全文获取类型
收费全文 | 22698篇 |
免费 | 3631篇 |
国内免费 | 5725篇 |
专业分类
测绘学 | 2085篇 |
大气科学 | 2352篇 |
地球物理 | 3359篇 |
地质学 | 12837篇 |
海洋学 | 3091篇 |
天文学 | 5220篇 |
综合类 | 1247篇 |
自然地理 | 1863篇 |
出版年
2024年 | 80篇 |
2023年 | 229篇 |
2022年 | 758篇 |
2021年 | 847篇 |
2020年 | 927篇 |
2019年 | 1096篇 |
2018年 | 819篇 |
2017年 | 780篇 |
2016年 | 888篇 |
2015年 | 1003篇 |
2014年 | 1400篇 |
2013年 | 1456篇 |
2012年 | 1461篇 |
2011年 | 1575篇 |
2010年 | 1578篇 |
2009年 | 1959篇 |
2008年 | 1796篇 |
2007年 | 1785篇 |
2006年 | 1761篇 |
2005年 | 1504篇 |
2004年 | 1332篇 |
2003年 | 1097篇 |
2002年 | 946篇 |
2001年 | 848篇 |
2000年 | 754篇 |
1999年 | 693篇 |
1998年 | 557篇 |
1997年 | 378篇 |
1996年 | 319篇 |
1995年 | 241篇 |
1994年 | 218篇 |
1993年 | 240篇 |
1992年 | 148篇 |
1991年 | 114篇 |
1990年 | 100篇 |
1989年 | 68篇 |
1988年 | 56篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 39篇 |
1984年 | 30篇 |
1983年 | 19篇 |
1982年 | 20篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 17篇 |
1976年 | 2篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
91.
The absolute magnitudeM
v
of the hydrogen deficient binary υ Sgr has been estimated as -4.8 ± 1.0 from the distribution of the interstellar reddening,
polarization and interstellar lines of the surrounding stars. From the ANS observations obtained at the time of the secondary
eclipse, it appears that the hotter secondary is surrounded by a disc with colours of a B8-B9 star. The λ 1550 CIv absorption
line arising in the stellar wind does not show any change in strength during the secondary minimum. The upper limit to the
mass-loss rate from the high temperature wind is estimated as ≤ 5 × 10-7 M⊙ yr-1 from the 2 cm and 6 cm radio observations.
Based on observations obtained with the Astronomical Netherlands Satellite and VLA. The National Radio Astronomy Observatory’s
Very Large Array at Socorro, New Mexico is operated by Associated Universities Inc. under contract with the National Science
Foundation. 相似文献
92.
93.
94.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae. 相似文献
95.
96.
97.
98.
Summary. Multiparameter inversions of multimode dispersion data are performed for two large regions: the Pacific Ocean and North America. Anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry. Two fundamental questions are studied in detail: (1) how to make the inverted models consistent when using different sets of parameters, (2) what is the significance of transversely isotropic inversion for the actual Earth's structure? It is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data. The models we have obtained are discussed in the light of these investigations. Considering an olivine-rich upper mantle, we make a tentative interpretation of these models in terms of preferred orientation of the a -axis of the crystals in one fixed horizontal direction. 相似文献
99.
100.
素土桩挤密地基由桩间挤密土和回填素土夯实的桩体组成,它是一种人工“复合地基”。其作用是通过素土桩挤密法提高地基土的密实度,从而对湿陷性黄土达到消除浅部或深部的部分或全部湿陷性的作用,并改善地基承载能力,减少地基变形。本文通过现场单桩、群桩单元体轻便触探、小环刀深层取样、开剖取样等方法对场地地基土挤密前、后干重度和压实系数进行了对比分析,判定用素土桩挤密法处理陇东湿陷性黄土地基的可行性。 相似文献