全文获取类型
收费全文 | 2482篇 |
免费 | 407篇 |
国内免费 | 504篇 |
专业分类
测绘学 | 123篇 |
大气科学 | 508篇 |
地球物理 | 859篇 |
地质学 | 978篇 |
海洋学 | 277篇 |
天文学 | 193篇 |
综合类 | 124篇 |
自然地理 | 331篇 |
出版年
2024年 | 9篇 |
2023年 | 31篇 |
2022年 | 54篇 |
2021年 | 70篇 |
2020年 | 62篇 |
2019年 | 107篇 |
2018年 | 72篇 |
2017年 | 99篇 |
2016年 | 108篇 |
2015年 | 98篇 |
2014年 | 149篇 |
2013年 | 283篇 |
2012年 | 156篇 |
2011年 | 107篇 |
2010年 | 105篇 |
2009年 | 180篇 |
2008年 | 161篇 |
2007年 | 135篇 |
2006年 | 134篇 |
2005年 | 138篇 |
2004年 | 101篇 |
2003年 | 100篇 |
2002年 | 86篇 |
2001年 | 76篇 |
2000年 | 60篇 |
1999年 | 56篇 |
1998年 | 39篇 |
1997年 | 48篇 |
1996年 | 88篇 |
1995年 | 155篇 |
1994年 | 166篇 |
1993年 | 43篇 |
1992年 | 17篇 |
1991年 | 21篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 14篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 3篇 |
排序方式: 共有3393条查询结果,搜索用时 15 毫秒
91.
Shi Zhi-dong Li Zhong-yuanUniversity of Science Technology of China Hefei PRC Advanced Centre for Earth Science Astronomy Third World Academy of Science 《紫金山天文台台刊》1996,(2)
Areview about K-H instability related to comet tail is presented.The effect of dust graing on KHI is theoretically analysed and relations of critical shear to excit KHI with the properties of dust grains both for sheared ion flow and for sheared dust flow re put out.Their possible application in comet tail is suggested. 相似文献
92.
在中子星磁轴吸积柱的上部,少数高能电子通过磁镜点反射,可使部份电子的速度分布形成非热分布,由此激发激射(Maser)不稳定性。波被放大,发射出频率近似为电子迴旋频率及其倍频的相干辐射。用此模型计算了HerX-1的迴旋线发射。发现不稳定性增长率与吸积柱中电子数密度成正比,因而比非相干散射产生的连续辐射随电子数密度增长更快;而且发射线的强度和能量均与脉冲相位关联。这个理论可解释近期的HerX-1观测结果。 相似文献
93.
The coherent plasma process such as parametric decay instability (PDI) has been applied to a homogeneous and unmagnetized
plasma. These instabilities cause anomalous absorption of strong electromagnetic radiation under specific conditions of energy
and momentum conservation and thus cause anomalous heating of the plasma. The maximum plasma temperatures reached are functions
of luminosity of the radio radiation and plasma parameters. We believe that these processes may be taking place in many astrophysical
objects. Here, the conditions in the sources 3C 273, 3C 48 and Crab Nebula are shown to be conducive to the excitation of
PDI. These processes also contribute towards the absorption of 21cm radiation 相似文献
94.
This study presents a new way to identify the sensitive areas for typhoon adaptive observations, that is, sensitive areas are determined by invoking the negative anomalies of moist potential vorticity (MPV). It is found that the areas of negative MPV are the symmetric instability areas and can be taken as sensitive areas for typhoon adaptive observations. Three typhoons in 2008, Nuri, Fung-wong, and Fengshen, were simulated with the help of MM5 model. It is shown that these typhoons are well simulated in the first 12 hours. Based on these investigations, the calculations of MPV are carried out sequentially. The result shows that the negative maxima of MPV are always around the typhoon eyes for all the cases, which means that the sensitive areas are also near them all the time. 相似文献
95.
A. M. Finkelstein E. A. Skurikhina I. F. Surkis A. V. Ipatov I. A. Rakhimov S. G. Smolentsev 《Astronomy Letters》2008,34(1):59-68
Regular high-precision determinations of the Earth’s orientation parameters (EOPs) on the Quasar VLBI Network were begun in
August 2006. The observations are performed within the framework of two national programs: daily sessions at three observatories
of the Network to determine all five EOPs (the RU-E program) and 8-h sessions on the Zelenchukskaya-Badary and Svetloe-Badary
baselines to determine the Universal Time (the RU-U program). The observations from August 2006 through May 2007 are analyzed.
The rms deviations of the EOP values obtained in the RU-E program from the IERS C04 series are 1.1 mas for X
p and Y
p, 37 μs for UT1-UTC, and 0.7 and 0.6 mas for X
c and Y
c, respectively. These results closely match the prospective requirements of GLONASS. The rms deviations of the Universal Times
obtained in the RU-U program from the IERS C04 series are 146 μs. We consider the immediate prospects for improving the accuracy
of EOP determinations in daily sessions and for implementing the e-VLBI mode for an online determination of the Universal
Time.
Original Russian Text ? A.M. Finkelstein, E.A. Skurikhina, I.F. Surkis, A.V. Ipatov, I.A. Rakhimov, S.G. Smolentsev, 2008,
published in Pis’ma v Astronomicheskiĭ Zhurnal, 2008, Vol. 34, No. 1, pp. 66–76. 相似文献
96.
Collisionless shocks in turbulent space plasmas accelerate particles by the Fermi mechanism to ultrarelativistic energies. The interaction of accelerated particles with the plasma inflow produces extended supersonic MHD flows of multicomponent plasma. We investigate the instabilities of a flow of three-component turbulent plasma with relativistic particles against long-wavelength perturbations with scales larger than the accelerated particle transport mean free path and the initial turbulence scales. The presence of turbulence allows us to formulate the system of single-fluid equations, the equation of motion for the medium as a whole, and the induction equation for the magnetic field with turbulent magnetic and kinematic viscosities. The current of accelerated particles enters into the induction equation with an effective magnetic diffusion coefficient. We have calculated the local growth rates of the perturbations related to the nonresonant long-wavelength instability of the current of accelerated particles for MHD perturbations in the WKB approximation. The amplification of long-wavelength magnetic field perturbations in the flow upstream of the shock front can affect significantly the maximum energies of the particles accelerated by a collisionless shock and can lead to the observed peculiarities of the synchrotron X-ray radiation in supernova remnants. 相似文献
97.
Giovanni Federico Gronchi 《Celestial Mechanics and Dynamical Astronomy》2009,103(4):301-326
Charlier’s theory (1910) provides a geometric interpretation of the occurrence of multiple solutions in Laplace’s method of
preliminary orbit determination, assuming geocentric observations. We introduce a generalization of this theory allowing to
take into account topocentric observations, that is observations made from the surface of the rotating Earth. The generalized
theory works for both Laplace’s and Gauss’ methods. We also provide a geometric definition of a curve that generalizes Charlier’s
limiting curve, separating regions with a different number of solutions. The results are generically different from Charlier’s:
they may change according to the value of a parameter that depends on the observations. 相似文献
98.
C. Sigismondi D. W. Dunham K. Guhl S. Andersson H. Bode O. Canales P. Colona O. Farago M. Fernández-Ocaña A. Gabel M. Haupt C. Herold R. Nugent P. Oliva M. Patel C. Perello W. Rothe J. Rovira T. Schaefer C. Schnabel D. Schwartz A. Selva W. Strickling A. Tegtmeier C. Tegtmeier B. Thome W. H. Warren 《Solar physics》2009,258(2):191-202
In the annular or total eclipses of 3 October 2005, 29 March 2006, 22 September 2006, and 1 August 2008, observational campaigns
were organized to record the phenomenon of Baily’s beads. These campaigns were internationally coordinated through the International
Occultation Timing Association (IOTA) at both its American and European sections. From the stations in the northern and southern
zones of grazing eclipse, the eclipses have been recorded on video. Afterward, as many beads as possible have been identified
by analyzing the video data of each observing station. The atlas presented in this paper includes 598 data points, obtained
by 23 observers operating at 28 different observing stations. The atlas lists the geographic positions of the observing stations
and the observed time instants of disappearance or reappearance of beads, identified by an angle measured relative to the
Moon’s axis of rotation. The atlas will serve as a basis for determining the solar diameter.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
99.
田谐项摄动是分析法轨道预报中的重要部分,其中包含大量倾角函数及其偏导数的计算.由于具有精度更高、速度更快的优点,倾角函数一般通过递推方法计算.以文献中提出的改进Gooding方法为基础,将其给出的程序稍加改进,在计算2–50阶倾角函数时缩短了约24%的计算时间.考虑到分析法预报过程中轨道平倾角变化很小,以泰勒展开式计算倾角函数,可极大提高计算速度,较大程度地减小分析法预报耗时,且引力场阶次越高,减小幅度越大,取50阶时预报耗时缩短了48%.另一方面,以2阶展开式计算倾角函数时,与改进Gooding法相比,分析法预报星历偏差很小.对于500 km高度的低轨卫星,分别以改进Gooding法和2阶泰勒展开式计算倾角函数,预报3天,当地球引力场阶次不高于50时,二者预报星历偏差RMS (Root Mean Square)低于1 mm,且随着轨道高度的增加,预报星历偏差RMS逐渐减小. 相似文献
100.