全文获取类型
收费全文 | 40118篇 |
免费 | 1013篇 |
国内免费 | 488篇 |
专业分类
测绘学 | 1104篇 |
大气科学 | 3567篇 |
地球物理 | 9576篇 |
地质学 | 14298篇 |
海洋学 | 2716篇 |
天文学 | 8057篇 |
综合类 | 177篇 |
自然地理 | 2124篇 |
出版年
2021年 | 303篇 |
2020年 | 333篇 |
2019年 | 300篇 |
2018年 | 871篇 |
2017年 | 841篇 |
2016年 | 1227篇 |
2015年 | 827篇 |
2014年 | 1138篇 |
2013年 | 1988篇 |
2012年 | 1224篇 |
2011年 | 1410篇 |
2010年 | 1285篇 |
2009年 | 1678篇 |
2008年 | 1402篇 |
2007年 | 1202篇 |
2006年 | 1288篇 |
2005年 | 1087篇 |
2004年 | 1033篇 |
2003年 | 1035篇 |
2002年 | 1013篇 |
2001年 | 905篇 |
2000年 | 933篇 |
1999年 | 756篇 |
1998年 | 777篇 |
1997年 | 776篇 |
1996年 | 683篇 |
1995年 | 661篇 |
1994年 | 620篇 |
1993年 | 526篇 |
1992年 | 498篇 |
1991年 | 487篇 |
1990年 | 506篇 |
1989年 | 481篇 |
1988年 | 440篇 |
1987年 | 534篇 |
1986年 | 513篇 |
1985年 | 536篇 |
1984年 | 634篇 |
1983年 | 646篇 |
1982年 | 589篇 |
1981年 | 571篇 |
1980年 | 525篇 |
1979年 | 513篇 |
1978年 | 528篇 |
1977年 | 466篇 |
1976年 | 414篇 |
1975年 | 432篇 |
1974年 | 464篇 |
1973年 | 460篇 |
1972年 | 292篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
G. Djurašević P. Rovithis H. Rovithis-Livaniou E. Fragoulopoulou 《Astrophysics and Space Science》2005,296(1-4):311-314
BV light curves of the eclipsing binary UV Leo obtained at the Kryonerion Astronomical Station of the National Observatory of
Athens, Greece, are analyzed. The analysis is based on a Roche configuration with two spots on the secondary surface. The
elements of the two components of the system are calculated and the spot characteristics are given. 相似文献
103.
J. CAMPSIE M. H. RASMUSSEN L. C. KOVACS F. DITTMER J. C. BAILEY N. O. HANSEN J. LAURSEN L. JOHNSON 《Polar research》1990,8(2):237-243
New aeromagnetic data, K-Ar age determinations of dredged marine igneous rocks, as well as other geophysical evidence have shed light on the chronology, nature and evolution of the northern Iceland Plateau. Correspondence between seismic refraction profiles taken on the Jan Mayen Ridge and westward through Jan Mayen Island, suppressed aeromagnetic anomalies, earthquake surface wave studies, and ages of dredged igneous rocks suggest these strata may form an extended region of thickened crust, possibly of Caledonian age, extending westward toward the Kolbeinsey Ridge and northwest to the south wall of the Jan Mayen Fracture Zone. 相似文献
104.
P. A. M. Van Hoof M. E. Foord R. F. Heeter J. E. Bailey H.-K. Chung M. E. Cuneo W. H. Goldstein V. Jonauskas F. P. Keenan R. Kisielius D. A. Liedahl C. Ramsbottom S. J. Rose P. T. Springer R. S. Thoe 《Astrophysics and Space Science》2005,298(1-2):147-153
In experiments at the high-power Z-facility at Sandia National Laboratory in Albuquerque, New Mexico, we have been able to
produce a low density photoionized laboratory plasma of Fe mixed with NaF. The conditions in the experiment allow a meaningful
comparison with X-ray emission from astrophysical sources. The charge state distributions of Fe, Na and F are determined in
this plasma using high resolution X-ray spectroscopy. Independent measurements of the density and radiation flux indicate
unprecedented values for the ionization parameter ξ = 20–25 erg cm s−1 under nearly steady-state conditions. First comparisons of the measured charge state distributions with X-ray photoionization
models show reasonable agreement, although many questions remain. 相似文献
105.
106.
T. Masuda T. Shibutani T. Ochiai S. Akagi H. Yamaguchi Y. Kugimiya N. Kimura T. Miyake 《Journal of Metamorphic Geology》2004,22(3):199-205
Evidence is presented of a lateral variation in differential stress during metamorphism along a regional metamorphic belt on the basis of the proportion of microboudinaged piemontite grains (p) in a quartz matrix in metacherts. It is proposed that p is a practical indicator of relative differential stress. Analysis of 123 metacherts from the 800 km long Sambagawa metamorphic belt, Japan, reveals that p‐values range from < 0.01 to 0.7 in this region. Most samples from Wakayama in the mid‐belt area have p‐values of 0.4–0.6, whereas those from western Shikoku have p‐values of < 0.1. This difference cannot be explained by variations in metamorphic temperature, and is instead attributed to a regional, lateral variation in differential stress during metamorphism. 相似文献
107.
A tachometer for measuring the displacements of the center of gravity of spectral line profiles is developed. The implementation of the device, basically a Fabry-Pérot etalon, is given. The spectral shifts are determined, using the frequency of a laser as reference. 相似文献
108.
We present a computer model calculation for the racemization of a possible excess of amino acids in the icy fraction of comet nuclei bring about by ionizing radiation released during the decay of26Al,40K,235U,238U and232Th. The model takes into account a total of 110 chemical reactions, of which 91 are needed to explain the radiation chemical processing of the major constituents of comet nuclei (Navarro-Gonzálezet al., 1992) and 19 are necessary to simulate the radiolysis of glycine/alanine mixtures in aqueous solutions (Navarro-Gonzálezet al., 1994 and 1996). It is predicted that an enantiomeric excess of alanine would not be destroyed by radioracemization during the decay of embedded radionuclides. Nevertheless, this enantiomeric excess could be attenuated by the formation of racemic amino acids in the interior of comet nuclei as a result of the radiation-induced polymerization of HCN. 相似文献
109.
Roberto F. Viotti Rosario González-Riestra Takashi Iijima Stefano Bernabei Riccardo Claudi Jochen Greiner Michael Friedjung Vito Francesco Polcaro Corinne Rossi 《Astrophysics and Space Science》2005,296(1-4):435-439
We review the main characteristics of the symbiotic system AG Draconis, with special emphasis on its optical and X-ray variations.
We also discuss the X-ray to visual energy distribution during quiescence and outburst and describe our spectroscopic and
X-ray observations during the 2003 outburst.
Based on X-ray observations collected with the XMM–Newton Observatory, on INES data from the IUE satellite, and on optical
spectra collected with the Asiago–Cima Ekar, Bologna–Loiano and La Palma–Galileo Italian telescopes. 相似文献
110.