全文获取类型
收费全文 | 21035篇 |
免费 | 3312篇 |
国内免费 | 4625篇 |
专业分类
测绘学 | 1158篇 |
大气科学 | 1360篇 |
地球物理 | 2580篇 |
地质学 | 12669篇 |
海洋学 | 2016篇 |
天文学 | 5082篇 |
综合类 | 1341篇 |
自然地理 | 2766篇 |
出版年
2024年 | 55篇 |
2023年 | 268篇 |
2022年 | 646篇 |
2021年 | 788篇 |
2020年 | 784篇 |
2019年 | 956篇 |
2018年 | 792篇 |
2017年 | 796篇 |
2016年 | 870篇 |
2015年 | 934篇 |
2014年 | 1334篇 |
2013年 | 1213篇 |
2012年 | 1428篇 |
2011年 | 1570篇 |
2010年 | 1464篇 |
2009年 | 1698篇 |
2008年 | 1652篇 |
2007年 | 1604篇 |
2006年 | 1550篇 |
2005年 | 1328篇 |
2004年 | 1133篇 |
2003年 | 993篇 |
2002年 | 804篇 |
2001年 | 755篇 |
2000年 | 630篇 |
1999年 | 580篇 |
1998年 | 459篇 |
1997年 | 308篇 |
1996年 | 275篇 |
1995年 | 230篇 |
1994年 | 225篇 |
1993年 | 198篇 |
1992年 | 159篇 |
1991年 | 119篇 |
1990年 | 76篇 |
1989年 | 48篇 |
1988年 | 63篇 |
1987年 | 23篇 |
1986年 | 25篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 18篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 15篇 |
1954年 | 2篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
通过对蓄水前后三峡库首区构造应力场进行三维数值模拟发现,相对于蓄水前,蓄水至135 m水位时,官渡口断裂-马鹿池断裂-牛口断裂围限区、秭归地理中心和九湾溪断裂带,出现了4个主应力下降区和共轭的主应力增长区,形成了差应力场;175 m水位与135 m水位相比,局部差应力场呈现逆向变化,即形成了加载效应与卸载效应的交替过程。这一过程,可能是水库诱发地震的诱震(或触震)因素。 相似文献
102.
Titan has been observed with UVES, the UV-Visual Echelle Spectrograph at the Very Large Telescope, with the aim of characterizing the zonal wind flow. We use a retrieval scheme originally developed for absolute stellar accelerometry [Connes, P., 1985. Astrophys. Space Sci., 110, 211-255] to extract the velocity signal by simultaneously taking into account all the lines present in the spectrum. The method allows to measure the Doppler shift induced at a given point by the zonal wind flow, with high precision. The short-wavelength channel (4200-5200 Å) probes one scale height higher than the long-wavelength one (5200-6200 Å), and we observe statistically significant evidence for stronger winds at higher altitudes. The results show a high dispersion. Globally, we detect prograde zonal winds, with lower limits of 62 and 50 m s−1 at the regions centered at 200 and 170 km altitude, but approximately a quarter of the measurements indicates null or retrograde winds. 相似文献
103.
104.
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
105.
106.
107.
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
108.
109.
110.
对广西岩溶区三个铅锌硫化物矿床风化带观测结果表明,中低山岩溶区硫化物矿床具有更强烈的风化淋滤作用,但次生晕面积较小;岩溶平原区硫化物矿床风化与元素表生迁移特征较相似于非岩溶区的情况,表现在可产生较宽的pH偏低带和较大面积的次生晕 相似文献