全文获取类型
收费全文 | 13540篇 |
免费 | 2799篇 |
国内免费 | 4479篇 |
专业分类
测绘学 | 1818篇 |
大气科学 | 2341篇 |
地球物理 | 3057篇 |
地质学 | 7892篇 |
海洋学 | 2215篇 |
天文学 | 315篇 |
综合类 | 1326篇 |
自然地理 | 1854篇 |
出版年
2024年 | 143篇 |
2023年 | 414篇 |
2022年 | 841篇 |
2021年 | 1009篇 |
2020年 | 786篇 |
2019年 | 965篇 |
2018年 | 912篇 |
2017年 | 930篇 |
2016年 | 938篇 |
2015年 | 857篇 |
2014年 | 1044篇 |
2013年 | 1056篇 |
2012年 | 1068篇 |
2011年 | 1071篇 |
2010年 | 1068篇 |
2009年 | 936篇 |
2008年 | 894篇 |
2007年 | 778篇 |
2006年 | 709篇 |
2005年 | 577篇 |
2004年 | 472篇 |
2003年 | 391篇 |
2002年 | 363篇 |
2001年 | 331篇 |
2000年 | 278篇 |
1999年 | 316篇 |
1998年 | 237篇 |
1997年 | 234篇 |
1996年 | 173篇 |
1995年 | 174篇 |
1994年 | 168篇 |
1993年 | 145篇 |
1992年 | 126篇 |
1991年 | 73篇 |
1990年 | 65篇 |
1989年 | 55篇 |
1988年 | 54篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 22篇 |
1979年 | 11篇 |
1976年 | 2篇 |
1958年 | 7篇 |
1957年 | 1篇 |
1954年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
921.
922.
本文把模糊模式识别的直接方法用于检测日本东海地区地震活动性、体积应变、地下水位、地下水氡含量、地倾斜和潮位中的前兆变化。此方法可消除诸如降雨和气温变化等干扰,使我们能更清晰地识别出地震前兆。此外,还把模糊相似方法和模糊聚类方法应用于识别地震空区及检验地震活动随时间变化的相似性。上述方法在日本其他地区同样有效,即将编入日本气象研究所板内地震预报计划中的计算机系统内。 相似文献
923.
Using the operational model(B model)of Beijing Meteorological Center,we do some of numerical experi-ments of crossing and rounding mountains in all velocity adjustment scheme,and study dynamic effect ofQinghai-Xizang Plateau and Rocky Mountains on lee cyclones.The results show that due to air flow roundthe Qinghai-Xizang Plateau,divergence is distributed in the shape of confluence which matches cyclogenesisarea and cyclonic track in East Asia.In the downstream of the Qinghai-Xizang Plateau,convergence inthe upper troposphere restrains cyclone development in the east of China mainland.In North America,air flow primarily crosses over Rocky Mountains.Air is adiabatically cooled when it flows upward in thewest flank of Rocky Mountains,while air is warmed when it flows downward in the lee side.The fact isimportant for the lee cyclogenesis and the lee frontogenesis of Rocky Mountains.Air flow crossing over RockyMountains is also the main cause for forming dryline in the mid-west of United States. 相似文献
924.
925.
湖南强风暴暖盖环境场研究 总被引:3,自引:1,他引:3
本文通过对湘中、湘北地区42次强风暴资料的分析,建立了一个强风暴环境场的天气学模式,着重讨论了暖盖(即对流层中下层的逆温层)的形成和维持机理. 暖盖是由于绕过青藏高原两侧的两支西风波动相互作用而产生的.它的存在有利于低空急流在其东部边缘的低空加强,而低空急流引起的垂直环流反过来又有利于暖盖的维持,当暖盖下降到低空急流轴附近时因受扰动而破坏,引起强风暴的发生. 相似文献
926.
The Lower Palaeozoic system is a series of iron-bearing rocks consisting mainly of shallow sea-fades carbonates. On the basis of microfacies analysis of the carbonate rocks, the Lower Palaeozoic sedimentary sea basin is divided into two broad sedimentary-tectonic regions of four sedimentary facies and eight subfacies. The original iron-rich carbonates were deposited in saltlakes, lagoons, etc. of the restricted basins. Over the long geological history, the original iron formations were reconstructed to various extents by late tectonic processes. Geological observations and studies on the equilibrium mechanism of oxygen/sulfur isotopic fractionation and the composition and temperature of fluid inclusions in the minerals indicate that thermal brines played an important role in reworking of the original iron-rich carbonate rocks, which led to the formation of sedimentary-reworked strata-bound ore deposit. 相似文献
927.
Presented in this paper are some primary data on the temperature, stratigraphical altitude and thickness of a certain uranium ore deposit. Taking these data as the parameters for the temperature, pressure and geochemical conditions of uranium mineralization under ideal geological conditions which constitute a finite variable series, in conjunction with the catastrophe theory developed by Rene Thom (1968), we have proposed a swallow-tail model fit to uranium mineralization. This model provides insight into the mechanism of uranium mineralization. Our study shows that the process of uranium mineralization is a discontinuous or catastrophic event. Temperature and pressure are considered important thermodynamic conditions which control the distribution pattern of uranium mineralization, and the principle of temperature-pressure correspondence for uranium mineralization has been also derived. Geological bodies of minerogenetic importance serve as favourable geochemical media for capturing ore-forming materials. Uranium mineralization of commercial importance depends on a delicate coupling between temperature,pressure, and geochemical condition. The loci of uranium mineralization in the model constitute the surfaceK, referred to as the surface of enrichment-mineralization, on which minerogenetic domain is expected. The model provides quantitatively clues to the process of uranium mineralization, i.e., a process from quantitative to qualitative changes. 相似文献
928.
929.
930.
The Rapid Inversion of 3-D Potential Field and Program Design 总被引:1,自引:0,他引:1
The application of three-dimensional inversion of gravity and magnetic fields is very important not only in geophysical researches, but also in the study of geological structures. A formula of potential field in frequency-domain, developed by Parker in 1973, can be used as a rapid and effective algorithm in gravity and magnetic inversion. The technique has been improved then by Oldenburg, Sprenke, Feng and others.In addition to a brief introduction of Parker's algorithm and its applications, this paper includes the following five parts: basic computational techniques, inversion of single layer, convergence and constraints, simultaneous inversion for density and topography as well as inversion of multilayers. The authors present relevant practical iterative formulas and its varieties when density distribution varies with depth in linear or exponential relation. In order to maintain computation stability and speed up iteration convergence, some approaches are taken in the program design, for instance shifting lower interface of the studied layer, inverting corrections of topography, reducing grid boundary effects and utilizing low-pass filter. With the consideration of the nonuniqueness of the inversion, a method of using seismic data to constrain the range ofpossible models is discussed. It is pointed out that the density variation generates less effects than those of topography on the spectrum of gravity anomaly in second order. Therefore density contrast and topography can be inverted simultaneously by an alternative weighting iteration. By analogy, the inversion of multilayer model can be done in the above procedure. An approach of model decomposition is useful in the computation of multilayer model. The techniques discussed in the present paper for gravitational field are also valid for magnetic field. 相似文献