全文获取类型
收费全文 | 20702篇 |
免费 | 5068篇 |
国内免费 | 5694篇 |
专业分类
测绘学 | 1331篇 |
大气科学 | 4153篇 |
地球物理 | 8103篇 |
地质学 | 9544篇 |
海洋学 | 4662篇 |
天文学 | 647篇 |
综合类 | 1401篇 |
自然地理 | 1623篇 |
出版年
2024年 | 153篇 |
2023年 | 401篇 |
2022年 | 689篇 |
2021年 | 799篇 |
2020年 | 888篇 |
2019年 | 1121篇 |
2018年 | 884篇 |
2017年 | 901篇 |
2016年 | 953篇 |
2015年 | 1094篇 |
2014年 | 1306篇 |
2013年 | 1384篇 |
2012年 | 1418篇 |
2011年 | 1421篇 |
2010年 | 1106篇 |
2009年 | 1462篇 |
2008年 | 1312篇 |
2007年 | 1675篇 |
2006年 | 1442篇 |
2005年 | 1168篇 |
2004年 | 1174篇 |
2003年 | 1031篇 |
2002年 | 939篇 |
2001年 | 777篇 |
2000年 | 800篇 |
1999年 | 729篇 |
1998年 | 692篇 |
1997年 | 621篇 |
1996年 | 597篇 |
1995年 | 490篇 |
1994年 | 471篇 |
1993年 | 369篇 |
1992年 | 287篇 |
1991年 | 226篇 |
1990年 | 173篇 |
1989年 | 136篇 |
1988年 | 123篇 |
1987年 | 82篇 |
1986年 | 33篇 |
1985年 | 29篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1954年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
The modified hybrid element method (MHEM) is utilized to predict and analyze wave forces on arbitrarily shaped multiple bodies. This method can be applied to waves of all water depths, i. e. shallow, intermediate, and deep waters, on slowly varying seabed. The MHEM employs the ICCG method to save CPU and storage, thus the computation of wave forces for large multi-body systems can be carried out on microcomputers. Numerical results of the present method are compared with experimental data and other solutions. It is shown that the MHEM provides more accurate solutions of the wave forces than other numerical methods do. Therefore, the methodology presented herein can be used in the design of coastal and ocean structures. 相似文献
112.
Low-frequency damping of a moored semisubmersible drilling platform was obtained from numerical extinction tests simulated in still water and in regular waves and from mean wave drift forces calculated at zero forward speed. The influence of drag forces was represented by the modified Morison equation. The platform as used for the 18th ITTC Comparative Mooring Study was analyzed in irregular beam waves. The computed time series of sway as well as the corresponding sway response spectrum compared favourably with model test measurements, demonstrating that this procedure to determine low-frequency damping can be effective. 相似文献
113.
互花米草及其对海岸的防护作用 总被引:28,自引:0,他引:28
本文论述了互花米草在滩涂中种植的时间、种植的方法及其生长的适应性。文中着重讨论互花米草在海岸工程中防浪和消浪能力。与工程护岸比较,互花米草护岸是最经济、合理和有效的。通过本文的讨论为今后利用互花米草进行海岸防护提供依据 相似文献
114.
Kern E. Kenyon 《Journal of Oceanography》1997,53(1):89-92
The effects of the gravity torques acting on the angular momentum of surface gravity waves are calculated theoretically. For
short crested waves the gravity torque is caused by the force of gravity on the orbiting fluid particles acting down the slopes
of the crests and troughs and in the direction parallel to the crests and troughs. The gravity torque tries to rotate the
angular momentum vectors, and thus the waves themselves, counterclockwise in the horizontal plane, as viewed from above, in
both hemispheres. The amount of rotation per unit time is computed to be significant assuming reasonable values for the along-crest
and trough slopes for waves in a storm area. The gravity torque has a frequency which is double the frequency of the waves.
For long crested waves the gravity torque acts in the vertical plane of the orbit and tries to decelerate the particles when
they rise and accelerate them when they fall. By disrupting the horizontal cyclostrophic balance of forces on the fluid particles
(centrifugal force versus pressure force) the gravity torque accounts qualitatively for the three characteristics of breaking
waves: that they break at the surface, that they break at the crest, and that the crest breaks in the direction of wave propagation. 相似文献
115.
E.R. Jefferys 《Applied Ocean Research》1984,6(1):31-39
Classical frequency and time domain models of a single degree of freedom wave power device are presented. In the time domain, a convolution integral is conventionally used to represent the fluid dynamic radiation force, characterised by added mass and damping in the frequency domain. This integral is replaced by an approximate ordinary differential equation (ODE) model which is faster and more convenient in simulations. A time domain model of the fluid dynamics of an oscillating water column (OWC) device is derived to illustrate the technique. Digital simulations of the OWC are used to compare the accuracy of the classical and ODE models. The simulation of the ODE model runs about six times as fast as the classical model based on convolution, yet characterises the fluid dynamics accurately. 相似文献
116.
Temperature data from 18 measurement series obtained during logging of the Oseberg field in the northern North Sea are presented. Because the measurement series are taken at approximately the same depth, they should give identical temperatures after depth correction, and are suitable for assessing the performance of different models used to determine virgin rock temperatures from well log information.We have used this data set to test the properties of the different models given by Shen and Beck (1986). Although these models were built to simulate closely the thermal recovery of a well and are unbiased, the uncertainties in the temperature estimates when applied to real data are found to be no less than those from simpler (biased) models. This fact confirms the conclusion of Hermanrud (1989a) who showed that physical factors other than those presently accounted for significantly influence the thermal recovery of a borehole. 相似文献
117.
Wave induced excess flow of momentum(WIEFM)is the averaged flow of momentum over a wave period due to wave presence,which may also be called 3-D radiation stress.In this paper,the 3-D current equations with WIEFM are derived from the averaged Navier-Stokes equations over a wave period,in which the velocity is separated into the large-scale background velocity,the wave particle velocity and the turbulent fluctuation velocity.A concept of wave fluctuating layer(WFL)is put forward,which is the vertical column from the wave trough to wave ridge.The mathematical expressions of WIEFM in WFL and below WFL are given separately.The parameterized expressions of WIEFM are set up according to the linear wave theory.The integration of WIEFM in the vertical direction equals the traditional radiation stress(namely 2-D radiation stress)given by Longuet-Higgins and Stewart. 相似文献
118.
119.
The VOF method and the k–ε model, combined with the equation of state of air at constant temperature, have been used to calculate the total horizontal wave force caused by monochromatic waves acting on a perforated caisson with a top cover. From comparison of various parameters, such as the total horizontal force, the pressure difference on the front wall, the pressure on the back wall and the pressure on the top cover, between the numerical results and test data, it can be seen that the numerical results agree well with the test data. It is concluded that the method described in this paper can be utilized to calculate wave forces acting on perforated caissons with a top cover in the case of nonovertopping, nonbreaking waves. A simplified method to calculate the total horizontal force has been developed, based on test data, using a least-squares method. A comparison between the numerical results and the values calculated from the simplified equations shows good agreement. Therefore the simplified equations can be used in engineering applications to evaluate the total horizontal force on a perforated caisson with a top cover. 相似文献
120.