全文获取类型
收费全文 | 65227篇 |
免费 | 782篇 |
国内免费 | 1229篇 |
专业分类
测绘学 | 2335篇 |
大气科学 | 4856篇 |
地球物理 | 12553篇 |
地质学 | 25371篇 |
海洋学 | 4846篇 |
天文学 | 11328篇 |
综合类 | 2219篇 |
自然地理 | 3730篇 |
出版年
2021年 | 410篇 |
2020年 | 407篇 |
2019年 | 459篇 |
2018年 | 5547篇 |
2017年 | 4755篇 |
2016年 | 3600篇 |
2015年 | 849篇 |
2014年 | 1100篇 |
2013年 | 2113篇 |
2012年 | 2073篇 |
2011年 | 4235篇 |
2010年 | 3432篇 |
2009年 | 4205篇 |
2008年 | 3463篇 |
2007年 | 3994篇 |
2006年 | 1642篇 |
2005年 | 1507篇 |
2004年 | 1672篇 |
2003年 | 1640篇 |
2002年 | 1441篇 |
2001年 | 1104篇 |
2000年 | 1037篇 |
1999年 | 829篇 |
1998年 | 841篇 |
1997年 | 834篇 |
1996年 | 673篇 |
1995年 | 660篇 |
1994年 | 621篇 |
1993年 | 573篇 |
1992年 | 528篇 |
1991年 | 500篇 |
1990年 | 516篇 |
1989年 | 501篇 |
1988年 | 479篇 |
1987年 | 561篇 |
1986年 | 494篇 |
1985年 | 609篇 |
1984年 | 655篇 |
1983年 | 599篇 |
1982年 | 535篇 |
1981年 | 603篇 |
1980年 | 491篇 |
1979年 | 465篇 |
1978年 | 439篇 |
1977年 | 438篇 |
1976年 | 390篇 |
1975年 | 379篇 |
1974年 | 380篇 |
1973年 | 388篇 |
1971年 | 229篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Data are presented on a partial solar eclipse, which occurred on January 4, 2011, and was observed with RT-3 (?? = 4.9 cm) and RT-2 (?? = 3.2 cm) radio telescopes at the Mountain Astronomical Station, Central Astronomical Observatory, Russian Academy of Sciences (MAS CAO RAS). The radioemission flux in two channels was registered using digital methods with a time resolution of 0.5 s. Comparisons were performed with observations in the optical, UV, and X-ray ranges. The following local sources of increased radioemission on the solar disk have been identified: sunspot groups 1 (NOAA 1142) and 126 (NOAA 1141), unipolar sunspot 127 (NOAA 1140), facula areas, and polar and midlatitude coronal holes. It has been indicated that the brightness of a unipolar sunspot (for ?? = 4.9 cm, I rel = 29.5; for ?? = 3.2 cm, I rel = 10.1) and two sunspot groups (for ?? = 4.9 cm, I rel = 10.1 and 14.2; for ?? = 3.2 cm, I rel = 5.1 and 6.2) is maximal. The radioemission flux of all found coronal holes is decreased, and the decrease is more contrasting in the 4.9-cm range as compared to such a decrease in the 3.2-cm range. Radio maps of the Sun and changes in the radioemission flux of undisturbed solar regions from the center to the limb for ?? = 4.9 and 3.2 cm have been constructed based on the eclipse data. 相似文献
992.
993.
The Caspian Sea is characterized in the geographic and ecological aspects, and the state of its ecosystem is estimated. The natural and anthropogenic processes that control the formation of the environmental conditions in the Caspian Sea and the distribution of principal commercial hydrobionts and their food items are analyzed. Data on modern tendencies in changes in the abiotic and biotic parameters of the ecosystem, their causes and mechanisms are summarized. Prospects of further changes related to the development of shelf fields of petroleum hydrocarbons are assessed. 相似文献
994.
D. V. Abramov M. N. Drobyshev V. N. Koneshov 《Izvestiya Physics of the Solid Earth》2013,49(4):548-553
Continuous high-precision long-term gravity measurements are carried out at the geophysical observatory located in the experimental base of Vladimir State University. The long time series of gravity acceleration and its standard deviation are obtained. The factors responsible for the increases in the studied deviations are analyzed. The recommendations for improving the accuracy of relative gravity measurements are formulated. 相似文献
995.
Adrian Costea Quoc T. Le Gia Ernst P. Stephan Thanh Tran 《Studia Geophysica et Geodaetica》2011,55(3):465-477
We consider the exterior Neumann problem of the Laplacian with boundary condition on spheroids. We propose to use spherical
radial basis functions in the solution of the boundary integral equation arising from the Dirichlet-to-Neumann map. Our meshless
approach with radial basis functions is particularly suitable for handling scattered satellite data. We also propose a preconditioning
technique based on an overlapping domain decomposition method to deal with ill-conditioned matrices arising from the approximation
problem. 相似文献
996.
Petrochemical studies of granitoid rocks from the eastern part of Kumaun region suggest that the leading edge of India represents an active arc during Late Paleoproterozoic times. It has been observed that melt generation for granodiorite rocks from the eastern Almora Nappe and Chhiplakot klippe along with the Askot klippe was caused through a subduction‐related process involving hydrous partial melting of a Paleoproterozoic amphibole‐ and/or garnet‐bearing mafic source with the involvement of sediments from the subduction zone. The medium‐ to high‐K basic rocks, common in subduction‐related magmatic arcs, can also explain the generation of the high‐K granodiorites of the Chhiplakot klippe. The augen gneisses from the eastern Almora nappe and Chhiplakot klippe along with the Askot klippe further show geochemical similarity with the associated granodiorites, suggesting there is a genetic linkage with one another. 相似文献
997.
L. Fedele D. D. Insinga A. T. Calvert V. Morra A. Perrotta C. Scarpati 《Bulletin of Volcanology》2011,73(9):1323-1336
The Campi Flegrei hosts numerous monogenetic vents inferred to be younger than the 15 ka Neapolitan Yellow Tuff. Sanidine
crystals from the three young Campi Flegrei vents of Fondi di Baia, Bacoli and Nisida were dated using 40Ar/39Ar geochronology. These vents, together with several other young edifices, occur roughly along the inner border of the Campi
Flegrei caldera, suggesting that the volcanic conduits are controlled by caldera-bounding faults. Plateau ages of ∼9.6 ka
(Fondi di Baia), ∼8.6 ka (Bacoli) and ∼3.9 ka (Nisida) indicate eruptive activity during intervals previously interpreted
as quiescent. A critical revision, involving calendar age correction of literature 14C data and available 40Ar/39Ar age data, is presented. A new reference chronostratigraphic framework for Holocene Phlegrean activity, which significantly
differs from the previously adopted ones, is proposed. This has important implications for understanding the Campi Flegrei
eruptive history and, ultimately, for the evaluation of related volcanic risk and hazard, for which the inferred history of
its recent activity is generally taken into account. 相似文献
998.
999.
1000.