全文获取类型
收费全文 | 55799篇 |
免费 | 13147篇 |
国内免费 | 21106篇 |
专业分类
测绘学 | 10083篇 |
大气科学 | 7034篇 |
地球物理 | 10706篇 |
地质学 | 38583篇 |
海洋学 | 10495篇 |
天文学 | 747篇 |
综合类 | 4737篇 |
自然地理 | 7667篇 |
出版年
2024年 | 650篇 |
2023年 | 1721篇 |
2022年 | 3478篇 |
2021年 | 4167篇 |
2020年 | 3405篇 |
2019年 | 3773篇 |
2018年 | 3266篇 |
2017年 | 3152篇 |
2016年 | 3196篇 |
2015年 | 3882篇 |
2014年 | 3584篇 |
2013年 | 4387篇 |
2012年 | 4776篇 |
2011年 | 5053篇 |
2010年 | 4810篇 |
2009年 | 4587篇 |
2008年 | 4365篇 |
2007年 | 4285篇 |
2006年 | 4280篇 |
2005年 | 3710篇 |
2004年 | 3360篇 |
2003年 | 2356篇 |
2002年 | 2209篇 |
2001年 | 1916篇 |
2000年 | 1544篇 |
1999年 | 759篇 |
1998年 | 498篇 |
1997年 | 423篇 |
1996年 | 276篇 |
1995年 | 214篇 |
1994年 | 181篇 |
1993年 | 374篇 |
1992年 | 345篇 |
1991年 | 173篇 |
1990年 | 95篇 |
1989年 | 92篇 |
1988年 | 56篇 |
1987年 | 108篇 |
1986年 | 88篇 |
1985年 | 47篇 |
1984年 | 45篇 |
1983年 | 34篇 |
1982年 | 35篇 |
1981年 | 24篇 |
1979年 | 33篇 |
1978年 | 14篇 |
1977年 | 20篇 |
1957年 | 18篇 |
1954年 | 37篇 |
1937年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Zuo Qihua Yang Zhengji .
Senior Engieer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1996,(3)
- The variation of the amplitude of waves with varying incident angles when waves propagate through a typical approach channel is discussed by a numerical calculation method, the result of which shows that the influence of the channel on wave propagation is obvious. When the wave propagation direction is in coincidence with the channel axis, the wave amplitude ratio will decrease with the increase of propagation distance. When the incident angle is 15 - 30 , there appears an area of larger wave amplitude ratio on the side slope facing the waves, but at the another side, the wave amplitude ratio is generally small, indicating that the channel has a shielding effect. When waves propagate across the channel perpendicularly, the wave amplitude ratio can be calculated with the shallow water coefficient. 相似文献
92.
Xu Shikai Wang Hongchuan Hong Guangwen
Engineer Nanjing Hydraulic Research Institute Nanjing .
Professor Research Institute of Coastal Ocean Engineering Hohai University Nanjing 《中国海洋工程》1996,(4)
To solve problems concerning wave elements and wave propagation, an effective way is the wave energy balance equation, which is widely applied in oceanography and ocean dynamics for its simple computation. The present papaer advances wave energy balance equations considering lateral energy transmission and energy loss as the governing equation for the study of wave refraction-diffraction. For the mathematical model, numerical simulation is made by means of difference method, and the result is verified with two examples. 相似文献
93.
Discussion on Coastal Erosion Near Xizhuang, Penglai, China 总被引:1,自引:0,他引:1
Wu Guiqiu Li Wei Professor First Institute of Oceanography State Oceanic Administration Qingdao Associate Researcher 《中国海洋工程》1994,(2)
-In this work, on the basis of the characteristics of coastal erosion near Xizhuang (Penglai, Shandong, China) and the in-situ measured data and theoretical calculation, the causes of coastal erosion there are obtained: (1) natural erosion, (2) beach sand borrowing, and (3) sand borrowing at the Dengzhou shoal near Xizhuang, which results in the loss of the function of the wave force resistance of the shoal. Since the wave energy is increased, the longshore sediment transport rate is increased. Coastal erosions are more and more serious. A scientific basis to reduced the calamity of coastal erosion in local area is presented. Some experiences are accumulated for studying coastal erosion. 相似文献
94.
Following Bagnold's approach, a relationship between sediment transport and energy dissipation is developed. The major assumption made in the study is that the near bed velocity plays a dominant role in the process of sediment transport. A general relationship between energy dissipation and sediment transport is first proposed. Then the equations for total sediment transport are derived by introducing the appropriate expression of energy dissipation rate under different conditions, such as open channel flows, combination of wave and current, as well as longshore sediment transport. Within the flows investigated, the derived relationships are fairly consistent with the available data over a wide range of conditions. 相似文献
95.
应用多组有理数时滞离散系统的比较原理和频域法,将多组有理数时滞区间系数离散系统化为多组有理数时滞定常离散系统,以判定其时滞无关稳定性,并举例说明了新定理的有效性和实用性。 相似文献
96.
97.
在浅层工程折射地震测量中 ,通常采用相遇观测系统采集数据和相应的解释方法进行解释 ;对于单边观测采集方法由于与其相应的解释方法较少而少被采用。本文提出 1种方法简单、精度可靠、可直接利用同一点相邻 2排列 2次观测的初至折射时间并适合于海洋走航式单边连续观测系统的折射初至资料解释方法。其精度基本与同观测段的采用相遇观测的差异时距方法解释的精度十分接近。该方法即适合于人工解释又适合于计算机自动解释。 相似文献
98.
银川盆地中更新世以来的孢粉记录及古气候研究 总被引:8,自引:1,他引:8
银川盆地中更新世以来的孢粉记录及据此所重建的古气候参数,揭示了该区中更新世以来的古气候演变特征,其演变经过了温湿→凉湿→温和→冷湿→温干→凉较湿→冷湿→温干→凉润→温较干→温干的变化,并与新疆地区,黄土高原以及深海δ^18O曲线进行了对比,结果表明,各地的古环境变化大致同步,该区由于位置靠西,邻近沙漠,最近地质历史时期的区域性干旱特色明显。 相似文献
99.
100.