全文获取类型
收费全文 | 64809篇 |
免费 | 24634篇 |
国内免费 | 50429篇 |
专业分类
测绘学 | 9195篇 |
大气科学 | 24338篇 |
地球物理 | 17534篇 |
地质学 | 52342篇 |
海洋学 | 20832篇 |
天文学 | 1108篇 |
综合类 | 6825篇 |
自然地理 | 7698篇 |
出版年
2024年 | 460篇 |
2023年 | 1080篇 |
2022年 | 2610篇 |
2021年 | 3337篇 |
2020年 | 3757篇 |
2019年 | 6995篇 |
2018年 | 6798篇 |
2017年 | 6319篇 |
2016年 | 6411篇 |
2015年 | 6480篇 |
2014年 | 5899篇 |
2013年 | 7038篇 |
2012年 | 7145篇 |
2011年 | 7183篇 |
2010年 | 7119篇 |
2009年 | 6353篇 |
2008年 | 5824篇 |
2007年 | 5664篇 |
2006年 | 5396篇 |
2005年 | 4663篇 |
2004年 | 4185篇 |
2003年 | 3583篇 |
2002年 | 3308篇 |
2001年 | 3011篇 |
2000年 | 2495篇 |
1999年 | 1975篇 |
1998年 | 1748篇 |
1997年 | 1812篇 |
1996年 | 1400篇 |
1995年 | 1311篇 |
1994年 | 1181篇 |
1993年 | 1156篇 |
1992年 | 1008篇 |
1991年 | 738篇 |
1990年 | 721篇 |
1989年 | 580篇 |
1988年 | 492篇 |
1987年 | 394篇 |
1986年 | 316篇 |
1985年 | 255篇 |
1984年 | 281篇 |
1983年 | 167篇 |
1982年 | 208篇 |
1981年 | 146篇 |
1980年 | 109篇 |
1979年 | 126篇 |
1978年 | 52篇 |
1977年 | 45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 837 毫秒
591.
Analysis of Dynamic Characteristics of Submarine Free Spanning Pipelines by Complex Damping Method 总被引:2,自引:0,他引:2
Considering the effect of the internal flowing fluid and the external marine environmental condition, the differential equation for the vortex-induced vibration (V1V) of the free spanning pipeline is derived and is discretized by the Hermit interpolation function. The free vibration equation with the damping term is solved by the complex damping method for the natural frequency, and then the effect of fluid damping on the natural frequency of the free spanning pipeline is analyzed.The results show that fluid damping has a significant influence on the damped natural frequency of the free spanning pipeline in the lock-in state, while it has little influence when the pipeline is out of the lock-in state. In the meantime,the change of the free span length has the same effect on the damped natural frequency and the undamped natural frequency. 相似文献
592.
An optimization mathematical model of the pile forces for piled breasting dolphins in the open sea under various loading conditions is presented. The optimum layout with the well distributed pile forces and the least number of piles is achieved by the multiplier penalty function method. Several engineering cases have been calculated and compared with the result of the conventional design method. It is shown that the number of piles can be reduced at least by 10%—20% and the piles‘ bearing state is improved greatly. 相似文献
593.
594.
595.
Semidiurnal and diurnal tidal waves in the Taiwan Strait are computed simultaneously by using finite difference method with two-dimensional nonlinear hydrodynamic equations. The agreement between the computed and observed results is considered satisfactory. 相似文献
596.
Two new species (Nitzschia sinensis Liu, sp. nov. and Podosira granulata Liu, sp. nov.) and one new variety (Xanthiopyxis microspinosa var. ellipticus Liu, var. nov.) collected from the urface sediments off the southern Huanghai Sea and the East China Sea are described and a list of diatoms from the surface sediments in the survey area and some new records in China are attached. 相似文献
597.
In 1979, we found many small colorless transparent and light yellow-green glassy spherules in the surface layer and core sediment samples taken from the west of the Central Pacific Occan, which are considered to be microtektites. This finding is worthy of further determination of the range of strewn field and origin of tektites. 相似文献
598.
Zhang Changkuan Wang Zhen Zhang Dongsheng
Associate Professor Dept. of Navigation Ocean Engineering Hohai University Nanjing
Lecturer Dept. of Navigation Ocean Engineering Hohai University Nanjing
Professor Dept. of Navigation Ocean Engineering Hohai University Nanjing 《中国海洋工程》1995,(2)
A numerical model of shoreline change of sand beaches based on long-term field wave data is proposed, the explicit and implicit finite difference forms of the model are described, and an application of the model is presented. Results of the application indicate that the model is sensitive to the order of the input wave data, and that the effects of long-term wave series and the effects of the mean annual wave conditions on the model are different. Instead of a single wave condition, the wave series will make the calibration and the verification of the model more practical and the results of the model more reasonable. 相似文献
599.
呼伦湖的近期扩张及其与全球气候变化的关系 总被引:10,自引:0,他引:10
通过近20多年湖泊水量平衡分析发现,湖泊水位变化主要由湖盆内径流补给量的丰枯决定。进一步分析揭示,呼伦湖地区乃至整个东北地区,本世纪以来随气温升高,随水有增加的趋势。降水增加导致入湖径流量,湖水位上升,呼伦湖本世纪以来的扩张与内蒙古东部地区其他内陆湖泊的变化一致,但这在我国乃至整个亚洲内陆干旱或半干旱区是独一无二的,为此成为这一地区气候变化的指示器。 相似文献
600.
渤海及黄海北部处在中纬度地带,每年冬季都有不同程度的结冰现象。以辽东湾结冰时间最长,全部结冰日数平均为100多天,约占全年的三分之一。从全海区看,建国后冰情较重的有1957、1968、1969、1977年的1、2月份,尤其是1969年,渤海海面发生了该海区历史上罕见的冰封,整个海面几乎全部被海冰所覆盖,严重阻碍了海上的航运交通及海上石油开采工作,从而给国民经济带来很大损失。 相似文献