全文获取类型
收费全文 | 5800篇 |
免费 | 1285篇 |
国内免费 | 1345篇 |
专业分类
测绘学 | 325篇 |
大气科学 | 1312篇 |
地球物理 | 1898篇 |
地质学 | 2155篇 |
海洋学 | 1765篇 |
天文学 | 234篇 |
综合类 | 383篇 |
自然地理 | 358篇 |
出版年
2024年 | 22篇 |
2023年 | 81篇 |
2022年 | 187篇 |
2021年 | 209篇 |
2020年 | 247篇 |
2019年 | 261篇 |
2018年 | 249篇 |
2017年 | 271篇 |
2016年 | 269篇 |
2015年 | 307篇 |
2014年 | 370篇 |
2013年 | 417篇 |
2012年 | 406篇 |
2011年 | 411篇 |
2010年 | 340篇 |
2009年 | 382篇 |
2008年 | 351篇 |
2007年 | 420篇 |
2006年 | 354篇 |
2005年 | 336篇 |
2004年 | 292篇 |
2003年 | 263篇 |
2002年 | 262篇 |
2001年 | 207篇 |
2000年 | 194篇 |
1999年 | 201篇 |
1998年 | 190篇 |
1997年 | 159篇 |
1996年 | 132篇 |
1995年 | 105篇 |
1994年 | 124篇 |
1993年 | 118篇 |
1992年 | 69篇 |
1991年 | 53篇 |
1990年 | 31篇 |
1989年 | 34篇 |
1988年 | 30篇 |
1987年 | 21篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1972年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有8430条查询结果,搜索用时 15 毫秒
131.
132.
Ryoko Tokeshi Kaoru Ichikawa Satoshi Fujii Kenji Sato Shoichiro Kojima 《Journal of Oceanography》2007,63(4):711-720
A method to extract geostrophic current in the daily mean HF radar data in the Kuroshio upstream region is established by
comparison with geostrophic velocity determined from the along-track altimetry data. The estimated Ekman current in the HF
velocity is 1.2% (1.5%) and 48° (38°)-clockwise rotated with respect to the daily mean wind in (outside) the Kuroshio. Furthermore,
additional temporal smoothing is found necessary to remove residual ageostrophic currents such as the inertial oscillation.
After removal of the ageostrophic components, the HF geostrophic velocity agrees well with that from the altimetry data with
rms difference 0.14 (0.12) m/s in (outside) the Kuroshio. 相似文献
133.
This study extends the investigations of the forces on a cylinder, laid on, or partly buried in the bed with a parallel twin dummy cylinder nearby and without it, and were determined by measuring the pressure distribution on the cylinder in the case of a steady current. The pressure distribution around the cylinder was measured by using pressure transducers. The forces on the cylinder were calculated by the integration of the measured pressures on the surface of the cylinder. Force coefficients were obtained for the ranges of Re=0.8×104–1.5×104 for the burial depth to diameter RATIO=0:0.7. The distance between axis of the measurement and dummy cylinders to diameter ratio (x/D) was 2, 1.5 and 1. The dummy cylinder was replaced downstream and upstream of the measurement cylinder. 相似文献
134.
借用河流水力学顺直河道中有两个次生横向环流的假说来解释潮流沙脊的成因,水槽实验和实际观察也支持了这一观点.正是这一次生的纵轴横向环流(即螺旋流)将泥沙从沟槽带向脊顶,建造了大致与潮流方向平行的潮流沙脊.根据底质粒度成份和分布特点.可分为粗底质沙脊和细底质沙脊两类.前者组成物质偏粗,底质分布为脊细槽粗,后者组成物质偏细,底质分布为脊粗槽细.这是因为影响颗粒起动流速的主导因素不同,前者以重力为主,后者以颗粒间粘结力为主.它们都反映沟槽中流速大于脊顶处流速. 相似文献
135.
136.
137.
138.
More than 40 national and regional geochemical mapping projects in the world carried out from 1973 to 1988 do not conform to common standards. In particular they have many analytical deficiencies. In the period 1988 to 1992, the International Geochemical Mapping project (Project 259 of UNESCO's IGCP Program) prepared recommendations designed to standardize geochemical mapping methods. The analytical requirements are an essential component of the overall recommendations. They included the following: 71 elements should be analyzed in future mapping projects; the detection limits of trace and ultratrace elements must be lower than the corresponding crustal abundances; and the Chinese GSD and Canadian STSD standard sample series should be used for the correlation of global data. A proposal was also made to collect 5000 composite samples, at very low sampling densities to cover the whole Earth's land surface. In 1997 an IUGS Working Group on Global Geochemical Baselines was formed to continue the work which began with IGCP 259. From 1997 up to now, new progress has been made especially in China and FOREGS countries under the aegis of this working group, including the study of suitable sampling media, development of a multi-element analytical system, new proficiency test for selection of competent laboratories and role of wide-spaced mapping in mineral exploration. One of the major problems awaiting solution has been the inability of many laboratories to meet the IGCP recommendations to generate high quality geochemical maps. Fortunately several laboratories in China and Europe have demonstrated an ability to meet the requirements and they will be well placed to render technical assistance to other countries. 相似文献
139.
140.