全文获取类型
收费全文 | 6275篇 |
免费 | 1703篇 |
国内免费 | 1538篇 |
专业分类
测绘学 | 81篇 |
大气科学 | 998篇 |
地球物理 | 3087篇 |
地质学 | 1733篇 |
海洋学 | 2829篇 |
天文学 | 75篇 |
综合类 | 318篇 |
自然地理 | 395篇 |
出版年
2024年 | 28篇 |
2023年 | 86篇 |
2022年 | 160篇 |
2021年 | 216篇 |
2020年 | 249篇 |
2019年 | 371篇 |
2018年 | 267篇 |
2017年 | 254篇 |
2016年 | 254篇 |
2015年 | 330篇 |
2014年 | 339篇 |
2013年 | 358篇 |
2012年 | 397篇 |
2011年 | 408篇 |
2010年 | 319篇 |
2009年 | 404篇 |
2008年 | 379篇 |
2007年 | 525篇 |
2006年 | 432篇 |
2005年 | 388篇 |
2004年 | 398篇 |
2003年 | 341篇 |
2002年 | 307篇 |
2001年 | 259篇 |
2000年 | 259篇 |
1999年 | 244篇 |
1998年 | 246篇 |
1997年 | 197篇 |
1996年 | 208篇 |
1995年 | 197篇 |
1994年 | 165篇 |
1993年 | 134篇 |
1992年 | 105篇 |
1991年 | 93篇 |
1990年 | 47篇 |
1989年 | 42篇 |
1988年 | 38篇 |
1987年 | 21篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1954年 | 10篇 |
排序方式: 共有9516条查询结果,搜索用时 234 毫秒
91.
Starting from the widespread phenomena of porous bottoms in the near shore region, considering fully the diversity of bottom topography and wave number variation, and including the effect of evanescent modes, a general linear wave theory for water waves propagating over uneven porous bottoms in the near shore region is established by use of Green‘s scond identity. This theory can be reduced to a number of the most typical mild-slope equations curreutly in use and provide a reliable research basis for follow-up development of nonlinear water wave theory involving porous bottoms. 相似文献
92.
Based on Hong‘s theory, previous random models, and a generalized expression suitable for FIT calculation, the interaction between irregular waves and vertical walls is numerically simulated. The results of simulation demonstrate that the wave energy changes with the incidence angle and the distance from the wall. Particularly, the Mach effect and the combined wave spectrum characteristics are analyzed in detail, which are significant in both theory and practice. 相似文献
93.
More and more researches show that neither the critical downward acceleration nor the critical slope of water waves is a universal constant. On the contrary, they vary with particular wave conditions. This fact moders the models either for the probability of wave breaking B or for the whitecap coverage W based on these criteria difficult to apply. In this paper and the one which follows we seek to develop models for the prediction of both B and W based on the kinematical criterion. First, several joint probabihstic distribution functions (PDFs) of wave characteristics are derived, based on which the breaking properties B and W are estimated. The estimation is made on the assumption that a wave breaks ff the horizontal velocity of water particles at its crest exceeds the local wave celerity, and whitecapping occurs in regions of fluid where water particles travel faster than the waves. The consequent B and W depend on wave spectral moments of orders 0 to 4.Then the JONSWAP spectrum is used to represent the fetch-limited sea waves in deep water, so as to relate the probahility of wave breaking and the whitecap coverage with wind parameters. To this end, the time-averaging technique proposed by Glazman (1986) is applied to the estimation of the spectral moments involved, and furthermore, the theoretical models are compared with available observations collected from published literature. From the comparison, the averaging time scale is determined. The final models show that the probability of wave breaking as well as the whitecap coverage depends on the dimensionless fetch. The agreement between these models and the database is reasonable. 相似文献
94.
95.
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
96.
根据香港附近海区1985,1986年两次台风大浪的实测资料,以有效波高为相应水平,对波群作统计分析,得出可供海洋工程参考的波群连长、波群重复长度、波群出现频率以及波群中最大波高与有效波高的关系等。并将统计值与理论值作比较,结果表明:统计值大于“连”的理论值,而与包线理论中采用合田修正公式的汁算值相近。 相似文献
97.
波浪波形的非接触测量近年来获得广泛的应用。本文以规则波为讨论对象,针对介质为空气的超声波测量方式进行波形测量误差分析,并结合实验室和实船试验进行对比分析。理论分析表明:在规则波取为坦谷波和STOKES波的前提下,超声波技术几乎产生相同的最大误差。定量分析表明,在对测量精度限制的条件下,对文中提及的各项参数应作有效的控制 相似文献
98.
Liu Shuxue Yu Yuxiu
Assistant Researcher State Key Laboratory of Coastal Offshore Engineering Dalian University of Technology 《中国海洋工程》1995,(1)
The directional spectrum is one of the basic characteristics of sea waves. The observations of directional spectrum of sea waves were successfully conducted at platform Bohai 8 during 1991 and 1992 using a wave gage array for the first time in China. Based on the field data, the directional spectrum which depends on the wave growth is given in this paper. Before observations, the effects of the type of gage array, the distance between the gages and the platform itself on the measured results and the precision of some methods for estimating the directional spectrum were investigated and compared with the methods of numerical simulations and model tests of multi-direcitonal irregular waves. This ensures the quality of the observations and estimations of the directional spectrum. 相似文献
99.