of the disparition brusque (DB) on the life of the filament, which was a quiescent filament in the vicinity of an active region, and then give the history of the development of the 7 May event. The main stages of the event are: (i) the formation of hot arches spanning the cool filament; (ii) rise of the filament, with plasma ejection into the corona, in which we note some spreading of loops from the main body, with two distinct rising velocity phases of the H filament; (iii) formation of X-ray arches below the filament, the foot points of the arcades being two-ribbon H flare patches. The dynamics of H and X-rays features are given. 相似文献
958.
J. Manfroid 《Astrophysics and Space Science》1978,53(2):479-487
We discuss the effects of inhomogeneities in HII regions. It is shown that some emission lines are strongly affected when the filling factor is substantially smaller than 1. 相似文献
959.
We have conducted a targeted high-sensitivity search for narrow-band signals near γ18 cm using the 91-m radiotelescope of the National Radio Astronomy Observatory. The search included 201 nearby solar-type stars and achieved a frequency resolution of 5.5 Hz over a 1.4-MHz bandwidth. This high spectral Mark I VLBI recording terminal in conjunction with the CDC 7600 computational facility at the NASA-Ames Research Center. This is the first high-resolution search for narrow-band signals in this wavelength regime. To date it is the most sensitive search per unit observing time of any search strategy which does not postulate a unique magic frequency. Our data show no evidence for narrow-band signals due to extraterrestrial intelligence at a 12-σ upper limit on signal strength of 1.1 × 10?23 W m?2. 相似文献
960.
J. B. Zirker 《Solar physics》1989,120(2):253-259
Non-redundant arrays offer a promising technique for producing diffraction-limited solar images. Pairs of two-dimensional non-redundant arrays yield sufficient information to recover the phases of all the spatial frequencies to which they respond. The algorithms to select and test such pairs are given and applied to a particular example.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献