全文获取类型
收费全文 | 37407篇 |
免费 | 263篇 |
国内免费 | 221篇 |
专业分类
测绘学 | 744篇 |
大气科学 | 1728篇 |
地球物理 | 7106篇 |
地质学 | 14721篇 |
海洋学 | 3544篇 |
天文学 | 8846篇 |
综合类 | 99篇 |
自然地理 | 1103篇 |
出版年
2022年 | 493篇 |
2021年 | 713篇 |
2020年 | 762篇 |
2019年 | 829篇 |
2018年 | 1705篇 |
2017年 | 1558篇 |
2016年 | 1655篇 |
2015年 | 618篇 |
2014年 | 1427篇 |
2013年 | 2045篇 |
2012年 | 1627篇 |
2011年 | 1905篇 |
2010年 | 1807篇 |
2009年 | 1998篇 |
2008年 | 1770篇 |
2007年 | 1987篇 |
2006年 | 1744篇 |
2005年 | 900篇 |
2004年 | 820篇 |
2003年 | 810篇 |
2002年 | 749篇 |
2001年 | 771篇 |
2000年 | 631篇 |
1999年 | 425篇 |
1998年 | 444篇 |
1997年 | 476篇 |
1996年 | 341篇 |
1995年 | 361篇 |
1994年 | 339篇 |
1993年 | 287篇 |
1992年 | 287篇 |
1991年 | 296篇 |
1990年 | 340篇 |
1989年 | 273篇 |
1988年 | 262篇 |
1987年 | 262篇 |
1986年 | 192篇 |
1985年 | 301篇 |
1984年 | 304篇 |
1983年 | 295篇 |
1982年 | 282篇 |
1981年 | 252篇 |
1980年 | 268篇 |
1979年 | 203篇 |
1978年 | 245篇 |
1977年 | 208篇 |
1976年 | 177篇 |
1975年 | 185篇 |
1974年 | 173篇 |
1973年 | 208篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
251.
G. A. Avanesov R. V. Gordeev V. A. Grishin B. S. Zhukov S. B. Zhukov E. V. Kolomeets E. B. Krasnopevtseva M. I. Kudelin A. A. Krupin V. M. Murav’ev A. A. Forsh 《Solar System Research》2010,44(5):444-450
A TV system for navigation and guidance (TVSNG) has been designed for solving the navigation and scientific tasks of the Phobos-Grunt mission. It consists of two narrow-angle and two wide-angle television cameras. Each camera has a built-in processor for the real-time processing of received images. The program of TVSNG observations includes three modes: Imaging of Stars, Sequential Imaging, and Landing. The first two modes will be used to calibrate the TVSNG against the stars, to take images of Phobos and Mars, and to detect the dust rings of Mars. In the Landing mode, the height and velocity components of the spacecraft during the landing on Phobos will be measured, and an autonomous selection of the landing site will be made. 相似文献
252.
Palynological results from Julietta Lake currently provide the most direct evidence to support the existence of a glacial refugium for Pinus pumila in mountains of southwestern Beringia. Both percentages and accumulation rates indicate the evergreen shrub survived until at least ∼ 19,000 14C yr BP in the Upper Kolyma region. Percentage data suggest numbers dwindled into the late glaciation, whereas pollen accumulation rates point towards a more rapid demise shortly after ∼ 19,000 14C yr BP. Pinus pumila did not re-establish in any great numbers until ∼ 8100 14C yr BP, despite the local presence ∼ 9800 14C yr BP of Larixdahurica, which shares similar summer temperature requirements. The postglacial thermal maximum (in Beringia ∼ 11,000-9000 14C yr BP) provided Pinus pumila shrubs with equally harsh albeit different conditions for survival than those present during the LGM. Regional records indicate that in this time of maximum warmth Pinus pumila likely sheltered in a second, lower-elevation refugium. Paleoclimatic models and modern ecology suggest that shifts in the nature of seasonal transitions and not only seasonal extremes have played important roles in the history of Pinus pumila over the last ∼ 21,000 14C yr BP. 相似文献
253.
D. V. Likhodeev Z. I. Dudarov R. A. Zhostkov D. A. Presnov S. M. Dolov K. B. Danilov 《Journal of Volcanology and Seismology》2017,11(6):413-418
This paper presents results from a study of the deep structure of the Elbrus edifice and adjacent areas using geophysical techniques. We confirmed the existence of a shallow magma chamber, derived a more accurate location of the chamber in the host rocks and its characteristic dimensions, and compared new results with known studies. More accurate estimates have been obtained for the temperature at the top of the magma chamber and new evidence is adduced concerning the deep structure of the fluid magmatic systems in the Elbrus volcanic area. 相似文献
254.
255.
256.
Muryshev K. E. Eliseev A. V. Denisov S. N. Mokhov I. I. Arzhanov M. M. Timazhev A. V. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(3):235-241
Izvestiya, Atmospheric and Oceanic Physics - The phase shift between changes in the global surface temperature Tg and atmospheric CO2 content $${{q}_{{{\text{C}}{{{\text{O}}}_{2}}}}}$$ has been... 相似文献
257.
On the Distance Function Between Two Keplerian Elliptic Orbits 总被引:1,自引:0,他引:1
Konstantin V. Kholshevnikov Nikolay N. Vassiliev 《Celestial Mechanics and Dynamical Astronomy》1999,75(2):75-83
The problem of finding critical points of the distance function between two Keplerian elliptic orbits is reduced to the determination
of all real roots of a trigonometric polynomial of degree 8. The coefficients of the polynomial are rational functions of
orbital parameters. Using computer algebra methods we show that a polynomial of a smaller degree with such properties does
not exist. This fact shows that our result cannot be improved and it allows us to construct an optimal algorithm to find the
minimal distance between two Keplerian orbits.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
258.
Visualization of a collapsing vertical packet of patches in a laboratory experiment and the results of acoustical sounding under field conditions allowed us to discriminate the stage of its evolution which was previously unknown. It is defined by the variations of the horizontal dimensions of patches and their effective scattering surface with a period ofT=150–250/N, whereN is the Brunt-Väisälä frequency. The horizontal dimensions of patches can reach 40% of their final dimensions at the evolution stage discriminated.Translated by Mikhail M. Trufanov. 相似文献
259.
260.
The authors elaborate upon the “multiplicity principle” in remote sensing, i.e., the need for repeated imaging at a variety of scales, spatial resolutions, spectral bands, and times of imaging in order to attain the maximum information possible. They then explore the ways it can be applied in agricultural research, through two different image comparison and interpretation strategies. A detailed example is presented of the use of a multitemporal imaging strategy for the recognition of several agricultural crops from false color composite imagery. Translated by Edward Torrey, Alexandria, VA 22308 from: G. V. Dobrovol'skiy and V. L. Andronikov, eds., Aerokosmicheskiye metody v pochvo-vedenii i ikh ispol'zovaniye v sel'skom khozyaystve: sbornik nauchnykh trudov [Remote Sensing Methods in Soil Science and Their Utilization in Agriculture: A Collection of Scientific Works]. Moscow: Nauka, 1990, pp. 47-55. 相似文献