全文获取类型
收费全文 | 51169篇 |
免费 | 364篇 |
国内免费 | 252篇 |
专业分类
测绘学 | 1256篇 |
大气科学 | 3230篇 |
地球物理 | 8978篇 |
地质学 | 22007篇 |
海洋学 | 4166篇 |
天文学 | 10132篇 |
综合类 | 224篇 |
自然地理 | 1792篇 |
出版年
2022年 | 350篇 |
2021年 | 546篇 |
2020年 | 520篇 |
2019年 | 609篇 |
2018年 | 3784篇 |
2017年 | 3451篇 |
2016年 | 2570篇 |
2015年 | 623篇 |
2014年 | 1109篇 |
2013年 | 1767篇 |
2012年 | 2158篇 |
2011年 | 3836篇 |
2010年 | 3505篇 |
2009年 | 3851篇 |
2008年 | 3154篇 |
2007年 | 3818篇 |
2006年 | 1484篇 |
2005年 | 1179篇 |
2004年 | 1114篇 |
2003年 | 1175篇 |
2002年 | 1046篇 |
2001年 | 739篇 |
2000年 | 663篇 |
1999年 | 484篇 |
1998年 | 493篇 |
1997年 | 478篇 |
1996年 | 357篇 |
1995年 | 377篇 |
1994年 | 341篇 |
1993年 | 272篇 |
1992年 | 272篇 |
1991年 | 263篇 |
1990年 | 285篇 |
1989年 | 254篇 |
1988年 | 232篇 |
1987年 | 272篇 |
1986年 | 243篇 |
1985年 | 307篇 |
1984年 | 285篇 |
1983年 | 296篇 |
1982年 | 267篇 |
1981年 | 261篇 |
1980年 | 269篇 |
1979年 | 260篇 |
1978年 | 238篇 |
1977年 | 216篇 |
1976年 | 191篇 |
1975年 | 193篇 |
1974年 | 193篇 |
1973年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
172.
J. van der Plicht B. van Geel S. J. P. Bohncke J. A. A. Bos M. Blaauw A. O. M. Speranza R. Muscheler S. Bjrck 《第四纪科学杂志》2004,19(3):263-269
Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric 14C; (ii) a temporary decline of atmospheric CO2; and (iii) an increase in the GRIP 10Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
173.
174.
S. P. Plunkett G. E. Brueckner K. P. Dere R. A. Howard M. J. Koomen C. M. Korendyke D. J. Michels J. D. Moses N. E. Moulton S. E. Paswaters O. C. St. Cyr D. G. Socker D. Wang G. M. Simnett D. K. Bedford D. A. Biesecker C. J. Eyles S. J. Tappin R. Schwenn P. L. Lamy A. Llebaria 《Solar physics》1997,175(2):699-718
We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line
transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light.
Two of these events, with speeds >25 km s-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with
erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly
different appearance and is more gradual than the other two, with a projected outward speed <10 km s-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line
corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from
close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic
regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of
these events to recent X-ray observations of CMEs is briefly discussed.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702 相似文献
175.
L. I. Onuora 《Astrophysics and Space Science》1987,136(1):11-15
The inflationary unvierse model predicts the density parameter 0 to be 1.0 with the cosmological constant 0 usually taken to be zero, whereas observational estimates give 00.2 and 010-57 cm–2. It was found, however, that the observed variation of angular diameter with redshift for extragalactic radio sources could be interpreted in terms of a low density universe with linear size evolution of the sources for either an inflationary model with 0 or an open model with =0. 相似文献
176.
Using the leaky-box model the upper limit of the antiproton-proton flux ratio at the top of the atmosphere has been estimated from the latest primary nucleon spectrum and accelerator data on
inclusive reactions. The estimated value of
flux ratio comes out to be (3.6±0.3)×10–4 is in accord with the previous results but still far from the measurements. 相似文献
177.
Observations made by the differential method in the H line have revealed longperiod (on a timescale of 40 to 80 min) line-of-sight velocity oscillations which increase in amplitude with distance from the centre to the solar limb and, as we believe, give rise to prominence oscillations. As a test, we present some results of simultaneous observations at the photospheric level where such periods are absent.Oscillatory processes in the solar chromosphere have been studied by many authors. Previous efforts in this vein led to the detection of shortperiod oscillations in both the mass velocities and radiation intensity (Deubner, 1981). The oscillation periods obtained do not, normally, exceed 10–20 min (Dubov, 1978). More recently, Merkulenko and Mishina (1985), using filter observations in the H line, found intensity fluctuations with periods not exceeding 78 min. However, the observing technique they used does not exclude the possibility that those fluctuations were due to the influence of the Earth's atmosphere. It is also interesting to note that in spectra obtained by Merkulenko and Mishina (1985), the amplitude of the 3 min oscillations is anomalously small and the 5 min period is altogether absent, while the majority of other papers treating the brightness oscillations in the chromosphere, do not report such periods in the first place. So far, we are not aware of any other evidence concerning the longperiod velocity oscillations in the chromosphere on a timescale of 40–80 min.Longperiod oscillations in prominences (filaments) in the range from 40 to 80 min, as found by Bashkirtsev et al. (1983) and Bashkirtsev and Mashnich (1984, 1985), indicate that such oscillations can exist in both the chromosphere and the corona (Hollweg et al., 1982).In this note we report on experimental evidence for the existence of longperiod oscillations of mass velocity in the solar chromosphere. 相似文献
178.
179.
L. I. Chetverikov 《Mathematical Geology》1991,23(1):33-40
This paper considers the present state of mathematical geology. Three directions are recognized: applied, theoretical, and mathematical. Applied mathematical geology includes formal use of mathematics to solve problems and computer processing of data. Success is achieved by a correspondence of mathematical methods used to the nature of geological data. This correspondence can be demonstrated by purely mathematical means. Theoretical mathematical geology uses mathematics as a language of geology; however, a number of methodological problems must be solved: formalization of initial geological concepts and creation of a strict conceptual basis, substantiation of initial principles of mathematical simulation, creation of theoretical geological models, problems of elementary and coincidence in geology, and methodological substantiations of possibilities of any mathematical model to approximate geological models. The essense and significance of these problems are considered. The main task of mathematical geology is to prove its correspondence to the nature of the geological objects studied, geological data obtained, and geological problems solvable. Finally, the main problems of mathematical geology are not so much mathematical as geological and methodological. 相似文献
180.
O. Ransome-Kuti 《GeoJournal》1991,25(4):434-436