全文获取类型
收费全文 | 73137篇 |
免费 | 710篇 |
国内免费 | 567篇 |
专业分类
测绘学 | 1962篇 |
大气科学 | 4473篇 |
地球物理 | 13437篇 |
地质学 | 29052篇 |
海洋学 | 6170篇 |
天文学 | 16260篇 |
综合类 | 276篇 |
自然地理 | 2784篇 |
出版年
2022年 | 537篇 |
2021年 | 837篇 |
2020年 | 897篇 |
2019年 | 1020篇 |
2018年 | 4159篇 |
2017年 | 3726篇 |
2016年 | 3260篇 |
2015年 | 1073篇 |
2014年 | 1953篇 |
2013年 | 3109篇 |
2012年 | 2889篇 |
2011年 | 4560篇 |
2010年 | 4071篇 |
2009年 | 4707篇 |
2008年 | 3966篇 |
2007年 | 4569篇 |
2006年 | 2679篇 |
2005年 | 1853篇 |
2004年 | 1799篇 |
2003年 | 1770篇 |
2002年 | 1587篇 |
2001年 | 1320篇 |
2000年 | 1236篇 |
1999年 | 931篇 |
1998年 | 928篇 |
1997年 | 947篇 |
1996年 | 706篇 |
1995年 | 724篇 |
1994年 | 712篇 |
1993年 | 577篇 |
1992年 | 573篇 |
1991年 | 526篇 |
1990年 | 617篇 |
1989年 | 519篇 |
1988年 | 490篇 |
1987年 | 515篇 |
1986年 | 413篇 |
1985年 | 596篇 |
1984年 | 620篇 |
1983年 | 598篇 |
1982年 | 564篇 |
1981年 | 500篇 |
1980年 | 523篇 |
1979年 | 406篇 |
1978年 | 433篇 |
1977年 | 398篇 |
1976年 | 347篇 |
1975年 | 358篇 |
1974年 | 338篇 |
1973年 | 359篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Summary We present compositions of reheated melt inclusions in clinopyroxene phenocrysts from three mafic xenoliths in Breccia Museo,
Campi Flegrei, Italy. Melt inclusion compositions are remarkably different from the compositions of known contemporary Campi
Flegrei lavas, being significantly enriched in K2O and depleted in Na2O. Some differences are also evident in FeO* (total Fe as FeO) and TiO2 contents. The clinopyroxene phenocrysts could not have crystallised from Campi Flegrei magmas. We suggest that they originated
from a volcanic system genetically very similar to, and possibly linked with, the >14 ka volcanic system of Mt. Somma, another
Campanian volcano ∼ 30 km east from Campi Flegrei, from which Vesuvius subsequently developed. This result indicates a close
relationship (or link) between the two volcanic systems which have until now been considered separate. We speculate that the
link was established prior to eruption of the Neapolitan Yellow Tuff (NYT) (∼ 12 ka). The xenoliths were derived from a volcanic
system older than the host breccias themselves. We suggest that this older volcanism had close similarities with the volcanism
of the older products of Mt. Somma (∼25 ka).
Received March 20, 2000; accepted November 2, 2000 相似文献
103.
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
104.
A. V. Mordvinov 《Solar physics》1996,163(2):309-317
A new numerical technique is applied to study long-term variations of total solar irradiance. The background solar flux is estimated not from, e.g., a running mean but as the mode on a moving short time interval. Statistical properties of short-term variations with respect to the running mode are studied. The probability distribution function describing the data from Nimbus-7 is asymmetric and departs from a Gaussian.The ratio of time-integrated short-term negative and positive deviations shows that the energy re-radiated from faculae makes up about 40% of the energy blocked by sunspots. The amplitude and phase relations are studied between deviations which decrease and increase the irradiance. They characterize the mechanism of energy transformation with frequency. The cross-covariance analysis reveals that some parts of the energy blocked by sunspots come to the surface of the Sun after long delays. 相似文献
105.
M. J. Carson J. C. Davies E. Daw R. J. Hollingworth V. A. Kudryavtsev T. B. Lawson P. K. Lightfoot J. E. McMillan B. Morgan S. M. Paling M. Robinson N. J. C. Spooner D. R. Tovey 《Astroparticle Physics》2004,21(6):667-687
Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10−9–10−10 pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector. 相似文献
106.
107.
The evolution of a subduction channel and orogenic wedge is simulated in 2D for an active continental margin, with P-T paths being displayed for selected markers. In our simulation, subduction erosion affects the active margin and a structural pattern develops within a few tens of millions of years, with four zones from the trench into the forearc: (i) an accretionary complex of low grade metamorphic sedimentary material, (ii) a wedge of nappes with alternating upper and lower crustal provenance, and minor interleaving of oceanic or hydrated mantle material, (iii) a megascale melange composed of high pressure (HP) and ultra-high pressure (UHP) metamorphic rocks extruded from the subduction channel, and (iv) the upward tilted frontal part of the remaining lid. The P–T paths and time scales correspond to those typically recorded in orogenic belts. The simulation shows that HP/UHP metamorphism of continental crust does not necessarily indicate collision, but that the material can be derived from the active margin by subduction erosion and extruded from the subduction channel beneath the forearc during ongoing subduction. 相似文献
108.
Astronomy Letters - The acceleration of anomalous cosmic rays (ACRs) at the heliospheric termination shock and their influence on the shock structure and location are analyzed in terms of a... 相似文献
109.
110.
The process of non-linear ambipolar diffusion in the region overlying the solar surface can be an effective mechanism for producing sharp magnetic structures and current sheets. These may be the sites responsible for the occurrence of connectivity of magnetic field lines, and the subsequent explosive input of energy for heating of some of the features in the atmosphere of the Sun.. 相似文献