全文获取类型
收费全文 | 1905篇 |
免费 | 71篇 |
国内免费 | 18篇 |
专业分类
测绘学 | 47篇 |
大气科学 | 126篇 |
地球物理 | 544篇 |
地质学 | 614篇 |
海洋学 | 210篇 |
天文学 | 306篇 |
综合类 | 6篇 |
自然地理 | 141篇 |
出版年
2021年 | 20篇 |
2020年 | 26篇 |
2019年 | 27篇 |
2018年 | 45篇 |
2017年 | 33篇 |
2016年 | 59篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 86篇 |
2012年 | 50篇 |
2011年 | 67篇 |
2010年 | 82篇 |
2009年 | 84篇 |
2008年 | 73篇 |
2007年 | 94篇 |
2006年 | 68篇 |
2005年 | 63篇 |
2004年 | 65篇 |
2003年 | 60篇 |
2002年 | 50篇 |
2001年 | 30篇 |
2000年 | 39篇 |
1999年 | 30篇 |
1998年 | 32篇 |
1997年 | 29篇 |
1996年 | 30篇 |
1995年 | 34篇 |
1994年 | 33篇 |
1993年 | 14篇 |
1992年 | 32篇 |
1991年 | 32篇 |
1990年 | 42篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 19篇 |
1985年 | 32篇 |
1984年 | 40篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 32篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 12篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1973年 | 16篇 |
1972年 | 12篇 |
排序方式: 共有1994条查询结果,搜索用时 17 毫秒
261.
The recent detection of very-high-energy (GeV – TeV) γ-ray emission from the Galactic black-hole candidate and microquasar LS 5039 has sparked renewed interest in jet models for
the high-energy emission in those objects. In this work, we have focused on models in which the high-energy emission results
from synchrotron and Compton emission by relativistic electrons in the jet (leptonic jet models). Particular attention has
been paid to a possible orbital modulation of the high-energy emission due to azimuthal asymmetries caused by the presence
of the companion star. Both orbital-phase dependentγγ absorption and Compton scattering of optical/UV photons from the companion star may lead to an orbital modulation of the
gamma-ray emission. We make specific predictions which should be testable with refined data from HESS and the upcoming GLAST
mission. 相似文献
262.
Charles N. Forward 《The Professional geographer》1982,34(3):289-296
The use of nonemployment sources of income as a supplement to labor force data in the determination of the urban economic base was investigated for major Canadian cities. It was found that investment and pension-government, the main nonemployment sources, were of increasing importance and that the cities, with one exception, were differentiated into two groups, one based more strongly on investment and the other on pension-government income. 相似文献
263.
264.
George B. McManus Kevin D. Wyman William T. Peterson Charles F. Wurster 《Estuarine, Coastal and Shelf Science》1983,17(4):421-430
The effects of feeding, egg laying, and fecal pellet production on the elimination of polychlorinated biphenyls (PCBs) from the marine copepod Acartia tonsa were studied in a series of experiments. Copepods were exposed to 14C-labelled Aroclor 1254 and allowed to depurate in clean seawater. Copepods fed during depuration eliminated PCBs more rapidly than unfed copepods whether or not the original PCB exposure medium had contained food. Both eggs and fecal pellets contained PCBs during depuration, with the weight specific concentration of PCB in the eggs (up to 407 ppm, dry weight) exceeding four times that in the females that produced them. Female copepods eliminated PCBs twice as rapidly as males, indicating that egg production is an important route for PCB elimination. 相似文献
265.
266.
Results are presented of a survey of isozyme frequencies in parthenogeneticArtimia from six salterns in the Shandong Peninsula, P.R.C. Three of the eleven enzymes we scored using polyacryamide gel electrophoresis
proved to be useful for analysis of electromorph frequency variation. These enzymes are tetrazolium oxidase (TO), lactate
dehydrogenase (LDH), and malate dehydrogenase (MDH). Each of these systems showed extensive isozyme variation both within
and between salterns. In addition, we have examined the possibility that electromorph frequencies may vary as the result of
natural selection for adaptation to specific salinity, or salinity-associated environmental conditions. An indication of clinal
variation was found in two series of ponds differing in salinity, however more extensive data are needed before it is possible
to conclude that these patterns are the result of natural selection. Finally, the use of isozyme analyses such as ours, for
unraveling taxonomic problems inArtemia is discussed. 相似文献
267.
A solution to the orbital motion of an Earth satellite at the critical inclination and with near-zero eccentricity is developed by the von Zeipel method to the first order in the eccentricity, and to the first order in the higher gravitational harmonics, using elements which do not degenerate at zero eccentricity. 相似文献
268.
269.
Charles Harris 《第四纪科学杂志》1991,6(1):67-77
The nature and origin of glacial sediments at Wylfa Head are described, and their significance with regard to sedimentary environments during Late Devensian deglaciation of the Irish Sea Basin is discussed. Recent models of deglaciation under glaciomarine conditions are challenged. The Quaternary sequence at Wylfa consists of eroded and glaciotectonically deformed bedrock, locally derived lodgement till, calcareous silt-rich lodgement till containing northern erratics, discontinuous units of orange-brown silty sand of possible aeolian origin, and grey laminated freshwater silts filling a small kettle hole. The till units thicken to the south where the surface is drumlinised. It is concluded that the landforms and deposits result from a warm-based Irish Sea glacier, which moved towards the southwest. Spatial variation in basal water pressure resulted from localised drainage through zones of more heavily jointed bedrock. Rapid glacial erosion occurred in areas where subglacial water pressure was relatively high, while deposition of the resulting basal sediment took place where water pressures were reduced. The glacier also carried basal calcareous silty till onshore, which was deposited by lodgement processes. None of the deposits at Wylfa are interpreted as glaciomarine in origin, and there is no evidence at this site for an isostatically induced marine transgression prior to deglaciation. 相似文献
270.
Mark Cropper M. Barlow M. A. C. Perryman Keith Horne R. Bingham M. Page P. Guttridge A. Smith A. Peacock D. Walker P. Charles 《Monthly notices of the Royal Astronomical Society》2003,344(1):33-44
We describe a multi-order spectrograph concept suitable for 8-m class telescopes, using the intrinsic spectral resolution of superconducting tunnelling junction detectors to sort the spectral orders. The spectrograph works at low orders, 1–5 or 1–6, and provides spectral coverage with a resolving power of R ≃ 8000 from the atmospheric cut-off at 320 nm to the long-wavelength end of the infrared H or K band at 1800 nm or 2400 nm. We calculate that the spectrograph would provide substantial throughput and wavelength coverage, together with high time resolution and sufficient dynamic range. The concept uses currently available technology, or technologies with short development horizons, restricting the spatial sampling to two linear arrays; however, an upgrade path to provide more spatial sampling is identified. All of the other challenging aspects of the concept – the cryogenics, thermal baffling and magnetic field biasing – are identified as being feasible. 相似文献