全文获取类型
| 收费全文 | 2117篇 |
| 免费 | 279篇 |
| 国内免费 | 278篇 |
专业分类
| 测绘学 | 118篇 |
| 大气科学 | 337篇 |
| 地球物理 | 709篇 |
| 地质学 | 531篇 |
| 海洋学 | 392篇 |
| 天文学 | 156篇 |
| 综合类 | 76篇 |
| 自然地理 | 355篇 |
出版年
| 2024年 | 5篇 |
| 2023年 | 9篇 |
| 2022年 | 50篇 |
| 2021年 | 49篇 |
| 2020年 | 59篇 |
| 2019年 | 79篇 |
| 2018年 | 58篇 |
| 2017年 | 91篇 |
| 2016年 | 79篇 |
| 2015年 | 84篇 |
| 2014年 | 101篇 |
| 2013年 | 129篇 |
| 2012年 | 63篇 |
| 2011年 | 100篇 |
| 2010年 | 100篇 |
| 2009年 | 136篇 |
| 2008年 | 137篇 |
| 2007年 | 134篇 |
| 2006年 | 131篇 |
| 2005年 | 123篇 |
| 2004年 | 121篇 |
| 2003年 | 94篇 |
| 2002年 | 82篇 |
| 2001年 | 78篇 |
| 2000年 | 102篇 |
| 1999年 | 67篇 |
| 1998年 | 73篇 |
| 1997年 | 50篇 |
| 1996年 | 39篇 |
| 1995年 | 27篇 |
| 1994年 | 45篇 |
| 1993年 | 32篇 |
| 1992年 | 31篇 |
| 1991年 | 22篇 |
| 1990年 | 16篇 |
| 1989年 | 20篇 |
| 1988年 | 11篇 |
| 1987年 | 10篇 |
| 1986年 | 4篇 |
| 1985年 | 7篇 |
| 1984年 | 7篇 |
| 1983年 | 2篇 |
| 1982年 | 7篇 |
| 1980年 | 1篇 |
| 1978年 | 5篇 |
| 1977年 | 2篇 |
| 1954年 | 2篇 |
排序方式： 共有2674条查询结果，搜索用时 31 毫秒
21.
A system of numerical tools to predict the non-local long-term impact of large-scale constructions on the environment is described. The predictions have to be results of successive examination of free water oscillations, turbulent boundary layers on the sea bottom, and turbulent pulsation effects on sediment transport. Numerical results related to free water oscillations in diverse gulfs are shown, and non-local effects of the dam construction are found for an example of the Baltic Sea. Feasibility of suggested tools for turbulent flow is manifested. 相似文献
22.
23.
Several large deployments of neutrally buoyant floats took place within the Antarctic Intermediate (AAIW), North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW) of the South Atlantic in the 1990s and a number of hydrographic sections were occupied as well. Here we use the spatially and temporally averaged velocities measured by these floats, combined with the hydrographic section data and various estimates of regional current transports from moored current meter arrays, to determine the circulation of the three major subthermocline water masses in a zonal strip across the South Atlantic between the latitudes of 19°S and 30°S. We concentrate on this region because the historical literature suggests that it is where the Deep Western Boundary Current containing NADW bifurcates. In support of this notion, we find that a net of about 5 Sv. of the 15–20 Sv that crosses 19°S does continue zonally eastward at least as far as the Mid-Atlantic Ridge. Once across the ridge it takes a circuit to the north along the ridge flanks before returning to the south in the eastern half of the Angola Basin. The data suggest that the NADW then continues on into the Indian Ocean. This scheme is discussed in the context of distributions of dissolved oxygen, silicate and salinity. In spite of the many float-years of data that were collected in the region a surprising result is that their impact on the computed solutions is quite modest. Although the focus is on the NADW we also discuss the circulation for the AAIW and AABW layers. 相似文献
24.
This article presents results from a series of Ko-consolidated compression and extension triaxial tests on specimens from undisturbed samples of Hong Kong Marine Deposits (HKMD). To investigate the strain-rate effects, a total of seven Ko-consolidated triaxial tests were conducted including four compression tests and three extension tests. After Ko-consolidation, the triaxial test specimens were sheared at step-changed axial strain rates under three different confining pressures of 50 kPa, 150 kPa, and 400 kPa, respectively. The step-changed strain rates were applied in the following order: +2%/h, +0.2%/h, +20%/h, -2%/h (unloading) and +2%/h (reloading) for the four compression tests and -2%/h, -0.2%/h, -20%/h, +2%/h (unloading) and -2%/h (reloading) for the three extension tests. The results are reported and analyzed in the paper. The results show that the strain rate effects, the stress-strain characteristics, and the effective stress paths of the specimens for tests in a compression state are different from those for tests in an extension stage. One order of magnitude increase in axial strain rate causes an average 8.6% increase in undrained shear strength for compression tests and a 12.1% increase for extension tests. It is also found that the failure mode of the specimens in compression is different from that in extension. The stress-strain behavior of specimens shows strain-softening and a clear shear band in compression tests, but strain-hardening without any clear shear band in extension tests for the same absolute value of axial strain. 相似文献
25.
26.
A two-dimensional hydrodynamic model application to the San Francisco Bay was performed using the Boundary-Fitted HYDROdynamic model (BFHYDRO). The model forcing functions consist of tidal elevations along the open boundary and fresh water flows from the Delta Outflow. The model-predicted surface elevations compare well with the observed surface elevations at five stations in San Francisco Bay. Mean error in the model predicted surface elevations and currents are less than 7 and 9%, respectively. Correlation coefficients for surface elevations and currents are higher than 0.94 and 0.95, respectively. The amplitudes and phases of the principal tidal constituents at 24 tidal stations in San Francisco Bay, obtained from a harmonic analysis of a 90-day simulation compare well with the observed data. The predicted amplitude and phase of the M2 tidal constituent at these stations are respectively within 8 cm and 8° of the observed data. Maximum errors in the K1 harmonic amplitudes and phases are less than 3 cm and 7° respectively. The asymmetric diurnal and semi-diurnal tidal ranges and spring and neap tidal cycles of the surface elevations and currents are well reproduced in the model at all stations. 相似文献
27.
This paper presents the results of a numerical performance analysis to demonstrate the worthiness of a recently patented new concept propulsor, the so-called “thrust-balanced propeller (TBP)”. The main advantage of this unconventional propulsor is its inherent ability to reduce the unsteady effect of blade forces and moments when it is operating in a non-uniform wake flow. The propulsor comprises a pair of diametrically opposed blades that are connected to one another and mounted so as to be rotatable together through a limited angle about their spindle axis. A quasi-hydrodynamic approach is described and applied to perform the numerical analysis using a state-of-the-art lifting surface procedure for conventional propellers. Performance comparisons with a conventional fixed-pitch propeller are made for the blade forces and moments, efficiency, cavitation extents and fluctuating hull pressures. Bearing in mind the quasi-static nature of the analyses, the results present favourable performance characteristics for the thrust-balanced propeller and support the worthiness of the concept. However, the concept needs to be proved through physical model tests, which are planned to take in a cavitation tunnel. 相似文献
28.
This paper describes the extension of a fluid-flow simulations method to capture the free surface evolution around a full-scale Tension Leg Platform (TLP). The focus is on the prediction of the resulting hydrodynamic loading on the various elements of the TLP in turbulent flow conditions and, in particular, on quantifying the effects of the free surface distortion on this loading. The basic method uses finite-volume techniques to discretize the differential equations governing conservation of mass and momentum in three dimensions. The time-averaged forms of the equations are used, and the effects of turbulence are accounted for by using a two-equation, eddy-viscosity closure. The method is extended here via the incorporation of surface-tracking algorithm on a moving grid to predict the free-surface shape. The algorithm was checked against experimental measurements from two benchmark flows: the flow over a submerged semi-circular cylinder and the flow around a floating parabolic hull. Predictions of forces on a model TLP were then obtained both with and without allowing for the deformation of the free surface. The results suggest that the free surface effects on the hydrodynamic loads are small for the values of Froude number typically encountered in offshore engineering practice. 相似文献
29.
30.