全文获取类型
收费全文 | 2855篇 |
免费 | 158篇 |
国内免费 | 33篇 |
专业分类
测绘学 | 95篇 |
大气科学 | 318篇 |
地球物理 | 751篇 |
地质学 | 895篇 |
海洋学 | 234篇 |
天文学 | 401篇 |
综合类 | 6篇 |
自然地理 | 346篇 |
出版年
2022年 | 15篇 |
2021年 | 53篇 |
2020年 | 61篇 |
2019年 | 56篇 |
2018年 | 75篇 |
2017年 | 86篇 |
2016年 | 112篇 |
2015年 | 93篇 |
2014年 | 109篇 |
2013年 | 197篇 |
2012年 | 126篇 |
2011年 | 162篇 |
2010年 | 142篇 |
2009年 | 151篇 |
2008年 | 155篇 |
2007年 | 148篇 |
2006年 | 147篇 |
2005年 | 122篇 |
2004年 | 109篇 |
2003年 | 103篇 |
2002年 | 94篇 |
2001年 | 58篇 |
2000年 | 67篇 |
1999年 | 48篇 |
1998年 | 42篇 |
1997年 | 38篇 |
1996年 | 37篇 |
1995年 | 32篇 |
1994年 | 23篇 |
1993年 | 23篇 |
1992年 | 14篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 31篇 |
1988年 | 13篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 12篇 |
1973年 | 6篇 |
排序方式: 共有3046条查询结果,搜索用时 15 毫秒
101.
102.
Paul Brickle Alexander I. ArkhipkinVladimir Laptikhovsky Andrew StocksAlison Taylor 《Estuarine, Coastal and Shelf Science》2009
The ontogenetic, seasonal, bathymetric and regional variations in the feeding spectrum of 922 specimens of southern blue whiting Micromesistius australis and 512 specimens of hoki Macruronus magellanicus were studied on the Falkland Islands’ shelf (Southwest Atlantic) between November 1999 and April 2003. A total of 49 different prey items were found in the stomach contents of the two species, with the hyperiid Themisto gaudichaudii and Euphausiacea being amongst the most important prey. Although the species composition did not change over fish size, the proportions of individual prey items in their diets did, with an increase in T. gaudichaudii and Euphausiacea with increasing fish size in southern blue whiting. The opposite occurred in hoki. Seasonal variations in the diet were found to mirror the seasonal abundance of prey around the Falkland Islands for the two species. Intra-specific differences in the diet of both predators reflected the distribution of prey, which in turn was determined by the water structure in the two regions sampled, leading to very different diets. In the limited time that the two species occupied the same space there was little or no competition resulting in almost total segregation of their trophic niches in space and time. 相似文献
103.
To lay down the foundation for an underwater omni-directional optical communication system for tele-operation, we tested a point-to-point optical communication system, using laser-emitting diodes (LEDs). The LEDs used in the test emitted light in the green and blue light spectrum and were tested in a pool and in a tank filled with lake water. The primary objective of these tests was to get profiles of the behaviors of such communication systems with respect to water characteristics such as turbidity levels, prior to building the proposed omni-directional optical communication. The results of the tests indicated that turbidity level, viewing angle and separation distance plays a significant role in the behavior of blue light in water. Furthermore, it was possible to graph the profile of the behavior of light with respect to the parameters of interest. The results of the tests and related research are discussed in this paper. 相似文献
104.
105.
Sumanta Dandapath Andrew Menezes Bishwajit Chakraborty John Kurian Koppella N. Prudhvi Raju 《Marine Geodesy》2018,41(2):177-200
An assessment of the multibeam sonar data of the central Western Continental Margins of India has been carried out to evaluate the seafloor geomorphology and processes by examining the geomorphological attributes e.g., slope, sediments, structures, etc. associated with geomorphic features. The variation in relief and the features located in the region have been mapped and interpreted collectively by utilizing several geospatial mapping tools. The backscatter strength across the area, apparently congruent with the local relief, has helped to examine the sediment movement on the seafloor. The prominent features found in the region include faults, pockmarks, mounds, submarine terraces, and submerged fossil reefs. Several areas with varying topography engender comparable fractal dimension at short scale breaks, and the probability density functions (PDFs) utilizing backscatter data depicting overlapping classes. The present study highlights how fractals and scale break parameters can be utilized to determine the seafloor processes and associated sedimentological dynamics in a complex geographical environment with strong bottom currents, seasonal upwelling, and faulted structure. The role and impact of the various geomorphic processes on the reworking of sediment movement and the overall progression of the seafloor morphology has been revealed for the first time in this part of the ocean bottom. 相似文献
106.
Sergei V.Antipin Ignacio Becker AlexANDer A.Belinski Darya M.Kolesnikova Karim Pichara Nikolay N.Samus Kirill V.Sokolovsky Alla V.Zharova Alexandra M.Zubareva 《天文和天体物理学研究(英文版)》2018,(8)
Using 172 plates taken with the 40-cm astrograph of the Sternberg Astronomical Institute(Lomonosov Moscow University) in 1976–1994 and digitized with a resolution of 2400 dpi, we discovered and studied 275 new variable stars. We present the list of our new variables with all necessary information concerning their brightness variations. As in our earlier studies, the new discoveries show a rather large number of high-amplitude Delta Scuti variables, predicting that many stars of this type remain not detected in the whole sky. We also performed automated classification of the newly discovered variable stars based on the Random Forest algorithm. The results of the automated classification were compared to traditional classification and showed that automated classification was possible even with noisy photographic data. However, further improvement of automated techniques is needed, which is especially important when considering the very large numbers of new discoveries expected from all-sky surveys. 相似文献
107.
108.
109.
Brian N. Tissot Barbara A. Best Eric H. Borneman Andrew W. Bruckner Cara H. Cooper Heather D’Agnes Timothy P. Fitzgerald Amanda Leland Susan Lieberman Amy Mathews Amos Rashid Sumaila Teresa M. Telecky Frazer McGilvray Brian J. Plankis Andrew L. Rhyne Glynnis G. Roberts Benjamin Starkhouse Todd C. Stevenson 《Marine Policy》2010
As the world’s largest importer of marine ornamental species for the aquaria, curio, home décor, and jewelry industries, the United States has an opportunity to leverage its considerable market power to promote more sustainable trade and reduce the effects of ornamental trade stress on coral reefs worldwide. Evidence indicates that collection of some coral reef animals for these trades has caused virtual elimination of local populations, major changes in age structure, and promotion of collection practices that destroy reef habitats. Management and enforcement of collection activities in major source countries such as Indonesia and the Philippines remain weak. Strengthening US trade laws and enforcement capabilities combined with increasing consumer and industry demand for responsible conservation can create strong incentives for improving management in source countries. This is particularly important in light of the March 2010 failure of the parties to the Convention on International Trade in Endangered Species (CITES) to take action on key groups of corals. 相似文献
110.
The Australian coast contains 10,685 beaches which occupy 49% of the 30,000 km coast and average 1.37 km in length. Their relatively short length is largely due to the presence of bedrock, calcarenite and laterite, which form boundaries to many of the beaches, as well as occurring as rocks, reefs and islands along and off the beaches. This geological inheritance plays a major role in Australian beach systems — determining their length and through wave refraction and attenuation influencing beach location, shape, type, morphodynamics and circulation, which in turn influence sediment transport and the backing dune and barrier systems. This paper uses a database covering every Australian beach to review the role of headlands, rocks and reefs on Australian beaches. Major effects are the short average beach length; reduction in breaker height resulting in lower energy beach types; wave refraction resulting in increased beach curvature; the presence of topographic rips on moderate and higher energy beaches and megarips during high wave conditions; and the interruption of and/or trapping of longshore sand transport leading to beach rotation. 相似文献