全文获取类型
收费全文 | 1059篇 |
免费 | 199篇 |
国内免费 | 283篇 |
专业分类
测绘学 | 41篇 |
大气科学 | 235篇 |
地球物理 | 257篇 |
地质学 | 500篇 |
海洋学 | 145篇 |
天文学 | 77篇 |
综合类 | 124篇 |
自然地理 | 162篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 45篇 |
2021年 | 47篇 |
2020年 | 47篇 |
2019年 | 51篇 |
2018年 | 62篇 |
2017年 | 53篇 |
2016年 | 56篇 |
2015年 | 68篇 |
2014年 | 77篇 |
2013年 | 72篇 |
2012年 | 78篇 |
2011年 | 68篇 |
2010年 | 63篇 |
2009年 | 60篇 |
2008年 | 66篇 |
2007年 | 56篇 |
2006年 | 41篇 |
2005年 | 28篇 |
2004年 | 25篇 |
2003年 | 23篇 |
2002年 | 25篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 33篇 |
1998年 | 35篇 |
1997年 | 45篇 |
1996年 | 29篇 |
1995年 | 36篇 |
1994年 | 38篇 |
1993年 | 29篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1541条查询结果,搜索用时 15 毫秒
11.
The dynamic torsional buckling and post-buckling of elasto-plastic circular cylindrical shell isstudied.By the usage of the Bodner-Partom constitutive relation,the present visco-plastic problem is treat-ed as an orthotropic elastic problem.Based on the nonlinear large deflection shell therory,the governingdynamic buckling equation is solved by the Runge-Kutta method,and the critical buckling stress is deter-mined by the B-R criterion.The present paper is mainly focused on the imperfection sensitivity,the strainrate sensitivity,and the dynamic post-buckling characters for the shell loaded dynamically with a constantshear strain rate.Numerical results show that the critical shear stress and imperfection sensitivity will in-crease with the increase of strain rate.It is found that the elastic buckling stress is more sensitive toimperfection than the visco-plastic buckling.The present research also reveals some dynamic post-bucklingcharacters for the cylindrical shell,and it is shown that the shell will vibra 相似文献
12.
Wang Deyu Zhang Shanyuan
Associate Prof. Depart of Naval Archi. Ocean Engineering Shanghai Jiaotong University Shanghai
Prof. Research Institute of Applied Mechanics Taiyuan University of Technology Taiyuan 《中国海洋工程》1996,(2)
- The shear failure of a rigid-plastic dented clamped tubular beam under the lateral impact of a mass is investigated. Both the denting and the impact point are in the middle span of the beam. It is assumed that denting does not spread during the shear sliding. Numerical results show that the axial force and lateral deflection of the beam are very small at the moment of the occurence of shear failure, which means that the finite deformation effect can be neglected in the shear failure analysis. Also, some aspects of the initial impact energy are investigated. 相似文献
13.
The colony-forming Phaeocystis species are causative agents of dense bloom occurrences in coastal waters worldwide. It is difficult to separate them because of the different morphologies associated with their colonial stages. In this study we applied molecular approaches to analyze the genetic variation of Phaeocystis globosa and Phaeocystis pouchetii from several geographic regions, and to assist in tracing the dispersal of bloom-forming Phaeocystis species in coastal waters of China. The sequences of the internal transcribed spacers (ITS1 and ITS2) of rDNA and the 5.8S ribosomal RNA gene of Phaeocystis strains were determined. Sequence comparison shows that P.globosa was the most divergent to P. pouchetii, exhibiting sequence divergence higher than 0.08. However, lower genetic divergences existed between strains of P.globosa. The sequence comparison of the Phaeocystis rDNA ITS clearly shows that the species isolated from the southeast coast of China is identified as P.globosa rather than P. cf. pouchetii or other species. Furthermore, the significance of rDNA variation in distinct global populations of P.globosa suggested it might have had sufficient time to accumulate detectable mutations at the rDNA locus, supporting the hypothesis of ancient dispersal of P.globosa to many areas, meaning that P.globosa blooms in the coastal waters of China are endemic rather than a newly introduced species or a foreign source. Finally, based on the high divergent region of rDNA ITS, a pair of species-specific primers for P.globosa were designed, they could be useful to detect the presence of this species in mixed plankton assemblages or flagellate stages that are recognized with diffculties by means of conventional microscopy. 相似文献
14.
15.
16.
I~IOXSea fog is a kind of dangerous weather. Chinese sea fog experts, Wang Binhua (1983),Hu Ruijin and Zhou Faxiu (1998) and Hu Jifu et al. (1996) studied sea fog rather Systematically. FOreign Experts also Paid great attention to sea fog. Ernlnons and Montgomery(1974), chipper (1994) and Rayrnond et al. (1989) have studied sea fog thorOUghly.HOwever, studies on Arctic sea ice have rarely been carried Out becauSe of the sever environment and less htnnan activity in the region. There … 相似文献
17.
18.
19.
Molecular identification of bloom-forming species Phaeocystis globosa(Prymnesiophyta)and its dispersal based on rDNA ITS sequence analysis 总被引:3,自引:1,他引:3
Abstract-The colony-forming Phaeocystis species are causative agents of dense bloom occurrences incoastal waters worldwide. It is difficult to separate them because of the different morphologies associatedwith their colonial stages. In this study we applied molecular approaches to analyze the genetic variationof Phaeocystis globosa and Phaeocystis pouchetii from several geogrtaphic regions, and to assist in tracingthe dispersal of bloom-forming Phaeocystis species in coastal waters of China. The Sequences of the inter-nal transcribed sacers (ITS1 and ITS2) of rDNA and the 5.8S ribosomal RNA gene of Phaeocystisstrains were determined. Sequence comparison shows that P.globosa was the most divergent toP. pouchetii, exhibiting sequence divergence higher than 0.08. However, lower genetic divergences ex-isted between strains of P.globosa. The sequence comparison of the Phaeocystis rDNA ITS clearlyshows that the species isolated from the southeast coast of China is identified as P. globosa rather thanP. cf. po 相似文献
20.