全文获取类型
收费全文 | 36762篇 |
免费 | 18760篇 |
国内免费 | 43179篇 |
专业分类
测绘学 | 2850篇 |
大气科学 | 21903篇 |
地球物理 | 13052篇 |
地质学 | 36367篇 |
海洋学 | 16137篇 |
天文学 | 1020篇 |
综合类 | 4726篇 |
自然地理 | 2646篇 |
出版年
2024年 | 148篇 |
2023年 | 314篇 |
2022年 | 671篇 |
2021年 | 974篇 |
2020年 | 2058篇 |
2019年 | 5540篇 |
2018年 | 5834篇 |
2017年 | 5519篇 |
2016年 | 5586篇 |
2015年 | 4898篇 |
2014年 | 4425篇 |
2013年 | 4947篇 |
2012年 | 4677篇 |
2011年 | 4491篇 |
2010年 | 4436篇 |
2009年 | 3738篇 |
2008年 | 2981篇 |
2007年 | 3013篇 |
2006年 | 2641篇 |
2005年 | 2505篇 |
2004年 | 2780篇 |
2003年 | 2532篇 |
2002年 | 2284篇 |
2001年 | 2079篇 |
2000年 | 1753篇 |
1999年 | 1882篇 |
1998年 | 1879篇 |
1997年 | 1969篇 |
1996年 | 1553篇 |
1995年 | 1511篇 |
1994年 | 1330篇 |
1993年 | 1311篇 |
1992年 | 1078篇 |
1991年 | 829篇 |
1990年 | 759篇 |
1989年 | 636篇 |
1988年 | 546篇 |
1987年 | 410篇 |
1986年 | 339篇 |
1985年 | 258篇 |
1984年 | 286篇 |
1983年 | 176篇 |
1982年 | 210篇 |
1981年 | 148篇 |
1980年 | 114篇 |
1979年 | 108篇 |
1978年 | 48篇 |
1977年 | 44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 234 毫秒
261.
262.
263.
264.
-Nonlinear tidal waves in a kind of estuary are studied in the paper using one-dimensional nonlinear hydrody-namic equations with friction. The estuary has exponentially varying width B=B0 e-bx and uniform depth h. The one-dimensional hydrodynamic equations are solved by perturbation method. It was found that our solution included two special cases, Pelisenpeki's solution and Airy's solution. The former can be got by letting b=0 in our solutions, and the latter by setting 6 = 0 and f= 0 (f is linear frictional coefficient). In terms of the second-order solution, the physical mechanism of nonlinear tidal waves in estuaries with gradually varying cross-section is explored. It is shown that, under the assumption of linear friction coefficient, shallow water constituent waves consist of two parts, one is produced by shallow water nonlinear effect outside the estuary, the other is generated by shallow water nonlinear effect inside estuary. In addition, the physical mechanism of the residual tidal current and 相似文献
265.
Tang Yuxiang 《海洋学报(英文版)》1990,9(4):487-498
A simple three-dimensional tidal model is used to examine the M2 tidal current distribution in a northeastern part of the East China Sea, especially the vertical variation of the current in the region. Computed M2 current is compared with observations available and found to be in good agreement.Main features of the calculating method in this study are: (1) Vertical variation of the tidal current is taken as a funetion of the depth-mean velocity: (2) the method is applicable to a variety of the vertical eddy viscosities; (3) it has a fine vertical resolution, especially near the sea bootom. So, this method not only enables us to get a steady state solution easily but also depicts effects of the friction on the vertical variation of the current much better. 相似文献
266.
本文介绍了LZY_(1-1)型光电浊度仪的设计原理,标定方法及使用结果,该仪器用经典法校准后,能快速测量大批量样品的悬浮物含量。 相似文献
267.
You Yuming Hou Min Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Assistant Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1992,(3)
- The data of landsat TM of multi-temporal for Lingdingyang Estuary, Pearl River in China is firstly used with suspended sediment concentration of field measurement to establish a correlative model equation. After the ratio processing of TM data and atmospheric correction, the images of suspended sediment concentration of different temporals are exported from the image processing systems AREIS II and III. These images express the characteristics of suspended sediment distribution, the mode of sediment transport and the extent of dispersion under the actions of tidal current and wind condition of different seasons. 相似文献
268.
269.
270.