全文获取类型
收费全文 | 16825篇 |
免费 | 1975篇 |
国内免费 | 3003篇 |
专业分类
测绘学 | 913篇 |
大气科学 | 2498篇 |
地球物理 | 3380篇 |
地质学 | 8217篇 |
海洋学 | 2324篇 |
天文学 | 1862篇 |
综合类 | 1023篇 |
自然地理 | 1586篇 |
出版年
2024年 | 83篇 |
2023年 | 228篇 |
2022年 | 720篇 |
2021年 | 913篇 |
2020年 | 833篇 |
2019年 | 885篇 |
2018年 | 1104篇 |
2017年 | 1020篇 |
2016年 | 1011篇 |
2015年 | 769篇 |
2014年 | 969篇 |
2013年 | 1042篇 |
2012年 | 1016篇 |
2011年 | 1104篇 |
2010年 | 997篇 |
2009年 | 942篇 |
2008年 | 894篇 |
2007年 | 933篇 |
2006年 | 830篇 |
2005年 | 442篇 |
2004年 | 376篇 |
2003年 | 427篇 |
2002年 | 490篇 |
2001年 | 455篇 |
2000年 | 341篇 |
1999年 | 368篇 |
1998年 | 285篇 |
1997年 | 310篇 |
1996年 | 256篇 |
1995年 | 258篇 |
1994年 | 230篇 |
1993年 | 184篇 |
1992年 | 166篇 |
1991年 | 107篇 |
1990年 | 94篇 |
1989年 | 109篇 |
1988年 | 79篇 |
1987年 | 63篇 |
1986年 | 57篇 |
1985年 | 43篇 |
1984年 | 42篇 |
1983年 | 41篇 |
1982年 | 40篇 |
1981年 | 25篇 |
1980年 | 24篇 |
1979年 | 28篇 |
1978年 | 17篇 |
1977年 | 17篇 |
1975年 | 22篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
261.
262.
A. V. Maslov V. N. Podkovyrov Yu. L. Ronkin M. T. Krupenin E. Z. Gareev V. M. Gorozhanin 《Stratigraphy and Geological Correlation》2006,14(2):126-149
In the mid-1980s, it was concluded based on geochemical study that Th, Sc, La concentrations and ratios Th/Sc, La/Sc and Eu/Eu* did not wary significantly in the post-Archean time. It was impossible to judge about compositional variations of upper crust during the Riphean and Vendian, because data of that time characterized a limited number of samples from the post-Archean basins of Australia, New Zealand, and Antarctic. Considered in this work are variations of Eu/Eu*, LREE/HREE, Th/Sc, and La/Sc ratios in Upper Precambrian fine-grained siliciclastic rock of the Southern Urals western flank (Bashkirian meganticlinorium) and Uchur-Maya region (Uchur-Maya plate and Yudoma-Maya belt). As is established, only the Eu anomaly in the studied siliciclastic rocks is practically identical to this parameter of the average post-Archean shale. Three other parameters plot on the Riphean-Vendian variation curves with positive and negative excursions of diverse magnitude, which do not coincide always in time. It is assumed that these excursions likely mark stages of local geodynamic activity, destruction of pre-Riphean cratons, and progressing recycling of sedimentary material during the Riphean. 相似文献
263.
264.
The excitation of the ballooning instability by the eigenoscillations of coronal loops is analyzed using the energy method. The second variation of the potential energy for the case of a plasma—plasma boundary is obtained via the linearized ideal MHD equations. It is shown that the eigenmodes of a magnetic tube and of a toroidal coronal loop coincide in a first approximation. The bending oscillations of the loops are able to excite the ballooning instability when β ? 1. The effects of the instability in solar coronal loops are discussed. 相似文献
265.
Morphotectonics and incision of the Kaoping submarine canyon, SW Taiwan orogenic wedge 总被引:1,自引:0,他引:1
The Kaoping submarine canyon developed on the frontal orogenic wedge off SW Taiwan and is the largest one among others. The canyon begins at the mouth of the Kaoping River, crosses the narrow shelf and broad slope region, and finally merges into the northern Manila Trench for a distance of about 260 km. Using reflection seismic sections and bathymetric mapping this paper reveals the geomorphic characteristics of the Kaoping Canyon strongly related to structural and sedimentary processes. The combined morphometry statistics analysis, seismic interpretations of structures and examinations of detailed bathymetric charts indicate that regional canyon morphology is strongly linked to intrusions of mud diapirs in the upper reach of the canyon and thrust faulting in the middle and lower reaches which produce two prominent morphological breaks of the course of the Kaoping Canyon with two sharp bends. Although excavation of floor and enlargement of the Kaoping Canyon are mainly attributed to downslope erosion of seabed, incision of this canyon is also strongly complicated by mud diapiric intrusions (upper reach), westward thrust faults (middle reach), and regional base level tilting (lower reach). The resultant cross-sectional morphology along the Kaoping Canyon changes considerably, ranging from U-shaped, broad V-shaped, to irregular troughs. The Kaoping Canyon may be served as a variant of canyon model of active margins with a distinct morphology of two sharp bends along the canyon course associated with structure deformation. 相似文献
266.
267.
V. T. Doroshenko S. G. Sergeev C. M. Gaskell Yu. V. Golubinskii E. S. Klimek E. A. Sergeeva 《Astronomy Reports》2006,50(9):708-713
We present the results of our U BV R c I c photoelectric and CCD photometry of the NLS1 galaxy Ark 564 in 1987–2004. Between late 1997 and 2002, a slight increase in brightness was observed followed by a small but systematic decline until 2004. Ark 564 has a low variability amplitude, within 0.2m in the U BV R c I c bands. The galaxy’s spectral energy distribution at 3600–9000 Å is unlike those for Seyfert 1 (Syl) galaxies. A delay of the Ic flux relative to the B flux of about three days was found, which is in agreement with the standard disk model. This delay probably reflects the geometric size of the region that emits the observed continuum. 相似文献
268.
V. V. Seredin Yu. A. Danilcheva L. O. Magazina I. G. Sharova 《Lithology and Mineral Resources》2006,41(3):280-301
Results of the study of a new Ge-bearing area of the Pavlovka brown coal deposit are presented. Ge is accumulated in bed III2 lying at the bottom of the Late Paleogene-Early Neogene coal-bearing sequence adjacent to the Middle Paleozoic granite basement. The Ge content in coals and coal-bearing rocks varies in different sections from 10 to 200–250 ppm, reaching up to 500–600 ppm in the highest-grade lower part of the bed. The metalliferous area reveals a geochemical zoning: complex Ge-Mo-W anomalies subsequently grades along the depth and strike into Mo-W and W anomalies. Orebodies, like those at many Ge-bearing coal deposits, are concentric in plan and dome-shaped in cross-section. Coals in their central parts, in addition to Ge, W, and Mo, are enriched in U, As, Be, Ag, and Au. Distribution of Ge and other trace elements in the metalliferous sequence and products of gravity separation of Ge-bearing coals is studied. These data indicate that most elements (W, Mo, U, As, Be) concentrated like Ge in the Ge-bearing bed relative to background values are restricted to the organic matter of coals. The electron microscopic study shows that Ge-bearing coals contain native metals and intermetallic compounds in association with carbonates, sulfides, and halogenides. Coal inclusions in the metalliferous and barren areas of the molasse section strongly differ in contents of Ge and associated trace elements. Ge was accumulated in the coals in the course of the interaction of ascending metalliferous solutions with organic matter of the buried peat bogs in Late Miocene. The solutions were presumably represented by N2-bearing thermal waters (contaminated by volcanogenic CO2) that are typical of granite terranes. 相似文献
269.
The complexes of metamorphic rocks that take part in the tectonic structure of the South Tien Shan are mostly confined to
the cores of large synforms and occupy high structural position therein. Problems of their age, origin, metamorphic conditions,
and relationships with the adjacent unmetamorphosed Paleozoic sequences have remained debatable throughout the history of
geological investigations. The results of detailed studies of the Kyrgyz-Ata Synform, a typical structure of the Turkestan-Alay
Zone in the South Tien Shan, are reported in this paper. The metamorphic rocks of the Kan Group participate in the structure
of this synform. On the basis of the study of structural assemblages and the kinematic analysis, it is concluded that the
multistage evolution of this tectonic unit proceeded under transpressive conditions of volcanic trough “crushing.” The detailed
study of rock alteration in the contact zone between the Kan Group and the Middle Devonian basic volcanic rocks allowed us
to suggest that the metamorphic Kan Group is not a self-dependent stratigraphic unit but represents an infrastructure (a metamorphosed
analogue of the volcanic sequence and underlying rocks) displaced tectonically over its own suprastructure. 相似文献
270.