全文获取类型
收费全文 | 7997篇 |
免费 | 1938篇 |
国内免费 | 1696篇 |
专业分类
测绘学 | 784篇 |
大气科学 | 1052篇 |
地球物理 | 3049篇 |
地质学 | 4175篇 |
海洋学 | 769篇 |
天文学 | 486篇 |
综合类 | 709篇 |
自然地理 | 607篇 |
出版年
2024年 | 34篇 |
2023年 | 81篇 |
2022年 | 198篇 |
2021年 | 267篇 |
2020年 | 281篇 |
2019年 | 367篇 |
2018年 | 262篇 |
2017年 | 300篇 |
2016年 | 327篇 |
2015年 | 378篇 |
2014年 | 443篇 |
2013年 | 493篇 |
2012年 | 532篇 |
2011年 | 553篇 |
2010年 | 410篇 |
2009年 | 544篇 |
2008年 | 470篇 |
2007年 | 609篇 |
2006年 | 548篇 |
2005年 | 454篇 |
2004年 | 428篇 |
2003年 | 407篇 |
2002年 | 346篇 |
2001年 | 319篇 |
2000年 | 342篇 |
1999年 | 324篇 |
1998年 | 291篇 |
1997年 | 266篇 |
1996年 | 251篇 |
1995年 | 195篇 |
1994年 | 192篇 |
1993年 | 171篇 |
1992年 | 132篇 |
1991年 | 89篇 |
1990年 | 85篇 |
1989年 | 74篇 |
1988年 | 54篇 |
1987年 | 36篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1972年 | 1篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
21.
用电测深研究地电断面、寻找隐伏多金属矿体时,以往采用ρ_s(或η_s)等值线断面图进行地质推断解释,因受浅源信号的干扰,效果差。本文提出了采用ρ_s(或η_s)差值法,能排除浅源干扰信号,反映出地电断面的相对变化,突出了深部微弱信息,取得了较好的地质解释效果。 相似文献
22.
Belinda Kalomeni E. Rennan PekÜnlÜ Kadri Yakut 《Astrophysics and Space Science》2005,296(1-4):477-480
In this study, we present a photometric study of AM Her, a prototype of a class of magnetic CVs. Optical photometry of AM
Her was obtained using the Russian–Turkish 1.5 m telescope at TüBİTAK National Observatory (TUG) in August 2003. The R band light curve of the system shows two maxima and two minima during one orbital cycle. In both observing nights the star
showed flickering at a significant level. The measured flickering time scale is about 5 min. 相似文献
23.
Hari Om Vats 《Journal of Astrophysics and Astronomy》2006,27(2-3):227-235
Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there
are two regimes of high speed solar wind streams with a threshold of ∼ 850 km s-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in
the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams
with +ve and-ve IMF. GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high
speed streams (< 850 km s-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic
activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective
in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle
23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and
other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm
of this cycle occurred when Bz was positive. 相似文献
24.
Rodger I. Thompson 《Astrophysics and Space Science》2003,284(2):353-356
Tests and constraints on current theories of galaxy formation and evolution are presented. They are derived from observations
of the Northern Hubble Deep Field with WFPC2 and NICMOS. Photometric redshifts, extinctions and spectral energy distributions
are calculated for all objects in the field. The tests and constraints are derived from the output of this analysis. The tests
of the predictions from hierarchical and pure luminosity evolution galaxy evolution calculations favor the hierarchical model.
Constraints are provided by the current luminosity function and its evolution to a redshift of 6.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
25.
Variables related to urban park awareness are identified and methods for relaxing assumptions of perfect information in park use models are discussed. Park awareness is related to park characteristics (age and degree of development of the park), population characteristics (race, age, length of residence, recreation participation), and distance. Park attributes are stronger predictors of both park awareness and use than is distance. These findings parallel similar research on the cognitive aspects of shopping decisions. 相似文献
26.
27.
28.
29.
揭示Rankine涡风场模式和Jelesnianski风场模式之间的联系,并设计了一种台风风场分布模式,它的风速分布曲线落在Jelesnianski和Rankine涡两个风场模式的风速分布曲线之间,具有一个既优于Jelesnianski又优于Rankine涡的风速衰减速率,因此它同时克服了Rankine涡模式计算风速偏小和Jelesnianski模式计算风速偏大的缺点,以一种比较合理的变化趋势向远方衰减,成为一个比较切合实际的台风风场分布模式。同时,文中提出的移行台风风场计算方法对宫崎正卫、上野武夫和Jelesnianski模式都有一定的改进。 相似文献
30.
本文查阅了从1973-1985,13年的历史资料,对石臼港沿岸波浪场进行了详细的分类、统计分析和计算,提出了各类较强天气系统影响石(即指石臼港)的极端区域,同时获得了石港沿岸各类天气系统影响下的波浪分布特点以及波高计算式,为保障石港的生产及港口建设为石港的波了提供了有益的分析数据和预报手段。 相似文献