全文获取类型
收费全文 | 3096篇 |
免费 | 540篇 |
国内免费 | 706篇 |
专业分类
测绘学 | 167篇 |
大气科学 | 799篇 |
地球物理 | 860篇 |
地质学 | 1325篇 |
海洋学 | 362篇 |
天文学 | 233篇 |
综合类 | 285篇 |
自然地理 | 311篇 |
出版年
2024年 | 12篇 |
2023年 | 32篇 |
2022年 | 117篇 |
2021年 | 140篇 |
2020年 | 123篇 |
2019年 | 132篇 |
2018年 | 139篇 |
2017年 | 151篇 |
2016年 | 165篇 |
2015年 | 156篇 |
2014年 | 180篇 |
2013年 | 186篇 |
2012年 | 173篇 |
2011年 | 245篇 |
2010年 | 159篇 |
2009年 | 209篇 |
2008年 | 161篇 |
2007年 | 159篇 |
2006年 | 153篇 |
2005年 | 110篇 |
2004年 | 96篇 |
2003年 | 93篇 |
2002年 | 105篇 |
2001年 | 77篇 |
2000年 | 98篇 |
1999年 | 106篇 |
1998年 | 119篇 |
1997年 | 111篇 |
1996年 | 101篇 |
1995年 | 75篇 |
1994年 | 73篇 |
1993年 | 79篇 |
1992年 | 44篇 |
1991年 | 42篇 |
1990年 | 29篇 |
1989年 | 27篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1972年 | 5篇 |
排序方式: 共有4342条查询结果,搜索用时 140 毫秒
1.
The geodynamic mechanism of the late Early Cretaceous magmatic flare‐up in the collisional zone between the Lhasa and Qiangtang terranes in Tibet is controversial because of a scarcity of robust evidence. To address this problem, we report geochronological, geochemical and Hf isotopic data for the newly discovered Gufeng gabbros from the Duolong Cu–Au mineral district of the western Bangong–Nujiang Suture Zone (BNSZ). The gabbro samples, dated at 126.3 ± 1.8 Ma, show geochemical similarities to typical ocean island basalt (OIB) and have positive εHf(t) values of +3.3 to +6.9. The gabbros were generated by decompression melting of deep upwelling asthenosphere. This event is best explained by slab break‐off and the resultant development of a slab window beneath central Tibet. 相似文献
2.
本文依据稳恒磁场中的高斯定理和安培环路定理,用迭代法推导出对称轴上的磁感应强度与空间任意一点磁感应强度的关系式,从而可得出轴对称稳恒磁场的无电流分布空间的解式。 相似文献
3.
本文针对低纬度地区频率域化磁极存在的问题,在频谱分析的基础上,提出了一种新的滤波方法即振幅滤波法。该方法能将低纬度地区化极磁场的频谱恢复到垂直磁化磁场的频谱,大大提高了低纬度地区化磁极的精度。 相似文献
4.
V2213 Cyg was discovered as a variable star by Pavlenko (1999) in 1998. We present our photometry of V2213 Cyg from 1998–2003
based on CCD observations with the K-380 Cassegrain telescope of CrAO and the 60 cm Zeiss telescope of SAI. Observations have
been carried out mostly in R and sometimes in B and V Johnson system. The total amount of data is 2270 points, covering ∼50 nights. We classify this binary as a W UMa-type contact
system. Using all data we determined the orbital period to be 0.350079 ± 0.000007 day. The mean brightness varies between
R = 14.35 and 14.05. The mean 1999–2003 orbital light curve has two humps and a primary minimum (I), which is 0.04 mag brighter
than the deeper secondary one (II). The mean humps have slightly different height. The difference between two individual maxima
varies within 0.1 mag, which may indicate an activity of the components. The highest hump is an asymmetrical one: it has sort
of a shoulder at phases 0.75–0.80, before entering the less deep primary minimum (phase 0.0). The system is rather reddened,
its colour indices are: B−V ∼ 0.8 and V−R ∼ 0.7, and give a spectral class of V2213 Cyg earlier than K. 相似文献
5.
Hector Socas-Navarro David Elmore Anna Pietarila Anthony Darnell Bruce W. Lites Steven Tomczyk Steven Hegwer 《Solar physics》2006,235(1-2):55-73
The Spectro-Polarimeter for Infrared and Optical Regions (SPINOR) is a new spectro-polarimeter that will serve as a facility
instrument for the Dunn Solar Telescope at the National Solar Observatory. This instrument is capable of achromatic polarimetry
over a very broad range of wavelengths, from 430 to 1600 nm, allowing for the simultaneous observation of several visible
and infrared spectral regions with full Stokes polarimetry. Another key feature of the design is its flexibility to observe
virtually any combination of spectral lines, limited only by practical considerations (e.g., the number of detectors available, space on the optical bench, etc.).
Visiting Astronomers, National Solar Observatory, operated by the Association of Universities for Research in Astronomy, Inc.
(AURA), under cooperative agreement with the National Science Foundation. 相似文献
6.
Back in the mid-nineteenth century British explorer James Clark Ross took his ships, HMS Terror and HMS Erebus , farther south than anyone else had been. He now lends his name to James Ross Island, a part-volcanic edifice that rises out of the sea off the north-east tip of the Antarctic Peninsula. The island records a geological history dating back to the Cretaceous, though its great peaks are volcanic. The most recent rocks of the island record a monumental struggle between fire and ice, the volcanoes, and the ice sheets that cover them. The glacigenic sediments that are interspersed with the volcanic rocks contain rich fossil assemblages which suggest that at times, the climate was warmer, with the ice retreating. Their study may help us to delimit the patterns of climate change in the Antarctic Peninsula region as Earth's global climate warms. 相似文献
7.
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
8.
Ding Zongxin 《中国海洋湖沼学报》1985,3(1):109-117
In this paper the influences of short-term wind on vertical structures of temperature and salinity, and the upwelling off
the Zhejiang coast are studied on the basis of hydrographic data and wind near the coast in Summer (1959–1979). It is pointed
out that the variations of vertical distributions of temperature and salinity, and upwelling in this region are closely related
to short-term (several days to a week) variation of wind observed. The occurrence of double thermocline, a special oceanographic
phenomenon, is partially related to unstable SSW wind field. SSW and NE winds in June are two dynamic factors making intermediate
warm water form or disappear.
Contribution No. 792 from the Institute of Oceanology, Academia Sinica.
This paper was published in Chinese inOceanologia et Limnologia Sinica
14 (1): 14–21, 1983. 相似文献
9.
The main limit to the time span of a numerical integration of the planetary orbits is no longer set by the availability of computer resources, but rather by the accumulation of the integration error. By the latter we mean the difference between the computed orbit and the dynamical behaviour of the real physical system, whatever the causes. The analysis of these causes requires an interdisciplinary effort: there are physical model and parameters errors, algorithm and discretisation errors, rounding off errors and reliability problems in the computer hardware and system software, as well as instabilities in the dynamical system. We list all the sources of integration error we are aware of and discuss their relevance in determining the present limit to the time span of a meaningful integration of the orbit of the planets. At present this limit is of the order of 108 years for the outer planets. We discuss in more detail the truncation error of multistep algorithms (when applied to eccentric orbits), the coefficient error, the method of Encke and the associated coordinate change error, the procedures used to test the numerical integration software and their limitations. Many problems remain open, including the one of a realistic statistical model of the rounding off error; at present, the latter can only be described by a semiempirical model based upon the simpleN
2 formula (N=number of steps, =machine accuracy), with an unknown numerical coefficient which is determined only a posteriori. 相似文献
10.
The data such as the H-spectrum-spectroheliographic (SSHG) observations, the H-chromospheric observations, etc., of a flare loop prominence which occurred on the western solar limb on 1981 April 27 have been obtained at Yunnan Observatory. The distribution of the internal motions and the macroscopical motion of the flare loop prominence with time and space in the course of its eruption and ascension is derived from the comprehensive analysis of the data. The possible physical pictures and the instability of the motions of the loop are inferred and discussed. 相似文献