全文获取类型
收费全文 | 48809篇 |
免费 | 8356篇 |
国内免费 | 10500篇 |
专业分类
测绘学 | 5140篇 |
大气科学 | 5385篇 |
地球物理 | 10105篇 |
地质学 | 28368篇 |
海洋学 | 5232篇 |
天文学 | 2239篇 |
综合类 | 3549篇 |
自然地理 | 7647篇 |
出版年
2024年 | 117篇 |
2023年 | 438篇 |
2022年 | 1215篇 |
2021年 | 1435篇 |
2020年 | 1510篇 |
2019年 | 1741篇 |
2018年 | 1489篇 |
2017年 | 1753篇 |
2016年 | 1891篇 |
2015年 | 2050篇 |
2014年 | 2528篇 |
2013年 | 2589篇 |
2012年 | 2842篇 |
2011年 | 3064篇 |
2010年 | 2592篇 |
2009年 | 3132篇 |
2008年 | 3114篇 |
2007年 | 3513篇 |
2006年 | 3359篇 |
2005年 | 3008篇 |
2004年 | 2804篇 |
2003年 | 2704篇 |
2002年 | 2336篇 |
2001年 | 2092篇 |
2000年 | 1960篇 |
1999年 | 1822篇 |
1998年 | 1570篇 |
1997年 | 1415篇 |
1996年 | 1294篇 |
1995年 | 1092篇 |
1994年 | 1128篇 |
1993年 | 961篇 |
1992年 | 741篇 |
1991年 | 536篇 |
1990年 | 467篇 |
1989年 | 371篇 |
1988年 | 284篇 |
1987年 | 187篇 |
1986年 | 132篇 |
1985年 | 94篇 |
1984年 | 40篇 |
1983年 | 31篇 |
1982年 | 39篇 |
1981年 | 27篇 |
1980年 | 30篇 |
1979年 | 31篇 |
1978年 | 37篇 |
1977年 | 24篇 |
1975年 | 4篇 |
1954年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
定性分析协方差方法及其改进型在AR(P)参数估计中的应用,提供了一种估计参数的计算机上机流程图,比较了协方差方法及其改进型谱估计结果。 相似文献
63.
T. H. BELL S. E. JOHNSON B. DAVIS A. FORDE N. HAYWARD C. WILKINS 《Journal of Metamorphic Geology》1992,10(3):295-307
Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non-coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens. 相似文献
64.
65.
讨论了应用曲面拟合技术和利用离散的重力观测点的重力变化对特定研究区的重力场变化进行数值模拟以获取该区重力变化空间梯度场图像的具体方法;并应用该方法获得了2004年3月福建安溪3.6级地震前的重力变化空间梯度场图像,发现空间梯度场图像能清晰地反映出地震前重力场群体性变化的差异性;利用此方法对2005年6月~2006年3月间台湾海峡西岸重力场变化进行数值模拟,获得其空间梯度场图像。 相似文献
66.
67.
68.
Abstract Zircons have been studied from different layers of migmatites (from Arvika, western Sweden and Nelaug, southern Norway) and from a paragneiss (from Arvika) associated with one of the migmatites. The main purpose of the investigation is to establish whether or not information about zircons can help in the elucidation of the parentage and rock-forming processes of migmatites.
The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence of characteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting. 相似文献
The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence of characteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting. 相似文献
69.
We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra. 相似文献
70.
MENGLi-li 《中国地理科学(英文版)》2003,13(2):190-192
The exploitation and utilization of the tour resources of tournament athletics, including skiling, boat sail-ing, archery, ice engraving, snow engraving, has become a new trend of the development of Chinese tourism. Due tothe unique cold climate and superior geographic location, Harbin is a promising city for developing tour resources of tourna-ment athletics. Based on the analysis of the superiority and peculiarity of Harbin, the speculation on development of tour resources of tournament athletics in Harbin is proposed as follows : 1 ) Harbin should develop its special tour resources of tournament athletics associated with needs of market; 2) Harbin should take the advantages of rich resources and devel-op ice and snow entertainment in winter and travel for sight-seeing and spending summer;, 3) the adjustment of the layoutof ice and snow resources should be based on the idea of taking Harbin as the center and all-side opening at the largescale in the way of radiation; 4) tourism should be developed by the combined efforts of various departments to make feasi-ble plan, and the organizers should pay much attention to ensuring the safetv of tourists. 相似文献