全文获取类型
收费全文 | 3248篇 |
免费 | 108篇 |
国内免费 | 92篇 |
专业分类
测绘学 | 70篇 |
大气科学 | 402篇 |
地球物理 | 812篇 |
地质学 | 1006篇 |
海洋学 | 648篇 |
天文学 | 302篇 |
综合类 | 46篇 |
自然地理 | 162篇 |
出版年
2023年 | 12篇 |
2022年 | 22篇 |
2021年 | 48篇 |
2020年 | 47篇 |
2019年 | 63篇 |
2018年 | 134篇 |
2017年 | 124篇 |
2016年 | 139篇 |
2015年 | 87篇 |
2014年 | 171篇 |
2013年 | 220篇 |
2012年 | 140篇 |
2011年 | 203篇 |
2010年 | 190篇 |
2009年 | 190篇 |
2008年 | 164篇 |
2007年 | 176篇 |
2006年 | 146篇 |
2005年 | 122篇 |
2004年 | 105篇 |
2003年 | 96篇 |
2002年 | 98篇 |
2001年 | 76篇 |
2000年 | 79篇 |
1999年 | 55篇 |
1998年 | 45篇 |
1997年 | 41篇 |
1996年 | 25篇 |
1995年 | 37篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 24篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 28篇 |
1983年 | 31篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 25篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 16篇 |
1975年 | 15篇 |
1974年 | 10篇 |
1973年 | 7篇 |
排序方式: 共有3448条查询结果,搜索用时 1 毫秒
751.
Lee A. Fuiman 《Journal of Sea Research》1997,37(3-4)
Eye migration, asymmetrical pigmentation, and a 90° rotation in posture are developmental changes that unify all flatfishes and facilitate a transition from a pelagic to a benthic existence. Settlement places the fish in new environmental conditions which may require different types and levels of performance for survival compared to those needed in the water column. Since structure and performance vary as a consequence of ontogeny, it is likely that natural selection has acted on the ontogeny of flatfishes differently from fishes that do not settle (pelagic fishes) to provide different survival skills by the time flatfishes settle. This paper provides examples of quantitative methods for comparing fish ontogenies in the context of three predictions: (1) different flatfish species undergo settlement at a common ontogenetic state; (2) they have a common set of skills at settlement that differ from those of pelagic species of the same ontogenetic state; and (3) skills or features that appear earlier in the ontogenetic program of flatfishes than in pelagic fishes suggest attributes that are important to survival in a benthic habitat. Preliminary comparisons suggest that flatfishes may have accelerated development of their mechanosensory system relative to pelagic species. Firm conclusions about ecologically important differences between the pelagic and benthic habitats derived from analyses of ontogenetic events will require more kinds of data from a broader selection of species. 相似文献
752.
The U.S. Geological Survey deep crustal studies reflection profile across the Gulf of Maine off southeastern New England was affected by three sources of noise: side-scattered noise, multiples, and 20-Hz whale sounds. The special processing most effective in minimizing this noise consisted of a combination of frequency-wavenumber (F-K) filtering, predictive deconvolution, and spectral whitening, each applied in the shot domain (prestack). Application of the F-K filter to remove side-scatter noise in the poststack domain resulted in a much poorer quality profile. The prestack noise suppression processing techniques resulted in a reflection profile with good signal-to-noise ratios and reliable strong reflections, especially at depths equivalent to the lower crust (24–34 km). Certain geologic features, such as a buried rift basin and a crustal fault are resolved much better within the upper crust after this processing. Finite difference migration of these data using realistic velocities produced excellent results. Migration was essential to distinguish between abundant dipping and subhorizontal reflections in the lower crust as well as to show an essentially transparent upper mantle. 相似文献
753.
Larry P. Atkinson Jackson O. Blanton Charles McClain Thomas N. Lee Masayuki Takahashi Takashi Ishimaru Joji Ishizaka 《Journal of Oceanography》1987,43(2):89-103
Hydrographic observations between the Izu Peninsula and Oshima Island, Japan, in May 1982, showed upwelling around the tip of the Peninsula and possibly also in the lee of Oshima Island. The upwelling introduced water as cold as 18 C with nitrate concentrations of 3M to the surface. Temperature/salinity analyses indicated that the upwelled water was of Kuroshio characteristics. Slightly fresher water was advected out of Sagami Bay in a coastal counter current.Contribution number 470 from the Shimoda Marine Research Center, University of Tsukuba. 相似文献
754.
Real-time video mosaicking of the ocean floor 总被引:2,自引:0,他引:2
An approach was developed for real-time creation of video mosaics of the ocean floor. The approach uses visual correspondence during both image acquisition and consolidation to insure that there are no gaps in the mosaic. The use of visual information for mosaic creation offers an accuracy previously unachievable in real time. A complete mosaicking approach was developed, including a technique for image registration and several strategies for image acquisition control. The approach was implemented and tested experimentally. Ocean-floor mosaics were created in real time using a remotely-operated vehicle. In addition, extensive mosaicking experiments were conducted in a test-tank environment using a semiautonomous underwater robot 相似文献
755.
Seismic-reflection profiles, sediment cores, and current velocities were assessed to study the impact of erosion and sediment redistribution on the pelagic sediment cap of Horizon Guyot, a flat-topped submarine volcanic ridge in the Mid-Pacific Mountains. These processes seem to concentrate their effect around the rim of the sediment cap. Sediment slumping occurs on the northwest perimeter of the guyot's sediment cap. Slope stability analysis suggests that if overconsolidation on Horizon Guyot is the result of current reworking or if local undercutting by bottom currents steepens the sea floor declivity, the sediment cap may be unstable during infrequent earthquake loading, transporting sediment from the guyot summit to the abyssal sea floor. 相似文献
756.
In situ cone-penetrometer tests at 11 stations in Norton Sound, Alaska, complement previous studies of geologic processes and provide
geotechnical data for an analysis of sediment response to loading. Assessment of the penetrometer records shows that various
geologic factors influence penetration resistance. On the Yukon prodelta, penetration resistance increases with the level
of storm wave or ice loading. In central and eastern Norton Sound, thermogenic and biogenic gas, as well as variations in
sediment texture and composition, effect a wide range of resistance to penetration. 相似文献
757.
The stratigraphic evolution of the Indus Fan and the history of sedimentation in the Arabian Sea 总被引:6,自引:1,他引:6
Clift Peter Gaedicke Christoph Edwards Rosemary Il Lee Jae Hildebrand Peter Amjad Shahid White Robert S. Schlüter Hans-Ulrich 《Marine Geophysical Researches》2002,23(3):223-245
The Indus Fan records the erosion of the western Himalayas and Karakoram since India began to collide with Asia during the Eocene, 50 Ma. Multi-channel seismic reflection data from the northern Arabian Sea correlated to industrial well Indus Marine A-1 on the Pakistan Shelf show that sedimentation patterns are variable through time, reflecting preferential sedimentation in deep water during periods of lower sea-level (e.g., middle Miocene, Pleistocene), the diversion of sediment toward the east following uplift of the Murray Ridge, and the autocyclic switching of fan lobes. Individual channel-levee systems are estimated to have been constructed over periods of 105–106 yr during the Late Miocene. Sediment velocities derived from sonobuoys and multi-channel stacking velocities allow sections to be time-depth converted and then backstripped to calculate sediment budgets through time. The middle Miocene is the period of most rapid accumulation, probably reflecting surface uplift in the source regions and strengthening of the monsoon at that time. Increasing sedimentation during the Pleistocene, after a late Miocene-Pliocene minimum, is apparently caused by faster erosion during intense glaciation. The sediment-unloaded geometry of the basement under the Pakistan Shelf shows a steep gradient, similar to the continent-ocean transition seen at other rifted volcanic margins, with basement depths on the oceanward side indistinguishable from oceanic crust. Consequently we suggest that the continent-ocean transition is located close to the present shelf break, rather than >350 km to the south, as previously proposed. 相似文献
758.
We examined the link between DNA strand breaks and hatching rates in grass shrimp, (Paleomonetes pugio), embryos exposed to 0.2 microM benzo[alpha] pyrene (BP), 5 microM cadmium (Cd) and 330 kJ/m(2) UV light, either alone or together. After exposure, embryos were transferred to clean seawater with or without 5 microM Cd. Hatching rates and DNA strand breaks (Comet Assay) were determined. DNA lesions caused by exposure to BP, UV light, or BP/cadmium were rapidly repaired and were not associated with any effects on hatching. Exposure to Cd after exposure to BP or UV did not affect embryological development or DNA repair. Exposure to BP/UV resulted in a high level of DNA lesions which were slowly repaired. Exposure to cadmium following BP/UV exposure inhibited hatching and DNA repair. Adducts formed during exposure to BP/UV exposure may be difficult to excise or may saturate the nucleotide excision repair system. 相似文献
759.
Jung-Mann Yun Young-Suk Song Jae-Ho Lee Tae-Hyung Kim 《Marine Georesources & Geotechnology》2006,24(1):29-45
A series of tests in both laboratory and field were performed to investigate the engineering and mechanical properties, especially flexural strength, of cement-stabilized soils. The strength of cement-stabilized soils mainly depends on water-to-cement ratio and curing temperature. The higher curing temperature and the longer curing time, the higher strength in cement-stabilized soils generates. The high ratio of water-to-cement results in lower strength. The compressive strength observed in the field is similar to the strength in the laboratory. Field tests on a cement-stabilized soil layer indicate that the strength is significantly affected by the thickness of the improved layer, which is directly related to the moment of inertia. In addition, the failure shape observed in a cement-stabilized layer in the field looks likes a bending failure type, because the flexural tensile strength, rather than the compressive strength, mainly dominates the failure of cement-stabilized layer. The flexural tensile strength is closely related to the moment of inertia. Therefore, the flexural tensile strength should be considered for determining the thickness and strength in improvement of soft clay. 相似文献
760.
Benthic amphipod,Grandidierella japonica widely inhabits the Korean coastal waters and is developed as a standard test species for sediment toxicity tests. We exposedG . japonica to various pollutants including 4 kinds of inorganic metals (Ag, Cd, Cu and Hg), tributyltin [TBT], ammonia and 7 polycyclic
aromatic hydrocarbon (PAH) compounds (acenaphthene, chrysene, fluoranthene, fluorene, naphthalene, phenanthrene and pyrene)
to estimate the no observed effect concentration (NOEC) and the median lethal concentration (LC50) of each pollutant during
the 96-hour acute exposure. Among all tested pollutants, TBT was most toxic toG. japonica, and Hg was most toxic among inorganic metals. The toxicity of pyrene toG. japonica was greatest among PAH compounds, followed by fluoranthene, phenanathrene, acenaphthene, fluorene and naphthalene. The toxicity
of PAH compounds was closely related to their physico-chemical characteristics such as Kow and water solubility.G. japonica responded adequately to pollutant concentrations and exposure durations, and the sensitivity ofG. japonica to various inorganic and organic pollutants was generally comparable to other amphipods used as standard test species in
ecotoxicological studies, indicating this species can be applied in the assessment of environments polluted by various harmful
substances. 相似文献