全文获取类型
收费全文 | 6666篇 |
免费 | 1013篇 |
国内免费 | 1569篇 |
专业分类
测绘学 | 196篇 |
大气科学 | 836篇 |
地球物理 | 802篇 |
地质学 | 4598篇 |
海洋学 | 283篇 |
天文学 | 26篇 |
综合类 | 400篇 |
自然地理 | 2107篇 |
出版年
2024年 | 23篇 |
2023年 | 75篇 |
2022年 | 211篇 |
2021年 | 284篇 |
2020年 | 257篇 |
2019年 | 327篇 |
2018年 | 258篇 |
2017年 | 244篇 |
2016年 | 320篇 |
2015年 | 288篇 |
2014年 | 468篇 |
2013年 | 436篇 |
2012年 | 451篇 |
2011年 | 424篇 |
2010年 | 323篇 |
2009年 | 332篇 |
2008年 | 384篇 |
2007年 | 420篇 |
2006年 | 404篇 |
2005年 | 395篇 |
2004年 | 337篇 |
2003年 | 318篇 |
2002年 | 315篇 |
2001年 | 241篇 |
2000年 | 271篇 |
1999年 | 232篇 |
1998年 | 236篇 |
1997年 | 190篇 |
1996年 | 142篇 |
1995年 | 107篇 |
1994年 | 94篇 |
1993年 | 101篇 |
1992年 | 85篇 |
1991年 | 46篇 |
1990年 | 51篇 |
1989年 | 20篇 |
1988年 | 30篇 |
1987年 | 27篇 |
1986年 | 26篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1954年 | 2篇 |
排序方式: 共有9248条查询结果,搜索用时 15 毫秒
1.
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
2.
REGIONAL DEMOGRAPHIC STRUCTURE OF THE UNITED STATES 总被引:1,自引:0,他引:1
Richard L. Morrill 《The Professional geographer》1990,42(1):38-53
This paper analyzes the surprisingly great variation in demographic character across the states, utilizing data on fertility, mortality, age, sex, mobility, household character, abortion, race and ethnicity. A fairly simple regional pattern is revealed that is less related to levels of economic development than to long-standing historical cultural differences. 相似文献
3.
DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHEHEXIREGION,CHINA肖洪浪,高前兆,李福兴DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHE... 相似文献
4.
随着河南区域化探扫面工作的结束,异常评价是摆在我们面前的当务之急。近年来,随着地质工作的不断深入,我们在异常评价程序及方法上作了一些探索,下面以桐柏县固庙—新集1:20万金银异常评价方法及效果为例,重点加以讨论。 相似文献
5.
6.
7.
本文简介海南省1:5万坝王岭、猴狝岭幅区域地质调查的地球化学简单分段法在地层划分中的应用。根据对下古生界变质岩与白垩系红层两条地层实测剖面的地球化学资料整理,用简单分段法进行划分、其效果较好。它的地球化学组分基本能反映原始沉积物的特点和其沉积环境,且与岩石地层的划分相互印证。 相似文献
8.
N. H. S. OLIVER I. CARTWRIGHT V. J. WALL S. D. GOLDING 《Journal of Metamorphic Geology》1993,11(5):705-720
Abstract Large calcite veins and pods in the Proterozoic Corella Formation of the Mount Isa Inlier provide evidence for kilometre-scale fluid transport during amphibolite facies metamorphism. These 10- to 100-m-scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 × 10-km Mary Kathleen Fold Belt, despite the isotopic heterogeneity of the surrounding wallrocks. The fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks. The pods have δ13Ccalcite values of –2 to –7% and δ18Ocalcite values of 10.5 to 12.5%. Away from the pods, metadolerite wallrocks have δ18Owhole-rock values of 3.5 to 7%. and unaltered banded calc-silicate and marble wallrocks have δ13Ccalcite of –1.6 to –0.6%, and δ18Ocalcite of 18 to 21%. In the alteration zones adjacent to the pods, the δ18O values of both metadolerite and calc-silicate rocks approach those of the pods. Large calcite pods hosted entirely in calc-silicates show little difference in isotopic composition from pods hosted entirely in metadolerite. Thus, 100- to 500-m-scale isotopic exchange with the surrounding metadolerites and calc-silicates does not explain the observation that the δ18O values of the pods are intermediate between these two rock types. Pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc-silicates. These data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the Corella Formation at the presently exposed crustal level, although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc-silicates, or thermal fluctuations attending deformation and metamorphism. The overall L-shaped trend of the data on plots of δ13C vs. δ18O is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc-silicate rocks. Localization of the vein systems in dilatant sites around metadolerite/calc-silicate boundaries indicates a strong structural control on fluid flow, and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km. The ultimate source for the external fluid is uncertain, but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle. Intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism. 相似文献
9.
Aimed at promoting regional coalitions and expanding the approach to economic links, this paper puts forward some new concepts
such as link intensity and receiving coefficient, expounds the indexes of quantitative analysis of economic links and establishes
the quantitative-analysis model of economic links. With help of the model, this paper calculates the values of the link intensities
between Su-Xi-Chang (Suzhou-Wuxi-Changzhou) region and Shanghai, and analyzes the regional difference of the economic links. 相似文献
10.