全文获取类型
| 收费全文 | 113篇 |
| 免费 | 6篇 |
| 国内免费 | 16篇 |
专业分类
| 测绘学 | 2篇 |
| 地球物理 | 36篇 |
| 地质学 | 81篇 |
| 海洋学 | 5篇 |
| 天文学 | 9篇 |
| 自然地理 | 2篇 |
出版年
| 2016年 | 3篇 |
| 2015年 | 3篇 |
| 2013年 | 3篇 |
| 2012年 | 5篇 |
| 2011年 | 5篇 |
| 2010年 | 1篇 |
| 2008年 | 4篇 |
| 2007年 | 11篇 |
| 2006年 | 1篇 |
| 2005年 | 6篇 |
| 2004年 | 9篇 |
| 2003年 | 3篇 |
| 2002年 | 6篇 |
| 2001年 | 2篇 |
| 2000年 | 9篇 |
| 1999年 | 3篇 |
| 1998年 | 5篇 |
| 1997年 | 9篇 |
| 1996年 | 4篇 |
| 1995年 | 7篇 |
| 1994年 | 7篇 |
| 1993年 | 4篇 |
| 1992年 | 5篇 |
| 1991年 | 4篇 |
| 1990年 | 7篇 |
| 1989年 | 7篇 |
| 1987年 | 1篇 |
| 1983年 | 1篇 |
排序方式： 共有135条查询结果，搜索用时 15 毫秒
1.
The competition between impact erosion and impact supply of volatiles to planetary atmospheres can determine whether a planet or satellite accumulates an atmosphere. In the absence of other processes (e.g., outgassing), we find either that a planetary atmosphere should be thick, or that there should be no atmosphere at all. The boundary between the two extreme cases is set by the mass and velocity distributions and intrinsic volatile content of the impactors. We apply our model specifically to Titan, Callisto, and Ganymede. The impacting population is identified with comets, either in the form of stray Uranus-Neptune planetesimals or as dislodged Kuiper belt comets. Systematically lower impact velocities on Titan allow it to retain a thick atmosphere, while Callisto and Ganymede get nothing. Titan's atmosphere may therefore be an expression of a late-accreting, volatile-rich veneer. An impact origin for Titan's atmosphere naturally accounts for the high D/H ratio it shares with Earth, the carbonaceous meteorites, and Halley. It also accounts for the general similarity of Titan's atmosphere to those of Triton and Pluto, which is otherwise puzzling in view of the radically different histories and bulk compositions of these objects. 相似文献
2.
Dunlop JB 《Post-Soviet geography》1994,35(4):204-215
The author "examines a range of issues surrounding the involuntary migration of Russian populations from the non-Russian republics of the former USSR. Among the questions addressed are possible magnitudes of in-migration into Russia (with special attention paid to conditions in one of the major source regions, Central Asia), attitudes in Russia regarding appropriate policy with respect to treatment of co-nationals in the near abroad and whether their return to Russia would have a positive or negative impact, and conditions in areas of Russia that presently are absorbing the greatest numbers of migrants. The assertion that Russian policy should seek aggressively to prevent the out-migration of Russian populations [from] the near abroad is assessed critically." 相似文献
3.
We have developed a coupled atmosphere and ocean model of Titan's surface. The atmospheric model is a 1-D spectrally-resolved radiative-convective model. The ocean thermodynamics are based upon solution theory. The ocean, initially composed of CH4, becomes progressively enriched in ethane over time. The partial pressures of N2 and CH4 in the atmosphere are dependent on the ocean temperature and composition. We find that the resulting system is stable against a runaway greenhouse. Accounting for the decreased solar luminosity, we find that Titan's surface temperature was about 20 K colder 4 Gyr ago. Without an ocean, but only small CH4 lakes, the temperature change is 12 K. In both cases we find that the surface of Titan may have been ice covered about 3 Gyr ago. In the lakes case condensation of N2 provides the ice, whereas in the ocean case the ocean freezes. The dominant factor influencing the evolution of Titan's surface temperature is the change in the solar constant--amplified, if an ocean is present, by the temperature dependence of the solubility of N2. Accretional heating can dramatically alter the surface temperature; a surface thermal flux of 500 erg cm-2 sec-1, representative of small levels of accretional heating, results in a approximately 20 K change in surface temperatures. 相似文献
4.
5.
6.
内蒙古准苏吉花斑岩型钼矿床是一个中型金属矿床,目前勘查区内还没有较深的钻孔资料。为探测深部隐伏金属矿和控矿构造及深部地质结构,在内蒙古准苏吉花钼矿区及其外围开展了高精度反射地震测量。该反射地震采用2台套大功率可控震源激发,5 m道间距,960道接收,80次覆盖的工作方法,获得了能清晰反映深部地质结构和构造的高精度反射地震剖面。在该剖面上,能够清楚地解释测区导矿和控矿构造及隐伏岩体分布及燕山期与华力西期岩体的交切关系,并据此讨论了地壳深部流体运移的路径和动力过程,为在该区寻找深部隐伏金属矿指明了新的找矿靶区。 相似文献
7.
哈拉湖位于青藏高原,在该区开展的地质调查、音频大地电磁测深和地球化学调查结果表明,该区具有良好的天然气水合物找矿前景。为寻找天然气水合物,在该区开展了高精度反射地震试验。反射地震采用1 200道接收,道间距2 m,偏移距1 m,炮间距8 m,覆盖次数150次,排列中间激发的观测系统,每道采用6个60 Hz检波器单点组合接收;采样间隔0.5 ms,记录长度2 s,宽频带采集;激发震源为大型车载可控震源。采用该工作方法得到的地震剖面信噪比和分辨率较高,构造形态特征明显。根据试验区地形地貌和地震剖面上反映的永冻土层厚度、断裂构造和高速层分布,结合其他资料,确定了验证孔位。 相似文献
8.
9.
10.
黑西哥ＦｒｅｓｎｉｌｌｏＡｇ－Ｐｂ－Ｚｎ地区的ＳａｎｔｏＮｉｎｏ脉中，银含在螺状硫银矿及三个含银矿盐固溶体系列的矿物中，这些硫盐矿物是：浓红银矿、淡红银矿、硫锑铜银矿、硒硫铜银矿、黝铜矿及脆银矿。 相似文献