全文获取类型
收费全文 | 17168篇 |
免费 | 2930篇 |
国内免费 | 3210篇 |
专业分类
测绘学 | 1893篇 |
大气科学 | 1297篇 |
地球物理 | 4332篇 |
地质学 | 7762篇 |
海洋学 | 2224篇 |
天文学 | 2076篇 |
综合类 | 990篇 |
自然地理 | 2734篇 |
出版年
2024年 | 92篇 |
2023年 | 302篇 |
2022年 | 604篇 |
2021年 | 639篇 |
2020年 | 722篇 |
2019年 | 785篇 |
2018年 | 616篇 |
2017年 | 692篇 |
2016年 | 724篇 |
2015年 | 760篇 |
2014年 | 845篇 |
2013年 | 868篇 |
2012年 | 930篇 |
2011年 | 979篇 |
2010年 | 790篇 |
2009年 | 1135篇 |
2008年 | 1058篇 |
2007年 | 1145篇 |
2006年 | 1101篇 |
2005年 | 931篇 |
2004年 | 929篇 |
2003年 | 918篇 |
2002年 | 746篇 |
2001年 | 676篇 |
2000年 | 654篇 |
1999年 | 566篇 |
1998年 | 619篇 |
1997年 | 381篇 |
1996年 | 356篇 |
1995年 | 325篇 |
1994年 | 302篇 |
1993年 | 260篇 |
1992年 | 216篇 |
1991年 | 128篇 |
1990年 | 96篇 |
1989年 | 107篇 |
1988年 | 67篇 |
1987年 | 74篇 |
1986年 | 47篇 |
1985年 | 25篇 |
1984年 | 10篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1973年 | 9篇 |
1971年 | 6篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
中国沿海星虫动物门名录 总被引:2,自引:0,他引:2
取1980~1989年间在我国沿海进行星虫动物区系调查的标本和有关资料做了整理、鉴定,共39种,分隶于2纲,4目,6科,12属。其中1种在我国为首次记录。 相似文献
102.
本文用耗散结构理论推导出南海热带气旋的移动公式,通过实际应用和实例检验,证明它对估计南海热带气旋路径演变有一定的实用价值。 相似文献
103.
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
104.
Descriptive Analysis and Classification of Benthic Communities in Some Mediterranean Coastal Lagoons (Central Italy) 总被引:3,自引:0,他引:3
Abstract. Benthic samples were taken seasonally at 32 stations in five coastal lagoons of Central Italy (Fogliano, Monaci, Caprolace, Fondi, and Lungo) during a two-year period (1982–1984). Composition and distribution of benthic populations in each lagoon as well as seasonal trends of species richness, density, diversity, and redundancy are presented and discussed.
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems. 相似文献
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems. 相似文献
105.
1 .IntroductionTheBohaiGulfisinfestedbyiceinthewholewinter,andoffshorestructuresthereexperiencenotonlywind ,waves ,currentsandearthquake ,butalsoiceloadswhicharecomplicatedbecauseofthedynamicinteractionbetweenicesheetsandstructures.Duanetal.( 2 0 0 0 )hadacomprehensivere viewofthelatestadvancesonice inducedvibration ,fatigueandfractureofoffshorestructures ,payingmuchattentiontothedifferencesinicebreakingmodeanddynamicsofstructuresindifferentice in festedwaters .Theypresentedcriticallythelates… 相似文献
106.
Many innovative floating offshore structures have been proposed for cost effectiveness of oil and gas exploration and production in water depths exceeding one thousand meters in recent years. One such type of platform is the offshore floating Spar platform. The Spar platform is modelled as a rigid body with six degrees-of-freedom, connected to the sea floor by multi-component catenary mooring lines, which are attached to the Spar platform at the fairleads. The response dependent stiffness matrix consists of two parts (a) the hydrostatics provide restoring force in heave, roll and pitch, (b) the mooring lines provide the restoring force which are represented here by nonlinear horizontal springs. A unidirectional regular wave model is used for computing the incident wave kinematics by Airy’s wave theory and force by Morison’s equation. The response analysis is performed in time domain to solve the dynamic behavior of the moored Spar platform as an integrated system using the iterative incremental Newmark’s Beta approach. Numerical studies are conducted for sea state conditions with and without coupling of degrees-of-freedom. 相似文献
107.
108.
In this paper, a new definition of structure system redundancy is proposed in view of the various measures for structure redundancy. By introducing the terms of structure system failure at the mechanism level and equivalent reliability index, the safety for existing offshore platforms can be evaluated by the semi-probabilistic method presented in this paper. Some numerical examples are given and satisfactory results have been obtained. 相似文献
109.
红树林遥感智能分类方法研究 总被引:13,自引:0,他引:13
利用GIS信息中的红树林地域分布规律作向导,充分利用械树林区的光谱信息进行红树林植被信息提取。在对比研究常规的红树林图象自理方法的基础上,提出了适用于红树林植被信息遥感监测的智能分类方法。 相似文献
110.
本文根据1980—1986年间鱼类生物学参数测定,结合体长分布资料的模拟分析,研究黄、渤海区牙鲆种群年龄结构、死亡动态以及在不同年龄和死亡率条件下世代资源生物量变化的规律。模型分析结果表明,当F=1.0和t_c=6.0a时,单位补充量最大群体产量为1492g。由此认为,现阶段牙鲆资源利用的最佳策略是通过增殖放流,增加资源补充;同时应适当控制捕捞压力,减少渔具对幼鱼资源的破坏并增设繁殖保护区,以追求最大持续产量。 相似文献