全文获取类型
收费全文 | 71305篇 |
免费 | 1128篇 |
国内免费 | 659篇 |
专业分类
测绘学 | 1716篇 |
大气科学 | 5037篇 |
地球物理 | 14229篇 |
地质学 | 25263篇 |
海洋学 | 6173篇 |
天文学 | 16332篇 |
综合类 | 208篇 |
自然地理 | 4134篇 |
出版年
2022年 | 396篇 |
2021年 | 704篇 |
2020年 | 778篇 |
2019年 | 827篇 |
2018年 | 1894篇 |
2017年 | 1760篇 |
2016年 | 2236篇 |
2015年 | 1321篇 |
2014年 | 2177篇 |
2013年 | 3772篇 |
2012年 | 2276篇 |
2011年 | 3123篇 |
2010年 | 2610篇 |
2009年 | 3508篇 |
2008年 | 3257篇 |
2007年 | 3047篇 |
2006年 | 2877篇 |
2005年 | 2354篇 |
2004年 | 2254篇 |
2003年 | 2111篇 |
2002年 | 1927篇 |
2001年 | 1801篇 |
2000年 | 1717篇 |
1999年 | 1378篇 |
1998年 | 1470篇 |
1997年 | 1390篇 |
1996年 | 1104篇 |
1995年 | 1143篇 |
1994年 | 962篇 |
1993年 | 872篇 |
1992年 | 856篇 |
1991年 | 759篇 |
1990年 | 856篇 |
1989年 | 717篇 |
1988年 | 652篇 |
1987年 | 814篇 |
1986年 | 663篇 |
1985年 | 859篇 |
1984年 | 922篇 |
1983年 | 866篇 |
1982年 | 833篇 |
1981年 | 709篇 |
1980年 | 664篇 |
1979年 | 608篇 |
1978年 | 603篇 |
1977年 | 554篇 |
1976年 | 539篇 |
1975年 | 499篇 |
1974年 | 507篇 |
1973年 | 470篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
691.
692.
The mean width and distribution of penumbral filaments of a sunspot have been estimated, using white light photographs obtained with a vacuum, Newtonian type, telescope. Three areas corresponding to the penumbra of a sunspot have been analysed. Data were collected during the solar eclipse of June 1973. The photometric profiles of the Moon limb over the photosphere have been analysed to obtain useful information on both, atmospheric and instrumental perturbation on each exposure. The mean value of the width of penumbral filaments is 0.37 arc sec.Now at INTA-Villafranca, S.T.S., P.O. Box 54065, Madrid, Spain. 相似文献
693.
Continuous measurements of the geomagnetic field variations at ground stations are important to investigate several aspects of magnetospheric dynamics related to variations in the solar wind conditions which, ultimately, originate from the Sun. We present a comparative analysis of geomagnetic field measurements at several ground stations with simultaneous magnetospheric and interplanetary observations in order to understand the origin and characteristics of the observed fluctuations. The results suggest that long period geomagnetic field fluctuations can be directly driven by solar wind density fluctuations at the same frequencies via the modulation of the magnetopause current. We also discuss the possible occurrence of additional contributions related with cavity/waveguide resonances of the entire magnetosphere as well as those of resonance processes of the geomagnetic field lines. 相似文献
694.
O. V. Verkhodanov V. V. Sokolov M. L. Khabibullina S. V. Karpov 《Astrophysical Bulletin》2010,65(3):238-249
We analyze the randomness of the sky distribution of cosmic gamma-ray bursts. These events are associated with massive galaxies,
spiral or elliptical, and therefore their positions should trace the large-scale structure, which, in turn, could show up
in the sky distribution of fluctuations of the cosmicmicrowave background (CMB). We test this hypothesis by mosaic correlation
mapping of the distributions of CMB peaks and burst positions, find the distribution of these two signals to be correlated,
and interpret this correlation as a possible systematic effect. 相似文献
695.
696.
We present new in situ measurements of solar wind electron density as a function of heliolatitude. The data were obtained on Ulysses during its fast transit from south solar pole to north solar pole, at heliocentric distance about 1.5 AU, near the 1996 solar activity minimum. The density is measured accurately using the method of quasi-thermal noise spectroscopy with the Ulysses radio experiment, at a higher time resolution than the particle analysers on board. At low heliolatitudes (22° S to 21° N) the histogram of our data shows three main classes of flows with densities centered at 3.5, 7, and 12 cm-3, close to the values previously found by near-ecliptic space probes, in the region where fast coronal hole wind alternates with slower streamer belt wind. Poleward of 22° latitude where Ulysses encountered fast wind coming from coronal holes, the histogram of our data shows a single class of flow centered at 2.9 cm-3 with a roughly normal distribution. We find a density nearly independent of latitude, with the mean density from the south coronal hole 10% larger than that from the north, which may stem from a genuine north/south asymmetry and/or from the small decrease in solar activity during the time of the observations. We finally compare the data with some analytical models. 相似文献
697.
698.
699.
700.
Exact Bianchi type-II, VIII and IX cosmological models are obtained in a scalar tensor theory proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) with perfect fluid as a source. Some physical and geometrical properties of the models are studied. It is observed that the models are free from initial singularities and they are expanding with time. 相似文献