全文获取类型
收费全文 | 52289篇 |
免费 | 21409篇 |
国内免费 | 47072篇 |
专业分类
测绘学 | 6589篇 |
大气科学 | 23157篇 |
地球物理 | 15539篇 |
地质学 | 44789篇 |
海洋学 | 18562篇 |
天文学 | 1115篇 |
综合类 | 5751篇 |
自然地理 | 5268篇 |
出版年
2024年 | 439篇 |
2023年 | 1009篇 |
2022年 | 1916篇 |
2021年 | 2511篇 |
2020年 | 3179篇 |
2019年 | 6364篇 |
2018年 | 6378篇 |
2017年 | 6068篇 |
2016年 | 6150篇 |
2015年 | 5892篇 |
2014年 | 5322篇 |
2013年 | 6091篇 |
2012年 | 6127篇 |
2011年 | 5893篇 |
2010年 | 5831篇 |
2009年 | 5101篇 |
2008年 | 4471篇 |
2007年 | 4359篇 |
2006年 | 3955篇 |
2005年 | 3519篇 |
2004年 | 3448篇 |
2003年 | 3005篇 |
2002年 | 2797篇 |
2001年 | 2464篇 |
2000年 | 1980篇 |
1999年 | 1765篇 |
1998年 | 1757篇 |
1997年 | 1787篇 |
1996年 | 1382篇 |
1995年 | 1333篇 |
1994年 | 1200篇 |
1993年 | 1164篇 |
1992年 | 987篇 |
1991年 | 750篇 |
1990年 | 718篇 |
1989年 | 585篇 |
1988年 | 505篇 |
1987年 | 397篇 |
1986年 | 316篇 |
1985年 | 251篇 |
1984年 | 287篇 |
1983年 | 175篇 |
1982年 | 206篇 |
1981年 | 148篇 |
1980年 | 110篇 |
1979年 | 123篇 |
1978年 | 52篇 |
1977年 | 42篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
271.
赵泉鸿 《海洋学报(英文版)》1987,6(3):413-420
A total of 91 species belonging to 57 genera were recovered from the coastal areas of the north East China Sea ana the south Yellow Sea, of which, 42 species of 30 genera were collected alive. The biocoenoses of estuaries, supralittoral and eulittoral zones are dominated by orackish and euryhaline species, of which Albileberis sheyangensis, A. sinensis, Leptocythere ventriclivosa, Loxoconcha ocellata, Sinocytheridea latiotata and S. longa are ubiquitous; Propontocypris euryhalina, Spinileberis furuyaensis and S. pulchra are restricted to the supralittoral zone; Neomonoceratina crispata and Pontocythere lit-toralis are only present in the eulittoral zone. The community structure of these biocoenoses is generally marked by low snecies diversity (H(S) and 5) and high incidence and dominance. Among the environmental factors investigated, it was found that salinity was the most important in controlling the distribution of living ostracods, and high-energy hydrodynamic condition was the main cause of the grea 相似文献
272.
A method combining boundary and finite element approaches as well as modal analysis to solve the acoustical scattering from elastic obstacle in infinite fluid is described. An elastic cylinder with finite length immersed in water is chosen as an example for numerical demonstration. The computed frequency response and direction pattern of the backscattering target strength of the cylinder are conformable to those measured. 相似文献
273.
This paper reports the season, environmental conditions and pattern of spawning, fecundity and hatching amount of king crab, Trachypleus tridentatus. The egg-diameter of this animal has seasonal variations, which is different from that reported in foreign countries. The egg cleavage of the animal is in the transitional pattern from holoblastic cleavage to surface division. Egg cleavage occurs firstly on one pole with false cleavage furrows, the number of division nucleus increases continuously which move outward from the yolks to form into a layer of blastomere on the surface of the blast together with some of egg plasma. The blastomere formed into the blastoderm and the polygonal cells encircled in this cell layer is equal to the "yolk cells" of insects during the period of egg cleavage. The formation of the periblas-tula is the result of egg cleavage. This paper makes application of the technique of vital staining in exploring the properties of the stained particles. The death of the blasts after stai 相似文献
274.
饱和潜水技术可大大延长水下作业时间、提高潜水作业效率,是开发海底资源、水下施工、援潜救生、海洋考察和科学研究不可缺少的一种手段.近20年来,取得了较大的进展,人体氦氧饱和潜水模拟实验的深度已达650米,现场饱和潜水为460米,巡潜已达501米. 相似文献
275.
Up to now, available method of numerical forecasting and suitable wind field model for the Bohai Sea storm surge have been few. In this paper, through the analysis of the weather situation is presented a mathematical model for the wind fields involved mainly the deformation field of a high pressure matched with a low pressure, the temperate cyclone, the cold wave and the northword typhoon. Meanwhile, numerical computations combined with the nonlinear storm surge models are made by using "ADI" method. The computed results are generally coincident with the practical observations. It has showed a success in the simulated wind field and the feasibility of using "ADI" method to forecast the Bohai Sea storm surge. 相似文献
276.
277.
278.
Qiu Dahong Zang Jun Jia Ying
Academician of the Chinese Academy of Sciences Professor the State Key Laboratory of Coastal Offshore Engineering 《中国海洋工程》1996,(2)
Based on the 2nd order cnoidal wave theory, the characters of shallow water standing waves and their action on vertical walls are studied in this paper. The theoretical expressions of the wave surface elevation in front of and the wave pressure on the vertical wall are obtained. In order to verify the theoretical results, model tests were made in the State Key Laboratory of Coastal and Offshore Engineering at DUT. For the wave surface elevation in front of the wall and the wave forces on the wall at the moment when the wave surface at the wall surface goes down to the bottom of the wave trough, the calculated results coincide quite well with the experimental results. For the wave forces on the wall at the moment when the wave surface at the wall surface goes up to the top of the wave crest, the theoretical expressions are modified by the experimental results. For the convenience of practical use, calculations are made for the wave conditions which usually occur in enginering practice by use of the inves 相似文献
279.
太湖表面定振波的数值计算和最大熵谱分析 总被引:1,自引:0,他引:1
利用水动力学方程对太湖表面的定振波进行计算,算得定振波周期约为452min,另外,利用1992年8月29-31日在太湖西山观测到的水位资料,采用最大熵谱法,分析太湖表面的定振波,得周期值约为450min。计算和分析的周期值基本吻合,取熵谱分析结果得太湖表面的单节点定振波周期值为450min。 相似文献
280.