全文获取类型
收费全文 | 3549篇 |
免费 | 536篇 |
国内免费 | 368篇 |
专业分类
测绘学 | 829篇 |
大气科学 | 211篇 |
地球物理 | 1158篇 |
地质学 | 1292篇 |
海洋学 | 469篇 |
天文学 | 44篇 |
综合类 | 225篇 |
自然地理 | 225篇 |
出版年
2024年 | 6篇 |
2023年 | 23篇 |
2022年 | 71篇 |
2021年 | 91篇 |
2020年 | 113篇 |
2019年 | 147篇 |
2018年 | 106篇 |
2017年 | 164篇 |
2016年 | 130篇 |
2015年 | 135篇 |
2014年 | 179篇 |
2013年 | 235篇 |
2012年 | 231篇 |
2011年 | 257篇 |
2010年 | 177篇 |
2009年 | 242篇 |
2008年 | 244篇 |
2007年 | 248篇 |
2006年 | 249篇 |
2005年 | 196篇 |
2004年 | 178篇 |
2003年 | 170篇 |
2002年 | 114篇 |
2001年 | 108篇 |
2000年 | 112篇 |
1999年 | 93篇 |
1998年 | 66篇 |
1997年 | 69篇 |
1996年 | 59篇 |
1995年 | 43篇 |
1994年 | 45篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 13篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有4453条查询结果,搜索用时 31 毫秒
991.
为了提高空间CCD相机中数字视频图像信息的传输带宽,增强图像传输抗电磁干扰能力并提高光纤链路的整体性能,开发了应用于大视场空间相机的数字视频图像信息高可靠光纤传输系统。首先,根据CCD成像单元特点和相机在轨工作环境得出了传输系统的输入速率,在此基础上并结合CCD视频处理结构设计并实现了9通道CCD图像数据光纤并行传输系统。然后,阐述了系统设计思想,并说明了高速串化器和光模块的设计理念。接着,提出了(16,8)纠错编码算法,阐述了该算法思想和实现电路。最后,在XX-X空间多光谱相机样机的传输系统上进行了试验验证。实验结果表明:该传输系统图像传输正确、工作稳定、可靠性高、实时强、无误码,单路有效数据率达到2.44Gbit/s。(16,8)纠错编码算法纠错能力强、易于硬件实现、占用资源少。纠错算法在3043Byte内可以纠正191bit错误。该传输系统满足了空间相机图像传输的要求。 相似文献
992.
三维实体模型是虚拟战场环境建立与应用的重要组成部分。本文重点研究了三维实体模型设计思路和制作技术方法,并以三维武器(飞机)模型作为实例进行了具体实践,阐述了基于3D-MAX设计武器模型的思路及实现过程、模型制作、模型渲染的技术方法。 相似文献
993.
《The Journal of geography》2012,111(4):154-165
Abstract Conventional geographical approaches to the city tend to place the study of urban form and urban space squarely within the political-economic and cultural branches of geography. Geographic pedagogy has tended to assume, therefore, that nature is absent from the city or exists only as a backdrop or stage on which urban economic and cultural activities take place. In contrast, there has been a recent groundswell of interest—originating in places as diverse as environmental activism, environmental history, landscape architecture, and environmental education—in reinterpreting the city as a space intimately connected with nature. This article examines the possibilities for integrating this rethinking of the relationship between city and nature into undergraduate education. Specifically, it outlines the rationale, objectives, and design of a course on urban ecology and examines the benefits and challenges of doing urban ecology as part of geographic education. 相似文献
994.
995.
996.
作者阐述了聚甲醛污水的水质特点,提出了聚甲醛污水工程的设计要点,介绍了两个聚甲醛污水工程实例,并对已实施的工程进行了总结。 相似文献
997.
998.
999.
Zenon Nieckarz Andrzej Kuak Stanisaw Ziba Marek Kubicki Stanisaw Michnowski Piotr Baraski 《Atmospheric Research》2009,91(2-4):184-187
This work presents the results of a comparison between the global storm activity rate IRS and electric field intensity E0Z. The permanent analysis of the IRS may become an important tool for testing Global Electric Circuit models. IRS is determined by a new method that uses the background component of the first 7 Schumann resonances (SR). The rate calculations are based on ELF observations carried out in 2005 and 2006 in the observatory station “Hylaty” of the Jagiellonian University in the Eastern Carpathians (Kułak, A., Zięba, S., Micek, S., Nieckarz, Z., 2003. Solar variations in extremely low frequency propagation parameters: I. A two-dimensional telegraph equation (TDTE) model of ELF propagation and fundamental parameters of Schumann resonances, J. Geophys. Res., 108, 1270, doi:10.1029/2002JA009304). Diurnal runs of the IRS rate were compared with diurnal runs of E0Z amplitudes registered at the Earth's surface in the Geophysical Observatory of the Polish Academy of Sciences in Świder (Kubicki, M., 2005. Results of Atmospheric Electricity and Meteorological Observations, S. Kalinowski Geophysical Observatory at Świder 2004, Pub. Inst. Geophysics Polish Academy of Sciences, D-68 (383), Warszawa.). The days with the highest values of the correlation coefficient (R) between amplitudes of both observed parameters characterizing atmosphere electric activity are shown. The seasonal changes of R, IRS and E0Z are also presented. 相似文献
1000.
Stanislav S. Davydenko Thomas C. Marshall Maribeth Stolzenburg 《Atmospheric Research》2009,91(2-4):165-177
This study examines the electricity in two thunderstorms, typical for their respective locales (the Great Plains and the New Mexico mountains), by modeling them as a set of steady-state horizontal layers of external currents. The model electric sources, corresponding to the charge separation processes in the thundercloud, are embedded in an exponential conducting atmosphere. The source parameters are determined by fitting the model electric field to measured profiles. The resulting currents to the ionosphere (i.e., the Wilson current) from the two storms are 0.53 A and 0.16 A, while the calculated electrical energies of the storms are 2.3 × 1010 J and 2.8 × 109 J, respectively. The more vigorous storm is estimated to transfer 16 000 C in the global circuit during 8.5 h of its lifetime, while the weaker mountain storm transferred about 1200 C in its entire 2-h lifetime. Removal of the screening charge layer from above the updraft region in one modeled storm leads to only a small increase in the net Wilson current of less than 3%, while it provides a substantial local disturbance of the electric field. Overall, the model findings indicate that differences in the Wilson currents and electrical energies of the two storms result from differences in their internal dynamical and electrical structures as well as their geographical locations. 相似文献