全文获取类型
收费全文 | 9819篇 |
免费 | 2295篇 |
国内免费 | 820篇 |
学科分类
地球科学 | 12934篇 |
出版年
2024年 | 35篇 |
2023年 | 125篇 |
2022年 | 246篇 |
2021年 | 313篇 |
2020年 | 404篇 |
2019年 | 445篇 |
2018年 | 357篇 |
2017年 | 343篇 |
2016年 | 318篇 |
2015年 | 381篇 |
2014年 | 473篇 |
2013年 | 500篇 |
2012年 | 553篇 |
2011年 | 561篇 |
2010年 | 473篇 |
2009年 | 536篇 |
2008年 | 548篇 |
2007年 | 685篇 |
2006年 | 719篇 |
2005年 | 580篇 |
2004年 | 594篇 |
2003年 | 501篇 |
2002年 | 431篇 |
2001年 | 311篇 |
2000年 | 346篇 |
1999年 | 296篇 |
1998年 | 285篇 |
1997年 | 240篇 |
1996年 | 273篇 |
1995年 | 215篇 |
1994年 | 215篇 |
1993年 | 185篇 |
1992年 | 115篇 |
1991年 | 74篇 |
1990年 | 56篇 |
1989年 | 56篇 |
1988年 | 45篇 |
1987年 | 31篇 |
1986年 | 27篇 |
1985年 | 7篇 |
1984年 | 1篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 17篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Calculation of transverse hydrodynamic coefficients using computational fluid dynamic approach 总被引:1,自引:0,他引:1
Computational Fluid Dynamic (CFD) based on Reynolds Averaged Navier–Stokes equation is used for determining the transverse hydrodynamic damping force and moment coefficients that are needed in the maneuverability study of marine vehicles. Computations are performed for two geometrical shapes representing typical AUVs presently in use. Results are compared with available data on similar geometries and from some of the available semi-empirical relations. It is found that the CFD predictions compares reasonable well with these results. In particular, the CFD predictions of forces and moments are found to be nonlinear with respect to the transverse velocity, and therefore both linear and nonlinear coefficients can be derived. A discussion on the sources of the component forces reveal that the total force and moment variations should in fact be nonlinear. 相似文献
5.
The longitudinal strength of turret mooring productive/storage tanker is studied.A numeri-cal example has been implemented according to the method presented in this paper to give practical il-lustration.From the results of the numerical example,it is concluded that the turret hole located near theforward of the amidships has small effect on the longitudinal strength of the ship hull.As for design ex-treme value of wave bending moment of storage tanker,statistic method is a more reasonablemethodology,especially with the consideration of the servere environmental conditions.The primary esti-mation of design section modulus of turret storage tanker can be determined by this design bending mo-ment. 相似文献
6.
7.
Robert P. Dziak Christopher G. Fox Robert W. Embley 《Marine Geophysical Researches》1991,13(3):203-208
Morphologic studies of an oceanic transform, the Blanco Transform Fault Zone (BTFZ), have shown it to consist of a series of extensional basins that offset the major strike-slip faults. The largest of the extensional basins, the Cascadia Depression, effectively divides the transform into a northwest segment, composed of several relatively short strike-slip faults, and a southeast segment dominated by fewer, longer faults. The regional seismicity distribution (m
b
4.0) and frequency-magnitude relationships (b-values) of the BTFZ show that the largest magnitude events are located on the southeast segment. Furthermore, estimates of the cumulative seismic moment release and seismic moment release rate along the southeast segment are significantly greater than that of the northwest segment. These observations suggest that slip along the southeast segment is accommodated by a greater number of large magnitude earthquakes. Comparison of the seismic moment rate, derived from empirical estimates, with the seismic moment rate determined from plate motion constraints suggests a difference in the seismic coupling strength between the segments. This difference in coupling may partially explain the disparity in earthquake size distribution. However, the results appear to confirm the relation between earthquake size and fault length, observed along continental strike-slip faults, for this oceanic transform. 相似文献
8.
R. E. Kirk K. Robertson R. B. Whitmarsh P. R. Miles 《Marine Geophysical Researches》1991,13(2):153-160
A technique has been devised for firing arrays of bottom shots on the ocean bed in depths upto 4000 m or more. Ten kilogram explosive charges are dropped from the surface while the shooting ship is navigated acoustically. They are detonated at preset times by an electronic timer which initiates an electrical detonator, detonating cord and cast PETN/TNT explosive. Ranges to ocean bottom seismographs, and the shot instants, can be calculated from the arrival-time differences of the direct and surface-reflected water waves. The accuracy, which is dependent on water-depth and range, was better than 22 m in range and 14 msec in shot instant for our experiments. 相似文献
9.
10.
一种直线特征标志的子像素定位方法 总被引:1,自引:0,他引:1
在近景摄影测量中,常常需要对直线特征的标志进行定位,而标志定位的精度会影响到整个测量的精度。不同特征的控制点标志,对应不同的识别方法,因此控制点标志的选择须根据不同的要求,进行综合研究分析。本文提出一种新的混合方法,首先采用Hough变换对直线特征标志进行直线检测,得到直线初值;然后采用灰度矩边缘直线拟合定位法,对标志点中心进行子像素定位。通过实验证明:经过Hough变换得到粗值的灰度矩边缘直线拟合定位法达到较高的定位精度,证明了该混合方法的有效性。 相似文献