全文获取类型
收费全文 | 7126篇 |
免费 | 1331篇 |
国内免费 | 2510篇 |
专业分类
测绘学 | 1121篇 |
大气科学 | 2062篇 |
地球物理 | 1914篇 |
地质学 | 4071篇 |
海洋学 | 388篇 |
天文学 | 24篇 |
综合类 | 901篇 |
自然地理 | 486篇 |
出版年
2024年 | 38篇 |
2023年 | 102篇 |
2022年 | 213篇 |
2021年 | 268篇 |
2020年 | 302篇 |
2019年 | 381篇 |
2018年 | 306篇 |
2017年 | 339篇 |
2016年 | 355篇 |
2015年 | 371篇 |
2014年 | 469篇 |
2013年 | 435篇 |
2012年 | 476篇 |
2011年 | 509篇 |
2010年 | 412篇 |
2009年 | 540篇 |
2008年 | 451篇 |
2007年 | 545篇 |
2006年 | 539篇 |
2005年 | 440篇 |
2004年 | 460篇 |
2003年 | 452篇 |
2002年 | 354篇 |
2001年 | 296篇 |
2000年 | 310篇 |
1999年 | 269篇 |
1998年 | 222篇 |
1997年 | 216篇 |
1996年 | 195篇 |
1995年 | 147篇 |
1994年 | 148篇 |
1993年 | 108篇 |
1992年 | 86篇 |
1991年 | 53篇 |
1990年 | 43篇 |
1989年 | 32篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 13篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1979年 | 3篇 |
1975年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
黔东南地区短期气候预测方法研究 总被引:2,自引:0,他引:2
根据大气环流特征和小气候相关关系,找出预测黔东南地区春季倒春寒、3~6月降水量趋势、夏季及6~8月气温变化趋势和夏季旱涝趋势指标,用以制作黔东南地区长期天气趋势预测。 相似文献
92.
93.
山西运城市森林火险等级预报系统 总被引:1,自引:0,他引:1
利用有关气象及森林火灾资料,分析了林林火灾的发生与气象条件、火条件及森林含水率的关系,计算了森林火险综合预报指标,建立了以预报方程,经试用效果良好。 相似文献
94.
青藏公路路基变形分析 总被引:29,自引:8,他引:29
为研究青藏公路多年冻土人为上限在退化过程中对路基变形产生的影响过程和程度, 在唐古拉山以南选择了3处具有代表性的路面进行了为期2 a的路面变形观测. 资料表明, 在多年冻土人为上限退化过程中随着公路路基结构、冻土类型的不同, 路基变形从冻胀和融沉过程、冻胀量和融沉量、发生的时间都有很大的不同. 在高含冰量多年冻土区采用半挖半填结构产生的路基变形最为剧烈, 在含冰量相对少且采用较高路堤结构的地段路基变形过程相对平缓. 同时结合探地雷达的勘察结果对路基下的融化区、多年冻土区的内部结构进行了分析. 结果显示,多年冻土人为上限的下移、地下冰的融化会在多年冻土人为上限以上的地质体中导致较强烈的层间错动和扰动. 相似文献
95.
将广义Kопытов预测模型和乙型水驱曲线方法有机的结合起来,得到了油田开发中后期——递减时期的一种预测水驱开发油田的含水率、产油量、产水量及其相应的累积产量随开发时间变化的方法,此方法克服了在水驱油田预测开发指标中二者所存在的局限性。 相似文献
96.
An experimental study of grain scale melt segregation mechanisms in two common crustal rock types 总被引:3,自引:0,他引:3
Creation of pathways for melt to migrate from its source is the necessary first step for transport of magma to the upper crust. To test the role of different dehydration‐melting reactions in the development of permeability during partial melting and deformation in the crust, we experimentally deformed two common crustal rock types. A muscovite‐biotite metapelite and a biotite gneiss were deformed at conditions below, at and above their fluid‐absent solidus. For the metapelite, temperatures ranged between 650 and 800 °C at Pc=700 MPa to investigate the muscovite‐dehydration melting reaction. For the biotite gneiss, temperatures ranged between 850 and 950 °C at Pc=1000 MPa to explore biotite dehydration‐melting under lower crustal conditions. Deformation for both sets of experiments was performed at the same strain rate (ε.) 1.37×10?5 s?1. In the presence of deformation, the positive ΔV and associated high dilational strain of the muscovite dehydration‐melting reaction produces an increase in melt pore pressure with partial melting of the metapelite. In contrast, the biotite dehydration‐melting reaction is not associated with a large dilational strain and during deformation and partial melting of the biotite gneiss melt pore pressure builds more gradually. Due to the different rates in pore pressure increase, melt‐enhanced deformation microstructures reflect the different dehydration melting reactions themselves. Permeability development in the two rocks differs because grain boundaries control melt distribution to a greater extent in the gneiss. Muscovite‐dehydration melting may develop melt pathways at low melt fractions due to a larger volume of melt, in comparison with biotite‐dehydration melting, generated at the solidus. This may be a viable physical mechanism in which rapid melt segregation from a metapelitic source rock can occur. Alternatively, the results from the gneiss experiments suggest continual draining of biotite‐derived magma from the lower crust with melt migration paths controlled by structural anisotropies in the protolith. 相似文献
97.
The deformation pattern and the dynamics of the southern sector of the Aeolian archipelago are investigated. A study on the ground deformation, measured over the last 20 years in the trilateration geodetic network between the islands of Vulcano and Lipari, has been conducted. Analysis of the relative displacements and the uniform strain tensor parameters, as well as the comparison between areal dilatation and the vertical variations deduced by precise levelling, allow distinguishing different phases associated both with the regional dynamics and the local volcanic context of the area. These phases, however, appear to be closely interrelated. The analysis of the deformation pattern allows to constrain the predominance of a roughly E–W trending extension and a N–S contraction at a regional scale. This regime is consistent with right-lateral movements along a NW–SE striking fault system. 相似文献
98.
The lack of earthquake-induced liquefaction features in Late Wisconsin and Holocene sediments in Genesee, Wyoming, and Allegany Counties suggests that the Clarendon–Linden fault system (CLF) did not generate large, moment magnitude, M≥6 earthquakes during the past 12,000 years. Given that it was the likely source of the 1929 M 4.9 Attica earthquake, however, the Clarenden–Linden fault system probably is capable of producing future M5 events. During this study, we reviewed newspaper accounts of the 1929 Attica earthquake, searched for earthquake-induced liquefaction features in sand and gravel pits and along tens of kilometers of river cutbanks, evaluated numerous soft-sediment deformation structures, compiled geotechnical data and performed liquefaction potential analysis of saturated sandy sediments. We found that the 1929 M 4.9 Attica earthquake probably did not induce liquefaction in its epicentral area and may have been generated by the western branch of the Clarendon–Linden fault system. Most soft-sediment deformation structures found during reconnaissance did not resemble earthquake-induced liquefaction features, and even the few that did could be attributed to non-seismic processes. Our analysis suggests that the magnitude threshold for liquefaction is between M 5.2 and 6, that a large (M≥6) earthquake would liquefy sediments at many sites in the area, and that a moderate earthquake (M 5–5.9) would liquefy sediments at some sites but perhaps not at enough sites to have been found during reconnaissance. We conclude that the Clarendon–Linden fault system could have produced small and moderate earthquakes, but probably not large events, during the Late Wisconsin and Holocene. 相似文献
99.
Static deformation of two monoclinic elastic half-spaces in welded contact due to a long inclined strike-slip fault situated
in one of the half-spaces is studied analytically and numerically. Closed-form algebraic expressions for the displacement
at any point of the medium are obtained. The variation of the displacement at the interface with the horizontal distance from
the fault is studied. The effect of anisotropy on the displacement field is examined. It is found that while the anisotropy
of the source half-space has a significant effect on the displacement at the interface, the anisotropy of the other half-space
has only a marginal effect. 相似文献
100.