全文获取类型
收费全文 | 4369篇 |
免费 | 179篇 |
国内免费 | 92篇 |
专业分类
测绘学 | 158篇 |
大气科学 | 309篇 |
地球物理 | 1145篇 |
地质学 | 1528篇 |
海洋学 | 389篇 |
天文学 | 716篇 |
综合类 | 21篇 |
自然地理 | 374篇 |
出版年
2022年 | 30篇 |
2021年 | 47篇 |
2020年 | 48篇 |
2019年 | 64篇 |
2018年 | 86篇 |
2017年 | 105篇 |
2016年 | 122篇 |
2015年 | 111篇 |
2014年 | 136篇 |
2013年 | 264篇 |
2012年 | 132篇 |
2011年 | 232篇 |
2010年 | 168篇 |
2009年 | 234篇 |
2008年 | 245篇 |
2007年 | 218篇 |
2006年 | 197篇 |
2005年 | 174篇 |
2004年 | 139篇 |
2003年 | 166篇 |
2002年 | 139篇 |
2001年 | 86篇 |
2000年 | 91篇 |
1999年 | 63篇 |
1998年 | 71篇 |
1997年 | 59篇 |
1996年 | 66篇 |
1995年 | 55篇 |
1994年 | 55篇 |
1993年 | 43篇 |
1992年 | 50篇 |
1991年 | 43篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 37篇 |
1987年 | 41篇 |
1986年 | 47篇 |
1985年 | 60篇 |
1984年 | 48篇 |
1983年 | 51篇 |
1982年 | 53篇 |
1981年 | 59篇 |
1980年 | 48篇 |
1979年 | 39篇 |
1978年 | 50篇 |
1977年 | 28篇 |
1976年 | 30篇 |
1975年 | 25篇 |
1974年 | 31篇 |
1973年 | 29篇 |
排序方式: 共有4640条查询结果,搜索用时 156 毫秒
531.
We present radio observations made with the Australia Telescope Compact Array to study the jets and lobes of three Fanaroff–Riley class I (FR I) radio galaxies: PKS B1234−723, 1452−517 and B2148−555. The total intensity and polarization radio images of the FR I jets are used to determine jet brightness and width variations, magnetic field structure and fractional polarization. The equipartition pressure is determined as a function of distance from the galaxies to probe the intergalactic medium. 相似文献
532.
All of the large impact features of the middle-sized icy satellites of Saturn and Uranus that were clearly observed by the Voyager spacecraft are described. New image mosaics and stereo-and-photoclinometrically-derived digital elevation models are presented. Landforms related to large impact features, such as secondary craters and possible antipodal effects are examined and evaluated. Of the large impacts, Odysseus on Tethys appears to have had the most profound effect on its “target” satellite of any of the impact features we examined. Our modeling suggests that the Odysseus impact may have caused the prompt formation of Ithaca Chasma, a belt of tectonic troughs that roughly follow a great circle normal to the center of Odysseus, although other hypotheses remain viable. We identify probable secondary cratering from Tirawa on Rhea. We attribute a number of converging coalescing crater chains on Rhea to a putative, possibly relatively fresh, ∼350 km-diameter impact feature. We examine the antipodes of Odysseus, the putative ∼350 km-diameter Rhean impact feature, and Tirawa, and conclude that evidence from Voyager data for damage from seismic focusing is equivocal, although our modeling results indicate that such damage may have occurred. We propose a number of observations and tests for Cassini that offer the opportunity to differentiate among the various explanations and speculations reviewed and evaluated in this study. 相似文献
533.
We present spectral variations of the binary X-ray pulsar LMC X-4 observed with the RXTE/PCA during different phases of its
30.5 day long third period. Only out-of-eclipse data were used for this study. The 3–25 keV spectrum, modeled with high energy
cut-off power-law and iron line emission is found to show strong dependence on the intensity state. Correlations between the
Fe line emission flux and different parameters of the continuum are presented here. 相似文献
534.
Houjie Wang Zuosheng Yang Yoshiki Saito J. Paul Liu Xiaoxia Sun 《Global and Planetary Change》2006,50(3-4):212-225
The Huanghe, the second largest river in China, is now under great pressure as a water resource. Using datasets of river water discharge, water consumption and regional precipitation for the past 50 years, we elucidate some connections between decreasing water discharges, global El Niño/Southern Oscillation (ENSO) events and anthropogenic impacts in the drainage basin. Global ENSO events, which directly affected the regional precipitation in the river basin, resulted in approximately 51% decrease in river water discharge to the sea. The degree of anthropogenic impacts on river water discharge is now as great as that of natural influences, accelerating the water losses in the hydrological cycle. The large dams and reservoirs regulated the water discharge and reduced the peak flows by storing the water in the flood season and releasing it in the dry season as needed for agricultural irrigation. Thus, as a result, large dams and reservoirs have shifted the seasonal distribution patterns of water discharge and water consumption and finally resulted in rapidly increasing water consumption. Meanwhile, the annual distribution pattern of water consumption also changed under the regulation of dams and reservoirs, indicating that the people living in the river basin consume the water more and more to suit actual agricultural schedule rather than depending upon natural pattern of annual precipitation. The combination of the increasing water consumption facilitated by the dams and reservoirs and the decreasing precipitation closely associated with the global ENSO events over the past half century has resulted in water scarcity in this world-famous river, as well as in a number of subsequent serious results for the river, delta and coastal ocean. 相似文献
535.
Ricardo Génova-Santos José Alberto Rubiño-Martín Rafael Rebolo † Kieran Cleary ‡ Rod D. Davies Richard J. Davis Clive Dickinson § Nelson Falcón ‡‡ Keith Grainge Carlos M. Gutiérrez Michael P. Hobson Michael E. Jones ¶ Rüdiger Kneissl Katy Lancaster Carmen P. Padilla-Torres Richard D. E. Saunders Paul F. Scott Angela C. Taylor ¶ Robert A. Watson †† 《Monthly notices of the Royal Astronomical Society》2005,363(1):79-92
536.
Observations of the lunar surface with the orbiting Apollo Alpha Particle Spectrometer during the Apollo 15 and Apollo 16 missions have shown spatial and temporal variations in radon emission. There are a number of well localized features in the spatial distribution of lunar222Rn and her daughter210Po which apparently correlate with sites of reported transient visual events. There are sources at Aristarchus, Grimaldi and possibly Tsiolkovsky. Activity of210Po shows enhancement at most maria edges at rates far in excess of222Rn activity. This demonstrates unequivocally the presence of time varying radon activity at the maria edges, taking place at the present time. The increased radon emission is probably caused by sporadic internal activity. In analogy to terrestial processes, radon may be merely a trace component accompanying the release of larger quantities of more common gases to the lunar surface. 相似文献
537.
Ohne ZusammenfassungMit 2 Textabbildungen. 相似文献
538.
David E. Lange Kent Frost Paul P. Sipiera Carleton B. Moore 《Meteoritics & planetary science》1974,9(4):271-280
The Canyonlands meteorite weighing 1,520 grams was found near the confluence of the Green and Colorado Rivers, Utah, near lat 38°11′N.; long 109°53′W. It is a shocked, brecciated H6 chondrite containing large black veins which do not differ in composition from the main chondritic mass. A black fusion crust remains on part of the meteorite. 相似文献
539.
Paul J. Coleman Jr. G. Schubert C. T. Russell L. R. Sharp 《Earth, Moon, and Planets》1972,4(3-4):419-429
A preliminary analysis of the data from the UCLA magnetometer on board the Apollo 15 subsatellite indicates that remnant magnetization is a characteristic property of the Moon, that its distribution is such as to produce a rather complex pattern or fine structure, and that a detailed mapping of its distribution is feasible with the present experiment. The analysis also shows that lunar induction fields produced by transients in the interplanetary magnetic field are detectable at the satellite orbit so that in principle the magnetometer data can be used to determine the latitudinal and longitudinal as well as radial dependences of the distribution of electrical conductivity within the Moon. Finally, the analysis indicates that the plasma void or diamagnetic cavity which forms behind the Moon when the Moon is in the solar wind, is detectable at the satellite's orbit and that the flow of the solar wind near the limbs is usually rather strongly disturbed.Publication No. 981. Institute of Geophysics and Planetary Physics. 相似文献
540.