全文获取类型
收费全文 | 32105篇 |
免费 | 1656篇 |
国内免费 | 2469篇 |
专业分类
测绘学 | 1483篇 |
大气科学 | 3011篇 |
地球物理 | 6435篇 |
地质学 | 12879篇 |
海洋学 | 3109篇 |
天文学 | 6103篇 |
综合类 | 651篇 |
自然地理 | 2559篇 |
出版年
2023年 | 271篇 |
2022年 | 542篇 |
2021年 | 698篇 |
2020年 | 619篇 |
2019年 | 710篇 |
2018年 | 951篇 |
2017年 | 930篇 |
2016年 | 1008篇 |
2015年 | 840篇 |
2014年 | 1124篇 |
2013年 | 1742篇 |
2012年 | 1234篇 |
2011年 | 1516篇 |
2010年 | 1327篇 |
2009年 | 1640篇 |
2008年 | 1457篇 |
2007年 | 1396篇 |
2006年 | 1315篇 |
2005年 | 1105篇 |
2004年 | 1059篇 |
2003年 | 966篇 |
2002年 | 893篇 |
2001年 | 783篇 |
2000年 | 729篇 |
1999年 | 660篇 |
1998年 | 660篇 |
1997年 | 657篇 |
1996年 | 498篇 |
1995年 | 474篇 |
1994年 | 432篇 |
1993年 | 372篇 |
1992年 | 361篇 |
1991年 | 300篇 |
1990年 | 332篇 |
1989年 | 298篇 |
1988年 | 250篇 |
1987年 | 320篇 |
1986年 | 262篇 |
1985年 | 349篇 |
1984年 | 387篇 |
1983年 | 376篇 |
1982年 | 337篇 |
1981年 | 315篇 |
1980年 | 319篇 |
1979年 | 289篇 |
1978年 | 311篇 |
1977年 | 264篇 |
1976年 | 267篇 |
1975年 | 275篇 |
1973年 | 238篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The light curve modeling of binary stars has continued to evolve since its founding by Henry Norris Russell (see Russell and Merrill 1952 and citations therein) nearly a century ago, accelerated in the 1950s by Kopal's introduction of Roche geometry into models and by the development of synthetic light curve computer code in the 1970's. Improved physics and the use of more kinds of observational input are providing another round of important advances that promise to enlarge our knowledge of both binary stars and ensembles containing them. Here we discuss the newer horizons of light curve modeling and the steps being taken toward them. 相似文献
22.
F. Molenkamp 《国际地质力学数值与分析法杂志》1991,15(3):147-168
To increase the insight into the phenomenon of liquefaction a theoretical study has been performed of material instability for undrained behaviour. Material instability concerns the instability of an equilibrium state of an infinite homogeneous solid for both uniform deformation and shear-band generation. In this paper shear-band generation is considered. In a companion paper the case of uniform deformation is elaborated and combined with the current results. In this paper it is shown that, for a contractant material, shear-band generation is accelerated by decreasing the drainage. 相似文献
23.
Richard T. Jones Jim D. Marshall Stephen F. Crowley Alan Bedford Nigel Richardson Jan Bloemendal Frank Oldfield 《第四纪科学杂志》2002,17(4):329-340
A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
24.
We report on SWS and LWS observations of the circumstellar disks of young stars of a few solar masses. The ISO spectra of
these objects present a diversity of emission features of carbon-rich and oxygen-rich grains. The similarity of the forsterite
spectra observed for Comet Hale-Bopp and the Haebe star HD100546 is particularly striking and provides a new argument that
huge comet swarms are formed in the disks surrounding young stars. While the data suggest that the formation of crystalline
silicates in the dust disks essentially occurs when a Haebe star has already reached the main sequence, no clear correlation
with stellar age only is apparent.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
25.
Generally speaking, variable stars are monitored through observing campaigns which coordinate multi-site telescopes at various
longitudes. A new practice is in progress: devoted networks involving robotic telescopes. We will review these two technologies
and will emphasize the NORT (Network of Oriental Robotic Telescopes) project which we are promoting in North Africa, Middle-Eastern
countries and Asia.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
26.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
27.
The Etna volcano is located in an apparently anomalous position on the hinge zone of the Apennines subduction and its Na-alkaline geochemistry does not favour a magma source from the deep slab as indicated for the Aeolian K-alkaline magmatism. The steeper dip of the regional foreland monocline at the front of the Apennines in the Ionian Sea than in Sicily, implies a larger rollback of the subduction hinge in the Ionian Sea. Moreover, the lengthening of the Apennines arc needs extension parallel to the arc. Therefore, the larger southeastward subduction rollback of the Ionian lithosphere with respect to the Hyblean plateau in Sicily, should kinematically produce right-lateral transtension and a sort of vertical 'slab window' which might explain (i) the Plio-Pleistocene alkaline magmatism of eastern Sicily (e.g. the Etna volcano) and (ii) the late Pliocene to present right lateral transtensional tectonics and seismicity of eastern Sicily. The area of transfer of different dip and rollback occurs along the inherited Mesozoic passive continental margin between Sicily and the oceanic Ionian Sea, i.e. the Malta escarpment. 相似文献
28.
Kaare L. Rasmussen Hans J. F. Olsen Raymond Gwozdz Evgeniy M. Kolesnikov 《Meteoritics & planetary science》2001,36(7):1001-1006
Abstract— Jull et al. propose an alternative interpretation of our depth vs. 14C data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable. 相似文献
29.
Theoretical studies have shown the possibility of high-temperature ('high enthalpy') geothermal reservoirs in the pre-Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén-4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica-thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations. 相似文献
30.
F. M. F. El-Sabaa 《Celestial Mechanics and Dynamical Astronomy》1985,37(1):71-79
The equation of motion of a rigid body in Kovaleveskaya case is reduced to a plane motion. By using the method of small parameters introduced by Poincaré, the existence of a periodic solution is established. 相似文献