全文获取类型
收费全文 | 11909篇 |
免费 | 1299篇 |
国内免费 | 1756篇 |
专业分类
测绘学 | 1466篇 |
大气科学 | 935篇 |
地球物理 | 929篇 |
地质学 | 3749篇 |
海洋学 | 1331篇 |
天文学 | 5277篇 |
综合类 | 634篇 |
自然地理 | 643篇 |
出版年
2024年 | 26篇 |
2023年 | 88篇 |
2022年 | 285篇 |
2021年 | 321篇 |
2020年 | 346篇 |
2019年 | 369篇 |
2018年 | 282篇 |
2017年 | 361篇 |
2016年 | 374篇 |
2015年 | 408篇 |
2014年 | 594篇 |
2013年 | 748篇 |
2012年 | 730篇 |
2011年 | 807篇 |
2010年 | 825篇 |
2009年 | 1106篇 |
2008年 | 1063篇 |
2007年 | 967篇 |
2006年 | 884篇 |
2005年 | 788篇 |
2004年 | 673篇 |
2003年 | 580篇 |
2002年 | 430篇 |
2001年 | 396篇 |
2000年 | 322篇 |
1999年 | 274篇 |
1998年 | 203篇 |
1997年 | 92篇 |
1996年 | 81篇 |
1995年 | 69篇 |
1994年 | 75篇 |
1993年 | 85篇 |
1992年 | 33篇 |
1991年 | 36篇 |
1990年 | 36篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 12篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 21篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 15篇 |
1954年 | 2篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
Hydrogen peroxide (H2O2) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 1015-1016 cm−2. However, a stringent upper limit of the H2O2 abundance on Mars (9×1014 cm−2) was derived in February 2001 from ground-based infrared spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. μm, Ls=112°). Here we report the detection of H2O2 on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls=206°) when the global water vapor abundance was ∼10 pr. μm. The spatial distribution of H2O2 shows a maximum in the morning around the sub-solar latitude. The mean H2O2 column density (6×1015 cm−2) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls=254°), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116-121). 相似文献
992.
993.
The science requirements on future gravity satellite missions, following from the previous contributions of this issue, are
summarized and visualized in terms of spatial scales, temporal behaviour and accuracy. This summary serves the identification
of four classes of future satellite mission of potential interest: high-altitude monitoring, satellite-to-satellite tracking,
gradiometry, and formation flights. Within each class several variants are defined. The gravity recovery performance of each
of these ideal missions is simulated. Despite some simplifying assumptions, these error simulations result in guidelines as
to which type of mission fulfils which requirements best. 相似文献
994.
995.
996.
Moist convective storms constitute a key aspect in the global energy budget of the atmospheres of the giant planets. Among them, Saturn is known to develop the largest scale convective storms in the Solar System, the Great White Spots (GWS) which occur rarely and have been detected once every 30 years approximately. On the average, Saturn seems to show much less convective storms than Jupiter with smaller size and reduced frequency and intensity. Here we present detailed simulations of the onset and development of storms at the Equator and mid-latitudes of Saturn. These are the regions where most of the recent convective activity of the planet has been observed. We use a 3D anelastic model with parameterized microphysics (Hueso and Sánchez-Lavega, 2001, Icarus 151, 257) studying the onset and evolution of water and ammonia moist convective storms up to sizes of a few hundred km. Water storms, while more difficult to initiate than in Jupiter, can be very energetic, arriving to the 150 mbar level and developing vertical velocities on the order of 150 m s−1. Ammonia storms develop easier but with a much smaller intensity unless very large abundances of ammonia (10 times solar) are present in Saturn's atmosphere. The Coriolis forces play a major role in the morphology and properties of water based storms. 相似文献
997.
998.
999.
1000.
The thin atmosphere of Neptune's moon Triton is dense enough to ablate micrometeoroids as they pass through. A combination of Triton's orbital velocity around Neptune and its orbital velocity around the Sun gives a maximum meteoroid impact velocity of approximately 19 km s−1, sufficient to heat the micrometeoroids to visibility as they enter. The ablation profiles of icy and stony micrometeoroids were calculated, along with the estimated brightness of the meteors. In contrast to the terrestrial case, visible meteors would extend very close to the surface of Triton. In addition, the variation in the meteoroid impact velocity as Triton orbits Neptune produces a large variation in the brightness of meteors with orbital phase, a unique Solar System phenomenon. 相似文献