全文获取类型
收费全文 | 7862篇 |
免费 | 245篇 |
国内免费 | 109篇 |
专业分类
测绘学 | 126篇 |
大气科学 | 574篇 |
地球物理 | 1771篇 |
地质学 | 3554篇 |
海洋学 | 745篇 |
天文学 | 984篇 |
综合类 | 81篇 |
自然地理 | 381篇 |
出版年
2023年 | 23篇 |
2022年 | 62篇 |
2021年 | 135篇 |
2020年 | 150篇 |
2019年 | 172篇 |
2018年 | 359篇 |
2017年 | 358篇 |
2016年 | 465篇 |
2015年 | 257篇 |
2014年 | 411篇 |
2013年 | 592篇 |
2012年 | 529篇 |
2011年 | 531篇 |
2010年 | 529篇 |
2009年 | 517篇 |
2008年 | 449篇 |
2007年 | 458篇 |
2006年 | 351篇 |
2005年 | 262篇 |
2004年 | 174篇 |
2003年 | 151篇 |
2002年 | 109篇 |
2001年 | 101篇 |
2000年 | 93篇 |
1999年 | 67篇 |
1998年 | 57篇 |
1997年 | 67篇 |
1996年 | 47篇 |
1995年 | 37篇 |
1994年 | 45篇 |
1993年 | 28篇 |
1992年 | 31篇 |
1991年 | 35篇 |
1990年 | 31篇 |
1989年 | 24篇 |
1988年 | 25篇 |
1987年 | 30篇 |
1986年 | 32篇 |
1985年 | 27篇 |
1984年 | 48篇 |
1983年 | 35篇 |
1982年 | 33篇 |
1981年 | 20篇 |
1980年 | 20篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 15篇 |
1975年 | 26篇 |
1974年 | 23篇 |
1973年 | 19篇 |
排序方式: 共有8216条查询结果,搜索用时 31 毫秒
1.
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
2.
This paper deals with the formation processes and the palaeoenvironmental significance of relict slope deposits located on the uppermost part of the north Portugal mountains. For this purpose, seven key sites representative of the different lithofacies have been selected and analysed in detail. The data show that three main dynamic processes are responsible for the emplacement of regional fossil slope deposits: runoff, debris flows and dry grain flows. The ubiquity of these processes and the lack of frost‐related features or landforms do not support the existence of severe Pleistocene climates in this part of the lberian Peninsula as postulated by previous work. Pedological data gathered at one of the study sites show that a subalpine environment was probably present at 700–800 m altitude between 29 and 14 kyr. Using data from the Pyrenees Mountains, a 6.5 to 12°C depression in mean annual temperature has been tentatively postulated for this Pleniglacial period. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
Mohamed Abd-Elsalam Marie 《Astrophysics and Space Science》1992,198(1):121-128
Astrometric cluster membership probabilities have been derived from proper motion of the open cluster NGC 2301. A comparison with previous investigations is presented. 相似文献
4.
M. A. Vashkov’yak 《Astronomy Letters》2001,27(7):464-469
We consider the structural peculiarities of Uranus’s satellite system associated with its separation into two groups: inner equatorial satellites moving in nearly circular orbits and distant irregular satellites with retrograde motion in highly elliptical orbits. The intermediate region is free from satellites in a wide range of semimajor axes. By analyzing the evolution of satellite orbits under the combined effect of solar attraction and Uranus’s oblateness, we offer a celestial-mechanical explanation for the absence of equatorial satellites in this region. M.L. Lidov’s studies during 1961–1963 have served as a basis for our analysis. 相似文献
5.
Surface waters of Alsea Bay, an unpolluted estuary on the Oregon coast, were analysed for nitrous oxide, nitrate and nitrite on a weekly or biweekly basis during the summer of 1979. The estuary was found to be a variable source of N2O to the atmosphere. Large and rapid increases in the concentrations of N2O, NO3?, and NO2? occurred at the beginning of the sampling period and are attributed to the influx of nutrient-rich upwelling water into the estuary with the tide. The subsequent decline in concentrations of nitrate, nitrite and nitrous oxide over the remainder of the summer is attributed to a decrease in upwelling intensity, a decline in nitrification rates and to assimilatory nitrate reduction. Measurements of nitrous oxide at six stations along the Alsea River were also made in September and October before and after the onset of the rainy season. Samples taken after flood conditions were established were systematically 50% higher than pre-flood samples. The data suggest that soil runoff results in elevated concentrations of N2O in rivers. 相似文献
6.
Milan Burša 《Studia Geophysica et Geodaetica》1991,35(3):145-150
Summary The estimate of the tidal long-term decrease in the angular velocity of the Earth's rotation due to the Sun is given as –(0.8±0.3)×10
–22
rad s
–2. It was computed on the basis of the observed total long-term decrease in , of the observed tidal deceleration of the Moon and the observed decrease in the second-degree zonal Stokes geopotential harmonic term. Adopting the estimate given, the product of the Love number and the tidal phase lag angle due to the Sun (in degrees) comes out as 0.53±0.20.
am a z nuuu u z mu au u, az : –(0,8±0,3) 10 –22 a¶rt; –2 . ¶rt; ua n a¶rt;a u , n a¶rt;a nuu u ¶rt;z ¶rt;uu u n a¶rt;a u mz az znmuaz naama ma. u num n au, m nu¶rt;u ua a a z u ( za¶rt;a) a z nuua a (0,53±0,20).相似文献
7.
M. Burša 《Studia Geophysica et Geodaetica》1991,35(2):61-74
Summary It has been shown that dynamically, on the basis of the distribution of angular momenta, the Jovian system cannot be considered an analogue within the Solar system. The total tidal decrease in the angular momentum of Jupiter and in its angular velocity of rotation have been estimated, as well as the loss of mechanical energy due to tidal dissipation. It has been concluded that there are no dynamical contradictions with the hypothesis of the common cosmogonic origin of Jupiter and of its eight close satellites.
aam, m ¶rt;uauu, n an¶rt;u m uma ¶rt;uu, um numa umam aayu um. a a y au ma uma ¶rt;uu numa u z mu z au u—a nuuz mu, ma a nmu au yuu um u—a ¶rt;uunauu. a au, m m ¶rt;uauu azau zunm m zuu aaa numa u z uau u nmu.相似文献
8.
9.
Philippe E. Raison Regis Jardin Daniel Bouëxière Rudy J. M. Konings Thorsten Geisler Claudiu C. Pavel Jean Rebizant Karin Popa 《Physics and Chemistry of Minerals》2008,35(10):603-609
The crystallographic structures of the synthetic cheralite, CaTh(PO4)2, and its homolog CaNp(PO4)2 have been investigated by X-ray diffraction at room temperature. Rietveld analyses showed that both compounds crystallize in the monoclinic system and are isostructural to monazite LnPO4 (Ln = La to Gd). The space group is P21/n (I.T. = 14) with Z = 2. The refined lattice parameters of CaTh(PO4)2 are a = 6.7085(8) Å, b = 6.9160(6) Å, c = 6.4152(6) Å, and β = 103.71(1)° with best fit parameters R wp = 4.87%, R p = 3.69% and R B = 3.99%. For CaNp(PO4)2, we obtained a = 6.6509(5) Å, b = 6.8390(3) Å, c = 6.3537(8) Å, and β = 104.12(6)° and R wp = 6.74%, R p = 5.23%, and R B = 6.05%. The results indicate significant distortions of bond length and angles of the PO4 tetrahedra in CaTh(PO4)2 and to a lesser extent in CaNp(PO4)2. The structural distortions were confirmed by Raman spectroscopy of CaTh(PO4)2. A comparison with the isostructural compounds LnPO4 (Ln = Ce and Sm) confirmed that the substitution of the large rare earth trivalent cations with Ca2+ and Th4+ introduces a distortion of the PO4 tetrahedra. 相似文献
10.
This review is devoted to problems in the photochemical modeling of atmospheric processes. The physicochemical and mathematical foundations underlying the construction of photochemical models are described, a classification of the atmospheric reactions is presented, and the features of photochemical modeling are considered under various irradiance conditions for various atmospheric layers and geographical regions. Atmospheric processes that are important to photochemical models are discussed. Applications involving photochemical models are outlined. Some results are presented to illustrate the capabilities of photochemical models. Special attention is given to relatively recent directions in photochemical modeling, such as data assimilation and inverse problems. The review can be used by experts in areas related to atmospheric chemistry as a basic source of knowledge on the subject and for the development of photochemical modules for atmospheric models. 相似文献