全文获取类型
收费全文 | 81420篇 |
免费 | 1523篇 |
国内免费 | 789篇 |
专业分类
测绘学 | 2167篇 |
大气科学 | 5899篇 |
地球物理 | 16599篇 |
地质学 | 29106篇 |
海洋学 | 6973篇 |
天文学 | 18381篇 |
综合类 | 260篇 |
自然地理 | 4347篇 |
出版年
2022年 | 482篇 |
2021年 | 859篇 |
2020年 | 924篇 |
2019年 | 974篇 |
2018年 | 2218篇 |
2017年 | 2115篇 |
2016年 | 2680篇 |
2015年 | 1553篇 |
2014年 | 2502篇 |
2013年 | 4248篇 |
2012年 | 2745篇 |
2011年 | 3491篇 |
2010年 | 3045篇 |
2009年 | 3964篇 |
2008年 | 3359篇 |
2007年 | 3358篇 |
2006年 | 3195篇 |
2005年 | 2476篇 |
2004年 | 2572篇 |
2003年 | 2398篇 |
2002年 | 2191篇 |
2001年 | 1975篇 |
2000年 | 1882篇 |
1999年 | 1533篇 |
1998年 | 1610篇 |
1997年 | 1489篇 |
1996年 | 1241篇 |
1995年 | 1220篇 |
1994年 | 1102篇 |
1993年 | 946篇 |
1992年 | 921篇 |
1991年 | 870篇 |
1990年 | 936篇 |
1989年 | 771篇 |
1988年 | 745篇 |
1987年 | 840篇 |
1986年 | 755篇 |
1985年 | 947篇 |
1984年 | 1054篇 |
1983年 | 974篇 |
1982年 | 904篇 |
1981年 | 838篇 |
1980年 | 792篇 |
1979年 | 770篇 |
1978年 | 800篇 |
1977年 | 660篇 |
1976年 | 617篇 |
1975年 | 659篇 |
1974年 | 575篇 |
1973年 | 611篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
261.
F.J. Davey 《Geophysical Journal International》1987,89(1):443-448
Summary. The active Australian-Pacific plate boundary passes through New Zealand. In the north, the Pacific plate subducts beneath the Australian plate with an accretionary wedge forming the eastern continental (Hikurangi) margin of the North Island. The structure of the region behind the Hikurangi margin changes from the extensional back-arc basin under central North Island to a postulated crustal downwarp under the southern North Island. A 100 km long multichannel seismic reflection profile was recorded across the region of crustal downwarp. The data show discontinuous coherent reflectors dipping westwards at the east end of the profile, and east dipping reflectors at the west end, from depths of 9 to 15 s two way time. Simple hand migration of these events indicate that the east dipping reflectors, interpreted as the base of the Australian plate crust, abut against the west dipping reflectors which are interpreted as marking the top of the subducted Pacific plate. Detailed earthquake hypocentre locations in the area show a dipping zone of high seismicity, the top of which coincides closely with the west dipping events, thus supporting this interpretation. 相似文献
262.
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
263.
The Indian team at ISRO has been part of the Whole Earth Telescope (WET) team since 1988 when we first participated in the
campaign on V471 Tau. We have been part of many other observing campaigns over the last decade. This presentation traces the
circumstances leading to our joining the WET team and how useful the coverage from the Indian longitude has been. The results
of several pulsators from the WET runs during which we participated are also described. These include PG1159-035 the prototype
of the GW Vir type of stars, RE J 0751+14 a cataclysmic variable, PG 1336-018 a binary with an sdB pulsator and finally HR
1217 a roAp star. The paper concludes with what the limitations are in our observations and how we can overcome them in the
future. 相似文献
264.
265.
266.
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
267.
268.
The uranium deposits in the basin of Franceville (Gabon) host the only natural fission reactors known in the world. Unique
geological conditions favoured a natural fission reaction 2 Ga ago. This was detected by anomalous isotopic compositions of
uranium and rare earth elements (REE), which are produced by the fission reaction. In total, 16 reactor zones were found.
Most of them are mined out. The reactor zone of Bangombé, is only 10–11 m below the surface. This site has been influenced
by surface weathering processes. Six drill cores have been sampled at the site of the reactor zone of Bangombé during the
course of the study and only one drill core (BAX 08) hit the core of the reactor. From these data and previous drilling campaigns,
the reactor size is estimated to be 10 cm thick, 2–3 m wide and 4–6 m long. The migration of fission products can be traced
by the anomalous isotope ratios of REE because of the fission process. The 149Sm/147Sm ratio close to the reactor zone is only 0.28 (normal: 0.92) because of the intense neutron capture of 149Sm and subsequent transmutation, whereas 147Sm is enriched by the fission reaction. Similar changes in isotopic patterns are detectable on other REE. The isotope ratios
of Sm and Nd of whole rock and fracture samples surrounding the reactor indicate that fission-genic REE migrated only a few
decimetres above and mainly below the reactor zone. Organic matter (bitumen) seems to act as a trap for fission-genic REE.
Additional REE-patterns show less intense weathering with increasing depth in the log profile and support a simple weathering
model.
Received: 26 November 1999 · Accepted: 2 May 2000 相似文献
269.
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
270.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae. 相似文献