全文获取类型
收费全文 | 5045篇 |
免费 | 839篇 |
国内免费 | 695篇 |
专业分类
测绘学 | 776篇 |
大气科学 | 506篇 |
地球物理 | 1927篇 |
地质学 | 1495篇 |
海洋学 | 532篇 |
天文学 | 223篇 |
综合类 | 472篇 |
自然地理 | 648篇 |
出版年
2024年 | 25篇 |
2023年 | 82篇 |
2022年 | 153篇 |
2021年 | 241篇 |
2020年 | 255篇 |
2019年 | 262篇 |
2018年 | 192篇 |
2017年 | 259篇 |
2016年 | 254篇 |
2015年 | 252篇 |
2014年 | 289篇 |
2013年 | 355篇 |
2012年 | 303篇 |
2011年 | 290篇 |
2010年 | 248篇 |
2009年 | 251篇 |
2008年 | 305篇 |
2007年 | 290篇 |
2006年 | 266篇 |
2005年 | 229篇 |
2004年 | 201篇 |
2003年 | 189篇 |
2002年 | 190篇 |
2001年 | 132篇 |
2000年 | 137篇 |
1999年 | 138篇 |
1998年 | 143篇 |
1997年 | 120篇 |
1996年 | 103篇 |
1995年 | 80篇 |
1994年 | 64篇 |
1993年 | 59篇 |
1992年 | 43篇 |
1991年 | 34篇 |
1990年 | 35篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1976年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有6579条查询结果,搜索用时 62 毫秒
41.
42.
Dehydration melting of solid amphibolite at 2.0 GPa: Effects of time and temperature 总被引:3,自引:0,他引:3
ZHOU Wenge XIE Hongsen LIU Yonggang ZHENG Xiaogang ZHAO Zhidan & ZHOU Hui . Laboratory of Material in the Earth’s Interior Institute of Geochemistry Chinese Academy of Sciences Guiyang China . Department of Geology China University of Geosciences Beijing China . Department of Geology Peking University Beijing China 《中国科学D辑(英文版)》2005,48(8):1120-1133
The dehydration melting of the natural rock at high pressure is important to investigating the magma formation in the earth’s interior. Since the 1970s, a lot of geological scientists have paid more atten- tion to the dehydration melting of the natural rock[1―5]. Previous experiments of dehydration melting and observations of fieldwork argued that the dehy- dration melting of the rock was probably the most important fashion for the melting of the lower crust rock[6―12]. The genesis of most … 相似文献
43.
模式内部变率是模拟结果不确定性的重要来源,然而它对于1.5℃和2℃升温阈值出现时间不确定性的影响尚不清楚。因此,基于耦合模式比较计划第五阶段(CMIP5)的多模式数据研究了模式内部变率对1.5℃和2℃升温阈值出现时间不确定性的影响以及对未来排放情景的敏感性。结果表明,模式内部变率对升温阈值出现时间模拟的影响与外强迫的影响相当,单个模式内部不同成员达到全球平均1.5℃或2℃增温的年份相差2~12年;其影响具有明显的空间差异,影响极大值出现在欧亚大陆以北洋面、白令海峡周围区域、北美东北部及其与格陵兰岛之间的海域、南半球高纬地区等;低排放情景下模式内部变率的影响大于高排放情景。 相似文献
44.
45.
Stephan Winter Zhang-Cai Yin 《International journal of geographical information science》2013,27(9):1349-1365
This article studies probabilistic time geography for space–time prisms, that is, for situations where observers know the location of an agent at one time and then again at another time. In the intervening period, the agent would have moved freely, according to its time budget. The article demonstrates that the probability of finding the agent somewhere in the space–time prism is not equally distributed, so any attempt of a quantitative time geographic analysis must consider the actual probability distribution. This article develops, implements, and demonstrates this distribution. A preceding article introduced probabilistic time geography for space–time cones. With cones and prisms, the elementary space–time volumes of time geography are provided. 相似文献
46.
<Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript>9 Tohoku earthquake in 2011 in Japan: precursors uncovered by natural time analysis 下载免费PDF全文
Panayiotis A. Varotsos Nicholas V. Sarlis Efthimios S. Skordas Mary S. Lazaridou-Varotsos 《地震科学(英文版)》2017,30(4):183-191
This paper reviews the precursory phenomena of the 2011 M W9 Tohoku earthquake in Japan that emerge solely when we analyze the seismicity data in a new time domain termed natural time. If we do not consider this analysis, important precursory changes cannot be identified and hence are missed. Natural time analysis has the privilege that enables the introduction of an order parameter of seismicity. In this frame, we find that the fluctuations of this parameter exhibit an unprecedented characteristic change, i.e., an evident minimum, approximately two months before Tohoku earthquake, which strikingly is almost simultaneous with unique anomalous geomagnetic field variations recorded mainly on the z component. This is consistent with our finding that such a characteristic change in seismicity appears when a seismic electric signal (SES) activity of the VAN method (from the initials of Varotsos, Alexopoulos, Nomicos) initiates, and provides a direct confirmation of the physical interconnection between SES and seismicity. 相似文献
47.
高原边坡复杂地形下短时强降水的云型特征分类 总被引:1,自引:0,他引:1
利用逐时雨量资料、常规高低空观测资料及FY-2卫星云图,对2010—2015年5—9月甘肃省高原边坡复杂地形下76次短时强降水过程个例的天气形势配置及卫星云图演变特征进行统计分析。结果表明,与甘肃省短时强降水过程相关的特征云型共有6类:副热带高压边沿型、逗点云型、冷锋前部型、冷锋尾部与南亚高压东侧叠置型、冷涡后部型、弱冷锋前部椭圆形MαCS型。其中,副热带高压边沿型、冷锋前部型、弱冷锋前部椭圆形MαCS型与低层暖平流强迫有关。逗点云型、冷锋尾部与南亚高压东侧叠置型主要受高低空冷暖平流强烈交汇影响。冷涡后部型是高空冷平流强迫下形成。冷锋尾部与南亚高压东侧叠置型具有较好的预报指示意义。 相似文献
48.
地心非旋转坐标系中的TWSTT计算模型 总被引:1,自引:0,他引:1
根据卫星双向时间传递(TWSTT)的基本原理,详细推导了地心非旋转坐标系中TWSTT的计算模型.并与地固系中的计算模型进行了分析比较,证明了两种计算模型在0.1ns亚纳秒量级上的等价性。 相似文献
49.
Watershed structure influences the timing, magnitude, and spatial location of water and solute entry to stream networks. In turn, stream reach transport velocities and stream network geometry (travel distances) further influence the timing of export from watersheds. Here, we examine how watershed and stream network organization can affect travel times of water from delivery to the stream network to arrival at the watershed outlet. We analysed watershed structure and network geometry and quantified the relationship between stream discharge and solute velocity across six study watersheds (11.4 to 62.8 km2) located in the Sawtooth Mountains of central Idaho, USA. Based on these analyses, we developed stream network travel time functions for each watershed. We found that watershed structure, stream network geometry, and the variable magnitude of inputs across the network can have a pronounced affect on water travel distances and velocities within a stream network. Accordingly, a sample taken at the watershed outlet is composed of water and solutes sourced from across the watershed that experienced a range of travel times in the stream network. We suggest that understanding and quantifying stream network travel time distributions are valuable for deconvolving signals observed at watershed outlets into their spatial and temporal sources, and separating terrestrial and in‐channel hydrological, biogeochemical, and ecological influences on in‐stream observations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
50.
The common-ray approximation eliminates problems with ray tracing through S-wave singularities and also considerably simplifies
the numerical algorithm of the coupling ray theory for S waves, but may introduce errors in travel times due to the perturbation
from the common reference ray. These travel-time errors can deteriorate the coupling-ray-theory solution at high frequencies.
It is thus of principal importance for numerical applications to estimate the errors due to the common-ray approximation applied.
The anisotropic-common-ray approximation of the coupling ray theory is more accurate than the isotropic-common-ray approximation.
We derive the equations for estimating the travel-time errors due to the anisotropic-common-ray (and also isotropic-common-ray)
approximation of the coupling ray theory. The errors of the common-ray approximations are calculated along the anisotropic
common rays in smooth velocity models without interfaces. The derivation is based on the general equations for the second-order
perturbations of travel time. 相似文献