全文获取类型
收费全文 | 19759篇 |
免费 | 3165篇 |
国内免费 | 4777篇 |
专业分类
测绘学 | 1728篇 |
大气科学 | 5015篇 |
地球物理 | 2838篇 |
地质学 | 6964篇 |
海洋学 | 2732篇 |
天文学 | 5203篇 |
综合类 | 1198篇 |
自然地理 | 2023篇 |
出版年
2024年 | 56篇 |
2023年 | 235篇 |
2022年 | 571篇 |
2021年 | 721篇 |
2020年 | 762篇 |
2019年 | 861篇 |
2018年 | 716篇 |
2017年 | 793篇 |
2016年 | 806篇 |
2015年 | 919篇 |
2014年 | 1272篇 |
2013年 | 1420篇 |
2012年 | 1391篇 |
2011年 | 1446篇 |
2010年 | 1336篇 |
2009年 | 1730篇 |
2008年 | 1551篇 |
2007年 | 1655篇 |
2006年 | 1405篇 |
2005年 | 1288篇 |
2004年 | 1086篇 |
2003年 | 874篇 |
2002年 | 714篇 |
2001年 | 653篇 |
2000年 | 570篇 |
1999年 | 534篇 |
1998年 | 471篇 |
1997年 | 259篇 |
1996年 | 230篇 |
1995年 | 230篇 |
1994年 | 225篇 |
1993年 | 226篇 |
1992年 | 116篇 |
1991年 | 106篇 |
1990年 | 84篇 |
1989年 | 69篇 |
1988年 | 69篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 39篇 |
1984年 | 35篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 21篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 16篇 |
1954年 | 3篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
林菁 《广东海洋大学学报》1996,(1)
分析了分频和CTC计数采样中误读数的原因和解决方法,并利用微机软件实现非线性校正。此传感器用于位移测量系统中,具有0.01mm的分辨率及优于1%的精度,可在-20~60℃温度范围内工作。 相似文献
98.
99.
G.H.L. Read 《Estuarine, Coastal and Shelf Science》1985,21(3):313-324
A dry (1979–1980) and a wet (1980–1981) season had a marked effect on the freshwater inflow into the Keiskamma estuary. Under low inflow conditions, which results in elevated salinities in the upper reaches, an upstream migration of adult Macrobrachium petersi (Hilgendorf) to freshwater takes place. During periods of increased river inflow adult M. petersi move downstream to the more saline reaches of the estuary. These two migratory responses have been interpreted as (a) a breeding migration under high inflow conditions which ensures that larvae are in close proximity to salinities that favour growth and development, and (b) an adult upstream migration back to freshwater to escape elevated estuarine salinities as a result of the low freshwater inflow. 相似文献
100.
通过杂质对导电类型的影响的研究,得出了同种矿物的不同导电类型与矿物形成温度的规律:电子型(n型)导电矿物的形成温度大于电子与空穴混合型导电矿物的形成温度,又大于空穴型(p型)导电矿物的形成温度,绝缘体矿物的形成温度低于上述三种导电类型矿物。应用矿物热电图谱仪,天然金刚石半导体测试仪对闪锌矿、黄铁矿、金刚石等矿物的导电类型进行了测试,并探讨了导电类型成因,证实了上述规律的正确性。 相似文献