全文获取类型
收费全文 | 258494篇 |
免费 | 4316篇 |
国内免费 | 3391篇 |
专业分类
测绘学 | 7094篇 |
大气科学 | 18989篇 |
地球物理 | 53979篇 |
地质学 | 89750篇 |
海洋学 | 21281篇 |
天文学 | 56220篇 |
综合类 | 1016篇 |
自然地理 | 17872篇 |
出版年
2021年 | 2238篇 |
2020年 | 2578篇 |
2019年 | 2844篇 |
2018年 | 3486篇 |
2017年 | 3177篇 |
2016年 | 5699篇 |
2015年 | 4204篇 |
2014年 | 6926篇 |
2013年 | 14237篇 |
2012年 | 6489篇 |
2011年 | 7893篇 |
2010年 | 6836篇 |
2009年 | 9509篇 |
2008年 | 8298篇 |
2007年 | 7715篇 |
2006年 | 9653篇 |
2005年 | 7711篇 |
2004年 | 7607篇 |
2003年 | 7110篇 |
2002年 | 6727篇 |
2001年 | 5993篇 |
2000年 | 5945篇 |
1999年 | 5207篇 |
1998年 | 5250篇 |
1997年 | 5045篇 |
1996年 | 4687篇 |
1995年 | 4428篇 |
1994年 | 4111篇 |
1993年 | 3861篇 |
1992年 | 3646篇 |
1991年 | 3603篇 |
1990年 | 3769篇 |
1989年 | 3514篇 |
1988年 | 3306篇 |
1987年 | 3847篇 |
1986年 | 3416篇 |
1985年 | 4229篇 |
1984年 | 4742篇 |
1983年 | 4416篇 |
1982年 | 4316篇 |
1981年 | 3932篇 |
1980年 | 3647篇 |
1979年 | 3513篇 |
1978年 | 3498篇 |
1977年 | 3277篇 |
1976年 | 3048篇 |
1975年 | 2961篇 |
1974年 | 2920篇 |
1973年 | 3079篇 |
1972年 | 2027篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Experimental studies of the elastohydrodynamics of towed flexible cylinders aided by video image processing are reported. A scale model of a prototype hydrophone array has been designed, fabricated, and tested in a speed range of 1.0 to 4.5 m/sec. The experiments were conducted in a 67-m long towing tank. The instrumented flexible member, 12.7 mm in diameter and 13.55 m long, was fixed at the one end and free at the other and was slightly lighter than neutrally bouyant. Three tail drogue configurations were employed. An integral part of the physical model tests was the development and utilization of a microcomputer based video image processing system for model configuration reconstitution. Instability characteristics, tail acceleration spectral densities, lift force due to curvature, and drag coefficients are quantified and discussed. 相似文献
992.
Abstract. The shell-boring gastropod Ocinebrina edwardsi (PAYR.) lives associated with Mytilus galloprovincialis LMK on which it preys. Predation is preferentially directed towards small (< 15 mm long) mussels. The predation rate (number of mussels eaten per gastropod per day) for medium sized mussels (16–25 mm long) during a year ranges from 0.03 to 0.11. The predation rate is directly influenced by the sea-water temperature. Predation follows a seasonal cycle reaching a maximum in July and a minimum in January. O. edwardsi drills selectively the median anterior region of the mussel valve, close to the dorsal edge. 相似文献
993.
994.
A method for the prediction of ocean waves was developed on the basis of the single-parameter growth equation of wind waves, proposed byToba (1978) on the basis of similarity in growing wind waves. The applicability of the method to actual problems was tested by hindcasting the wave characteristics with the method, for two cases with differing time and space scales, one in Kii Channel Approach, Japan, and the other in the North Atlantic Ocean. The results showed that the present method can predict waves within an error of 1.3 m in wave heights, which ranged from 3 to 12 m. 相似文献
995.
Katherine M. Papastephanou Stephen M. Bollens Anne M. Slaughter 《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):3078
Cross-shelf distribution and abundance of copepod nauplii and copepodids were measured during three summer upwelling seasons (2000–2002) in a coastal upwelling zone off northern California. These 3 years varied considerably in the intensity of winds, abundance of chlorophyll, and water temperature. The cruises in 2000 were characterized by relaxation conditions, with generally high levels of chlorophyll and high water temperature. The cruises in 2001 and 2002 were dominated by strong and persistent upwelling events, leading to lower chlorophyll and water temperatures. The copepod assemblage was dominated by Oithona spp., Acartia spp. and Pseudocalanus spp., with Metridia pacifica (lucens), Microsetella rosea, Oncaea spp. and Tortanus discaudatus also common during all 3 years. The cross-shelf distribution of copepods was generally shifted offshore during upwelling and onshore during relaxation events, although some variability between species occurred. Abundance of all life stages generally exhibited a negative correlation with cross-shelf transport averaged over at least 1–4 days and lagged by 0–3 days, indicating lower abundances during and immediately after active upwelling. However, copepod nauplii seemed to respond positively to wind events lasting 1–5 days followed by a period of relaxation lasting 6 or 7 days. These rapid rates of change in abundance are probably too great to be due to in situ growth and reproduction alone; physical processes must also play a role. These results suggest a highly dynamic relationship between copepods and upwelling events off northern California, with species-specific responses to upwelling to be expected. 相似文献
996.
- In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques. 相似文献
997.
C. Ranz-Guerra 《Geo-Marine Letters》1991,11(3-4):172-173
Mud is a complex mixture of water and solid particles and acoustics can help on its control. The mud layer, as an acoustic
channel, is characterized by its propagation constant relating the wave frequency, the sound velocity, and the energy absorption.
If the input acoustic pulse is known, it is feasible to easily characterize the mud layer as a low pass filter (absorption);
if it is also possible to insonify the mud with sound of both low and high frequencies, the sound speed of the mud mixture
can be evaluated, and the propagation constant is then known. 相似文献
998.
999.
1000.