全文获取类型
收费全文 | 5490篇 |
免费 | 858篇 |
国内免费 | 626篇 |
专业分类
测绘学 | 966篇 |
大气科学 | 320篇 |
地球物理 | 2007篇 |
地质学 | 2060篇 |
海洋学 | 701篇 |
天文学 | 228篇 |
综合类 | 285篇 |
自然地理 | 407篇 |
出版年
2024年 | 14篇 |
2023年 | 45篇 |
2022年 | 136篇 |
2021年 | 129篇 |
2020年 | 173篇 |
2019年 | 226篇 |
2018年 | 171篇 |
2017年 | 234篇 |
2016年 | 197篇 |
2015年 | 215篇 |
2014年 | 259篇 |
2013年 | 343篇 |
2012年 | 316篇 |
2011年 | 366篇 |
2010年 | 265篇 |
2009年 | 352篇 |
2008年 | 345篇 |
2007年 | 361篇 |
2006年 | 391篇 |
2005年 | 329篇 |
2004年 | 285篇 |
2003年 | 264篇 |
2002年 | 183篇 |
2001年 | 195篇 |
2000年 | 179篇 |
1999年 | 157篇 |
1998年 | 110篇 |
1997年 | 132篇 |
1996年 | 105篇 |
1995年 | 97篇 |
1994年 | 88篇 |
1993年 | 57篇 |
1992年 | 51篇 |
1991年 | 31篇 |
1990年 | 43篇 |
1989年 | 32篇 |
1988年 | 30篇 |
1987年 | 8篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有6974条查询结果,搜索用时 828 毫秒
21.
在基于互联网的应用、信息数字化、多种技术发展较为成熟及适应公众需求的基础上,对矿物数字博物馆的建设做了简要的分析,将矿物按矿物一结晶学分类方案将馆藏矿物进行合理的分类,设计了七大功能结构和相应的子结构,并对矿物所要展示的内容设定了标准.建设矿物数字博物馆旨在利用三维技术、多媒体技术、文字信息等,将矿物从宏观的外形到抽象的晶体形态和微观的晶体结构及其最小单位结构通过网络的形式具体展现给观众.矿物数字博物馆的建设可以为人们认知整个矿物世界搭建一个良好的平台,在科研教学、推动国民科学普及教育、培养创新人才方面发挥重要作用. 相似文献
22.
23.
A three-dimensional fixed offshore platform in deep water modeled by the finite element method is studied in this paper. Analysis of the dynamic response of the MDOF structure is realized taking the non-linearity of the wave drag force and the wave-structure interaction into account. The structural response statistics, which have Gaussian distributions, are used to evaluate the vibration effect of the structure without TMD and with TMD. And an optimal method to design TMD controlling the first mode of the multi-mode structure is proposed. Moreover, the probabilities of occurrence of sea states at the platform site are considered for prediction of the long-term effect of a TMD. Simulation results demonstrate that the long-term effect of a well-designed TMD is good and the practical use is possible due to the good stability of its optimal parameters under different sea states. 相似文献
24.
A Forced System of Two Cylinders with Various Spacings 总被引:3,自引:0,他引:3
The spectrum characteristics and wake structures for a circular cylinder oscillating in a wake are investigated by use of the currently modified virtual boundary method. A forced system of two cylinders with a small spacing ( the downstream one is made to oscillate in the transverse direction) is studied and interesting flow characteristics are observed. A vortex switch and the change of vortex modes (between 2S mode and 2P mode) are observed in the “lock-in“ region. Vortex bands are formed and lost with the increasing excitation frequency. Information concerning saddle points in the flow field is obtained for different excitation frequencies. For a forced system of two cylinders with a large spacing, the upstream cylinder sheds vortexes because there is no downstream cylinder oscillating in the wake. No distinct “lock-in“ response is found for the downstream cylinder. 相似文献
25.
In most design applications such as alignment of the berthing structure and breakwater alignment, it becomes necessary to determine the direction of design wave. There are two different approaches to determine wave direction. One involves the use of first order Fourier coefficients (mean wave direction) while the other uses second order Fourier coefficients (principal wave direction). Both the average wave direction over the entire frequency range (0.03–0.58 Hz) and the direction corresponding to the peak frequency are used in practice. In the present study, comparison is made on wave directions estimated based on first and second order Fourier coefficients using data collected at four locations in the west and east coasts of India. Study shows that at all locations, the mean and principal wave directions for frequencies ranging from 0.07 to 0.25 Hz (±0.5 times peak frequency) co-vary with a correlation coefficient of 0.99 but at lower and higher frequencies, difference between the parameters is large. Average difference between the mean wave direction at peak frequency and the average over the frequency related to spectral energy more than 20% of maximum value is less, around 13°. Study shows that average difference in the sea and swell directions is around 39°. 相似文献
26.
1 .IntroductionTheappraisalofagooddesignforaverylargefloatingstructure(VLFS)thatwillserveinaspeci fiedoceanarearequiresthatthestructuralsystembeeconomicallydesigned ,therequirementsforitsfunctionbesatisfiedandthestructurekeepsstableinitswholeserviceperio… 相似文献
27.
Gao Yinli Yan Shuwang Wang Jinying
Graduate Student Tianjin University Tianjin
Professor Tianjin University Tianjin
Senior Engineer China Offshore Oil Engineering Co. 《中国海洋工程》1995,(1)
This paper introduces a stability design system of submarine pipelines. The system can provide a reasonable design procedure for users with reference to domestic and foreign methods and in the light of home engineering experience. 相似文献
28.
29.
A surface panel method treating a boundary-value problem of the Dirichlet type with the free surface is presented to design a three-dimensional body corresponding to a prescribed pressure distribution. The free surface boundary condition is linearized with respect to the oncoming flow, and computed by four-point finite difference scheme. Sample designs for submerged spheroids and Wigley hull are carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but also by experiment. 相似文献
30.
首次将列率谱分析的方法引入到随机海浪的研究。根据不同环境条件下实验室资料,对列率谱与频率谱进行了比较。结果表明,列率频对频率谱高频部分有明显改善,特别对二倍频含能段的分辨具有明显的优越性。另外,列率谱具有计算速度快、简单易行、分辨率高等优点。 相似文献