全文获取类型
收费全文 | 66925篇 |
免费 | 1136篇 |
国内免费 | 608篇 |
专业分类
测绘学 | 1550篇 |
大气科学 | 4679篇 |
地球物理 | 12889篇 |
地质学 | 24332篇 |
海洋学 | 6402篇 |
天文学 | 15024篇 |
综合类 | 154篇 |
自然地理 | 3639篇 |
出版年
2022年 | 418篇 |
2021年 | 741篇 |
2020年 | 818篇 |
2019年 | 892篇 |
2018年 | 2046篇 |
2017年 | 1928篇 |
2016年 | 2135篇 |
2015年 | 1128篇 |
2014年 | 1922篇 |
2013年 | 3487篇 |
2012年 | 2200篇 |
2011年 | 2840篇 |
2010年 | 2508篇 |
2009年 | 3217篇 |
2008年 | 2729篇 |
2007年 | 2865篇 |
2006年 | 2620篇 |
2005年 | 2309篇 |
2004年 | 2420篇 |
2003年 | 2142篇 |
2002年 | 1773篇 |
2001年 | 1535篇 |
2000年 | 1441篇 |
1999年 | 1181篇 |
1998年 | 1203篇 |
1997年 | 1202篇 |
1996年 | 938篇 |
1995年 | 916篇 |
1994年 | 896篇 |
1993年 | 789篇 |
1992年 | 729篇 |
1991年 | 727篇 |
1990年 | 760篇 |
1989年 | 659篇 |
1988年 | 645篇 |
1987年 | 755篇 |
1986年 | 653篇 |
1985年 | 857篇 |
1984年 | 873篇 |
1983年 | 803篇 |
1982年 | 756篇 |
1981年 | 728篇 |
1980年 | 661篇 |
1979年 | 608篇 |
1978年 | 598篇 |
1977年 | 569篇 |
1976年 | 519篇 |
1975年 | 513篇 |
1974年 | 512篇 |
1973年 | 512篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
M.S. Hanner E. Tedesco A.T. Tokunaga G.J. Veeder D.F. Lester F.C. Witteborn J.D. Bregman J. Gradie L. Lebofsky 《Icarus》1985,64(1):11-19
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm. 相似文献
62.
N. I. Kobanov 《Solar physics》1990,125(1):25-30
Using a differential method we have carried out observations of oscillations in six sunspots. Spectral lines Fe i 5434 Å and Fe i 5576 Å were used. Horizontal waves are not observed in the sunspot umbra photosphere. Results obtained indicate that, at least, the sunspot umbra oscillates as a single whole. 相似文献
63.
N. N. Chugai 《Astronomy Letters》2006,32(11):739-746
I study the question of whether the asymmetry of 56Ni ejecta that results in the asymmetry of the Hα emission line at the nebular epoch of the type-IIP supernova SN 2004dj can account for the recently detected polarization of the supernova radiation. I have developed a model of the Hα profile and luminosity with nonthermal ionization and excitation in a spherically symmetric envelope for an asymmetric bipolar 56Ni distribution. I have calculated the polarized radiation transfer against the background of the recovered electron density distribution. The observed polarization is shown to be reproduced at the nebular epoch around day 140 for the same parameters of the envelope, and the 56Ni distribution for which the evolution of the Hα luminosity and profile is explained. Yet the model polarization decreases with time more slowly than is observed. The origin of the additional component responsible for the early polarization on day 107 is discussed. 相似文献
64.
65.
66.
D. Montes M. C. Gálvez M. J. Fernández-Figueroa I. Crespo-Chacón 《Astrophysics and Space Science》2006,304(1-4):367-369
High resolution echelle spectroscopic observations taken with the FEROS spectrograph at the 2.2 m telescope ESO confirm the binary nature of the flare M3.5V star LU Vel (GJ 375, RE J0958-462) previously reported by Christian and Mathioudakis (2002). Emission of similar intensity from both components is detected in the Balmer, Na i D1&D2, He i D3, Ca ii H&K, and Ca ii IRT lines. We have determined precise radial velocities by cross correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of the system. The binary consists of two near-equal M3.5V components with an orbital period shorter than 2 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics. 相似文献
67.
Measurements of 18O concentrations in precipitation, soil solution, spring and runoff are used to determine water transit time in the small granitic Strengbach catchment (0·8 km2; 883–1146 m above sea level) located in the Vosges Mountains of northeastern France. Water transit times were calculated by applying the exponential, exponential piston and dispersion models of the FlowPC program to isotopic input (rainfall) and output (spring and stream water) data sets during the period 1989–95. The input function of the model was modified compared with the former version of the model and estimated by a deterministic approach based on a simplified hydrological balance. The fit between observed and calculated output data showed marked improvements compared with results obtained using the initial version of the model. An exponential piston version of the model applied to spring water indicates a 38·5 month mean transit time, which suggests that the volume in the aquifer, expressed in water depth, is 2·4 m. A considerable thickness (>45 m) of fractured bedrock may be involved for such a volume of water to be stored in the aquifer. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
68.
69.
Green Lake Landslide is an ancient giant rock slide in gneiss and granodiorite located in the deeply glaciated Fiordland region of New Zealand. The landslide covers an area of 45 km2 and has a volume of about 27 km3. It is believed to be New Zealand's largest landslide, and possibly the largest landslide of its type on Earth. It is one of 39 known very large (106–107 m3) and giant (≥108 m3) postglacial landslides in Fiordland discussed in the paper. Green Lake Landslide resulted in the collapse of a 9 km segment of the southern Hunter Mountains. Slide debris moved up to 2.5 km laterally and 700 m vertically, and formed a landslide dam about 800 m high, impounding a lake about 11 km long that was eventually infilled with sediments. Geomorphic evidence supported by radiocarbon dating indicates that Green Lake Landslide probably occurred 12 000–13 000 years ago, near the end of the last (Otira) glaciation. The landslide is described, and its geomorphic significance, age, failure mechanism, cause, and relevance in the region are discussed, in relation to other large landslides and recent earthquake-induced landslides in Fiordland. The slope failure occurred on a low-angle fault zone undercut by glacial erosion, and was probably triggered by strong shaking (MM IX–X) associated with a large (≥ M 7.5–8) earthquake, on the Alpine Fault c. 80 km to the northwest. Geology was a major factor that controlled the style and size of Green Lake landslide, and in that respect it is significantly different from most other gigantic landslides. Future large earthquakes on the Alpine Fault in Fiordland are likely to trigger more very large and giant landslides across the region, causing ground damage and devastation on a scale that has not occurred during the last 160 years, with potentially disastrous effects on towns, tourist centres, roads, and infrastructure. The probability of such an event occurring within the next 50 years may be as high as 45%. 相似文献
70.
This paper describes a wide-field survey made at 34.5 MHz using GEETEE,1 the low frequency telescope at Gauribidanur (latitude
13°36′12′′N). This telescope was used in the transit mode and by per forming 1-D synthesis along the north-south direction
the entire observable sky was mapped in a single day. This minimized the problems that hinder wide-field low-frequency mapping.
This survey covers the declination range of-50° to + 70° (- 33° to +61° without aliasing) and the complete 24 hours of right
ascension. The synthesized beam has a resolution of 26′ x 42′ sec (δ- 14°. 1). The sensitivity of the survey is 5 Jy/beam (1σ). Special care has been taken to ensure that the antenna responds
to all angular scale structures and is suitable for studies of both point sources and extended objects
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Roman Research Institute, Bangalore. 相似文献