全文获取类型
| 收费全文 | 17903篇 |
| 免费 | 2671篇 |
| 国内免费 | 1830篇 |
专业分类
| 测绘学 | 4881篇 |
| 大气科学 | 1994篇 |
| 地球物理 | 6505篇 |
| 地质学 | 3591篇 |
| 海洋学 | 1281篇 |
| 天文学 | 1222篇 |
| 综合类 | 1490篇 |
| 自然地理 | 1440篇 |
出版年
| 2024年 | 72篇 |
| 2023年 | 157篇 |
| 2022年 | 498篇 |
| 2021年 | 640篇 |
| 2020年 | 695篇 |
| 2019年 | 658篇 |
| 2018年 | 582篇 |
| 2017年 | 889篇 |
| 2016年 | 805篇 |
| 2015年 | 827篇 |
| 2014年 | 1043篇 |
| 2013年 | 1166篇 |
| 2012年 | 1002篇 |
| 2011年 | 985篇 |
| 2010年 | 805篇 |
| 2009年 | 1059篇 |
| 2008年 | 1089篇 |
| 2007年 | 1204篇 |
| 2006年 | 1133篇 |
| 2005年 | 942篇 |
| 2004年 | 886篇 |
| 2003年 | 709篇 |
| 2002年 | 658篇 |
| 2001年 | 526篇 |
| 2000年 | 475篇 |
| 1999年 | 431篇 |
| 1998年 | 391篇 |
| 1997年 | 312篇 |
| 1996年 | 362篇 |
| 1995年 | 323篇 |
| 1994年 | 235篇 |
| 1993年 | 219篇 |
| 1992年 | 137篇 |
| 1991年 | 105篇 |
| 1990年 | 76篇 |
| 1989年 | 68篇 |
| 1988年 | 59篇 |
| 1987年 | 28篇 |
| 1986年 | 24篇 |
| 1985年 | 14篇 |
| 1984年 | 22篇 |
| 1982年 | 8篇 |
| 1981年 | 7篇 |
| 1980年 | 10篇 |
| 1979年 | 9篇 |
| 1978年 | 6篇 |
| 1977年 | 19篇 |
| 1972年 | 4篇 |
| 1971年 | 5篇 |
| 1954年 | 11篇 |
排序方式： 共有10000条查询结果，搜索用时 375 毫秒
51.
E. Biémont P. Palmeri P. Quinet G. Paquin Z. G. Zhang G. Somesfalean S. Svanberg 《Monthly notices of the Royal Astronomical Society》2001,328(4):1085-1090
Lifetimes of six levels belonging to the 4f10 6p configuration of Ho iii have been measured for the first time using the time-resolved laser-induced fluorescence method. They are compared with multiconfigurational pseudo-relativistic Hartree–Fock calculations. A very good agreement is found. Using the experimental lifetimes and theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for this ion. 相似文献
52.
53.
Using a set of compilations of measurements for extragalactic radio sources, we construct all-sky maps of the Faraday rotation produced by the Galactic magnetic field. In order to generate the maps, we treat the radio source positions as a kind of 'mask' and construct combinations of spherical harmonic modes that are orthogonal on the masked sky. As long as relatively small multipoles are used, the resulting maps are quite stable to changes in the selection criteria for the sources, and show clearly the structure of the local Galactic magnetic field. We also suggest the use of these maps as templates for cosmic microwave background (CMB) foreground analysis, illustrating the idea with a cross-correlation analysis between the Wilkinson Microwave Anisotropy Probe ( WMAP ) data and our maps. We find a significant cross-correlation, indicating the presence of a significant residual contamination. 相似文献
54.
55.
球状星团是银河系中最年老的天体之一，是储存着银河系早期演化珍贵信息的“化石”．球状星团的天体测量，主要包括球状星因天区内恒星相对自行的测定，并由这些相对自行数据采用适当方法定出星团的绝对自行，或者直接测定绝对自行．利用这些自行数据，或者进一步与测光和视向速度数据结合，可以开展与球状星团的距离、运动、动力学状况、质量、年龄、演化等等以及银河系的结构和演化等有关的一系列重要的研究．在本文中对本世纪70年代中期以来在球状星团相对自行测定和成员概率估计、内部运动检测、绝对自行测定和空间运动研究这三方面取得的成果和进展以及存在的问题作了评述． 相似文献
56.
密度和压缩系数的散射层析成像法 总被引：1，自引：1，他引：0
本文在速度成像的基础上研究了同时对密度和压缩系数成像的散射波层析成像法.对不同散射角度的计算可以得到一系列反演图像,拟合这些图像,从而可以有效地达到对密度和压缩系数（或速度）成像的目的.与单纯的速度成像相比,增加了反演的难度.首先是对资料的方位性要求增加;其次是对资料的利用率下降.即便如此,从对较少量的炮点和检波点资料的数值计算来看,仍取得了满意的成像结果.我们对组成字母“A”的散射体结构进行了成像计算,结果能够同时再现密度和压缩系数,成像清晰,表明了方法的可行性,并能应用于复杂结构的成像问题. 相似文献
57.
Results of a single group participating in an international experiment are analyzed. The experiment served to verify computational predictions of the ground-motion variations due to near-surface geological effects at a site established for that purpose by the California Department of Conservation. Based on an acceleration record at a rock location, and geotechnical model of medium, records at the other locations of a nearby sedimentary deposit were predicted. A 2-D finite-difference sensitivity analysis suggested that the lateral wave-propagation effects are negligibly small, and locally 1-D computations are sufficient for the present site. Those computations are compared with observations not available to the authors during the blind prediction. Peak accelerations, peak velocities and RMS accelerations were predicted with errors less than 159%, 114% and 62%, respectively. Maxima of the response spectra were fitted within a factor of 2. The predicted and observed Husid's plots (i.e., the normalized cumulative plots of the acceleration squared) have the correlation coefficients 0.98. The detected misfits do not show any simple relation to the instrument location, component, frequency, or time. 相似文献
58.
《山西地震综合数据处理系统》是遵循《国家地震局数据库技术规范》,以PDP-11/23~+小型机与IBM/PC联机为硬件支撑,以网状型数据库为核心,含前期处理、库管理、数据检索、科学计算、分析会商5个子系统的较大型应用软件系统。具有对数据进行收集、录入、预处理、存储、管理、加工及应用等功能。整个系统通过总控菜单程序实现了异种机间上百个模块的调度,使查询-处理一体化。该系统把地震数据库、日常监测数据处理、专家地震预报系统有机地衔接于一体,可直接服务于地震科研和震情会商。该系统的建设是山西省重大科技攻关项目,也是国家地震局的合同制项目。 相似文献
59.
A new multidimensional scaling (MS) technique, referred to as the Pijk model, is formulated on the basis of associations among triple objects (samples or variables), instead of pairs of objects as used in the usual MS methods, such as factor analysis. The computational scheme provided for this method is the reduction of an original problem to a standard eigenvalue-eigenvector problem. The major goal of the technique is simplification and reduction of data structures and the rescaling of original objects into a new and reduced space, so that patterns and relations of the original objects can be conventiently examined in two-dimensional factor plots. The Pïjk method is illustrated and tested by using a set of geochemical data related to the epithermal gold and silver vein deposits in the Walker Lake quadrangle of Nevada and California. The characteristics of element associations suggested in the Pijk analysis are consistent with field observations. A preliminary comparison between the new method and the ordinary factor analysis also is made on the basis of the same data set. Results are encouraging in that analysis by the Pijk model captures triple-object associations that might be missed by the ordinary factor analysis which considers only pair-variable correlations 相似文献
60.
