全文获取类型
收费全文 | 20653篇 |
免费 | 5061篇 |
国内免费 | 8314篇 |
专业分类
测绘学 | 3379篇 |
大气科学 | 2567篇 |
地球物理 | 4403篇 |
地质学 | 15408篇 |
海洋学 | 3214篇 |
天文学 | 430篇 |
综合类 | 2018篇 |
自然地理 | 2609篇 |
出版年
2024年 | 157篇 |
2023年 | 376篇 |
2022年 | 1037篇 |
2021年 | 1341篇 |
2020年 | 1021篇 |
2019年 | 1160篇 |
2018年 | 1029篇 |
2017年 | 969篇 |
2016年 | 961篇 |
2015年 | 1257篇 |
2014年 | 1145篇 |
2013年 | 1446篇 |
2012年 | 1562篇 |
2011年 | 2006篇 |
2010年 | 1779篇 |
2009年 | 1785篇 |
2008年 | 1535篇 |
2007年 | 1598篇 |
2006年 | 1766篇 |
2005年 | 1583篇 |
2004年 | 1868篇 |
2003年 | 1252篇 |
2002年 | 1044篇 |
2001年 | 850篇 |
2000年 | 631篇 |
1999年 | 411篇 |
1998年 | 357篇 |
1997年 | 316篇 |
1996年 | 207篇 |
1995年 | 158篇 |
1994年 | 143篇 |
1993年 | 331篇 |
1992年 | 305篇 |
1991年 | 144篇 |
1990年 | 54篇 |
1989年 | 80篇 |
1988年 | 28篇 |
1987年 | 65篇 |
1986年 | 35篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1954年 | 12篇 |
1937年 | 16篇 |
1933年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
181.
Non-Simultaneous Failure of Ice in Front of Multi-Leg Structures 总被引:4,自引:1,他引:4
Because the multi-leg jacket structure is the major type of offshore structures in the Bohai Sea, the study of non-si-multaneous failure of i鏴 on multi-leg structures is important. However, the non-simultaneous failure has not been consid-ered in engineering design until now, obviously resulting in costly design and notable waste. To resolve this problem, this paper, by means of analysis of experimental data, calculates the coefficient of the non-simultaneous failure for the double-pile structure, the square four-leg structure, the single-line multi-pile structure, and the conical structure, respectively, and provides some reference criteria for engineering design. 相似文献
182.
A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentr 相似文献
183.
Chen Tieyun Zhang Huiyuan Professor Shanghai Jiao Tong University Shanghai
Doctor of Engineering Shenzhen Shipbuilding Trading Co. LTD. 《中国海洋工程》1993,(1)
- Stress concentration analysis of multiplanar tubular DT joints plays an important role in the fatigue design of offshore platforms. A semi-analytic method for stress analysis under the condition of any loads is briefly introduced in the paper. Nineteen multiplanar tubular DT joints with one of two braces of the same dimension subjected to axial loads and out- of- plane bending moments are computed for parametric stress analysis by using the present method. The influence of geometrical parameters on the stresses of multiplanar tubular DT joints is discussed and compared with corresponding uniplanar T joints. The regression formulae for the stress at hot spot of multiplanar DT joints are found by modification of SCF of corresponding uniplanar T joints. The parametric formulae for the maximum stress by superposition. Finally, the influences of stiffening effect and load-interaction effect on the maximum stress of DT joints are discussed. 相似文献
184.
185.
动力定位系统发展状况及研究方法 总被引:21,自引:2,他引:21
动力定位系统(Dynamic Positioning System)是一种闭环的控制系统,其采用推力器来提供抵抗风、浪、流等作用在船上的环境力,从而使船尽可能地保持在海平面上要求的位置上,其定位成本不会随着水深增加而增加,并且操作也比较方便。本文对动力定位系统发展及各组成部分进行了介绍,以期对动力定位系统有个比较完整的认识。 相似文献
186.
187.
1 .IntroductionTheglobalairtemperatureroseabout 0 .5~ 0 .6°Coverthepast 2 0thcentury ,andtheglobalmeansealevelincreasedbyabout2 0cmduringtheperiod .Theregionalmeansealevelriseswiththerisingglobalmeansealevel.Zuoetal.( 1 997)indicatedthatthemeanrisingrateofabsolutemeansealevelalongtheChinacoastontheassumptionofunifiedisostaticdatumis 2mm a .Woodworth( 1 999)analyzedsealevelspanning 1 76 8tothepresentinLiverpool,andobtainedaseculartrendforheperiodupto 1 880of0 .39± 0 .1 7mm a ,andatrendfort… 相似文献
188.
The analytical method (AM) for separation of composite waves is presented based on the Hilbert transform. It is ap-plicable to both regular and irregular trains of waves. The wave data series measured with two wave gauges in the experi-ments are separated into two series of incident and reflected waves. Then, the reflection coefficient can be easily ob-tained. The arrival of reflected waves can also be detected for improveraent of the accuracy of the reflection coefficient. The reflection performance of the physical model can be estimated exactly without calculation of wave height and phase difference. Numerical samples developed to test the method are proved to be accurate. Physical experiments are conduct-ed and compared with Goda s method and satisfactory results are obtained. 相似文献
189.
-In previous and this studies it appears that the linear and nonlinear wave theory can notaccurately and easily predict the water particle velocities.Therefore,different from the theoretical consider-ations,in this study we have attempted to determine the transfer function empirically.Laboratory experi-ments were performed under various wave conditions.The empirical formulas of the transfer function ofthe wave height,angular frequency and water particle velocity were obtained on the basis of these test databy dimensional analysis and regression analysis.In intermediate and deep water depth conditions,thetransfer function was only a function of a nondimensional parameter which is composed of the angular fre-quency,the depth of the velocity gauge under the still water level,water depth and the acceleration of grav-ity.Finally,the empirical formulas were compared with experimental data and observational data formpresent and Cavaleri's(1978)studies.The empirical formulas were found to be in sufficient correl 相似文献
190.
赵耀南 《海洋学报(英文版)》1983,2(1):155-164
The wave period will strongly affect the wave load, and the prevailing method of marine structure design, as adopted nowadays, will not obtain the requisite maximum wave load on structure. This paper presents a new method to determine the design wave that is conditioned by the principle of equal return period by selecting a set of the worst wave height and period which would produce the maximum wave load as a design wave. In this way, not onlythe given design criterion keeps constant but also the design load in the worst case can be obtained. 相似文献