全文获取类型
收费全文 | 53705篇 |
免费 | 576篇 |
国内免费 | 331篇 |
专业分类
测绘学 | 1567篇 |
大气科学 | 4023篇 |
地球物理 | 9693篇 |
地质学 | 22493篇 |
海洋学 | 4060篇 |
天文学 | 10114篇 |
综合类 | 252篇 |
自然地理 | 2410篇 |
出版年
2022年 | 207篇 |
2021年 | 329篇 |
2020年 | 358篇 |
2019年 | 367篇 |
2018年 | 3823篇 |
2017年 | 3553篇 |
2016年 | 2552篇 |
2015年 | 711篇 |
2014年 | 1002篇 |
2013年 | 1777篇 |
2012年 | 2089篇 |
2011年 | 3967篇 |
2010年 | 3593篇 |
2009年 | 3942篇 |
2008年 | 3185篇 |
2007年 | 3796篇 |
2006年 | 1260篇 |
2005年 | 1351篇 |
2004年 | 1221篇 |
2003年 | 1230篇 |
2002年 | 1040篇 |
2001年 | 755篇 |
2000年 | 760篇 |
1999年 | 569篇 |
1998年 | 530篇 |
1997年 | 610篇 |
1996年 | 476篇 |
1995年 | 480篇 |
1994年 | 487篇 |
1993年 | 392篇 |
1992年 | 392篇 |
1991年 | 379篇 |
1990年 | 386篇 |
1989年 | 355篇 |
1988年 | 351篇 |
1987年 | 382篇 |
1986年 | 338篇 |
1985年 | 436篇 |
1984年 | 425篇 |
1983年 | 448篇 |
1982年 | 420篇 |
1981年 | 381篇 |
1980年 | 427篇 |
1979年 | 332篇 |
1978年 | 306篇 |
1977年 | 297篇 |
1976年 | 273篇 |
1975年 | 270篇 |
1974年 | 279篇 |
1973年 | 258篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
After briefly recalling basic facts about the metallicity gradients inspiral galaxies, we summarize two recent N-body gas-dynamical modelsthat implement a non-instantaneous gas recycling and point our their potential for an improved treatment of the chemical evolution ingalactic disks. 相似文献
83.
Knowledge of the optical constants of elemental sulfur has potential applications to Venus, Jupiter, Io, Amalthea, and the Earth. The real part, n, of the index of refraction of liquid sulfur (at 133°C) and of solid orthorhombic sulfur (at 25°C) for the wavelength range 0.4–2.0 μm were measured ellipsometrically. The imaginary part, k, of the refractive index of liquid sulfur was obtained by transmittance measurements at the same temperature and wavelength range. The reflectance of semi-infinite slabs of solid and liquid sulfur is calculated using the measured n and k values. We confirm that sulfur melts on Io would be classified as “black” by the Voyager imaging system. 相似文献
84.
85.
Jack B. Zirker 《Solar physics》1985,100(1-2):281-287
This paper reviews research highlights of the past five years. Considerable progress has been made in observing and interpreting coronal mass ejections. The stability of coronal loops is much better understood and new observations of the onset of wind streams in coronal holes have been made. Observations from the Solar Maximum Mission should helpt to clarify the physics of the active corona.The mechanisms that heat the corona and accelerate the high-speed wind streams remain to be identified, however.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
86.
Ralph B. Baldwin 《Icarus》1985,61(1):63-91
This paper contains a reasonably successful attempt to determine relative ages and then absolute ages of individual craters younger than Imbrium, and the rate of infalls onto the Moon as a function of time. After the tail of the massive premare bombardment became depleted before 3 aeons (1 aeon = 109 years) ago, there was a period of minimal numbers of infalls. The rate of infalls increased rather steadily from this minimum to the present. The rate in the geologically recent past (0.3 aeon) was about two times that found for the period immediately after the last of the major lave outpourings (3.2 aeons). Absolute ages were determined for large craters (?8 km) from crater counts on the surfaces within and on the rims of the large craters. Key dates were 0 and 0.3 aeon for terrestrial meteoritic craters, 3.2, 3.5, 3.8, and 3.82 aeons for the various mare surfaces according to the determinations of D.E. Wilhelms (1980, Geologic history of the Moon, U.S. Geol. Surv. Prof. Pap.) and 3.85 aeons from the formation of Imbrium. 相似文献
87.
88.
Philip B. James 《Icarus》1985,64(2):249-264
The Martian CO2 cycle, which includes the seasonal condensation and subsequent sublimation of up to 30% of the planet's atmosphere, produces meridional winds due to the consequent mass flux of CO2. These winds currently display strong seasonal and hemispheric asymmetries due to the large asymmetries in the distribution of insolation on Mars. It is proposed that asymmetric meridional advection of water vapor on the planet due to these CO2 condensation winds is capable of explaining the observed dessication of Mars' south polar region at the current time. A simple model for water vapor transport is used to verify this hypothesis and to speculate on the effects of changes in orbital parameters on the seasonal water cycle. 相似文献
89.
90.
The FAST/SKA site selection in Guizhou province 总被引:1,自引:0,他引:1
Many karst depressions with diameters of 300 m to 500 m, suitable for constructing Arecibo-style radio telescopes, were identified
in the south of Guizhou Province by Remote Sensing (RS) and Geographic Information System (GIS) technologies together with
field investigations. Fundamental topography and landform databases were established for 391candidate depressions, and using
GIS the3-dimensional images of depressions, at a scale of 1:10000, were then simulated to fit a spherical antenna.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献