全文获取类型
| 收费全文 | 15148篇 |
| 免费 | 1914篇 |
| 国内免费 | 2986篇 |
专业分类
| 测绘学 | 516篇 |
| 大气科学 | 990篇 |
| 地球物理 | 1466篇 |
| 地质学 | 8383篇 |
| 海洋学 | 1359篇 |
| 天文学 | 5205篇 |
| 综合类 | 747篇 |
| 自然地理 | 1382篇 |
出版年
| 2024年 | 51篇 |
| 2023年 | 168篇 |
| 2022年 | 419篇 |
| 2021年 | 451篇 |
| 2020年 | 462篇 |
| 2019年 | 549篇 |
| 2018年 | 449篇 |
| 2017年 | 448篇 |
| 2016年 | 510篇 |
| 2015年 | 563篇 |
| 2014年 | 824篇 |
| 2013年 | 852篇 |
| 2012年 | 864篇 |
| 2011年 | 994篇 |
| 2010年 | 1023篇 |
| 2009年 | 1300篇 |
| 2008年 | 1225篇 |
| 2007年 | 1159篇 |
| 2006年 | 1097篇 |
| 2005年 | 954篇 |
| 2004年 | 857篇 |
| 2003年 | 723篇 |
| 2002年 | 628篇 |
| 2001年 | 586篇 |
| 2000年 | 540篇 |
| 1999年 | 500篇 |
| 1998年 | 387篇 |
| 1997年 | 229篇 |
| 1996年 | 233篇 |
| 1995年 | 162篇 |
| 1994年 | 160篇 |
| 1993年 | 159篇 |
| 1992年 | 98篇 |
| 1991年 | 84篇 |
| 1990年 | 63篇 |
| 1989年 | 61篇 |
| 1988年 | 46篇 |
| 1987年 | 24篇 |
| 1986年 | 23篇 |
| 1985年 | 26篇 |
| 1984年 | 19篇 |
| 1983年 | 17篇 |
| 1982年 | 15篇 |
| 1981年 | 6篇 |
| 1980年 | 11篇 |
| 1979年 | 3篇 |
| 1978年 | 5篇 |
| 1977年 | 15篇 |
| 1877年 | 1篇 |
| 1875年 | 1篇 |
排序方式： 共有10000条查询结果，搜索用时 31 毫秒
81.
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
82.
83.
84.
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
85.
86.
87.
88.
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
89.
Natural and agricultural wetlands are considered to be the major sources of global atmospheric methane (CH4). A one‐dimensional model was developed to simulate methane emission and used to examine the influence of various physical processes on the rate of methane emission. Three processes involved in the methane emission are implemented in the model: production, reoxidation and transport. Three transport pathways were considered: diffusion across water–air or soil–air interfaces, ebullition and diffusion through plants. These pathways are influenced by soil properties, plant growth, water‐table conditions, temperature and external inputs (e.g. fertilizer). The model was used to examine the seasonal variation of the methane emission at a rice field in Hunan, China, which was observed during a field experiment for consecutive (early and late) rice seasons in 1992. The observed seasonal variations of methane emission, and role of plants in transporting methane to the atmosphere, are captured by the model simulation. Further model applications were conducted to simulate effects of fertilizer and water‐level condition on the methane emission. The results indicate that unfermented organic fertilizer produces a higher methane emission rate than mineral fertilizer. The simulations with treatments of a deep‐water covering and constant moisture reduced the methane emission. The rice field study provides a framework for further development of the model towards simulations based on spatially distributed variables (e.g. water table, soil temperature and vegetation) at a regional scale. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
90.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1990,11(4):533-540
Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is
not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the
mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates
a luminosity somewhat above the main sequence 相似文献