全文获取类型
收费全文 | 19657篇 |
免费 | 3889篇 |
国内免费 | 5149篇 |
专业分类
测绘学 | 1614篇 |
大气科学 | 3753篇 |
地球物理 | 4979篇 |
地质学 | 10325篇 |
海洋学 | 2592篇 |
天文学 | 842篇 |
综合类 | 2004篇 |
自然地理 | 2586篇 |
出版年
2024年 | 121篇 |
2023年 | 378篇 |
2022年 | 1112篇 |
2021年 | 1231篇 |
2020年 | 1038篇 |
2019年 | 1217篇 |
2018年 | 1330篇 |
2017年 | 1147篇 |
2016年 | 1247篇 |
2015年 | 1093篇 |
2014年 | 1306篇 |
2013年 | 1302篇 |
2012年 | 1279篇 |
2011年 | 1273篇 |
2010年 | 1253篇 |
2009年 | 1129篇 |
2008年 | 1071篇 |
2007年 | 925篇 |
2006年 | 760篇 |
2005年 | 699篇 |
2004年 | 551篇 |
2003年 | 498篇 |
2002年 | 496篇 |
2001年 | 550篇 |
2000年 | 553篇 |
1999年 | 763篇 |
1998年 | 636篇 |
1997年 | 551篇 |
1996年 | 545篇 |
1995年 | 440篇 |
1994年 | 410篇 |
1993年 | 367篇 |
1992年 | 333篇 |
1991年 | 215篇 |
1990年 | 177篇 |
1989年 | 153篇 |
1988年 | 130篇 |
1987年 | 85篇 |
1986年 | 74篇 |
1985年 | 56篇 |
1984年 | 43篇 |
1983年 | 30篇 |
1982年 | 29篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1976年 | 5篇 |
1958年 | 13篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
81.
82.
83.
Samples of O isotopic tracer were mlleMed at Sections P3,P25,PcM-t/2-E and PCM-1/2.w in both the Fast China Sea and the area to the east of the Ryūkyū-gunto during October-November,1991.Analytical results of the δ18O are as follows: (1) In the Kuroshio area,the δ18O isolines are almost parallel to the 200 m isobath.The value of δ18O is negative and reaches minimum mt the main axis of the Kuroshio,and increases on both sides.(2) In the Taiwan Warm Current (TWC) area there is a high δ18O tongue extending to the northeast.(3) In the area near the coast,the distribution of δ18O isoline shows that the Changjiang River runoff diffuses seaward and the land-ocean isotopic effect from the nearshore to the offshore.(4) The values of δ18O are from -1.0×10-3 to -0.5×10-3 in the shelf.(5) There is a low mre of δ18O value(<-1.6×10-3) at the 600 m layer in the Kuroshio area,which is quite in accord with the existence of a low salinity mre (S G 34.30) between the 600 and 800 m layers in the same area.Finally,the mrrelations of the δ18O with the salinity and temperature,the upwelling and so on are discussed. 相似文献
84.
本文揭示了天津海岸带影响经济开发的四个方面的地质环境特点;着重探讨三个方面的环境工程地质问题;并防止其形成和减轻地灾害的对策进行了研究。 相似文献
85.
86.
Numericalsimulationofthree-dimensionaltidalcurrentintheBobalSea¥DenZhenxing;YangLianwu;andJoseOzer(ReceivedMay1,1993;accepted... 相似文献
87.
The 25-h measurements of current speed, flow direction, water depth, suspended sediment concentration and salinity were carried out at six anchored stations in the study area during spring and neap tides in winter of 1987 and summer of 1989. Caculations and analyses of the data obtained show that large amounts of suspended sediments are moved back and forth under the action of tidal current, and the net transport of sediment is small, with its predominance upstream in winter and downstream in summer. These calculations and analyses also suggest that the advective transport of sediment is dominant, while the vertical gravitational circulation of the suspended sediment comes next. Meantime, it is indicated that tidal currents play a major role in the suspended sediment transport, and residual flows have effect on the net transport of the suspended sediment, which is more remarkable during neap tide than during spring tide. 相似文献
88.
89.
The study of the Kuroshio in the East China Sea and the currents east of the Ryukyu Islands 总被引:3,自引:0,他引:3
In this study, the inverse method is used to compute the Kuroshio in the East China Sea and southeast of Kyushu and the currents east of the Ryukyu Islands, on the basis of hydrographic data obtained during September-October, 1987 by R/V Chofu Maru. The results show that: (1)A part of the Taiwan Warm Current has a tendency to converge to the shelf break; (2) the Kuroshio flows across the section C3 (PN) with a reduced current width, and the velocity of the Kuroshio at the section C3 increases and its maximum current speed is about 158 cm/s, and its volume transport here is about 26×106m3/s; (3) the Kuroshio has two current cores at the sections C3 (PN) and B2 (at the Tokara Strait); (4) the currents east of the Ryukyu Islands are found to flow northward over the Ryukyu Trench during September-October, 1987. The velocities of the currents are not strong throughout the depths. At the section C2 east of the Ryukyu Islands, the maximum current speed is at the 699 m levei and its magnitude is 25 cm/s, and i 相似文献
90.
Study of zooplankton ecology in Zhejiang coastal upwelling system-Zooplankton biomass and abundance of major groups 总被引:1,自引:0,他引:1
He Dehu Yang Guanming Fang Shaojin Shen Weilin Liu Hongbin Gao Aigen Huang Shuxin 《海洋学报(英文版)》1988,7(4):607-620
The studied area is a shallow water area that belongs to the East China Sea continent shelf. The distribution of zooplankton biomass is higher inshore than offshore. The maximum abundance is in the inshore edge of the centre of upwelling, which is the superposed area of the salinity front and temperature front, due to the fact that the mixture of three different waters has brought about a concentration of nutrients. The herbivorous Euphausia, Copepoda and Tunicata are the major groups of the abundant area. Tunicata possess the possibility to compete against other kinds of herbivorous zooplankton. This means that there is negative correlation between the distribution of Tunicata and that of Copepoda and Euphausia. The positions of maximum areas of zooplankton biomass, phytoplankton individual and the concentration of phosphates and chlorophyll-a overlap one another. In the centre of upwelling, zooplankton can not adapt itself to the environment of lower temperature and less oxygen even with rich nutrient 相似文献