全文获取类型
收费全文 | 7582篇 |
免费 | 442篇 |
国内免费 | 84篇 |
专业分类
测绘学 | 199篇 |
大气科学 | 834篇 |
地球物理 | 1993篇 |
地质学 | 3010篇 |
海洋学 | 429篇 |
天文学 | 1239篇 |
综合类 | 32篇 |
自然地理 | 372篇 |
出版年
2023年 | 36篇 |
2022年 | 53篇 |
2021年 | 146篇 |
2020年 | 154篇 |
2019年 | 129篇 |
2018年 | 350篇 |
2017年 | 373篇 |
2016年 | 478篇 |
2015年 | 339篇 |
2014年 | 422篇 |
2013年 | 601篇 |
2012年 | 480篇 |
2011年 | 436篇 |
2010年 | 420篇 |
2009年 | 431篇 |
2008年 | 295篇 |
2007年 | 239篇 |
2006年 | 223篇 |
2005年 | 172篇 |
2004年 | 189篇 |
2003年 | 147篇 |
2002年 | 166篇 |
2001年 | 128篇 |
2000年 | 106篇 |
1999年 | 86篇 |
1998年 | 85篇 |
1997年 | 114篇 |
1996年 | 66篇 |
1995年 | 85篇 |
1994年 | 87篇 |
1993年 | 53篇 |
1992年 | 36篇 |
1991年 | 46篇 |
1990年 | 66篇 |
1989年 | 34篇 |
1988年 | 30篇 |
1987年 | 51篇 |
1986年 | 35篇 |
1985年 | 46篇 |
1984年 | 52篇 |
1983年 | 39篇 |
1982年 | 46篇 |
1981年 | 54篇 |
1980年 | 30篇 |
1979年 | 31篇 |
1978年 | 26篇 |
1977年 | 31篇 |
1975年 | 24篇 |
1974年 | 25篇 |
1973年 | 26篇 |
排序方式: 共有8108条查询结果,搜索用时 15 毫秒
21.
Gérard Daigne Patrick Charlot Christine Ducourant Jean-François Lestrade 《Astrophysics and Space Science》2003,286(1-2):255-260
The question of positioning the optical counterparts of the ICRF quasars is outlined in the perspective of future space astrometry
missions, which ultimately will bring a new realization of the ICRS in the optical range. Ground-based interferometry with
a dual-field observing mode (PRIMA/VLTI),together with the missions DIVA and FAME, will have a key role in building an extragalactic
reference frame in the optical/near-IR range with about the same accuracy as that of the present (VLBI) primary frame.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
22.
23.
Szilárd Csizmadia Zsolt Kővári Péter Klagyivik 《Astrophysics and Space Science》2006,304(1-4):355-357
We carried out optical and Hα photometry of two contact binaries (V861 Herculis, EQ Tauri). The light curve modeling revealed stellar spots in both contact systems and strong Hα excess in the position of the observed stellar spots. A correlation was found between the V−R and R−Hα colour indices of V861 Her. 相似文献
24.
During a campaign of optical observations at high latitude, a bi-dimensional study of the wave structure of the OH layer has been performed in December 1981 from Sodankyla (Finland). This site is one of the three stations of the EISCAT ionosphere sounding system. It has been found that a wave field covering an area of 1 million km2 may extend to latitudes as high as 70°N. The OH wave structure shows many similarities with noctilucent clouds. The fairly large horizontal wavelength, of the order of 40 km cannot easily be explained by a wave motion at an interface. The observed wave structure seems to be a result of the propagation of an internal gravity wave in the 80–100 km region. This wave structure was often recorded during the same time as an active aurora was present. As a result, it appears that the perturbation might be correlated with particle precipitations at auroral latitudes. 相似文献
25.
26.
A fully relativistic electron maser is proposed for the explanation of certain non-thermal solar and stellar radio bursts. This mechanism (maser synchrotron) is based on a gyroresonant interaction between waves and electrons of high energies and uses the free energy contained in an electronic distribution function that peaks for energies around 1 MeV.By a calculation of the growth rates of the three electromagnetic modes, we show that the X-mode prevails for values of
p/
cup to 2 or 3. This result is very different from the standard cyclotron maser case where such values of
p/
clead to quench the X-mode growth. Hence, the synchrotron maser instability appears to be a direct and efficient amplification process for considerably larger physical conditions than the cyclotron maser. In addition, the radiation, emitted over the second gyroharmonic, freely propagates without a strong reabsorbtion at the 2
clayer. All these points can constitute major advantages of this mechanism in an astrophysical context.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986. 相似文献
27.
We integrated numerically, in the frame of the four body problem Sun-Jupiter-Saturn-asteroid the orbit of the asteroid 1974 MA, an Earth-crosser, which is located in a region where three resonances overlap: the two secular resonances
5 and
16 and the mean motion resonance 5/1. The numerical integration yields a qualitative orbital evolution of this particular region. 相似文献
28.
H. Flanquart C. Meur-Férec Ph. Deboudt V. Morel A.-P. Hellequin et al. 《GeoJournal》1991,24(2):223-223
Reports
Littoral '92 相似文献29.
B. Andersen V. Domingo A. Jiménez A. Jones S. Korzennik P. L. Pallé F. Pérez Hernández C. Régulo T. Roca Cortés L. L. Tomás 《Solar physics》1988,116(2):391-399
Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a seasonal variation of about 15%, the best atmospheric conditions being in winter and autumn. Moreover, in anyone day the extinction coefficient in the afternoon is always lower than the one in the morning by 7%. A one-year period fluctuation, with an amplitude of 0.035 mag, has been identified in the instrumental magnitudes outside the atmosphere, and is interpreted as the variation produced by the different Sun-Earth distance from winter to summer. Finally, the study made to detect periodic time fluctuations in both, Sun's magnitude and extinction coefficients, has given null results at levels of 0.04 and 1.8%, respectively. 相似文献
30.
J. P. Vallée 《Astrophysics and Space Science》1988,149(2):225-231
Recent observations of the longest known head-tail galaxy IC 711, at long wavelengths have shown it to extend farther than previously known. At δ 74 cm, Vallée and Roger (1987) found it to stretch 17′ (930 kpc) behind the optical nucleus of this elliptical galaxy. At δ92 cm, Vallée and Strom (1988) found it to stretch 18.3′ (1 Mpc) behind the optical nucleus. What new physics can be learned from it? To that end, a theoretical simulation in 3 dimensions of the longest head-tail galaxy has been performed, building the radio trail cell by cell inside a volume of space composed of 8 million cells, with each cell being assigned a proper radio emissivity. Matching ram pressure theory and recent observations yields a primary fast decrease of the radio luminosity with time or distance from the optical nucleus of the galaxy, and a secondary periodic variation of the radio luminosity every 500 kpc. Near the end of the tail, a sudden and unpredicted flare-up of the observed width of the tail requires a sudden change in the jet's physical conditions about 2 Gyr earlier, or that of the surroundings. These simulations provide some additional constraints on the ram pressure theory. Along the tail ridge, particle aging and particle acceleration must combine to give a luminosity function that mimics an exponential decrease with time. Across the tail ridge, no edge brightening is necessary, suggesting that particle aging and particle acceleration must combine via central turbulences and central instabilities (not by edge effects). The disappearance of the radio trail at two points along the radio ridge is unexpected from the ram pressure theory. Thus particle aging and particle acceleration must combine once more to mimic a sinusoidal modulation with time of the radio luminosity, perhaps near the nucleus inside the optical galaxy. 相似文献