全文获取类型
收费全文 | 4864篇 |
免费 | 1006篇 |
国内免费 | 1166篇 |
专业分类
测绘学 | 282篇 |
大气科学 | 1312篇 |
地球物理 | 1532篇 |
地质学 | 1699篇 |
海洋学 | 1031篇 |
天文学 | 153篇 |
综合类 | 437篇 |
自然地理 | 590篇 |
出版年
2024年 | 17篇 |
2023年 | 48篇 |
2022年 | 147篇 |
2021年 | 152篇 |
2020年 | 193篇 |
2019年 | 220篇 |
2018年 | 188篇 |
2017年 | 230篇 |
2016年 | 210篇 |
2015年 | 247篇 |
2014年 | 313篇 |
2013年 | 312篇 |
2012年 | 311篇 |
2011年 | 315篇 |
2010年 | 252篇 |
2009年 | 295篇 |
2008年 | 314篇 |
2007年 | 318篇 |
2006年 | 293篇 |
2005年 | 330篇 |
2004年 | 235篇 |
2003年 | 216篇 |
2002年 | 166篇 |
2001年 | 176篇 |
2000年 | 202篇 |
1999年 | 193篇 |
1998年 | 185篇 |
1997年 | 157篇 |
1996年 | 130篇 |
1995年 | 116篇 |
1994年 | 106篇 |
1993年 | 109篇 |
1992年 | 74篇 |
1991年 | 57篇 |
1990年 | 40篇 |
1989年 | 35篇 |
1988年 | 36篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 11篇 |
1981年 | 3篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1954年 | 2篇 |
排序方式: 共有7036条查询结果,搜索用时 281 毫秒
971.
基于小波变换的SPIHT图像压缩方案是一种实用高性能图象压缩编码算法,但原始SPIHT算法链表式编码限制了其在高速处理中的应用。本文提出了一种改进的SPIHT压缩编码算法,在确保恢复图像质量与原始算法基本相当的基础上,改进算法可以采用并行流水结构实现,有利于高速处理中的应用,可以对高达40×8Mbit/s的原始图像实时压缩和去压缩。 相似文献
972.
973.
974.
通过综合利用ECMWF提供的热带风场、气压场、高度场等资料,对24例影响广西的热带气旋环境流场和一些物理量特征进行了较为深入的分析。结果表明:大多数热带气旋的发生、发展都与赤道西风急流向东扩展或热带气旋东侧南风急流向北扩展有关;造成广西大范围台风暴雨的因素不仅取决于台风登陆地点和登陆后的路径以及中心是否直接进入广西内陆有关,而且还与副热带高压脊线的位置和面积指数、强度指数的变化关系密切。登陆台风在影响广西的过程中,其台风东侧的偏南风急流中心涌进广西和正涡度中心进入广西对产生大范围的暴雨起着重要的作用。 相似文献
975.
在干燥条件下对辉长岩的摩擦本构参数进行了实验研究。结果表明 :1 )辉长岩模拟断层泥的摩擦速度依赖性参数 (a -b)基本为正或者接近于没有速度依赖性 ,表明在干燥条件下不具备不稳定滑动的成核条件 ,对下地壳地震成核的可能性有参考意义 ;2 )摩擦强度在干燥条件下与Byerlee定律高度一致 ,表明在下地壳的高温环境下Byerlee定律仍可给出适当的强度估计 ,至少在干燥条件下如此 ;3)Byerlee定律给出的剪应力强度与正应力的关系中有一个截距 ,但是本研究中关于模拟断层泥的结果却没有明显的截距 ,表明断层物质的有无在摩擦强度的表现上存在重要差异 相似文献
976.
N.J.T. Edberg K. Ågren M.W. Morooka S.W.H. Cowley A.J. Coates M.K. Dougherty 《Planetary and Space Science》2011,59(8):788-797
During the final three of the five consecutive and similar Cassini Titan flybys T55-T59 we observe a region characterized by high plasma densities (electron densities of 1-8 cm−3) in the tail/nightside of Titan. This region is observed progressively farther downtail from pass to pass and is interpreted as a plume of ionospheric plasma escaping Titan, which appears steady in both location and time. The ions in this plasma plume are moving in the direction away from Titan and are a mixture of both light and heavy ions with composition revealing that their origin are in Titan's ionosphere, while the electrons are more isotropically distributed. Magnetic field measurements indicate the presence of a current sheet at the inner edge of this region. We discuss the mechanisms behind this outflow, and suggest that it could be caused by ambipolar diffusion, magnetic moment pumping or dispersive Alfvén waves. 相似文献
977.
As a recent trend, the continuous increase of new technologies for space observations of new missions to Mars, Venus, and Titan, has stimulated vigorous experimental and theoretical studies on the collision process induced by interactions between plasma and planetary atmosphere. In order to facilitate the comprehension of these processes, this brief paper chose a collection of cross section data not always easily accessible. With the purpose of making a useful collection of such data we have collected both experimental and theoretical estimate for most of the expected collisions processes. 相似文献
978.
D. A. Robertson 《新西兰海洋与淡水研究杂志》2013,47(4):611-620
The embryonic wet weight, dry weight, yolk volume, energy content, and oxygen consumption of the southern pigfish Congiopodus leucopaecilus (Richardson, 1846) were followed from fertilisation to yolk sac absorption, at 11.5°c and salinity of 34.5%6. Measurements of yolk energy and catabolic energy changes did not show any evidence of an energy deficit before the onset of feeding capability. 相似文献
979.
Calibration chamber tests were conducted on open‐ended model piles driven into dried siliceous sands with different soil conditions in order to clarify the effect of soil conditions on load transfer mechanism in the soil plug. The model pile used in the test series was devised so that the bearing capacity of an open‐ended pile could be measured as three components: outside shaft resistance, plug resistance, and tip resistance. Under the assumption that the unit shaft resistance due to pile‐soil plug interaction varies linearly near the pile tip, the plug resistance was estimated. The plug capacity, which was defined as the plug resistance at ultimate condition, is mainly dependent on the ambient lateral pressure and relative density. The length of wedged plug that transfers the load decreases with the decrease of relative density, but it is independent of the ambient pressure and penetration depth. Under several assumptions, the value of earth pressure coefficient in the soil plug can be calculated. It gradually reduces with increase in the longitudinal distance from the pile tip. At the bottom of the soil plug, it tends to decrease with increase in the penetration depth and relative density, and to increase with the increase of ambient pressure. This may be attributed to (1) the decrease of friction angle as a result of increase in the effective vertical stress, (2) the difference in the dilation degree of the soil plug during driving with ambient pressures, and (3) the difference in compaction degree of soil plug during driving with relative densities. Based on the test results, an empirical equation was suggested to compute the earth pressure coefficient to be used in the calculation of plug capacity using one‐dimensional analysis, and it produces proper plug capacities for all soil conditions. 相似文献
980.
The time-dependent feature of soft soils has gained intensive attraction in recent years. Due to the high water content and viscous property, the Hong Kong marine deposit (HKMD) frequently poses a challenge to geotechnical practice, particularly to the reclamation in Hong Kong. A key issue related to reclamation design, foundation construction and maintenance is excess settlement/deformation of the ground. Formation of HKMD typically goes through sedimentation and self-weight consolidation. A series of one-dimensional settling column consolidation tests, together with conventional oedometer tests were conducted on the HKMD. By normalizing parameter in settling stage, a unique global relationship of effective stress, σz′ and strain, ?z could be established. Results reveal that the settling curve and settling rate are significantly affected by the sediment concentration in self-weight consolidation. After the primary self-weight consolidation, the settling rate is reduced in the “secondary self-weight consolidation.” 相似文献