全文获取类型
收费全文 | 61986篇 |
免费 | 11216篇 |
国内免费 | 15501篇 |
专业分类
测绘学 | 4971篇 |
大气科学 | 8653篇 |
地球物理 | 11361篇 |
地质学 | 38104篇 |
海洋学 | 8088篇 |
天文学 | 2307篇 |
综合类 | 4662篇 |
自然地理 | 10557篇 |
出版年
2024年 | 272篇 |
2023年 | 770篇 |
2022年 | 1910篇 |
2021年 | 2235篇 |
2020年 | 2272篇 |
2019年 | 2854篇 |
2018年 | 2212篇 |
2017年 | 2390篇 |
2016年 | 2606篇 |
2015年 | 2844篇 |
2014年 | 3610篇 |
2013年 | 3380篇 |
2012年 | 3888篇 |
2011年 | 4120篇 |
2010年 | 3528篇 |
2009年 | 4111篇 |
2008年 | 4031篇 |
2007年 | 4472篇 |
2006年 | 4380篇 |
2005年 | 3871篇 |
2004年 | 3573篇 |
2003年 | 3355篇 |
2002年 | 2920篇 |
2001年 | 2589篇 |
2000年 | 2310篇 |
1999年 | 2153篇 |
1998年 | 1841篇 |
1997年 | 1641篇 |
1996年 | 1491篇 |
1995年 | 1275篇 |
1994年 | 1267篇 |
1993年 | 1082篇 |
1992年 | 860篇 |
1991年 | 617篇 |
1990年 | 510篇 |
1989年 | 446篇 |
1988年 | 307篇 |
1987年 | 201篇 |
1986年 | 138篇 |
1985年 | 87篇 |
1984年 | 37篇 |
1983年 | 29篇 |
1982年 | 33篇 |
1981年 | 26篇 |
1980年 | 26篇 |
1979年 | 34篇 |
1978年 | 38篇 |
1977年 | 24篇 |
1975年 | 4篇 |
1954年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
171.
A calculation formula on spherical pattern of Qinghai-Tibet plateau moving model is established. Tibet massif moves norward by east in speed of 28 mm/a, Ganshu-Qinghai massif moves to northeast in speed of 15 mm/a, Qomolangma Feng moves northward by a few east in speed of 35 ~42 mm/a. The low latitude perimeter is longer than the nigh latitude perimeter. When the Tibet massif moves northward, its latitude perimeter must be contracted and the Tibet massif must move eastward by Coriolis. Coriolis force is inertial in earth rotation. It makes the fall body turning to east and the rising block turning westward. In the Northern Hemisphere, it makes the northward body turning to east and the southward block turning to west.This is the reason why the tectonic zones of western Pacific are different from those of eastern Pacific. 相似文献
172.
Jean-Francois Guéguen Pho Hoang-Trong Hilaire Legros 《Geophysical Journal International》1987,89(3):839-855
Summary. A first-order form of the Euler's equations for rays in an ellipsoidal model of the Earth is obtained. The conditions affecting the velocity law for a monotonic increase, with respect to the arc length, in the angular distance to the epicentre, and in the angle of incidence, are the same in the ellipsoidal and spherical models. It is therefore possible to trace rays and to compute travel times directly in an ellipsoidal earth as in the spherical model. Thus comparison with the rays of the same coordinates in a spherical earth provides an estimate of the various deviations of these rays due to the Earth's flattening, and the corresponding travel-time differences, for mantle P -waves and for shallow earthquakes. All these deviations are functions both of the latitude and of the epicentral distance. The difference in the distance to the Earth's centre at points with the same geocentric latitude on rays in the ellipsoidal and in the spherical model may reach several kilometres. Directly related to the deformation of the isovelocity surfaces, this difference is the only cause of significant perturbation in travel times. Other differences, such as that corresponding to the ray torsion, are of the first order in ellipticity, and may exceed 1 km. They induce only small differences in travel time, less than 0.01s. Thus, we show that the ellipticity correction obtained by Jeffreys (1935) and Bullen (1937) by a perturbational method can be recovered by a direct evaluation of the travel times in an ellipsoidal model of the Earth. Moreover, as stated by Dziewonski & Gilbert (1976), we verify the non-dependence of this correction on the choice of the velocity law. 相似文献
173.
《The Professional geographer》1987,39(1):85-94
Reviews of geographic software in this article: DEMO-GRAPHICS: WORLD POPULATIONS AND PROJECTIONS. ESP GAUSS. CEMODEL S. Damus LIMDEP. William H. Greene MICROSTAT 4.1 OTIS PCIPS. (Personal Computer Image Processing System) . H.J. Meyers and R. Bernstein. REGRESSION ANALYSIS OF TIME SERIES (RATS) SPSS/PC+ URBAN DATA MANAGEMENT SOFTWARE (UDMS) 相似文献
174.
卞菊梅 《地球科学与环境学报》1995,(1)
本文主要依据地形图和航空照片解译,并经已有地质、钻孔资料验证及野外实地考察的方法来研究地形面及其变形特征,由此确定渭河盆地活断层的分布、最新活动特征及活动规律,为地震预报及地震危险性分析提供依据。 相似文献
175.
176.
To determine if Cu mediated reactions on atmospheric particles are important to HO2 chemistry in the ambient atmosphere, Cu molalities were calculated from measured Cu aerosol particle concentrations, mass and number size distribution data from a site in central Sweden. A comparison of characteristic times indicates that at low relative humidities the reaction is limited by the mass transport of gas phase HO2 to the particle surface and not by the chemical kinetics of the aqueous reaction. Comparison of half-lives for particle reactions and the gas phase destruction of HO2 to form H2O2 indicate that heterogeneous reactions on aerosol particles may have important consequences on the chemistry of HO2 and H2O2 in the troposphere. 相似文献
177.
论裸眼井中的“共振纵波”和“共振横波” 总被引:3,自引:0,他引:3
一、引言 文献[1]和[2]指出,充流体裸眼井中存在频率确定、波速恒定、且沿传播方向不衰减的“共振纵波”和“共振横波”。本文的目的在于论证并指出,这两种波是不存在的。 二、论证 设一点源位于z=0的井轴上,则井轴上z处的声波频率响应为 相似文献
178.
A new multidimensional scaling (MS) technique, referred to as the Pijk model, is formulated on the basis of associations among triple objects (samples or variables), instead of pairs of objects as used in the usual MS methods, such as factor analysis. The computational scheme provided for this method is the reduction of an original problem to a standard eigenvalue-eigenvector problem. The major goal of the technique is simplification and reduction of data structures and the rescaling of original objects into a new and reduced space, so that patterns and relations of the original objects can be conventiently examined in two-dimensional factor plots. The Pïjk method is illustrated and tested by using a set of geochemical data related to the epithermal gold and silver vein deposits in the Walker Lake quadrangle of Nevada and California. The characteristics of element associations suggested in the Pijk analysis are consistent with field observations. A preliminary comparison between the new method and the ordinary factor analysis also is made on the basis of the same data set. Results are encouraging in that analysis by the Pijk model captures triple-object associations that might be missed by the ordinary factor analysis which considers only pair-variable correlations 相似文献
179.
180.
本文较系统地总结了我国北西部金矿主要类型、矿化特征和金矿时空分布规律,在此基础上划分出4个成矿区、12条成矿带、32条成矿亚带,从而指明了找矿方向,为贯彻“以铀为主,综合找矿,多种经营,搞活地质”的方针,提供了较好的参考资料。 相似文献