全文获取类型
收费全文 | 64853篇 |
免费 | 1099篇 |
国内免费 | 329篇 |
专业分类
测绘学 | 1555篇 |
大气科学 | 4624篇 |
地球物理 | 12405篇 |
地质学 | 26350篇 |
海洋学 | 5059篇 |
天文学 | 12901篇 |
综合类 | 257篇 |
自然地理 | 3130篇 |
出版年
2022年 | 300篇 |
2021年 | 551篇 |
2020年 | 628篇 |
2019年 | 676篇 |
2018年 | 3981篇 |
2017年 | 3762篇 |
2016年 | 2872篇 |
2015年 | 972篇 |
2014年 | 1385篇 |
2013年 | 2318篇 |
2012年 | 2547篇 |
2011年 | 4405篇 |
2010年 | 4023篇 |
2009年 | 4479篇 |
2008年 | 3647篇 |
2007年 | 4207篇 |
2006年 | 1769篇 |
2005年 | 1637篇 |
2004年 | 1574篇 |
2003年 | 1638篇 |
2002年 | 1354篇 |
2001年 | 985篇 |
2000年 | 909篇 |
1999年 | 785篇 |
1998年 | 774篇 |
1997年 | 797篇 |
1996年 | 632篇 |
1995年 | 634篇 |
1994年 | 553篇 |
1993年 | 490篇 |
1992年 | 436篇 |
1991年 | 456篇 |
1990年 | 490篇 |
1989年 | 416篇 |
1988年 | 388篇 |
1987年 | 436篇 |
1986年 | 443篇 |
1985年 | 539篇 |
1984年 | 580篇 |
1983年 | 568篇 |
1982年 | 528篇 |
1981年 | 500篇 |
1980年 | 467篇 |
1979年 | 432篇 |
1978年 | 393篇 |
1977年 | 405篇 |
1976年 | 362篇 |
1975年 | 367篇 |
1974年 | 354篇 |
1973年 | 389篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
B. A. Ivanov 《Solar System Research》2005,39(5):381-409
Multi-ring impact basins have been found on the surfaces of almost all planetary bodies in the Solar system with solid crusts. The details of their formation mechanism are still unclear. We present results of our numerical modeling of the formation of the largest known terrestrial impact craters. The geological and geophysical data on these structures accumulated over many decades are used to place constraints on the parameters of available numerical models with a dual purpose: (i) to choose parameters in available mechanical models for the crustal response of planetary bodies to a large impact and (ii) to use numerical modeling to refine the possible range of original diameters and the morphology of partially eroded terrestrial craters. We present numerical modeling results for the Vredefort, Sudbury, Chicxulub, and Popigai impact craters and compare these results with available geological and geophysical information. 相似文献
23.
The main properties of the first- and second-order moments of polarized hydrogen lines, forming in the presence of stationary electric and magnetic fields, are reviewed. The analytical results presented here apply directly to the case of optically-thin emission lines in the LTE regime. Some applications of such results to electric- and magnetic-field diagnostics in (solar) plasmas are then briefly considered.On leave from the Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy 相似文献
24.
C. Beaugé 《Celestial Mechanics and Dynamical Astronomy》1996,64(4):313-350
Starting with a simple Taylor-based expansion of the inverse of the distance between two bodies, we are able to obtain a series expansion of the disturbing function of the three-body problem (planar elliptic case) which is valid for all points of the phase space outside the immediate vicinity of the collision points. In particular, the expansion is valid for very high values of the eccentricity of the perturbed body. Furthermore, in the case of an interior mean-motion resonant configuration, the above-mentioned expression is easily averaged with respect to the synodic period, yielding once again a global expansion of (R) valid for very high eccentricities.Comparisons between these results and the numerically computed exact function are presented for various resonances and values of the eccentricity. Maximum errors are determined in each case and their origin is established. Lastly, we discuss the applicability of the present expansion to practical problems. 相似文献
25.
26.
Results of several fits of the lunar theory ELP 2000-82B and of Moons' theory of libration are presented. The theories are fitted both to JPL numerical integrations and to LLR observations 相似文献
27.
The orbits of (69230) Hermes and 2002 SY50 are similar and the Earth approaches both of them twice: at the end of October the local orbital minimum distances are smaller
than 0.007 AU, and at the end of April the distances are smaller than 0.04 AU. This gives us opportunities to observe the
meteors associated with these asteroids. Using the geocentric parameters of the orbital close encounters (the theoretical
radiants) and our D
N
distance function (Valsecchi et al. Mon. Not. R. Astron. Soc. 304 (1999) 743), we searched for meteoroids originated by Hermes and 2002 SY50. A search among 1830 good quality photographic meteors gave negative results: we found no meteor dynamically similar to Hermes
or 2002 SY50. In a second search, done in a set of 62150 radio meteors, we applied two methods (M1, M2) and in both cases we found two
streams; the streams found with the M1 method had 43 and 30 members, those found with the M2 method had 39 and 14 members.
However, these results do not look convincing, due to the small number of common members in the corresponding streams. We
therefore conclude that amongst the IAU meteors used in our search there are no compact streams associated with Hermes and
2002 SY50. 相似文献
28.
29.
The elm decline of 5000 14C yr ago has been the most widely discussed phenomenon in post‐glacial vegetation history. This pan‐European reduction of elm populations, echoed in the decimation of elmwoods in Europe during the twentieth century, has attracted a series of interrelated hypotheses involving climate change, human activity, disease and soil deterioration. The elm bark beetle (Scolytus scolytus L.) is an essential component of disease explanations. We present evidence for the presence of the beetle over a prolonged period (ca. 7950–4910 yr BP [8800–5660 cal. yr BP]) from a lowland raised mire deposit in northeast Scotland, with its final appearance at this site, and the first and only appearance in another mire of a single scolytid find, around the time of the elm decline. The subfossil S. scolytus finds are not only the first from Scotland, but they also represent the most comprehensive sequence of finds anywhere. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献