全文获取类型
收费全文 | 12117篇 |
免费 | 2625篇 |
国内免费 | 4319篇 |
专业分类
测绘学 | 788篇 |
大气科学 | 1028篇 |
地球物理 | 3428篇 |
地质学 | 10757篇 |
海洋学 | 1034篇 |
天文学 | 486篇 |
综合类 | 862篇 |
自然地理 | 678篇 |
出版年
2024年 | 100篇 |
2023年 | 256篇 |
2022年 | 458篇 |
2021年 | 555篇 |
2020年 | 545篇 |
2019年 | 670篇 |
2018年 | 542篇 |
2017年 | 606篇 |
2016年 | 647篇 |
2015年 | 715篇 |
2014年 | 833篇 |
2013年 | 821篇 |
2012年 | 903篇 |
2011年 | 879篇 |
2010年 | 670篇 |
2009年 | 792篇 |
2008年 | 691篇 |
2007年 | 877篇 |
2006年 | 849篇 |
2005年 | 706篇 |
2004年 | 661篇 |
2003年 | 608篇 |
2002年 | 508篇 |
2001年 | 494篇 |
2000年 | 491篇 |
1999年 | 446篇 |
1998年 | 461篇 |
1997年 | 432篇 |
1996年 | 348篇 |
1995年 | 268篇 |
1994年 | 253篇 |
1993年 | 221篇 |
1992年 | 176篇 |
1991年 | 121篇 |
1990年 | 112篇 |
1989年 | 97篇 |
1988年 | 76篇 |
1987年 | 49篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1982年 | 6篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
利用THEMIS THC卫星观测数据统计分析近地等离子体片中磁场扰动和等离子体整体流的速度扰动的关系,研究Alfven波动的活动性.研究结果表明:1)等离子体整体流的速度扰动幅度依赖于平均速度的大小,速度扰动幅度随平均速度的增加而增加;2)速度扰动幅度与磁场扰动幅度存在较强的正相关性;3)磁场扰动幅度与AE指数密切相关,磁场扰动幅度随着AE指数增加而增加,而速度扰动幅度与AE指数之间没有明显的相关性;4)Alfven比与AE指数的相关系数较小,但能够看出Alfven比随着AE指数增加而减小的趋势;5)速度扰动幅度和磁场扰动幅度与尾向距离及距中性片距离的关系不明显. 相似文献
992.
采用三维有限元方法分析了基坑开挖工程在防渗体出现局部失效情况下,引起渗流在失效部位的集中及渗流场空间状况。提出了以一维通道嵌入三维块体的方法模拟管涌发展过程及渗流场变化特征。讨论了管涌通道渗透性对基坑管涌发展规律的影响。 相似文献
993.
994.
995.
This paper provides data on variations in the contents of As, Sb, Ni, V, Pb, Cu, Cr, Au, Zn, Sc, and Al, measured in the thalli of a saxicolous lichen species,Xanthoria calcicola Ochsner s.l., collected in northeastern Sicily, near an industrial zone and along a belt crossing areas of known ores containing sulfides of heavy metals. A total of 91 lichen samples were collected on roof tiles (39) and on rocks (52). In the industrial zone, analysis of lichen thalli revealed high contents of nickel and vanadium, decreasing at increasing distances from the source of contamination. The results have also revealed the versatility ofXanthoria calcicola in geochemical prospecting for heavy metals such as Pb, Zn, As, Au, Sb, Ni, V, and Cu. The contents of these elements in the analyzed lichens highlight the same geochemical associations observed in prospecting surveys on samples of river sediments and identify similar anomalies. Interpretation of data in terms of enrichment factors (EFs) turned out to be particularly useful. 相似文献
996.
997.
Benjamin K. Norris Julia C. Mullarney Karin R. Bryan Stephen M. Henderson 《地球表面变化过程与地形》2021,46(3):573-592
Within a wave-exposed mangrove forest, novel field observations are presented, comparing millimeter-scale turbulent water velocity fluctuations with contemporaneous subtidal bed elevation changes. High-resolution velocity and bed level measurements were collected from the unvegetated mudflat, at the mangrove forest fringe, and within the forest interior over multiple tidal cycles (flood–ebb) during a 2-week period. Measurements demonstrated that the spatial variability in vegetation density is a control on sediment transport at sub-meter scales. Scour around single and dense clusters of pneumatophores was predicted by a standard hydraulic engineering equation for wave-induced scour around regular cylinders, when the cylinder diameter in the equations was replaced with the representative diameter of the dense pneumatophore clusters. Waves were dissipated as they propagated into the forest, but dissipation at infragravity periods (> 30 s) was observed to be less than dissipation at shorter periods (< 30 s), consistent with the predictions of a simple model. Cross-wavelet analysis revealed that infragravity-frequency fluctuations in the bed level were occasionally coherent with velocity, possibly indicating scour upstream of dense pneumatophore patches when infragravity waves reinforced tidal currents. Consequently, infragravity waves were a likely driver of sediment transport within the mangrove forest. Near-bed turbulent kinetic energy, estimated from the turbulent dissipation rate, was also correlated with bed level changes. Specifically, within the mangrove forest and over the unvegetated mudflat, high-energy events were associated with erosion or near-zero bed level change, whereas low-energy events were associated with accretion. In contrast, no single relationship between bed level changes and mean current velocity was applicable across both vegetated and unvegetated regions. These observations support the theory that sediment mobilization scales with turbulent energy, rather than mean velocity, a distinction that becomes important when vegetation controls the development of turbulence. 相似文献
998.
IntroductionThe history of studying the changes in deep geoelectric conductivity of an earthquake preparation using the parameters of geomagnetic short-period variations has been about 30 years. At first, Japanese calculated the real transfer functions as well as the a and b coefficients of Parkinson vector by taking the measurement of graph and using empirical formula. There are some examples, such as the 1923 Kanto M=7.9 earthquake (Yanagihara, 1972), the 1966 Tashkent M=5.5 earthquake, t… 相似文献
999.
1000.
分析1980-1987年欧洲中长期预报中心(ECMWF)每日风场、温度场格点资料及同期南海区域测站和船舶资料,讨论南海低层风场的气候特征。南海为典型的季风活动区,冬季盛行东北季风,夏季盛行西南季风。流场的季节转换表现为季风系统的交替,相应不同的季风系统,南北温度梯度有一逆转过程,南海北部是温度梯度大且发生明显逆转的海区。12°N以南海区气温全年变化极小,整个海区大气温度的季节变化不如流场变化快和显著。 相似文献