全文获取类型
收费全文 | 24386篇 |
免费 | 4171篇 |
国内免费 | 6384篇 |
专业分类
测绘学 | 4648篇 |
大气科学 | 4690篇 |
地球物理 | 5749篇 |
地质学 | 10638篇 |
海洋学 | 3512篇 |
天文学 | 235篇 |
综合类 | 1986篇 |
自然地理 | 3483篇 |
出版年
2024年 | 159篇 |
2023年 | 429篇 |
2022年 | 886篇 |
2021年 | 1061篇 |
2020年 | 1226篇 |
2019年 | 1343篇 |
2018年 | 1123篇 |
2017年 | 1295篇 |
2016年 | 1424篇 |
2015年 | 1514篇 |
2014年 | 1597篇 |
2013年 | 1817篇 |
2012年 | 1664篇 |
2011年 | 1677篇 |
2010年 | 1358篇 |
2009年 | 1521篇 |
2008年 | 1534篇 |
2007年 | 1581篇 |
2006年 | 1500篇 |
2005年 | 1324篇 |
2004年 | 1175篇 |
2003年 | 1011篇 |
2002年 | 949篇 |
2001年 | 789篇 |
2000年 | 734篇 |
1999年 | 652篇 |
1998年 | 607篇 |
1997年 | 529篇 |
1996年 | 474篇 |
1995年 | 426篇 |
1994年 | 383篇 |
1993年 | 322篇 |
1992年 | 197篇 |
1991年 | 175篇 |
1990年 | 114篇 |
1989年 | 87篇 |
1988年 | 90篇 |
1987年 | 60篇 |
1986年 | 27篇 |
1985年 | 30篇 |
1984年 | 15篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1972年 | 1篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
A numerical model to compute wave field is developed. It is based on the Berkhoff diffraction-refraction equation, in which an energy dissipation term is added, to take into account the breaking and the bottom friction phenomena. The energy dissipation function, by breaking and by bottom friction, is introduced in the Berkhoff equation to obtain a new equation of propagation.The resolution is done with the hybrid finite element method, where lagrangians elements are used. 相似文献
23.
24.
25.
AbstractWith the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing. 相似文献
26.
I. Brandariz P. Castro M. Montes F. Penedo M.E. Sastre de Vicente 《Marine Chemistry》2006,102(3-4):291-299
Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl2 or CaCl2), with binary mixtures of MgCl2 and CaCl2, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl2, while it is increased by the other electrolytes used in this work. 相似文献
27.
A comparison of two three-dimensional numerical modeling systems for tidal elevations and velocities in the coastal waters is presented. The two modeling systems are: (1) the Princeton Ocean Model (POM) and (2) the MIKE 3 flow model. The model performance results for Singapore's coastal waters show that the predicted tidal elevations from the two hydrodynamic modeling systems are almost identical and are in very good agreement with field measurement data. The simulated tidal current velocities match well with field measurement data at the selected stations, but it seems that the POM provides the slightly better simulation, compared to the MIKE 3 flow model. The depth profiles of the velocities obtained from the two modeling systems may be greatly different at some time, due to the vertical diffusion coefficient calculated from different turbulent sub-models in the two modeling systems. The POM generally predicts larger peak tidal velocities. The maximum speed differences for the model results from the two modeling systems occur in the top and differ from time to time and from location to location, reaching up to 20%. 相似文献
28.
29.
Darío R. Minkoff Mauricio Escapa Flix E. Ferramola Silvio D. Maraschín Jorge O. Pierini Gerardo M.E. Perillo Claudio Delrieux 《Estuarine, Coastal and Shelf Science》2006,69(3-4):403
The Bahía Blanca Estuary (38° 50′ S, and 62° 30′ W) presents salt marshes where interactions between the local flora (Sarcocornia perennis) and fauna (Chasmagnathus granulatus) generate some kind of salt pans that alter the normal water circulation and condition its flow and course towards tidal creeks. The crab–vegetation dynamics in the salt marsh presents variations that cannot be quantified in a reasonable period of time. The interaction between S. perennis plant and C. granulatus crab is based on simple laws, but its result is a complex biological mechanism that causes an erosive process on the salt marsh and favors the formation of tidal creeks. To study it, a Cellular Automata model is proposed, based on the laws deduced from the observation of these phenomena in the field, and then verified with measurable data within macroscale time units. Therefore, the objective of this article is to model how the interaction between C. granulatus and S. perennis modifies the landscape of the salt marsh and influences the path of tidal creeks. The model copies the basic laws that rule the problem based on purely biological factors.The Cellular Automata model proved capable of reproducing the effects of the interaction between plants and crabs in the salt marsh. A study of the water drainage of the basins showed that this interaction does indeed modify the development of tidal creeks. Model dynamics would likewise follow different laws, which would provide a different formula for the probability of patch dilation. The patch shape can be obtained changing the pattern that dilates. 相似文献
30.
The phase one project of the twin jetties at the Tao-er Estuary yields no effect on the flow, and there is a large area of deposition. A numerical model is employed to simulate the flow field, and the scouring and silting in the channel be-tween the two jetties are analyzed. The results show that the effective tidal flux between the two jetties is reduced due to the notch located at the heel of the east jetty, and the effect of contraction-flush is not obvious. As for the regulation of this kind of estuary under the tide action, the capability of tidal flux should be fully used. 相似文献