收费全文 | 1218篇 |
免费 | 276篇 |
国内免费 | 508篇 |
测绘学 | 16篇 |
大气科学 | 424篇 |
地球物理 | 283篇 |
地质学 | 826篇 |
海洋学 | 214篇 |
天文学 | 8篇 |
综合类 | 89篇 |
自然地理 | 142篇 |
2024年 | 9篇 |
2023年 | 20篇 |
2022年 | 41篇 |
2021年 | 40篇 |
2020年 | 58篇 |
2019年 | 60篇 |
2018年 | 50篇 |
2017年 | 74篇 |
2016年 | 60篇 |
2015年 | 81篇 |
2014年 | 90篇 |
2013年 | 95篇 |
2012年 | 90篇 |
2011年 | 107篇 |
2010年 | 86篇 |
2009年 | 87篇 |
2008年 | 92篇 |
2007年 | 110篇 |
2006年 | 91篇 |
2005年 | 79篇 |
2004年 | 72篇 |
2003年 | 64篇 |
2002年 | 61篇 |
2001年 | 61篇 |
2000年 | 50篇 |
1999年 | 42篇 |
1998年 | 43篇 |
1997年 | 33篇 |
1996年 | 29篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1954年 | 1篇 |
相似文献
24.
W. Kirchner F. Welter A. Bongartz J. Kames S. Schweighoefer U. Schurath 《Journal of Atmospheric Chemistry》1990,10(4):427-449
A liquid jet of 90 m diameter and variable length has been utilized to determine absorption rates and, hence, mass accommodation coefficients , of atmospheric trace gases. The compounds investigated are HCl (0.01), HNO3 (0.01), N2O5 (0.005), peroxyacetyl nitrate (>0.001), and HONO (0.005). It is concluded that the absorption of these trace gases by liquid atmospheric water is not significantly retarded by interfacial mass transport. The strengths and limitations of the liquid jet technique for measuring mass accommodation coefficients are explored. 相似文献
25.
在野外调查和收集现有资料基础上,对下河泉水源地水文地质条件、泉水流量动态、水源地保证程度与可能的环境问题进行了分析,论证了建立下河泉水源地的可行性. 相似文献
26.
27.
28.
The solubility of Ti- and P-rich accessory minerals has been examined as a function of pressure and K2O/Na2O ratio in two series of highly evolved silicate systems. These systems correspond to (a) alkaline, varying from alkaline to peralkaline with increasing K2O/Na2O ratio; and (b) strongly metaluminous (essentially trondhjemitic at the lowest K2O/Na2O ratio) and remaining metaluminous with increasing K2O/Na2O ratio (to 3). The experiments were conducted at a fixed temperature of 1000 °C, with water contents varying from 5 wt.% at low pressure (0.5 GPa), increasing through 5–10 wt.% at 1.5–2.5 GPa to 10 wt.% at 3.5 GPa. Pressure was extended outside the normal crustal range, so that the results may also be applied to derivation of hydrous silicic melts from subducted oceanic crust.
For the alkaline composition series, the TiO2 content of the melt at Ti-rich mineral saturation decreases with increasing pressure but is unchanged with increasing K content (at fixed pressure). The P2O5 content of the alkaline melts at apatite saturation increases with increased pressure at 3.5 GPa only, but decreases with increasing K content (and peralkalinity). For the metaluminous composition series (termed as “trondhjemite-based series” (T series)), the TiO2 content of the melt at Ti-rich mineral saturation decreases with increasing pressure and with increasing K content (at fixed pressure). The P2O5 content of the T series melts at apatite saturation is unchanged with increasing pressure, but decreases with increasing K content. The contrasting results for P and Ti saturation levels, as a function of pressure in both compositions, point to contrasting behaviour of Ti and P in the structure of evolved silicate melts. Ti content at Ti-rich mineral saturation is lower in the alkaline compared with the T series at 0.5 GPa, but is similar at higher pressures, whereas P content at apatite saturation is lower in the T series at all pressures studied. The results have application to A-type granite suites that are alkaline to peralkaline, and to I-type metaluminous suites that frequently exhibit differing K2O/Na2O ratios from one suite to another. 相似文献 29.
Introduction The tidal variation signals of the solid Earth recorded with the modern measuring techniques can be used to provide effectively the means to cognize the Earths motion, deformation and structure character, especially to monitor the material motion in the Earths interior. In the recent 20 years, the distribution character of the global gravity field has made great progress since the continuous and deep theoretical studies in geophysics and geodesy domains. The successful manufactur… 相似文献
30.
Moon Kyum Kim Yun Mook Lim Seong Yong Cho Kyung Hwan Cho Kang Won Lee 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):1151-1158
A three-dimensional soil–structure–liquid interaction problem is numerically simulated in order to analyze the dynamic behavior of a base-isolated liquid storage tank subjected to seismic ground motion. A dynamic analysis of a liquid storage tank is carried out using a hybrid formulation, which combines the finite shell elements for structures and the boundary elements for liquid and soil. The system is composed of three parts: the liquid–structure interaction part, the soil–foundation interaction part, and the base-isolation part. In the liquid–structure interaction part, the tank structure is modeled using the finite elements and the liquid is modeled using the internal boundary elements, which satisfy the free surface boundary condition. In the soil–foundation interaction part, the foundation is modeled using the finite elements and the half-space soil media are modeled using the external boundary elements, which satisfy the radiation condition in the infinite domain. Finally, above two parts are connected with the base-isolation system to solve the system's behavior. Numerical examples are presented to demonstrate the accuracy of the developed method, and an earthquake response analysis is carried out to demonstrate the applicability of the developed technique. The properties of a real LNG tank located in the west coast of Korea are used. The effects of the ground and the base-isolation system on the behavior of the tank are analyzed. 相似文献
|