全文获取类型
收费全文 | 869篇 |
免费 | 169篇 |
国内免费 | 229篇 |
专业分类
测绘学 | 138篇 |
大气科学 | 67篇 |
地球物理 | 166篇 |
地质学 | 556篇 |
海洋学 | 205篇 |
天文学 | 39篇 |
综合类 | 68篇 |
自然地理 | 28篇 |
出版年
2023年 | 11篇 |
2022年 | 41篇 |
2021年 | 33篇 |
2020年 | 35篇 |
2019年 | 48篇 |
2018年 | 26篇 |
2017年 | 28篇 |
2016年 | 40篇 |
2015年 | 32篇 |
2014年 | 51篇 |
2013年 | 63篇 |
2012年 | 57篇 |
2011年 | 55篇 |
2010年 | 52篇 |
2009年 | 45篇 |
2008年 | 61篇 |
2007年 | 60篇 |
2006年 | 47篇 |
2005年 | 40篇 |
2004年 | 45篇 |
2003年 | 32篇 |
2002年 | 40篇 |
2001年 | 32篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 23篇 |
1997年 | 22篇 |
1996年 | 29篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有1267条查询结果,搜索用时 156 毫秒
131.
M. ROBYR W. D. CARLSON C. PASSCHIER P. VONLANTHEN 《Journal of Metamorphic Geology》2009,27(6):423-437
The growth history of two populations of snowball garnet from the Lukmanier Pass area (central Swiss Alps) was examined through a detailed analysis of three-dimensional geometry, chemical zoning and crystallographic orientation. The first population, collected in the hinge of a chevron-type fold, shows an apparent rotation of 360°. The first 270° are characterized by spiral-shaped inclusion trails, gradual and concentric Mn zoning and a single crystallographic orientation, whereas in the last 90°, crenulated inclusion trails and secondary Mn maxima centred on distinct crystallographic garnet domains are observed. Microstructural, geochemical and textural data indicate a radical change in growth regime between the two growth sequences. In the first 270°, growth occurred under rotational non-coaxial flow, whereas in the last 90°, garnet grew under a non-rotational shortening regime. The second population, collected in the limb of the same chevron-type fold structure, is characterized by a spiral geometry that does not exceed 270° of apparent rotation. These garnet microstructures do not record any evidence for a modification of the stress field during garnet growth. Concentric Mn zoning as well as a single crystallographic orientation are observed for the entire spiral. Electron backscatter diffraction data indicate that nearly all central domains in the snowball garnet are characterized by one [001] axis oriented (sub-)parallel to the symmetry axis and by another [001] axis oriented (sub-)parallel to the orientation of the internal foliation. These features suggest that the crystallographic orientation across the garnet spiral is not random and that a relation exists among the symmetry axis, the internal foliation and the crystallographic orientation. 相似文献
132.
C. E. JACOBSON 《Journal of Metamorphic Geology》1989,7(5):507-513
ABSTRACT Metabasites and metagreywackes from the Pelona and Rand Schists of southern California were analysed using three different electron microprobes. For all three instruments, the estimated Fe3+ contents of calcic amphibole, chlorite and epidote are positively correlated. For some samples, there is an additional correlation between high estimated Fe3+ and the presence of magnetite. These results imply that microprobe analyses can be used to discern relative differences in Fe3+. However, microprobe data and calculations on the sensitivity of the correction procedures to systematic analytical errors indicate that estimated values of Fe3+ are not significant in an absolute sense. Thus, estimates of Fe3+ are meaningful when comparing samples analysed with a single microprobe, but must be used with caution when comparing analyses obtained on more than one probe. 相似文献
133.
本文介绍了一个根据测站的经度(或纬度)打印任意空间剖面图的实用程序,通过自定义坐标,可打印在国家气象局制的6300号底图上。本程序采用BASIC语言,已在 Apple-Ⅱ上实现,对其中的部分语句修改后,也可以用于IBM-PC等其它微机上,用本程序制图,速度快,准确性高,可作为日常性的天气分析预报工具。 相似文献
134.
马桂芝 《地球科学与环境学报》1995,(2)
塑性图是由卡萨格兰德(A·Casagrande)于1942年首次提出的,该图将阿太量(A·Aeterberg)界限(液限、塑限)应用于土质分类.本文根据塑性图判别理论并应用塑性图,对陕西省特殊土(黄土、三趾马红土、膨胀土等)进行了判别,结果为黄土位于CLY区,三趾马红土和膨胀土位于CHE区,其效果较好,达到了分类的目的. 相似文献
135.
针对多模辅助算法均方误差高的缺点,提出了两种基于星座图改进的盲均衡算法.首先利用16QAM星座图信息,增加多模辅助算法代价函数中信号点的均衡数目,得到改进的多模辅助算法,与多模辅助算法相比,改进后的算法稳态均方误差更低,而且收敛速度略有提高;其次将改进的多模辅助算法和判决引导算法相结合,根据均方误差调整两种算法的比例,得到的混合算法进一步降低了稳态均方误差.水声信道仿真结果表明:提出的两种算法都可以有效地降低均方误差,适用于对精度要求较高的场合. 相似文献
136.
对传统纸质图摘纵横断数据采集的一般流程进行分析,从相关步骤环节入手,分析缺点。编写的图摘纵横断软件对步骤环节进行改进,作业人员完成对数字化电子地形图中图摘纵横断的数据采集过程,从而完成了传统纸质图摘纵横断数据采集的成果要求,同时进一步提供了为检验人员对数据的完整性、正确性加以核对的便利性。通过作业人员的实践,取得了良好的效果。 相似文献
137.
138.
139.
We present the first in situ measurements of the secondary electron emission efficiency of lunar regolith, utilizing Lunar Prospector measurements of secondary electrons emitted from the negatively charged night side and accelerated upward by surface electric fields. By comparing measurements of secondary currents emitted from the surface and incident primary electron currents, we find that the secondary yield of lunar regolith is a factor of ∼3 lower than that measured for samples in the laboratory. This lower yield significantly affects current balance at the lunar surface and the resulting equilibrium surface potentials. This information must be folded into models of the near-surface plasma sheath, in order to predict the effects on dust and other components of the lunar environment, and ultimately determine the importance for surface exploration and scientific investigations on the Moon. 相似文献
140.
As an important measurement parameter, global total electron content (TEC) is appropriate for the study of the Sun–Earth connection.
In this paper, the wavelet technique is employed to investigate the periodicities in global mean TEC during 1995–2008. Analysis
results show several remarkable components (including 27-day, semiannual and annual cycles) existing in global mean TEC with
obvious time-variable characteristics, besides 11-year cycle. After analyzing sunspot numbers and solar extreme ultra-violet
(EUV) radiation variations during this time period, except for semiannual variations, close correlation between global mean
TEC and solar variations is found, especially, a strong resemblance of the 27-day fluctuation exists in global mean TEC, sunspot
and solar EUV radiation variations. 相似文献