全文获取类型
收费全文 | 44998篇 |
免费 | 381篇 |
国内免费 | 262篇 |
专业分类
测绘学 | 939篇 |
大气科学 | 2320篇 |
地球物理 | 8540篇 |
地质学 | 17426篇 |
海洋学 | 4288篇 |
天文学 | 10494篇 |
综合类 | 154篇 |
自然地理 | 1480篇 |
出版年
2022年 | 532篇 |
2021年 | 807篇 |
2020年 | 848篇 |
2019年 | 914篇 |
2018年 | 1929篇 |
2017年 | 1745篇 |
2016年 | 1879篇 |
2015年 | 741篇 |
2014年 | 1651篇 |
2013年 | 2437篇 |
2012年 | 1866篇 |
2011年 | 2243篇 |
2010年 | 2077篇 |
2009年 | 2391篇 |
2008年 | 2106篇 |
2007年 | 2320篇 |
2006年 | 2008篇 |
2005年 | 1146篇 |
2004年 | 1067篇 |
2003年 | 1029篇 |
2002年 | 964篇 |
2001年 | 939篇 |
2000年 | 831篇 |
1999年 | 561篇 |
1998年 | 595篇 |
1997年 | 619篇 |
1996年 | 438篇 |
1995年 | 468篇 |
1994年 | 436篇 |
1993年 | 366篇 |
1992年 | 342篇 |
1991年 | 368篇 |
1990年 | 415篇 |
1989年 | 335篇 |
1988年 | 323篇 |
1987年 | 352篇 |
1986年 | 266篇 |
1985年 | 395篇 |
1984年 | 389篇 |
1983年 | 391篇 |
1982年 | 354篇 |
1981年 | 325篇 |
1980年 | 350篇 |
1979年 | 283篇 |
1978年 | 314篇 |
1977年 | 270篇 |
1976年 | 227篇 |
1975年 | 242篇 |
1974年 | 233篇 |
1973年 | 264篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
M.R. Kaplan A. Coronato N.R.J. Hulton J.O. Rabassa P.W. Kubik S.P.H.T. Freeman 《Geomorphology》2007,87(4):284-301
We measured in situ 10Be, 26Al and36Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained 40Ar/39Ar ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforms are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter. 相似文献
92.
We report the data on changes in snow cover characteristics obtained at meteorological stations Tulun and Bokhan and in their neighborhoods for the period 1961–1990. We examine the changes in snow cover, air temperature and soil temperature at depths of 20, 40 and 80 cm. 相似文献
93.
V. A. Brumberg 《Celestial Mechanics and Dynamical Astronomy》2010,106(3):209-234
As we are now approaching 2015, both the General Relativity Theory (GRT) and the relativistic Celestial Mechanics based on
it will soon arrive at their 100 year anniversaries. There is no border between Newtonian and relativistic Celestial Mechanics.
The five-decade period of intensive development of Celestial Mechanics in the second half of the 20th century left many interesting
techniques and problems uncompleted. This lecture reviews some problems of Newtonian and relativistic Celestial Mechanics
worthy of further investigation. Concerning Newtonian mechanics, these problems include general solution of the three-body
problem by means of the series of polynomials, construction of the short-term and long-term theories of motion using the fast
converging elliptic function expansions, and representation of the rotation of the planets in the form compatible with the
General Planetary Theory reducing the problem to the combined secular system for translatory motion and rotation. Relativistic
problems considered here include the determination of the main relativistic effects in the motion of a satellite, e.g. the
Moon, and in the rotation of the primary planet using the Newtonian theories of motion and rotation combined with the relativistic
transformation of the reference systems, the use of the linearized weak-field GRT metric as a basis of relativistic Celestial
Mechanics in the post-Newtonian approximation, and the motion of the Solar System bodies at the cosmological background in
the framework of the basic cosmological models. The exposition of the chosen relativistic problems is preceded by reminding
the basic features of relativistic Celestial Mechanics with discussing some present tendencies concerning the Parametrized
Post-Newtonian formalism, International Astronomical Union resolutions, and standardization of the GRT routines. 相似文献
94.
95.
96.
V. V. Usov 《Astrophysics and Space Science》1988,140(1):39-47
During the evolution of the neutron star its magnetic field first decays exponentially with the time and then may becomes quasi-stationary. The non-decaying magnetic field of the neutron star is generated by a degenerate electron gas which is in the Landau orbital ferromagnetism (LOFER) state. Possibly, due to the neutron star transition into the LOFER state, magnetic fields remained sufficiently strong in the case of such old magnetic neutron stars as powerful X-ray sources (e.g., Her X-1), millisecond pulsars and the binary pulsar PSR 0655+64. 相似文献
97.
Quasi-biennial oscillations of solar activity are investigated using several global indices. The Singular Spectrum Analysis is used to separate out and study quasi-biennial oscillations; this method is one of the modifications of the main components method. The principal components of the solar cycle are stable 11-year, secular, and quasi-biennial variations. The periods and shapes of individual variations in each quasi-biennial train depend on the length and power of the particular 11-year cycle. 相似文献
98.
99.
V. N. Yershov 《Astrophysics and Space Science》2014,354(1):97-101
Two UV serendipitous source catalogues are presented which were compiled based on the observations with two similar UV telescopes, one being on-board the ESA’s XMM Newton observatory and another—on-board the NASA’s Swift satellite. Both telescopes have similar optical and registration systems providing photometry in three ultraviolet and three visible bands. After processing a 10 years long series of observations from XMM and 5 years from Swift, we have compiled two source catalogues containing more than 4 million sources for XMM and 6 million sources for Swift. We describe the processing algorithms and present catalogue characteristics in comparison with each other. 相似文献
100.
Occultations and eclipses from ancient times down to the present are analysed to determine changes in the length of the day. By subtracting the expected tidal contribution from the observed changes, the non-tidal variations are obtained. The non-tidal varations are shown to occur on time-scales of decades and millennia. 相似文献