全文获取类型
收费全文 | 78855篇 |
免费 | 1150篇 |
国内免费 | 597篇 |
专业分类
测绘学 | 1873篇 |
大气科学 | 5256篇 |
地球物理 | 14555篇 |
地质学 | 31095篇 |
海洋学 | 6699篇 |
天文学 | 16951篇 |
综合类 | 289篇 |
自然地理 | 3884篇 |
出版年
2022年 | 458篇 |
2021年 | 748篇 |
2020年 | 864篇 |
2019年 | 959篇 |
2018年 | 4045篇 |
2017年 | 3744篇 |
2016年 | 3141篇 |
2015年 | 1125篇 |
2014年 | 1877篇 |
2013年 | 3215篇 |
2012年 | 2875篇 |
2011年 | 4790篇 |
2010年 | 4232篇 |
2009年 | 4933篇 |
2008年 | 4153篇 |
2007年 | 4664篇 |
2006年 | 2603篇 |
2005年 | 2039篇 |
2004年 | 1941篇 |
2003年 | 2014篇 |
2002年 | 1773篇 |
2001年 | 1406篇 |
2000年 | 1316篇 |
1999年 | 1114篇 |
1998年 | 1111篇 |
1997年 | 1079篇 |
1996年 | 928篇 |
1995年 | 868篇 |
1994年 | 821篇 |
1993年 | 700篇 |
1992年 | 658篇 |
1991年 | 669篇 |
1990年 | 723篇 |
1989年 | 587篇 |
1988年 | 571篇 |
1987年 | 638篇 |
1986年 | 600篇 |
1985年 | 779篇 |
1984年 | 789篇 |
1983年 | 763篇 |
1982年 | 733篇 |
1981年 | 649篇 |
1980年 | 668篇 |
1979年 | 586篇 |
1978年 | 565篇 |
1977年 | 535篇 |
1976年 | 499篇 |
1975年 | 506篇 |
1974年 | 482篇 |
1973年 | 517篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
171.
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
172.
173.
174.
We show how the Yarkovsky effect can be understood as a heat engine. The output of the engine, manifested in the rate of change in semimajor axis of the body, has a maximum at an intermediate heat capacity, depending on the rotation rate of the body. This maximum arises because the work output depends on the product of the solar heat absorbed by the body and transported from its morning to evening side (this am-pm heat flux increases with heat capacity) and the Carnot efficiency (which declines with heat capacity). 相似文献
175.
We performed polarization observations of giant radio pulses from the millisecond pulsar B1937+21. The observations were carried out in July 2002 with the 64-m Kalyazin radio telescope at a frequency of 600 MHz in two polarization channels with left-and right-hand circular polarizations (RCP and LCP). We used the S2 data acquisition system with a time resolution of 125 ns. The duration of an observing session was 20 min. We detected twelve giant radio pulses with peak flux densities higher than 1000 Jy; five and seven of these pulses appeared in the RCP and LCP channels, respectively. We found no event that exceeded the established detection threshold simultaneously in the two polarization channels. Thus, we may conclude that the detected giant pulses have a high degree of circular polarization, with the frequency of occurrence of RCP and LCP pulses being the same. 相似文献
176.
Michael E. ZOLENSKY Andrei V. IVANOV S. Vincent YANG David W. MITTLEFEHLDT Kazumasa OHSUMI 《Meteoritics & planetary science》1996,31(4):484-493
Abstract Kaidun is a breccia of disparate enstatite and carbonaceous chondrite clasts that continues to provide real surprises. Many Kaidun clasts have been intensely altered by aqueous fluids, as evidenced by the widespread occurrence of ferromagnesian phyllosilicates and by the presence of carbonate- and phyllo-silicate-filled veins. In this report, we describe an unusual CM lithology containing many mineralogical features not previously reported from any meteorite, including pyrrhotite, with exclusive needlelike morphologies and thick mantles of phyllosilicate, and complex aggregates of phyllosilicate, melanite garnet, crosscut by pentlandite veins. The latter features appear to be due in large part to extensive hydrothermal alteration at temperatures on the order of 450 °C, which is significantly higher than that attained during secondary processing from other known CM material. 相似文献
177.
G. Djurašević P. Rovithis H. Rovithis-Livaniou E. Fragoulopoulou 《Astrophysics and Space Science》2005,296(1-4):311-314
BV light curves of the eclipsing binary UV Leo obtained at the Kryonerion Astronomical Station of the National Observatory of
Athens, Greece, are analyzed. The analysis is based on a Roche configuration with two spots on the secondary surface. The
elements of the two components of the system are calculated and the spot characteristics are given. 相似文献
178.
The spectra of active galaxies and their nuclei are rich in emission and absorption line features. A major aim of present
research is the development of self-consistent hydrodynamic models for the production of the line-forming regions. We here
review such modelling and stress the central role played by shock phenomena induced by winds and explosions on scales ranging
from the circumstellar to the intergalactic. 相似文献
179.
J. CAMPSIE M. H. RASMUSSEN L. C. KOVACS F. DITTMER J. C. BAILEY N. O. HANSEN J. LAURSEN L. JOHNSON 《Polar research》1990,8(2):237-243
New aeromagnetic data, K-Ar age determinations of dredged marine igneous rocks, as well as other geophysical evidence have shed light on the chronology, nature and evolution of the northern Iceland Plateau. Correspondence between seismic refraction profiles taken on the Jan Mayen Ridge and westward through Jan Mayen Island, suppressed aeromagnetic anomalies, earthquake surface wave studies, and ages of dredged igneous rocks suggest these strata may form an extended region of thickened crust, possibly of Caledonian age, extending westward toward the Kolbeinsey Ridge and northwest to the south wall of the Jan Mayen Fracture Zone. 相似文献
180.
The Indian team at ISRO has been part of the Whole Earth Telescope (WET) team since 1988 when we first participated in the
campaign on V471 Tau. We have been part of many other observing campaigns over the last decade. This presentation traces the
circumstances leading to our joining the WET team and how useful the coverage from the Indian longitude has been. The results
of several pulsators from the WET runs during which we participated are also described. These include PG1159-035 the prototype
of the GW Vir type of stars, RE J 0751+14 a cataclysmic variable, PG 1336-018 a binary with an sdB pulsator and finally HR
1217 a roAp star. The paper concludes with what the limitations are in our observations and how we can overcome them in the
future. 相似文献