全文获取类型
收费全文 | 36360篇 |
免费 | 14239篇 |
国内免费 | 3936篇 |
专业分类
测绘学 | 4184篇 |
大气科学 | 5585篇 |
地球物理 | 6768篇 |
地质学 | 21304篇 |
海洋学 | 4808篇 |
天文学 | 3473篇 |
综合类 | 2633篇 |
自然地理 | 5780篇 |
出版年
2025年 | 198篇 |
2024年 | 1190篇 |
2023年 | 971篇 |
2022年 | 1576篇 |
2021年 | 1738篇 |
2020年 | 1645篇 |
2019年 | 1912篇 |
2018年 | 1362篇 |
2017年 | 1612篇 |
2016年 | 1628篇 |
2015年 | 1737篇 |
2014年 | 2193篇 |
2013年 | 2208篇 |
2012年 | 2331篇 |
2011年 | 2379篇 |
2010年 | 2065篇 |
2009年 | 2567篇 |
2008年 | 2466篇 |
2007年 | 2557篇 |
2006年 | 2485篇 |
2005年 | 2322篇 |
2004年 | 2028篇 |
2003年 | 1910篇 |
2002年 | 1681篇 |
2001年 | 1466篇 |
2000年 | 1464篇 |
1999年 | 1302篇 |
1998年 | 1113篇 |
1997年 | 804篇 |
1996年 | 688篇 |
1995年 | 564篇 |
1994年 | 551篇 |
1993年 | 458篇 |
1992年 | 330篇 |
1991年 | 283篇 |
1990年 | 190篇 |
1989年 | 158篇 |
1988年 | 127篇 |
1987年 | 76篇 |
1986年 | 39篇 |
1985年 | 33篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
31.
Warps and cosmic infall 总被引:1,自引:0,他引:1
32.
33.
V. I. Dokuchaev 《Astronomy Letters》2002,28(8):522-526
We discuss the possible observational manifestation of the formation of massive black holes in galactic nuclei in the form of an intense high-energy neutrino flux. A short-lived (≤10 yr) hidden neutrino source results from the natural dynamicalal evolution of a central star cluster in the galactic nucleus before its gravitational collapse. The central star cluster at the final evolutionary stage consists of degenerate compact stars (neutron stars and stellar-mass black holes) and is embedded in a massive gaseous envelope produced by destructive collisions of normal stars. Multiple fireballs from frequent collisions of neutron stars give rise to a tenuous quasi-stationary cavity in the central part of the massive envelope. The cavity is filled with shock waves on which an effective cosmic-ray acceleration takes place. Allthe accelerated particles, except the secondary high-energy neutrinos, are absorbed in the dense envelope. The neutrino signal that carries information on the dynamicals of the collapsing galactic nucleus can be recorded by a neutrino detector with an effective area S∼1 km2. 相似文献
34.
G. V. Ovchinnikova A. B. Kuznetsov I. M. Vasil’eva I. M. Gorokhov M. T. Krupenin A. V. Maslov T. L. Turchenko 《Stratigraphy and Geological Correlation》2008,16(2):138-142
The mineral composition and U-Pb and Rb-Sr systematics of phosphorites from the Satka Formation of Lower Riphean carbonates, the Burzyan Group of Southern Urals, are studied. Phosphorites occurring as small lenses between stromatolite layers are composed largely of fluorapatite with admixture of detrital quartz, feldspars, illite, and chlorite. Phosphorite samples have been subjected to stepwise dissolution in 1 N (fraction L-1) and 2 N (fraction L-2) HCl. As is established, the maximum apatite content is characteristic of fraction L-1, while fraction L-2 is enriched in products of dolomite and sulfide dissolution and in elements leached from siliciclastic components. The Sr content in the Satka apatites (280–560 ppm) is substantially lower as compared with that in unaltered marine apatite. The 87Sr/86Sr “initial ratio in the phosphorites studied (0.71705–0.72484) and host dolomites from the lower part of the Satka Formation is significantly higher than in the Early Riphean seawater that indicates a reset of the Rb-Sr original systems in sediments. The Pb-Pb age of 1340 ± 30 Ma (MSWD = 6.4) estimated based on 7 data points characterizing fractions L-1 and L-2 is younger than the formation time of overlying Burzyan sediments, being consistent, within the error range, with date of the Mashak rifting event recorded at the Early-Middle Riphean boundary. The comparative U-Pb characteristics of two soluble fractions (L-1 and L-2) and silicate residue of phosphorites show that epigenetic redistribution of Pb and U was characteristic of the phosphorite horizon only. The initial Pb isotope composition and μ (238U/204Pb) estimated according to model by Stacey and Kramers for the early diagenetic fluids in carbonate and phosphate sediments of the Satka Formation suggest that they were in isotopic equilibrium with erosion products of the Taratash crystalline complex. 相似文献
35.
The magnetic fields and energy flows in an astronomical jet described by our earlier model are calculated in detail. Though the field distribution varies with the external pressure function p ( z ) , it depends only weakly on the other boundary conditions. Individual field lines were plotted; the lines become nearly vertical at the bottom and are twisted at the top. An animation of a field line's motion was made, which shows the line being wound up by the accretion disc's differential rotation and rising as a result of this. The distribution of Poynting flux within the jet indicates that much of the energy flows up the jet from the inside of the accretion disc but a substantial fraction flows back down to the outside. 相似文献
36.
Sudhanshu Barway Yogesh Wadadekar Ajit K. Kembhavi Y. D. Mayya 《Monthly notices of the Royal Astronomical Society》2009,394(4):1991-2000
We consider the luminosity and environmental dependence of structural parameters of lenticular galaxies in the near-infrared K band. Using a 2D galaxy image decomposition technique, we extract bulge and disc structural parameters for a sample of 36 lenticular galaxies observed by us in the K band. By combining data from the literature for field and cluster lenticulars with our data, we study correlations between parameters that characterize the bulge and the disc as a function of luminosity and environment. We find that scaling relations such as the Kormendy relation, photometric plane and other correlations involving bulge and disc parameters show a luminosity dependence. This dependence can be explained in terms of galaxy formation models in which faint lenticulars ( M T > −24.5) formed via secular formation processes that likely formed the pseudo-bulges of late-type disc galaxies, while brighter lenticulars ( M T < −24.5) formed through a different formation mechanism most likely involving major mergers. On probing variations in lenticular properties as a function of environment, we find that faint cluster lenticulars show systematic differences with respect to faint field lenticulars. These differences support the idea that the bulge and disc components fade after the galaxy falls into a cluster, while simultaneously undergoing a transformation from spiral to lenticular morphologies. 相似文献
37.
地基微波辐射计能够克服星载遥感对低层大气不敏感的缺点,在边界层大气探测方面更具优势.一维变分反演算法考虑了辐射传输过程等物理机制,在应用于微波辐射计的反演时具有很高的可信度.针对微波辐射计信息含量较低以及一维变分算法收敛率不高等问题,提出利用地面气象要素改进算法在近地面层的反演精度和引入正则化算子提升算法的收敛特性.利用探空数据对上述改进方法的提升效果进行验证,结果表明:地面气象要素的引入使得反演算法在地表温湿度的均方根误差分别降低了78.2%和55.5%,对于上层大气温湿廓线也有小幅提升;正则化算子对算法的反演时间和反演精度影响很小,但是可以显著地减少未收敛样本个数和提升反演廓线的质量. 相似文献
38.
贵港市气象科技服务发展存在的问题与对策 总被引:1,自引:0,他引:1
通过对贵港市气象科技服务现状和存在问题的分析总结,提出发展气象科技服务的建议和措施。 相似文献
39.
40.
刘传正 《中国地质灾害与防治学报》2024,40(5):1-4
线状工程地质灾害预防应对工作要考虑工程全寿命周期的安全问题,具体划分为规划选线、设计施工和工程运营三个阶段分别考量并制定针对性对策。规划选线阶段主要是规避地质灾害风险,设计施工阶段主要是采取工程措施预防可能遭遇或引发的地质灾害,工程运营阶段主要是监测预警和高效处置可能发生或正在发生的地质灾害。 相似文献