全文获取类型
收费全文 | 677篇 |
免费 | 23篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 23篇 |
地球物理 | 145篇 |
地质学 | 167篇 |
海洋学 | 170篇 |
天文学 | 141篇 |
综合类 | 10篇 |
自然地理 | 51篇 |
出版年
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 23篇 |
2016年 | 14篇 |
2015年 | 10篇 |
2014年 | 30篇 |
2013年 | 26篇 |
2012年 | 13篇 |
2011年 | 25篇 |
2010年 | 21篇 |
2009年 | 34篇 |
2008年 | 28篇 |
2007年 | 36篇 |
2006年 | 36篇 |
2005年 | 32篇 |
2004年 | 40篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 29篇 |
2000年 | 20篇 |
1999年 | 13篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1961年 | 2篇 |
排序方式: 共有710条查询结果,搜索用时 15 毫秒
571.
Takashi Tsuji 《Journal of Astrophysics and Astronomy》1981,2(1):95-113
It is shown that the infrared flux method for determining stellar effective temperatures (Blackwell and Shallis 1977; Blackwell,
Petford and Shallis 1980) can be applied to cool carbon stars. Although the spectra of cool carbon stars are highly line blanketed,
the spectral region between 3 and 4 μm (L-band in the infrared photometry system) is found to be relatively free from strong
line absorption. The ratioR
L of bolometric flux toL flux can then be used as a measure of effective temperature. On the basis of the predicted line-blanketed flux based on model
atmospheres, with an empirical correction for the effect of 3 μm absorption due to polyatomic species (HCN, C2H2), it is shown thatR
L is roughly proportional to T3
eff. The high sensitivity ofR
L to Teff makes it a very good measure of effective temperature, and the usual difficulty due to differential line blanketing effect
in the analyses of photometric indices of cool carbon stars can be minimized.
It is found that the majority of N-type carbon stars with small variability (SRb and Lb variables) are confined to the effective
temperature range between 2400 and 3200 K, in contrast to M-giant stars (M0 III - M6 III, including SRb and Lb variables)
that are confined to the effective temperature range between 3200 and 3900 K. The effective temperatures based on the infrared
flux method show good agreement with those derived directly from angular diameter measurements of 5 carbon stars. On the basis
of the new effective temperature scale for carbon stars, it is shown that the well known C-classification does not represent
a temperature sequence. On the other hand, colour temperatures based on various photometric indices all show good correlations
with our derived effective temperatures.
An erratum to this article is available at . 相似文献
572.
Atsushi Takenouchi Akira Yamaguchi Takashi Mikouchi Richard Greenwood Sojiro Yamazaki 《Meteoritics & planetary science》2023,58(10):1406-1428
Asuka (A) 12325 is the first poikilitic shergottite having a depleted pattern in light rare earth elements (REE). Compared with known poikilitic shergottites, A 12325 has smaller but more abundant pyroxene oikocrysts with remarkable Fe-rich pigeonite rims, indicating that A 12325 cooled relatively faster at a shallower part of the crust. The redox condition (logfO2 = IW + 0.6-IW + 1.7) and Fe-rich chemical compositions of each mineral in A 12325 are close to enriched shergottites. The intermediate shergottites could not form by a simple mixing between parent magmas of A 12325 and enriched shergottites. Although A 12325 contains various high-pressure minerals such as majorite and ringwoodite, plagioclase is only partly maskelynitized. Therefore, the maximum shock pressure may be within 17–22 GPa. Thermal conduction and ringwoodite growth calculation around a shock vein revealed that the shock dwell time of A 12325 is at least 40 ms. The weaker shock pressure and longer shock dwell time in A 12325 may be attained by an impact event similar to those of nakhlites and Northwest Africa (NWA) 8159. Such a weak shock ejection event may be as common on Mars as a severe shock event recorded in shergottites. Alteration of sulfide observed in A 12325 may imply the presence of magmatic fluid in its reservoir on Mars. A 12325 expands a chemical variety of Martian rocks and has a unique shock history among poikilitic shergottites while A 12325 also implies that poikilitic shergottites are common rocks on Mars regardless of their sources. 相似文献
573.
Kazuhisa Goto Ryuji Tada Eiichi Tajika Timothy J. Bralower Takashi Hasegawa Takafumi Matsui 《Meteoritics & planetary science》2004,39(8):1233-1247
Abstract— The possibility of ocean water invasion into the Chicxulub crater following the impact at the Cretaceous/Tertiary boundary was investigated based on examination of an impactite between approximately 794.63 and 894.94 m in the Yaxcopoil‐1 (Yax‐1) core. The presence of cross lamination in the uppermost part of the impactite suggests the influence of an ocean current at least during the sedimentation of this interval. Abundant occurrence of nannofossils of late Campanian to early Maastrichtian age in the matrices of samples from the upper part of the impactite suggests that the carbonate sediments deposited on the inner rim margin and outside the crater were eroded and transported into the crater most likely by ocean water that invaded the crater after its formation. The maximum grain size of limestone lithics and vesicular melt fragments, and grain and bulk chemical compositions show a cyclic variation in the upper part of the impactite. The upward fining grain size and the absence of erosional contact at the base of each cycle suggest that the sediments were derived from resuspension of units elsewhere in the crater, most likely by high energy currents association with ocean water invasion. 相似文献
574.
Identification of magnetite in lunar regolith breccia 60016: Evidence for oxidized conditions at the lunar surface 下载免费PDF全文
Katherine H. Joy Channon Visscher Michael E. Zolensky Takashi Mikouchi Kenji Hagiya Kazumasa Ohsumi David A. Kring 《Meteoritics & planetary science》2015,50(7):1157-1172
Lunar regolith breccias are temporal archives of magmatic and impact bombardment processes on the Moon. Apollo 16 sample 60016 is an “ancient” feldspathic regolith breccia that was converted from a soil to a rock at ~3.8 Ga. The breccia contains a small (70 × 50 μm) rock fragment composed dominantly of an Fe‐oxide phase with disseminated domains of troilite. Fragments of plagioclase (An95‐97), pyroxene (En74‐75, Fs21‐22,Wo3‐4), and olivine (Fo66‐67) are distributed in and adjacent to the Fe‐oxide. The silicate minerals have lunar compositions that are similar to anorthosites. Mineral chemistry, synchrotron X‐ray absorption near edge spectroscopy (XANES) and X‐ray diffraction (XRD) studies demonstrate that the oxide phase is magnetite with an estimated Fe3+/ΣFe ratio of ~0.45. The presence of magnetite in 60016 indicates that oxygen fugacity during formation was equilibrated at, or above, the Fe‐magnetite or wüstite–magnetite oxygen buffer. This discovery provides direct evidence for oxidized conditions on the Moon. Thermodynamic modeling shows that magnetite could have been formed from oxidization‐driven mineral replacement of Fe‐metal or desulphurisation from Fe‐sulfides (troilite) at low temperatures (<570 °C) in equilibrium with H2O steam/liquid or CO2 gas. Oxidizing conditions may have arisen from vapor transport during degassing of a magmatic source region, or from a hybrid endogenic–exogenic process when gases were released during an impacting asteroid or comet impact. 相似文献
575.
Masateru Ishiguro Takahiro Hiroi David J. Tholen Sho Sasaki Yuji Ueda Tokuhiro Nimura Masanao Abe Beth E. Clark Aya Yamamoto Fumi Yoshida Ryosuke Nakamura Naru Hirata Hideaki Miyamoto Yasuhiro Yokota Tatsuaki Hashimoto Takashi Kubota Akiko M. Nakamura Robert W. Gaskell Jun Saito 《Meteoritics & planetary science》2007,42(10):1791-1800
Abstract— We obtained color images of near‐Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8–3.7 m/pixel. Whole‐disk spectra are adjusted to the telescopic data obtained by the University of Hawai'i's 88‐inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk‐resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite‐like materials have been exposed through weathered layers by excavation. By also examining close‐up images obtained during touchdown rehearsal, we find that most rocks in Itokawa's rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels. 相似文献
576.
It was found that the heliographic longitudinal distribution of the occurrence of coronal mass ejections (CMEs) was not uniform around the solar minimum of cycle 21. This is confirmed by using the 2 test for goodness of fit. Sunspot groups and flares show similar non-uniform distributions during the same period. This suggests that there was a longitudinal range where both large-scale and small-scale solar magnetic activities were very low around the solar minimum of cycle 21. The longitudinal range with low activity was more than 150 degrees and continued for approximately four rotations. As solar activity increased, CMEs occurred almost uniformly in heliographic longitude. 相似文献
577.
Primary data on the organic geochemistry of the Tetori Group provide basic information about depositional environments and thermal maturation of organic matter through two geological sections in the Hokuriku region, central Japan. The thermal maturity of organic matter was evaluated by the methylphenanthrene index‐1. The maturity progressively increases stratigraphically down through the Izumi section in Fukui Prefecture. The estimated vitrinite reflectance equivalent is <1.35% near the top of the section, gradually increasing to >2.0% near the base. The thermal maturation process can account for stratigraphic changes in abundance of PAHs through this section. However, the occasional occurrence of coronene in the middle of the Izumi section is attributed to possible paleo‐wildfires that supplied more coronene to the depositional site. The stratigraphic distribution of PAHs through the Tateyama section, Toyama Prefecture, also can be explained by the same scenario as envisaged for the Izumi section, but weathering and/or other secondary factors may have partly modified primary signals for this section. Polycyclic aromatic sulfur compounds were observed in nearly all samples from both sections, even in samples for which a freshwater paleoenvironment is surmised. Most plausibly, some reduced sulfur was re‐oxidized to elemental sulfur, which persisted in the sediments and may have contributed to the formation of aromatic sulfur compounds. Hence, polycyclic aromatic sulfur compounds do not provide an index to separate marine environments from the freshwater settings for the Tetori Group. 相似文献
578.
Takashi OKAI 《Geostandards and Geoanalytical Research》1991,15(2):187-189
The zirconium content of 31 geochemical reference samples has been determined by a spectrophotometric method with Xylenol orange after sample decomposition by acid digestion and alkali fusion. The agreement between the present results and published data is generally good. 相似文献
579.
Heavy rainfall on the south side of the Rokko Mountains has often caused severe landslides and debris flows. Analysis of the annual summation of rainfall in excess of 100 mm/day shows that the rainfall in this area has dominant periodicities of about 25–30, 10–13, and 5–7 years. The period of about 25–30 years corresponds to that of occurrence of the natural disasters produced by heavy rainfall; years when the maximum rainfall correspond to years when there have been severe landslides and debris flows in the area. Temporal change in this rainfall may provide a first approximation for erosional force. Analyses of tree ring width from these mountains indicate that the sequences have a dominant periodicity of about 25–30 years. Cross-spectral analyses for rainfall and ring width in this area show high coherency for the periods of about 25–30 years; evidence that variations in the ring width may be used as proxy data for erosional force. 相似文献
580.