全文获取类型
收费全文 | 9273篇 |
免费 | 1533篇 |
国内免费 | 1861篇 |
专业分类
测绘学 | 187篇 |
大气科学 | 256篇 |
地球物理 | 1408篇 |
地质学 | 5661篇 |
海洋学 | 720篇 |
天文学 | 2139篇 |
综合类 | 406篇 |
自然地理 | 1890篇 |
出版年
2024年 | 44篇 |
2023年 | 146篇 |
2022年 | 393篇 |
2021年 | 406篇 |
2020年 | 394篇 |
2019年 | 379篇 |
2018年 | 343篇 |
2017年 | 349篇 |
2016年 | 353篇 |
2015年 | 392篇 |
2014年 | 418篇 |
2013年 | 486篇 |
2012年 | 442篇 |
2011年 | 457篇 |
2010年 | 394篇 |
2009年 | 671篇 |
2008年 | 591篇 |
2007年 | 612篇 |
2006年 | 643篇 |
2005年 | 499篇 |
2004年 | 518篇 |
2003年 | 537篇 |
2002年 | 448篇 |
2001年 | 384篇 |
2000年 | 406篇 |
1999年 | 326篇 |
1998年 | 347篇 |
1997年 | 253篇 |
1996年 | 183篇 |
1995年 | 167篇 |
1994年 | 175篇 |
1993年 | 117篇 |
1992年 | 120篇 |
1991年 | 75篇 |
1990年 | 66篇 |
1989年 | 42篇 |
1988年 | 28篇 |
1987年 | 23篇 |
1986年 | 14篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
51.
The silica-scaled chrysophytes are being used increasingly in paleolimnological studies of lake acidification. This study compares the distribution of scaled chrysophytes in the surface sediment of a calibration set of lakes from the Adirondack Park and from northern New England. With the exception of two taxa, species distributions with respect to pH are similar in the two regions. The stratigraphic distribution of chrysophytes is then compared in five Adirondack and three New England lakes. All the presently acid lakes indicate recent lake acidification, with more acid tolerant chrysophytes increasing in relative frequency in the recent sediments. Because the timing of these species changes is unrelated to any watershed disturbances that may have occurred in the lakes' catchments, atmospheric deposition of acids is believed responsible for these recent pH changes.This is the seventh of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series. 相似文献
52.
M. G. Abrahamyan 《Astrophysics》2004,47(4):555-567
The equilibrium of elliptical Riemann disks with a polytropic equation of state and their evolution under the influence of viscosity and gravitational radiation inside spheroidal halos with a relative surface mass density k. The evolutionary trajectory of a disk inside a halo with k<0.5, which is analogous to the evolution of an isolated disk, differs from that of a disk inside a denser halo. 相似文献
53.
54.
55.
Andrew J. L. Harris Anna L. Butterworth Richard W. Carlton Ian Downey Peter Miller Pedro Navarro David A. Rothery 《Bulletin of Volcanology》1997,59(1):49-64
Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations
where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced
very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large
(3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion
rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at
Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated
near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement
to conventional monitoring methods.
Received: 21 January 1997 / Accepted: 3 April 1997 相似文献
56.
V. Castellani S. Degl'Innocenti P. G. Prada Moroni 《Monthly notices of the Royal Astronomical Society》2001,320(1):66-72
We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed mismatch between theoretical predictions and observations of the coolest Hyades MS stars. Finally, we show that current theoretical models probably give too faint He burning luminosities unlike the case of less massive He burning models, with degenerate progenitors, which have been suggested to suffer the opposite discrepancy. 相似文献
57.
58.
We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase
of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for
by the field growth theories. 相似文献
59.
CLIMATICTRENDINDICATEDBYVARIATIONSOFGLACIERSANDLAKESINTHETIANSHANMOUNTAINS¥HuRuji;YangChuande;MaHong;JiangFengqing(XinjiangIn... 相似文献
60.
Miniature gravity corer for recovering short sediment cores 总被引:12,自引:0,他引:12
John R. Glew 《Journal of Paleolimnology》1991,5(3):285-287