全文获取类型
| 收费全文 | 13480篇 |
| 免费 | 3084篇 |
| 国内免费 | 2501篇 |
专业分类
| 测绘学 | 896篇 |
| 大气科学 | 706篇 |
| 地球物理 | 1500篇 |
| 地质学 | 7720篇 |
| 海洋学 | 1415篇 |
| 天文学 | 5143篇 |
| 综合类 | 721篇 |
| 自然地理 | 964篇 |
出版年
| 2024年 | 34篇 |
| 2023年 | 126篇 |
| 2022年 | 372篇 |
| 2021年 | 493篇 |
| 2020年 | 470篇 |
| 2019年 | 548篇 |
| 2018年 | 480篇 |
| 2017年 | 480篇 |
| 2016年 | 553篇 |
| 2015年 | 544篇 |
| 2014年 | 902篇 |
| 2013年 | 933篇 |
| 2012年 | 950篇 |
| 2011年 | 1092篇 |
| 2010年 | 1037篇 |
| 2009年 | 1315篇 |
| 2008年 | 1224篇 |
| 2007年 | 1136篇 |
| 2006年 | 1011篇 |
| 2005年 | 878篇 |
| 2004年 | 766篇 |
| 2003年 | 665篇 |
| 2002年 | 515篇 |
| 2001年 | 481篇 |
| 2000年 | 413篇 |
| 1999年 | 375篇 |
| 1998年 | 285篇 |
| 1997年 | 129篇 |
| 1996年 | 139篇 |
| 1995年 | 99篇 |
| 1994年 | 109篇 |
| 1993年 | 104篇 |
| 1992年 | 58篇 |
| 1991年 | 51篇 |
| 1990年 | 48篇 |
| 1989年 | 39篇 |
| 1988年 | 31篇 |
| 1987年 | 17篇 |
| 1986年 | 27篇 |
| 1985年 | 30篇 |
| 1984年 | 24篇 |
| 1983年 | 15篇 |
| 1982年 | 16篇 |
| 1981年 | 6篇 |
| 1980年 | 11篇 |
| 1979年 | 4篇 |
| 1978年 | 5篇 |
| 1977年 | 17篇 |
| 1972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
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.
89.
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
90.
J. William Miller Jr. 《Mathematical Geology》1991,23(2):201-218
A computer simulation method has been developed to find efficient drilling grids for mineral deposits. A well-known ore deposit is used as a model to develop an efficient pattern for undiscovered ore bodies in the same area or in other prospects where similar geometry is suspected. The model for this study is the Austinville, Virginia deposit, a Mississippi Valley-type deposit composed of 17 ore bodies totaling 34 million short tons (30 million metric tons). The method employs a computer program that simulates drilling the model deposit with different patterns, including various levels of follow-up drilling. Follow-up holes are drilled in fences at one half the original spacing around holes in the grid that show ore-grade mineralization. Each pattern is drilled 100 times from random starting locations to provide a range of outcomes of drilling, including the best, worst, and most likely. For this study, patterns of 100 drill holes were composed of 10 fences spaced 1000–5000 feet (305–1524 m) apart, each with 10 holes spaced 200–1000 feet (61–305 m) apart. In all, 25 grids were used with zero to three levels of follow-up drilling. The 600/2000 grid, with drill holes spaced 600 feet (183 m) apart in fences spaced 2000 feet (610 m) apart, was compared with the 200/5000 grid because they represented contrasting outcomes. The 600/2000 grid penetrated many ore bodies consistently but with few multiple hits to individual ore bodies; whereas the 200/5000 grid inconsistently penetrated few ore bodies with many multiple hits. The 600/2000 grid was more efficient than the 200/5000 grid at hitting large ore bodies of 1,000,000 short tons or greater (900,000 metric tons or greater) and was made more effective by adding one cycle of follow-up drilling. The 600/2000 grid had a 97% chance of hitting one or more large ore bodies with at least one drill hole per ore body, and the 200/5000 grid had a 64% chance. Once hit, there was an 82% chance that the largest ore body would be penetrated by three or more holes when using the 600/2000 grid and an 88% chance using the 200/5000 grid. 相似文献