全文获取类型
收费全文 | 87678篇 |
免费 | 1939篇 |
国内免费 | 683篇 |
专业分类
测绘学 | 2169篇 |
大气科学 | 6825篇 |
地球物理 | 18922篇 |
地质学 | 29296篇 |
海洋学 | 7318篇 |
天文学 | 19563篇 |
综合类 | 202篇 |
自然地理 | 6005篇 |
出版年
2021年 | 555篇 |
2020年 | 718篇 |
2019年 | 720篇 |
2018年 | 1493篇 |
2017年 | 1455篇 |
2016年 | 2017篇 |
2015年 | 1455篇 |
2014年 | 1997篇 |
2013年 | 4342篇 |
2012年 | 2216篇 |
2011年 | 3155篇 |
2010年 | 2728篇 |
2009年 | 3900篇 |
2008年 | 3496篇 |
2007年 | 3179篇 |
2006年 | 3189篇 |
2005年 | 2739篇 |
2004年 | 2833篇 |
2003年 | 2642篇 |
2002年 | 2486篇 |
2001年 | 2280篇 |
2000年 | 2215篇 |
1999年 | 1911篇 |
1998年 | 1925篇 |
1997年 | 1870篇 |
1996年 | 1589篇 |
1995年 | 1520篇 |
1994年 | 1394篇 |
1993年 | 1250篇 |
1992年 | 1196篇 |
1991年 | 1040篇 |
1990年 | 1235篇 |
1989年 | 1077篇 |
1988年 | 935篇 |
1987年 | 1166篇 |
1986年 | 1033篇 |
1985年 | 1303篇 |
1984年 | 1495篇 |
1983年 | 1422篇 |
1982年 | 1285篇 |
1981年 | 1239篇 |
1980年 | 1081篇 |
1979年 | 1062篇 |
1978年 | 1131篇 |
1977年 | 1020篇 |
1976年 | 975篇 |
1975年 | 937篇 |
1974年 | 903篇 |
1973年 | 928篇 |
1972年 | 587篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
411.
The temporal association between the kinematic parameters of chromospheric dark features (DF) and the production of radio type-III bursts is investigated during a period of five months. The Doppler shifts inside six different DF are measured by means of the Meudon Multichannel Subtracting Double Pass Spectrograph (MSDP) during periods of some minutes around 24 type-III bursts. The position of the radio bursts has been checked to be associated with the same active region observed by MSDP, by using the Nançay Radioheliograph. It appears that 23 out of 24 bursts take place when the DF is totally or predominantly blue-shifted. In 18 out of 21 cases, a maximum of the outward velocity is observed in the optical image closest in time to the radio burst. The following peculiarities are also shown by the analyzed DF:
- All of them present a lengthened shape, in most cases pointing toward a sunspot: a bright region coinciding with a parasitic polarity is observed in between.
- Horizontal velocities along the DF major axis are often observed, always in a direction opposite to the sunspots.
412.
The data of Paper I (Doddet al., 1986), representing a catalogue of parameters measured for bright galaxies in field 444 of the Southern Sky Survey, are examined in a search for non-random effects. A global trend of bimodal alignment of galaxies in this field is found. This effect is present even for galaxies of large apparent ellipticity (e0.5) and is interpreted as revealing a real physical phenomenon on the large scale in this field. Analysis of nearest neighbouring pairs of galaxies reveals evidence also for small-scale interactions. The difference in apparent ellipticities between close pairs is larger than would be expected if the galaxies were randomly distributed. Nearest neighbouring galaxies also show a strong preference to be aligned with their major axes parallel. The results are discussed with regard to theories for galaxy formation. 相似文献
413.
The analytic construction of the direct periodic orbits in the circular 3-body problem is given in explicit form to the linear terms in . It is shown to be in good agreement with the numerically found orbits for large values of . 相似文献
414.
Profiles of the O i 7773 triplet obtained at a spatial resolution 0.5 are analyzed using spectral line inversion techniques. Inferences are made about departures from LTE, convective velocity fields, and solar temperature fluctuations. 相似文献
415.
J. L. Halbwachs 《Astrophysics and Space Science》1985,110(1):149-152
The frequency of binaries with degenerate secondary components was evaluated according to the spectral types of the primaries. It appears that this proportion is 25% for binaries with giant primary components, and less than about 17% for dwarfs.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846). 相似文献
416.
J. B. Zirker 《Solar physics》1985,102(1-2):33-40
An analysis of prominence hydrogen lines is presented in the spectral band 10–20 . The results are consistent with earlier work.Operated by the Association of Universities for Research in Astronomy, Inc., under contrast AST 84-18716 with the National Science Foundation. 相似文献
417.
"An attempt is made in the light of an analysis of population changes occurring in several sub-districts of Greater Santiago in the period between the last population censuses of 1970 and 1982, based on small-area census units (distritos and communas) to draw attention to the effects on the spatial growth of the city resulting from changed conditions in the political and juridical sphere since the change of power in 1973." The effect of changes in government policy concerning the liberalization of the property market and the illegal occupation of land are noted. (summary in ENG) 相似文献
418.
F. D'Antona 《Astrophysics and Space Science》1985,112(2):361-365
Recent computations (D'Antona and Mazzitelli, 1982), together with the general scheme of evolution of cataclysmic binaries (CBs), lead to conclude that the secondaries in those CBs having periods shorter than 4.5 hr have a large3He content in the envelope, ranging from 10–4 (P=4.5 hr) to >2×10–3 (P=3 hr) in mass fraction, if the nova systems have an age of some billion years. The consequence on the frequency of novae outbursts is shortly examined. If lithium is produced by galactic novae, the7Li content of old disk stars should be very close to the Population II content.Presented at the 5th European Workshop on White Dwarfs, Kiel, 1984. 相似文献
419.
M. E. Gedalin J. G. Lominadze L. Stenflo V. N. Tsytovich 《Astrophysics and Space Science》1985,108(2):393-400
Wave conversion mechanisms causing large-frequency shifts are considered for an electron-positron plasma in a strong magnetic field. In particular, we discuss the effects of the nonlinear erenkov as well as the cyclotron resonances in order to associate pulsar radio-emissions with our present model for nonlinear conversion of high-frequency radiation into the low-frequency region. 相似文献
420.
The gravitational instability of a nonrotating isothermal gaseous disk permeated by a uniform frozen-in magnetic field is investigated using a fourth-order perturbation technique. From the results it is found that the disk is stable whenn/B
0 < (4/33
G)–1/2, wheren andB are the column density of the disk and unperturbed magnetic field, respectively, andG is the gravitational constant. The disk is gravitationally unstable only whenn/B
0 > (4/33
G)–1/2. 相似文献