全文获取类型
收费全文 | 27943篇 |
免费 | 5471篇 |
国内免费 | 5463篇 |
专业分类
测绘学 | 1248篇 |
大气科学 | 2428篇 |
地球物理 | 7838篇 |
地质学 | 14533篇 |
海洋学 | 4392篇 |
天文学 | 2074篇 |
综合类 | 1706篇 |
自然地理 | 4658篇 |
出版年
2024年 | 134篇 |
2023年 | 334篇 |
2022年 | 787篇 |
2021年 | 1043篇 |
2020年 | 1067篇 |
2019年 | 1267篇 |
2018年 | 1048篇 |
2017年 | 1105篇 |
2016年 | 1099篇 |
2015年 | 1249篇 |
2014年 | 1547篇 |
2013年 | 1754篇 |
2012年 | 1588篇 |
2011年 | 1745篇 |
2010年 | 1524篇 |
2009年 | 1839篇 |
2008年 | 1803篇 |
2007年 | 1908篇 |
2006年 | 1938篇 |
2005年 | 1652篇 |
2004年 | 1611篇 |
2003年 | 1513篇 |
2002年 | 1278篇 |
2001年 | 1158篇 |
2000年 | 1070篇 |
1999年 | 923篇 |
1998年 | 936篇 |
1997年 | 665篇 |
1996年 | 567篇 |
1995年 | 545篇 |
1994年 | 492篇 |
1993年 | 404篇 |
1992年 | 318篇 |
1991年 | 218篇 |
1990年 | 150篇 |
1989年 | 168篇 |
1988年 | 100篇 |
1987年 | 96篇 |
1986年 | 61篇 |
1985年 | 47篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 7篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1976年 | 5篇 |
1971年 | 6篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
81.
82.
83.
84.
研究油藏内部油水渗流方向时,主要考虑渗透率影响,引入两个水平方向渗透率比、水平与垂向渗透率比参数来分析。前者反映样品所在储层平面上两个水平方向渗流能力的差异,后者反映样品所在储层水平与垂向渗流能力的差异,并经小柱样测试和全岩心测试两种方法确定两个参数。通过对塔中4号油藏CⅠ油组9口井2306个样品两种渗透率比值分布直方图分析,研究了CⅠ油组渗透率的非均质性及其渗流方向:CI油组储层在水平方向的渗流能力有很大差异,具有明显的方向性。储层垂向渗流能力明显小于水平方向的渗流能力。 相似文献
85.
Natalia Orlova Vladimir Korchagin Nobuhiro Kikuchi Shoken. M. Miyama Aleksei Moiseev 《Astrophysics and Space Science》2003,284(2):739-742
We have tested the applicability of the global modal approach in the density wave theory of spiral structure for a sample
of spiral galaxies with measured axisymmetric background properties. We report here the results of the simulations for four
galaxies: NGC 488, NGC 628, NGC 1566, and NGC 3938. Using the observed radial distributions for the stellar velocity dispersions
and the rotation velocities we have constructed the equilibrium models for the galactic disks in each galaxy and implemented
two kinds of stability analyses - the linear global analysis and 2D-nonlinear simulations. In general, the global modal approach
is able to reproduce the observed properties of the spiral arms in the galactic disks. The growth of spirals in the galactic
disks can be physically understood in terms of amplification by over-reflection at the corotation resonance. Our results support
the global modal approach as a theoretical explanation of spiral structure in galaxies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
86.
The magnitude and spatial distribution of snow on sea ice are both integral components of the ocean–sea‐ice–atmosphere system. Although there exists a number of algorithms to estimate the snow water equivalent (SWE) on terrestrial surfaces, to date there is no precise method to estimate SWE on sea ice. Physical snow properties and in situ microwave radiometry at 19, 37 and 85 GHz, V and H polarization were collected for a 10‐day period over 20 first‐year sea ice sites. We present and compare the in situ physical, electrical and microwave emission properties of snow over smooth Arctic first‐year sea ice for 19 of the 20 sites sampled. Physical processes creating the observed vertical patterns in the physical and electrical properties are discussed. An algorithm is then developed from the relationship between the SWE and the brightness temperature measured at 37 GHz (55°) H polarization and the air temperature. The multiple regression between these variables is able to account for over 90% of the variability in the measured SWE. This algorithm is validated with a small in situ data set collected during the 1999 field experiment. We then compare our data against the NASA snow thickness algorithm, designed as part of the NASA Earth Enterprise Program. The results indicated a lack of agreement between the NASA algorithm and the algorithm developed here. This lack of agreement is attributed to differences in scale between the Special Sensor Microwave/Imager and surface radiometers and to differences in the Antarctic versus Arctic snow physical and electrical properties. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
87.
88.
In 1903 the Swiss Federal Research Institute WSL started its first forest hydrology measurements with the aim to deliver a sound scientific basis for the implementation of new forest legislation introduced in Switzerland in 1876. This legislation was triggered by several large floods that occurred in Switzerland, for which a major cause was widely seen as the poor condition of forests at that time. Consequently, hydrologic research at WSL first focused on the influence of forests on floods. In the second half of the 20th century, other hydrological issues such as water quality, snow hydrology and sediment transport complemented the hydrologic research at WSL. Some recent results of this work are presented in three papers joining this introductory paper to mark the 100th anniversary of hydrologic research at WSL. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
89.
90.