全文获取类型
收费全文 | 53634篇 |
免费 | 697篇 |
国内免费 | 562篇 |
专业分类
测绘学 | 1449篇 |
大气科学 | 3802篇 |
地球物理 | 9900篇 |
地质学 | 19208篇 |
海洋学 | 4910篇 |
天文学 | 12901篇 |
综合类 | 188篇 |
自然地理 | 2535篇 |
出版年
2022年 | 365篇 |
2021年 | 630篇 |
2020年 | 658篇 |
2019年 | 707篇 |
2018年 | 1583篇 |
2017年 | 1504篇 |
2016年 | 1872篇 |
2015年 | 990篇 |
2014年 | 1747篇 |
2013年 | 2866篇 |
2012年 | 1856篇 |
2011年 | 2373篇 |
2010年 | 2070篇 |
2009年 | 2678篇 |
2008年 | 2296篇 |
2007年 | 2350篇 |
2006年 | 2193篇 |
2005年 | 1622篇 |
2004年 | 1638篇 |
2003年 | 1549篇 |
2002年 | 1472篇 |
2001年 | 1298篇 |
2000年 | 1218篇 |
1999年 | 993篇 |
1998年 | 1039篇 |
1997年 | 947篇 |
1996年 | 816篇 |
1995年 | 782篇 |
1994年 | 685篇 |
1993年 | 605篇 |
1992年 | 592篇 |
1991年 | 593篇 |
1990年 | 622篇 |
1989年 | 493篇 |
1988年 | 504篇 |
1987年 | 528篇 |
1986年 | 488篇 |
1985年 | 611篇 |
1984年 | 674篇 |
1983年 | 592篇 |
1982年 | 561篇 |
1981年 | 499篇 |
1980年 | 469篇 |
1979年 | 478篇 |
1978年 | 458篇 |
1977年 | 368篇 |
1976年 | 346篇 |
1975年 | 357篇 |
1974年 | 308篇 |
1973年 | 342篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
211.
212.
P. Rodríguez-Gil B. T. Gänsicke H.-J. Hagen S. Araujo-Betancor A. Aungwerojwit C. Allende Prieto D. Boyd J. Casares D. Engels O. Giannakis E. T. Harlaftis J. Kube H. Lehto I. G. Martínez-Pais R. Schwarz W. Skidmore A. Staude M. A. P. Torres 《Monthly notices of the Royal Astronomical Society》2007,377(4):1747-1762
213.
This is an analysis of the dependence of the flare activity of the well known flare star UV Ceti on the linear distance between
the components of this binary system. It is shown that its flaring activity clearly depends on the mutual distance of the
components, while this kind of variability is not seen in isolated flare stars. 相似文献
214.
215.
The release of plasma in the jovian magnetotail is observed in the form of plasmoids, travelling compression regions, field-aligned particle beams and flux-rope like events. We demonstrate that electrons propagate along the magnetic field lines in the plasma sheet boundary layer (PSBL), while close to the current sheet center the electron distribution is isotropic. The evidences of the counterstreaming electron beams in the PSBLs are also presented. Most of the field-aligned energetic ion beams are associated with the field-aligned electron beams and about half of them have the bipolar fluctuation of the meridional magnetic field component. Moreover they often show a normal velocity dispersion for the different species which fits well in the scenario of particle propagation from a single source. All features above are observed during jovian reconfiguration events which are typically bonded with plasma flow reversals. From all these characteristics, which are based on energetic particle and magnetic field measurements, we believe that the reconfiguration processes in the jovian magnetotail are associated with reconnection. 相似文献
216.
This paper traces the theoretical development of the regional concept and the use of regionalization techniques in Soviet geography and seeks to compare this history with comparable trends in Western geography. It is severely critical of the major and rapid paradigm shifts noticed in post-war Western geographical science and relates these to shifts in the approach to global development issues. 相似文献
217.
K. S. Adhav A. S. Bansod M. S. Desale R. B. Raut 《Astrophysics and Space Science》2011,331(2):689-695
We have studied Locally Rotationally Symmetric (LRS) Bianchi type-I space-time having constant deceleration parameter and
filled with perfect fluid in the Hoyle-Narlikar C-field cosmology. Here, the creation field C is a function of time t only. The geometrical and physical aspects for the models are also studied. 相似文献
218.
The tendency of network bright points (NBPs) to form in their surface distribution non-random, small-scale clusters is studied by a 2-D nearest-neighbours test, based on observational data for the distance between separate NBPs. High-resolution photographs taken from long time series obtained at4308 with the 50-cm refractor of Pic du Midi Observatory are used. Three different epochs of the solar cycle were chosen. The results obtained suggest that the degree of clustering depends on the solar cycle phase. Supposing that the NBPs are good tracers of the kilogauss small-scale magnetic field, we use them to obtain information about the subphotospheric small-scale magnetic field organisation and its dependence on the solar cycle phase. 相似文献
219.
We investigate the spatial and temporal variations of the high-degree mode frequencies calculated over localized regions of the Sun during the extended minimum phase between solar cycles 23 and 24. The frequency shifts measured relative to the spatial average over the solar disk indicate that the correlation between the frequency shift and magnetic field strength during the low-activity phase is weak. The disk-averaged frequency shifts computed relative to a minimal activity period also reveal a moderate correlation with different activity indices, with a maximum linear correlation of about 72?%. From the investigation of the frequency shifts at different latitudinal bands, we do not find a consensus period for the onset of solar cycle 24. The frequency shifts corresponding to most of the latitudes in the northern hemisphere and 30° south of the equator indicate the minimum epoch to be February 2008, which is earlier than inferred from solar activity indices. 相似文献
220.
The intellection of seismic wave propagation in coal measures demands direct observation of the wavefield progression. Two vertical seismic profiles with high spatial and temporal sampling, were recently recorded in the Sydney Basin coalfields as part of an experimental coal seismic program. Static corrections and interval velocities were obtained by an automated system to determine first kicks and pulse rise times. Upgoing and downgoing waves were separated in the f—k-plane using a novel technique of contour slice filtering. The isolated upgoing waves clearly display reflections from the major coal seams within the stratigraphic sequence. The downgoing wave spectra were subjected to attenuation analysis. The deduced specific quality factor Q for Permian coal measure rocks lies in the range 20–70. Similar estimates were obtained in the time domain from measurements of pulse broadening. Synthetic VSP seismograms, computed using an exact recursive formulation, are an indispensable aid to interpretation. They illustrate the filtering effects of coal seams and sequences, and the effects of the contribution of internal and free-surface multiple reflections in the recorded wavetrains. 相似文献