全文获取类型
收费全文 | 2661篇 |
免费 | 602篇 |
国内免费 | 725篇 |
专业分类
测绘学 | 135篇 |
大气科学 | 770篇 |
地球物理 | 605篇 |
地质学 | 1458篇 |
海洋学 | 253篇 |
天文学 | 136篇 |
综合类 | 291篇 |
自然地理 | 340篇 |
出版年
2024年 | 4篇 |
2023年 | 57篇 |
2022年 | 139篇 |
2021年 | 112篇 |
2020年 | 92篇 |
2019年 | 122篇 |
2018年 | 126篇 |
2017年 | 118篇 |
2016年 | 148篇 |
2015年 | 133篇 |
2014年 | 179篇 |
2013年 | 179篇 |
2012年 | 154篇 |
2011年 | 154篇 |
2010年 | 163篇 |
2009年 | 136篇 |
2008年 | 133篇 |
2007年 | 126篇 |
2006年 | 105篇 |
2005年 | 95篇 |
2004年 | 67篇 |
2003年 | 55篇 |
2002年 | 65篇 |
2001年 | 80篇 |
2000年 | 92篇 |
1999年 | 151篇 |
1998年 | 127篇 |
1997年 | 138篇 |
1996年 | 126篇 |
1995年 | 128篇 |
1994年 | 106篇 |
1993年 | 75篇 |
1992年 | 58篇 |
1991年 | 57篇 |
1990年 | 39篇 |
1989年 | 35篇 |
1988年 | 30篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1962年 | 2篇 |
排序方式: 共有3988条查询结果,搜索用时 15 毫秒
991.
中天山造山作用的同位素年代分期 总被引:5,自引:0,他引:5
我们把近年来所获得的一些年龄数据以及前人已有的年龄数据与区域地层接触关系作了对比,发现二者有意想不到的一致性,据此将中天山造山作用划分为5期,年龄分别大约为452—439Ma,412—402Ma,355—345Ma,334—327Ma和315—289Ma。中生代还可能有3期构造热事件,年龄大约为226—200Ma,165—160Ma和83Ma,代表了中天山的后期演化。上述年龄数据主要是从中天山南缘断裂带构造岩中获得的,它与区域年龄一致,这说明沿中天山两条边界断裂的逆冲推覆可能是导致中天山造山带变形的基本方式和原因。 相似文献
992.
Zhou Ming-feng Yao Qi-junLi Sheng Luo Zhi-quanYang Ji 《Chinese Astronomy and Astrophysics》2011,35(3):327
In order to assess the submillimeter wave observational conditions of Yangbajin, a Portable Submillimeter Telescope (POST) is used to measure the zenith atmospheric opacity at 460 GHz from November 2008 to December 2008. The results show that the quartiles of atmospheric opacity during the observing time at 460 GHz at Yangbajin Observatory is 1.25, 1.42 and 1.63, and the time proportion of atmospheric opacity less than 1 is about 3.4%. At last, the submillimeter wave site conditions of Yangbajin with those of other submillimeter observatories in the world are compared, and the possible causes that may influence the submillimeter atmospheric opacity are explored. 相似文献
993.
994.
We present high-precision,multi-band CCD photometry of two less-studied close binaries V1123 Tau and V1128 Tau.Complete covered light curves and a number of new times of light minima of the two eclipsing systems were obtained,based on which,revised orbital elements and new ephemerides were given.By adopting the Wilson-Devinney method,the light curves were analyzed.The photometric solutions confirm the W UMa-type nature of the binary systems.With the less-massive secondary slightly cooler than the primary,V1... 相似文献
995.
2004年入冬后清远市首次低温霜冻分析 总被引:6,自引:4,他引:2
本文通过分析2004年12月5~14日清远市北部地区出现的大面积连续低温霜冻天气,发现低温的出现与850hPa的负变高和露点温度有一定的对应关系,霜冻出现和结束与环流形势密切相关。 相似文献
996.
四川石棉县大水沟碲矿床地质与成因 总被引:10,自引:0,他引:10
四川石棉大水沟碲矿是我国发现的世界首例独立磅矿床,并具Te、Bi、Se、Au、Ag多元素矿化。通过对该矿床的地质特征、矿石学与流体包裹体、同位素地球化学进行分析研究后,指出该矿床受韧性-脆性剪切带构造岩片和隐伏花岗岩底辟热穹隆的双重控制,以中下三叠统动热变质大理岩-绿片岩-千枚岩组合地层为赋矿围岩,热液蚀变发育碳酸盐化、硅化等。流体包裹体和稳定同位素地球化学研究表明,流体属低氧逸度、高二氧化碳逸度,深成中温热液成矿作用,物质来源于地壳深部,后期受大气降水影响。K-Ar法测年与铅同位素两阶段模式年龄一致,成矿时代属燕山早期(144.2-150Ma),与区域分布的花岗岩关系密切。 相似文献
997.
998.
To reduce noise during electrical prospecting, we hereby propose a new method using correlation identification technology and conventional electrical exploration devices. A correlation operation can be carried out with the transmitted pseudo-random sequence and received time signal to suppress the random noise, and the time-domain impulse response and frequency response of the frequency domain of the underground media can be obtained. At the same time, using a dual Cole–Cole model to fit a complex resistivity spectrum, which is close to the frequency response, we can get a variety of induced polarization parameters and electromagnetic parameters of subsurface, which can provide more useful information for the exploration of mineral resources. This time domain prospecting method can effectively improve the efficiency of the spectral induced polarization method. In this article, we have carried out theoretical calculations and a simulation to prove the feasibility of such a method. 相似文献
999.
To quantify wave attenuation by (introduced) Spartina alterniflora vegetation at an exposed macrotidal coast in the Yangtze Estuary, China, wave parameters and water depth were measured during
13 consecutive tides at nine locations ranging from 10 m seaward to 50 m landward of the low marsh edge. During this period,
the incident wave height ranged from <0.1 to 1.5 m, the maximum of which is much higher than observed in other marsh areas
around the world. Our measurements and calculations showed that the wave attenuation rate per unit distance was 1 to 2 magnitudes
higher over the marsh than over an adjacent mudflat. Although the elevation gradient of the marsh margin was significantly
higher than that of the adjacent mudflat, more than 80% of wave attenuation was ascribed to the presence of vegetation, suggesting
that shoaling effects were of minor importance. On average, waves reaching the marsh were eliminated over a distance of ∼80 m,
although a marsh distance of ≥100 m was needed before the maximum height waves were fully attenuated during high tides. These
attenuation distances were longer than those previously found in American salt marshes, mainly due to the macrotidal and exposed
conditions at the present site. The ratio of water depth to plant height showed an inverse correlation with wave attenuation
rate, indicating that plant height is a crucial factor determining the efficiency of wave attenuation. Consequently, the tall
shoots of the introduced S. alterniflora makes this species much more efficient at attenuating waves than the shorter, native pioneer species in the Yangtze Estuary,
and should therefore be considered as a factor in coastal management during the present era of sea-level rise and global change.
We also found that wave attenuation across the salt marsh can be predicted using published models when a suitable coefficient
is incorporated to account for drag, which varies in place and time due to differences in plant characteristics and abiotic
conditions (i.e., bed gradient, initial water depth, and wave action). 相似文献
1000.
Haishan Luo Michel Quintard Gérald Debenest Farid Laouafa 《Computational Geosciences》2012,16(4):913-932
In this paper, a local non-equilibrium diffuse interface model is introduced for describing solid–liquid dissolution problems. The model is developed based on the analysis of Golfier et al. (J Fluid Mech 457:213–254, 2002) upon the dissolution of a porous domain, with the additional requirement that density variations with the mass fraction are taken into account. The control equations are generated by the upscaling of the balance equations for a solid–liquid dissolution using a volume averaging theory. This results into a diffuse interface model (DIM) that does not require an explicit treatment of the dissolving interface, e.g., the use of arbitrary Lagrangian–Eulerian (ALE) methods, for instance. Test cases were performed to study the features and influences of the effective coefficients inside the DIM. In particular, an optimum expression for the solid–liquid exchange coefficient is obtained from a comparison with the referenced solution by ALE simulations. Finally, a Ra–Pe diagram illustrates the interaction of natural convection and forced convection in the dissolution problem. 相似文献