全文获取类型
收费全文 | 7305篇 |
免费 | 282篇 |
国内免费 | 115篇 |
专业分类
测绘学 | 226篇 |
大气科学 | 670篇 |
地球物理 | 1771篇 |
地质学 | 2522篇 |
海洋学 | 662篇 |
天文学 | 1081篇 |
综合类 | 30篇 |
自然地理 | 740篇 |
出版年
2022年 | 42篇 |
2021年 | 79篇 |
2020年 | 88篇 |
2019年 | 110篇 |
2018年 | 172篇 |
2017年 | 169篇 |
2016年 | 193篇 |
2015年 | 183篇 |
2014年 | 250篇 |
2013年 | 404篇 |
2012年 | 285篇 |
2011年 | 329篇 |
2010年 | 262篇 |
2009年 | 376篇 |
2008年 | 352篇 |
2007年 | 323篇 |
2006年 | 282篇 |
2005年 | 227篇 |
2004年 | 248篇 |
2003年 | 228篇 |
2002年 | 234篇 |
2001年 | 158篇 |
2000年 | 171篇 |
1999年 | 134篇 |
1998年 | 134篇 |
1997年 | 117篇 |
1996年 | 100篇 |
1995年 | 106篇 |
1994年 | 89篇 |
1993年 | 81篇 |
1992年 | 88篇 |
1991年 | 82篇 |
1990年 | 80篇 |
1989年 | 69篇 |
1988年 | 66篇 |
1987年 | 86篇 |
1986年 | 60篇 |
1985年 | 96篇 |
1984年 | 110篇 |
1983年 | 99篇 |
1982年 | 98篇 |
1981年 | 100篇 |
1980年 | 86篇 |
1979年 | 79篇 |
1978年 | 47篇 |
1977年 | 69篇 |
1976年 | 79篇 |
1975年 | 54篇 |
1974年 | 71篇 |
1973年 | 56篇 |
排序方式: 共有7702条查询结果,搜索用时 46 毫秒
21.
Peter Nielsen 《Coastal Engineering》1985,9(3):261-276
An empirical analysis is performed on the most detailed, recent measurements of turbulent oscillatory boundary layer flow. The measurements show that throughout elevations where the flow can be considered horizontally uniform, one deficit model is sufficient for describing the fundamental mode. Some general properties of the non dimensional velocity deficit D1(z) appear with striking consistency. First of all the identity , which is a theoretical result for smooth laminar flow, seems to hold with great accuracy for a large range of turbulent flow conditions as well. This is of principal theoretical interest because all previous analytical eddy viscosity models as well as numerical mixing length models predict a consistent and fairly large difference between Arg D1 and . If the identity between and Arg D1 extends all the way to the bed, it means that the bed shear stress leads the free stream velocity by 45 degrees. It is also found that the structure of smooth turbulent oscillatory flows as measured by Kalkanis (1964) corresponds to a sharp maximum in the normalized energy dissipation rate. 相似文献
22.
Alan M Bond Julie R Bradbury Henry A Hudson John S Garnham Peter J Hanna Stanley Strother 《Marine Chemistry》1985,16(1):1-9
Evidence was found that uptake of lead from seawater in both model and natural systems by the leaves of the seagrass Zostera muelleri does occur for live, dead and scraped leaves at all the lead concentrations tested. Positive uptake of lead was measured using the three analytical techniques of radio-tracer, differential pulse anodic stripping voltammetry and atomic absorption spectrometry; similar uptake profiles were obtained for each technique. Profiles always showed an initial rapid uptake phase followed by a gradual transition to a plateau phase at which an approximate equilibrium between lead attached to seagrass and free ionic lead in seawater was reached. The presence of active lead uptake processes was indicated in experiments which attempted to remove lead from leaves by a chelating agent. 相似文献
23.
24.
We show how the Yarkovsky effect can be understood as a heat engine. The output of the engine, manifested in the rate of change in semimajor axis of the body, has a maximum at an intermediate heat capacity, depending on the rotation rate of the body. This maximum arises because the work output depends on the product of the solar heat absorbed by the body and transported from its morning to evening side (this am-pm heat flux increases with heat capacity) and the Carnot efficiency (which declines with heat capacity). 相似文献
25.
26.
27.
28.
This paper considers the problem of estimatingm, the number of components in a finite mixture of distributions from a parametric family. A step-up procedure using the bootstrap method is proposed. Some properties of the procedure are illustrated with simulation studies. An example of the method, applied to orientation of beach clasts, is given. 相似文献
29.
Andrew J. L. Harris Anna L. Butterworth Richard W. Carlton Ian Downey Peter Miller Pedro Navarro David A. Rothery 《Bulletin of Volcanology》1997,59(1):49-64
Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations
where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced
very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large
(3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion
rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at
Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated
near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement
to conventional monitoring methods.
Received: 21 January 1997 / Accepted: 3 April 1997 相似文献
30.
Topographic features affect the scattering properties of planetary surfaces by casting shadows and altering the local incidence and emission angles. Measurements of this phenomenon were obtained on the Cornell goniometer for both high and low albedo surfaces. For the low albedo surface, the decrease in reflected radiation due to topography increases sharply with increasing phase angle, whereas for the high albedo sample the effects are approximately constant between phase angles of 30 and 70°. The observations are in good agreement with a theoretical model in the case of the dark surface. However, for the high albedo surface the model overestimates the effects by about a factor of 2, since it does not include the partial illumination of shadows by multiple scattering. For both high and low albedo surfaces, the effects of topography do not become significant until a phase angle of 30–40°. 相似文献