全文获取类型
收费全文 | 18952篇 |
免费 | 3626篇 |
国内免费 | 4890篇 |
专业分类
测绘学 | 1840篇 |
大气科学 | 3674篇 |
地球物理 | 4576篇 |
地质学 | 9558篇 |
海洋学 | 2919篇 |
天文学 | 972篇 |
综合类 | 1748篇 |
自然地理 | 2181篇 |
出版年
2024年 | 71篇 |
2023年 | 269篇 |
2022年 | 808篇 |
2021年 | 910篇 |
2020年 | 745篇 |
2019年 | 928篇 |
2018年 | 928篇 |
2017年 | 939篇 |
2016年 | 1068篇 |
2015年 | 1003篇 |
2014年 | 1093篇 |
2013年 | 1231篇 |
2012年 | 1269篇 |
2011年 | 1265篇 |
2010年 | 1359篇 |
2009年 | 1209篇 |
2008年 | 1259篇 |
2007年 | 1106篇 |
2006年 | 941篇 |
2005年 | 879篇 |
2004年 | 658篇 |
2003年 | 627篇 |
2002年 | 622篇 |
2001年 | 662篇 |
2000年 | 634篇 |
1999年 | 724篇 |
1998年 | 603篇 |
1997年 | 533篇 |
1996年 | 522篇 |
1995年 | 449篇 |
1994年 | 365篇 |
1993年 | 356篇 |
1992年 | 284篇 |
1991年 | 231篇 |
1990年 | 178篇 |
1989年 | 146篇 |
1988年 | 147篇 |
1987年 | 71篇 |
1986年 | 67篇 |
1985年 | 50篇 |
1984年 | 34篇 |
1983年 | 23篇 |
1982年 | 38篇 |
1981年 | 36篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 10篇 |
1976年 | 9篇 |
1958年 | 20篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
In this paper, the morphogenesis, stratigraphic sequences and dates of the coral reefs in the middle and north parts of the South China Sea are discussed, the position of the distributary regions of Cenozoic coral reefs in plate tectonics, the relationships of coral-reef evolutionary characteristics and dates with sea-basin spreading. Neogene sea-water transgression and Quaternary global climate-eustatic fluctuation are expounded and proved, and the latitudinal variation of the distribution of coral reefs in various geologic times are summed up. 相似文献
142.
西沙群岛及其附近海域多毛类动物地理学的研究 总被引:5,自引:1,他引:5
西沙群岛及其附近海域蕴藏着极其丰富的水产资源,是我国的良好渔场之一,自古以来就是我国渔民的渔捞基地.解放以来,在党的领导下,对我国神圣领土西沙群岛进行了大规模的开发和建设.中国科学院海洋研究所和中国科学院南海海洋研究所等单位,进行了多次海洋生物资源调查,我们曾报告过113种浮游和底栖多毛类.根据1975-1976年补充调查的标本,又发现了过去未报告过的多毛类70种,截至目前西沙群岛及其附近海域的多毛类共有183种.本文根据现在掌握的资料对我国西沙群岛及其附近海域多毛类动物地理学做一初步分析. 相似文献
143.
本文报道了1990年在平湖对虾养殖场用几种药物治疗聚缩虫病所做的试验。结果表明,高锰酸钾和新洁尔灭的疗效较为显著。 相似文献
144.
A new three-dimensional, non-hydrostatic free surface flow model is presented. For simulating water wave motions over uneven bottoms, the model employs an explicit project method on a Cartesian the staggered gird system to solve the complete three-dimensional Navier–Stokes equations. A bi-conjugated gradient method with a pre-conditioning procedure is used to solve the resulting matrix system. The model is capable of resolving non-hydrostatic pressure by incorporating the integral method of the top-layer pressure treatment, and predicting wave propagation and interaction over irregular bottom by including a partial bottom-cell treatment. Four examples of surface wave propagation are used to demonstrate the capability of the model. Using a small of vertical layers (e.g. 2–3 layers), it is shown that the model could effectively and accurately resolve wave shoaling, non-linearity, dispersion, fission, refraction, and diffraction phenomena. 相似文献
145.
1 IntroductionBothEpinephelus malabaricusandE. coioidesbelong to the genusEpinephelus(Perciformes: Ser-ranidae: Epinephelinae).They are warm water reeffishes that have similar distribution ranges as well assimilar morphological characteristics, which have… 相似文献
146.
On the radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas 总被引:1,自引:0,他引:1
The radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas of finite depth is investigated. The analytical expressions for the radiated and diffracted potentials are derived as infinite series by use of the method of separation of variables. The unknown coefficients in the series are determined by the eigenfunction expansion matching method. The expressions for wave forces, hydrodynamic coefficients and reflection and transmission coefficients are given and verified by the boundary element method. Using the present analytical solution, the hydrodynamic influences of the angle of incidence, the submergence, the width and the thickness of the structure on the wave forces, hydrodynamic coefficients, and reflection and transmission coefficients are discussed in detail. 相似文献
147.
Sloshing in a two-dimensional rectangular tank in horizontal motion is analysed based on the velocity potential theory. It is found that even when the first-order excitation is away from all the natural frequencies of the tank, second-order resonance can still occur when the sum-frequency or the difference-frequency is equal to one of the natural frequencies corresponding to the even mode. However, such resonance is not excited when the sum or difference frequency is equal to the natural frequency of an odd mode. 相似文献
148.
149.
应用多年的实测资料 ,分析了曹娥江河口高水位成因 ,结果表明 ,曹娥江河口洪水位具有山溪性和可冲性的特点 ,人类活动对高水位有较大影响。应用统计分析法和成因分析法推求 1 %设计高水位 ,讨论了成因分析法中上、下边界条件的选取 ,其选取原则对其他潮汐河口确定设计高水位具有借鉴意义 相似文献
150.
The responses of a spar constrained by slack mooring lines to steep ocean waves and tensions in the mooring lines are simulated using two different numerical schemes: a quasi-static approach (SMACOS) and a coupled dynamic approach (COUPLE). The two approaches are the same in computing wave loads on the structure. Their difference is in modeling dynamic forces of mooring lines; that is the dynamic forces are included in the computation of COUPLE but neglected in SMACOS. The numerical simulation is examined against the laboratory measurements of the JIP Spar in a water depth of 318 m. The dynamic coupling effects between the JIP Spar and its mooring lines in different water depths (318, 618 and 1018 m) are investigated by the comparison of numerical simulations obtained using the quasi-static and coupled dynamic approaches. It is found that the damping of mooring lines reduces the slow-drift surge and pitch of the Spar, especially in deep water. The reduction in the amplitude of slow-drift surge can reach about 10% in a water depth of 1018 m. The tension in mooring lines may greatly increase in the wave frequency range when dynamic forces in mooring lines are considered. The mooring-line tension in the wave frequency range predicted by the coupled dynamic approach can be eight times as great as the corresponding prediction by the quasi-static approach in a water depth of 1018 m. This finding may have important implications for the estimation of the fatigue strength and life span of the mooring lines deployed in deep water oceans. 相似文献