全文获取类型
收费全文 | 6826篇 |
免费 | 1555篇 |
国内免费 | 3023篇 |
专业分类
测绘学 | 330篇 |
大气科学 | 1013篇 |
地球物理 | 1883篇 |
地质学 | 5821篇 |
海洋学 | 838篇 |
天文学 | 213篇 |
综合类 | 841篇 |
自然地理 | 465篇 |
出版年
2023年 | 35篇 |
2022年 | 80篇 |
2021年 | 118篇 |
2020年 | 82篇 |
2019年 | 99篇 |
2018年 | 109篇 |
2017年 | 106篇 |
2016年 | 116篇 |
2015年 | 129篇 |
2014年 | 138篇 |
2013年 | 137篇 |
2012年 | 124篇 |
2011年 | 589篇 |
2010年 | 399篇 |
2009年 | 553篇 |
2008年 | 238篇 |
2007年 | 383篇 |
2006年 | 564篇 |
2005年 | 642篇 |
2004年 | 1238篇 |
2003年 | 816篇 |
2002年 | 577篇 |
2001年 | 471篇 |
2000年 | 353篇 |
1999年 | 379篇 |
1998年 | 420篇 |
1997年 | 373篇 |
1996年 | 264篇 |
1995年 | 237篇 |
1994年 | 200篇 |
1993年 | 387篇 |
1992年 | 345篇 |
1991年 | 183篇 |
1990年 | 77篇 |
1989年 | 91篇 |
1988年 | 33篇 |
1987年 | 67篇 |
1986年 | 44篇 |
1985年 | 10篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1978年 | 13篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1950年 | 8篇 |
1943年 | 7篇 |
1940年 | 9篇 |
1937年 | 15篇 |
1933年 | 13篇 |
1924年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 384 毫秒
61.
62.
Cao Guoao Shen Yilei
Dr.Professor Tongji University Shanghai
Shanghai College of Architectural Municipal Engineering Shanghai 《中国海洋工程》1991,(1)
In this paper, the responses of the interaction system of R.C. gravity single-leg platform to seismic excitation are mainly analysed. A set of nonlinear equations for the interaction system are established by using the wave, one is the soil-structure interaction and the other is the fluid-structure interaction. The seismic response of the interaction system is analysed for the influence of the asymmetric structure, fluid action, etc. with the input of seismic SH waves in any direction. The numerical results are given for a simple example. 相似文献
63.
本文继续报道我国西沙群岛海产色球藻目 Chroococcales 的十种蓝藻,隶于三科六属,有八种是我国海产蓝藻的新记录,它们是:铜锈微囊藻 Microcystis aeruginosa Kuetzing,小形色球藻 Chroococcus minor ( Kuetzing) Naegeli,湖沼色球藻盐泽变种 C. limneticus Lemm.var. subsalsus Lemm,易变色球藻 C.varius A.Braun,膜状色球藻C. membraninus ( Meneghini) Naegeli,圆胞束球藻 Gomphasphaeria aponina Kuetzing,附钙管鞘藻 Hormathonema epilithicum Ercegovic 和透明拟丝藻 Johannesbaptistia pellucida ( Dickie) Taylor at Drouet。其中透明拟丝藻形态特征独特,这对于蓝藻类的研究,特别是研究从色球藻目进化到丝状蓝藻类的系统演化具有重要价值,早已为藻类学家们所重视。该种也是我国海产蓝藻属的新记录。
迄今为止,藻类学家们一致认为色球藻目是蓝藻门 Cyanophyta 中最原始、最低级的类群,其植物体最简单,大都是单细胞或简单的群体,而且都十分微小,常被肥厚的胶质鞘所包埋,这就使该目蓝藻能适应复杂的自然环境。所以,在地质学和古生物学的研究中它已引起许多学者的注意。有关该目海产种类的分类研究,我国仅有少数报道,这方面的工作还有待深入。 相似文献
64.
Chemical forms of Ba are determined in samples of suspension and sediment from the Zhujiang Estuary. Their interfacial geochemical processes are discussed. Total suspended Ba content is between 2. 4 and 40. 4 μg/L, and mostly exists in the crystalline form (43. 5%), secondly in the Fe-Mn oxidative form (23.1%). Percentages of organic, carbonate and exchangeable forms are 14. 8%, 11. l%and 7.4%, respectively. Total content of Ba in the sediment is between 158. 6 and 48. 0 ug/g. Percentages of crystalline form, Fe-Mn oxidative form and carbonate form are 78. 4% ,13. 5%and 8. 2%, respectively. Organic and exchangeable forms are not detected. The study on the mechanism of interfacial movement suggests that the salinity range of 10 is the turning point for the varied distribution of Ba. The subsidence of crystalline form affects the decrease of Ba content in suspension. The decrease mostly takes place in the salinity range lower than 10, which corresponds to the high value of Ba content in the sediment. The 相似文献
65.
A new approach to high-order Boussinesq-type equations with ambient currents is presented. The current velocity is assumed to be uniform over depth and of the same magnitude as the shallow water wave celerity. The wave velocity field is expressed in terms of the horizontal and vertical wave velocity components at an arbitrary water depth level. Linear operators are introduced to improve the accuracy of the kinematic condition at the sea bottom. The dynamic and kinematic conditions at the free surface are expressed in terms of wave velocity variables defined directly on the free surface. The new equations provide high accuracy of linear properties as well as nonlinear properties from shallow to deep water, and extend the applicable range of relative water depth in the case of opposing currents. 相似文献
66.
1 .IntroductionTheBohaiGulfisinfestedbyiceinthewholewinter,andoffshorestructuresthereexperiencenotonlywind ,waves ,currentsandearthquake ,butalsoiceloadswhicharecomplicatedbecauseofthedynamicinteractionbetweenicesheetsandstructures.Duanetal.( 2 0 0 0 )hadacomprehensivere viewofthelatestadvancesonice inducedvibration ,fatigueandfractureofoffshorestructures ,payingmuchattentiontothedifferencesinicebreakingmodeanddynamicsofstructuresindifferentice in festedwaters .Theypresentedcriticallythelates… 相似文献
67.
Li Yucheng Wang Fenglong Professor Dalian University of Technology Dalian Senior Engineer Dalian University of Technology Dalian 《中国海洋工程》1993,(1)
- The wave-current forces on vertical piles in side-by-side arrangement induced by irregular waves with opposing current are investigated experimentally in this paper. The characteristics in both time and frequency domain of in-line, lift and resultant forces are analyzed. The grouping effect coefficients of inline, lift and resultant forces on piles related to KC number and relative spacing parameters are given. These results are compared with those in the case of irregular waves combined with following currents. It is found that the results in these two cases are quite different. The range of KC number tested is 10- 60, the range of Reynolds number is (0.55-3.43) ×104. 相似文献
68.
Zhang Furan Zhao Jun Zhang Xueqin Assistant Researcher Tianjin Research Institute of Water Transport Engineering Tianjin Assistant Engineer Tianjin Research Institute of Water Transport Engineering Tianjin 《中国海洋工程》1993,(2)
In respect of an offshore berthing pillar, the test study result of current force acting on mooring ships is described in this paper. Empirical and semi-empirical relationships of current force coefficient are given according to the angle between the flow direction and the ship's longitudinal axis, which are coincident with the result of theoretical analysis. 相似文献
69.
A Computational Model for Velocity Separation in Shallow Sea 总被引:1,自引:0,他引:1
Based on the hydrodynamical feature and the theoretical velocity profiles of tidal flow and vvind-induced flow in shal-low sea, a computational model is established for the first time, which can separate observed velocity into tidal velocity and wind-induced velocity by use of the least square method. With the model, not only the surface velocities of tidal flow and vvind-induced flow are obtained, but also the bed roughness height is determined and the wind velocity above the wa-ter surface is estimated. For verification of the model, the observed velocity in the Yellow River Estuary and the laborato-ry test is separated, then it is applied to the Yangtze River Estuary. All the results are satisfactory. The research results show that the model is simple in method, feasible in process and reasonable in result. The model is a valid approach to analysis and computation of field dala, and can be applied to separate the observed velocity in shallow sea; at the same time, reasonable boundary conditions of th 相似文献
70.
Nicholas Dodd 《中国海洋工程》1995,(2)
A nonlinear short-wave-averaged (surf beat) model is presented. The model is based on that of Roelvink (1993), but the numerical techniques used in the solution are based on the so-called weighted-averaged flux (WAF) method (eg Watson et al., 1992), with time-operator splitting used for the treatment of some of the source terms. This method allows a small number of computational points to be used, and is particularly efficient in modelling breaking long waves. The short-wave (or primary-wave) energy equation is solved using a more traditional Lax-Wendroff technique. Results of validation indicate that the model performs satisfactorily in most respects. 相似文献