全文获取类型
收费全文 | 25732篇 |
免费 | 363篇 |
国内免费 | 315篇 |
专业分类
测绘学 | 751篇 |
大气科学 | 1801篇 |
地球物理 | 4971篇 |
地质学 | 8870篇 |
海洋学 | 2295篇 |
天文学 | 6349篇 |
综合类 | 53篇 |
自然地理 | 1320篇 |
出版年
2021年 | 206篇 |
2020年 | 238篇 |
2019年 | 302篇 |
2018年 | 617篇 |
2017年 | 599篇 |
2016年 | 739篇 |
2015年 | 420篇 |
2014年 | 710篇 |
2013年 | 1311篇 |
2012年 | 807篇 |
2011年 | 1048篇 |
2010年 | 962篇 |
2009年 | 1266篇 |
2008年 | 1137篇 |
2007年 | 1157篇 |
2006年 | 1130篇 |
2005年 | 849篇 |
2004年 | 841篇 |
2003年 | 768篇 |
2002年 | 723篇 |
2001年 | 627篇 |
2000年 | 641篇 |
1999年 | 566篇 |
1998年 | 558篇 |
1997年 | 533篇 |
1996年 | 397篇 |
1995年 | 399篇 |
1994年 | 412篇 |
1993年 | 319篇 |
1992年 | 312篇 |
1991年 | 259篇 |
1990年 | 314篇 |
1989年 | 277篇 |
1988年 | 255篇 |
1987年 | 283篇 |
1986年 | 240篇 |
1985年 | 319篇 |
1984年 | 341篇 |
1983年 | 336篇 |
1982年 | 317篇 |
1981年 | 258篇 |
1980年 | 273篇 |
1979年 | 219篇 |
1978年 | 210篇 |
1977年 | 218篇 |
1976年 | 185篇 |
1975年 | 197篇 |
1974年 | 179篇 |
1973年 | 167篇 |
1972年 | 115篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
T.H. Torsvik 《Physics of the Earth and Planetary Interiors》1985,39(3):194-207
Thermal demagnetization studies of lavas in the Strathmore area of the Midland Valley, Scotland, support overall palaeomagnetic data found in previous studies of these rocks. Reduced directional scatter as compared to some earlier studies, is attributed to more effective demagnetization, resolving some of the directional complexity of previous studies. Combined magnetic fabric and directional analysis suggest that at least some deviating directions may be explained by local tectonism. The existence of almost antiparallel directional groups and field tests give supporting evidence for a “primary” (deuteric) origin of the main magnetization of these rocks. Additionally, a second remanence component having shallow reverse directions of magnetization, is attributed to later remagnetization in Old Red Sandstone time. The Midland Valley results are seen in conjunction with other Palaeozoic palaeomagnetic results and possible geodynamic implications are discussed. 相似文献
72.
To study the crystal chemistry of bernalite, Fe(OH)3, and the nature of the octahedral Fe3+ environment, Mössbauer spectra were recorded from 80 to 350 K, optical spectra were recorded at room temperature and a sample was studied using transmission electron microscopy. The Mössbauer spectrum of bernalite consists of a single six-line magnetic spectrum at 80 K. A broadened six-line magnetic spectrum with significantly less intensity is observed at higher temperatures, and is attributed to a small fraction of bernalite occurring as small particles. The variation of hyperfine magnetic field data for bulk bernalite with temperature is well described by the Weiss molecular field model with parameters of H
0 = 55.7±0.3 T and T
N = 427±5K. The centre shift data were fitted to the Debye model with parameters 0=0.482±0.005 mm/s (relative to -Fe) and M=492±30 K. The quadrupole shift is near zero at 300 K, and does not vary significantly with temperature. Absorption spectra in the visible and near infrared range show three crystal field bands of Fe3+ at 11 300, 16000 and 23 200 cm-1, giving a crystal field splitting of 14 570 cm-1 and Racah parameters of B=629 cm-1 and C=3381 cm-1. Infrared reflection spectra show two distinct OH-stretching frequencies, which could correspond to two structurally different types of OH groups. A band was also observed at 2250 cm-1, suggesting the presence of molecular CO2 in the large cation site. Analytical transmission electron microscopy indicates that Si occurs within the bernalite structure as well as along domain boundaries. Electron diffraction and imaging show that bernalite is polysynthetically twinned along {100} planes with twin domains ranging from 3 to 20 nm in thickness. Results are discussed with respect to the nature of the octahedral Fe3+ site, and compared with values for other iron oxides and hydroxides. 相似文献
73.
The population and distribution of carbon-oxidizing and sulfate-reducing bacteria in the soils of the Mozhaisk Reservoir are studied. 相似文献
74.
The distribution of sites where globular clusters have crossed the Galactic disk during the last 100 million years has been analyzed using the most recent kinematic data for 133 globular clusters (GCs). ThreeGCs (NGC 6341, NGC 7078, and ω Cen) whose distances between the positions where they crossed the Galactic disk and trajectories of the Gould Belt are less than 20% of their heliocentric distances at the crossing time (82, 98, and 96 million years ago, respectively) have been identified. For each of the clusters, this was their next to last, rather than their last, crossing of the Galactic disk. The passage of any one of these three GCs through the disk could potentially have initiated the formation of the Gould Belt. 相似文献
75.
76.
G. T. Bloomfield 《New Zealand geographer》1967,23(1):90-91
Book reviewed in this article:
GEOGRAPHY, ITS SCOPE AND SPIRIT. By J. O. M. Broek
GEOGRAPHY AS HUMAN ECOLOGY: METHODOLOGY BY EXAMPLE. Edited by S. R. Eyre and G. R. J. Jones
A PREFACE TO ECONOMIC GEOGRAPHY. By H. H. McCarty and J. B. Lindberg
A PROLOGUE TO POPULATION GEOGRAPHY. By W. Zelinsky 相似文献
GEOGRAPHY, ITS SCOPE AND SPIRIT. By J. O. M. Broek
GEOGRAPHY AS HUMAN ECOLOGY: METHODOLOGY BY EXAMPLE. Edited by S. R. Eyre and G. R. J. Jones
A PREFACE TO ECONOMIC GEOGRAPHY. By H. H. McCarty and J. B. Lindberg
A PROLOGUE TO POPULATION GEOGRAPHY. By W. Zelinsky 相似文献
77.
78.
N. V. Makarova V. M. Makeev T. V. Sukhanova P. S. Miklyaev A. L. Dorozhko I. V. Korobova 《Moscow University Geology Bulletin》2012,67(4):209-217
The neotectonic structures of the Lower Oka (Nizhneokskii) Region formed under different geodynamic conditions. This is attested by the morphology, orientation, internal structure, and jointing of the structures. The Oka-Tsna arc formed under the effect of tension from an inner source on the one hand and stress from the Alpian belt on the other hand. The latitudinally-oriented structures of the northwestern slope of the Tokmovo arc emerged as a result of uplift and widening. Both types of structure are combined within the limits of the Oka-Murom trough, which is a geodynamically active zone. 相似文献
79.
80.
L. De Marchi J. Orm D. T. King D. R. Adrian J. J. Hagerty T. A. Gaither 《Meteoritics & planetary science》2019,54(11):2864-2878
Sedimentological (line‐logging) analysis of two drill cores, FC77‐3 and FC67‐3, situated, respectively, in the northwestern and southeastern quadrants of the Flynn Creek impact structure's crater‐moat area reveals that the ~27 m thick crater moat‐filling breccia consists of three subequal parts. These parts, which were deposited during early modification stage of this marine‐target impact structure, are distinguished on the basis of vertical trends in sorting, grain size, and counts of clasts per meter in comparison with other well‐known marine‐target impact structures, namely Lockne, Tvären, and Chesapeake Bay. The lower part is interpreted to represent mainly slump deposits, and the middle part is interpreted to represent a stage intermediate between slump and marine resurge, that is, a traction flow driven by overriding suspension flow. The upper part (size graded, and relatively well sorted and fine grained) is interpreted to represent marine resurge flow only. The upper part is capped by a relatively thin and relatively fine‐grained calcarenite to calcisiltite deposit. 相似文献