全文获取类型
收费全文 | 65442篇 |
免费 | 919篇 |
国内免费 | 510篇 |
专业分类
测绘学 | 1578篇 |
大气科学 | 4735篇 |
地球物理 | 12852篇 |
地质学 | 23163篇 |
海洋学 | 5887篇 |
天文学 | 14527篇 |
综合类 | 132篇 |
自然地理 | 3997篇 |
出版年
2021年 | 624篇 |
2020年 | 645篇 |
2019年 | 711篇 |
2018年 | 1525篇 |
2017年 | 1439篇 |
2016年 | 1786篇 |
2015年 | 994篇 |
2014年 | 1655篇 |
2013年 | 3368篇 |
2012年 | 1889篇 |
2011年 | 2585篇 |
2010年 | 2335篇 |
2009年 | 3030篇 |
2008年 | 2587篇 |
2007年 | 2627篇 |
2006年 | 2473篇 |
2005年 | 1941篇 |
2004年 | 1915篇 |
2003年 | 1832篇 |
2002年 | 1793篇 |
2001年 | 1619篇 |
2000年 | 1527篇 |
1999年 | 1250篇 |
1998年 | 1240篇 |
1997年 | 1309篇 |
1996年 | 1046篇 |
1995年 | 1056篇 |
1994年 | 990篇 |
1993年 | 883篇 |
1992年 | 848篇 |
1991年 | 792篇 |
1990年 | 823篇 |
1989年 | 775篇 |
1988年 | 761篇 |
1987年 | 857篇 |
1986年 | 745篇 |
1985年 | 954篇 |
1984年 | 994篇 |
1983年 | 972篇 |
1982年 | 874篇 |
1981年 | 888篇 |
1980年 | 822篇 |
1979年 | 735篇 |
1978年 | 698篇 |
1977年 | 683篇 |
1976年 | 611篇 |
1975年 | 593篇 |
1974年 | 601篇 |
1973年 | 605篇 |
1971年 | 373篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
The problem of the diversity of the geochemical types of carbon dioxide waters (CDW) in petrografically and mineralogically uniform crystalline rock masses is solved with allowance made for the effect of different boundary conditions (physicochemical parameters) on the geochemical effect of interaction in the rock–water system. The formation of the entire geochemical spectrum of CDW in crystalline rock masses is shown to be explicable on the basis of a model of interaction in granite–water systems at different mass ratios of reacting rock (S) and water (L), different temperatures T, and equilibrium concentrations of dissolved CO2 (P
CO2). 相似文献
122.
Natural Resources Research - Exploration ventures in frontier areas have high risks. Before committing to them, firms prepare regional resource assessments to evaluate the potential payoffs. With... 相似文献
123.
124.
Shear wave statics using receiver functions 总被引:1,自引:0,他引:1
125.
Responses of interrill runoff and erosion rates to vegetation change in southern Arizona 总被引:1,自引:0,他引:1
Vegetation change, fi-om grassland to shrubland, has occurred over much of the Sonoran and Chihuahuan Deserts during the past century. The effect of this vegetation change on interrill runoff and erosion was examined by conducting rainfall-simulation experiments on large runoff plots on contemporary grassland and shrubland hillslopes. These experiments show that, compared to the grassland, the interrill portions of shrubland hillslopes (1) have higher runoff rates, (2) experience equilibrium runoff conditions much more frequently, (3) exhibit higher overland flow velocities, and (4) are subject to greater rates of erosion. The environmental change that has led to the vegetation change has been relatively minor, but its geomorphic impact has been substantial. 相似文献
126.
G. D. Nastrom 《Annales Geophysicae》1997,15(6):786-796
The spectral width observed by Doppler radars can be due to several effects including the atmospheric turbulence within the radar sample volume plus effects associated with the background flow and the radar geometry and configuration. This study re-examines simple models for the effects due to finite beam-width and vertical shear of the horizontal wind. Analytic solutions of 1- and 2-dimensional models are presented. Comparisons of the simple 2-dimensional model with numerical integrations of a 3-dimensional model with a symmetrical Gaussian beam show that the 2-dimensional model is usually adequate. The solution of the 2-dimensional model gives a formula that can be applied easily to large data sets. Analysis of the analytic solutions of the 2-dimensional model for off-vertical beams reveals a term that has not been included in mathematical formulas for spectral broadening in the past. This term arises from the simultaneous effects of the changing geometry due to curvature within a finite beamwidth and the vertical wind shear. The magnitude of this effect can be comparable to that of the well-known effects of beam-broadening and wind shear, and since it can have either algebraic sign, it can significantly reduce (or increase) the expected spectral broadening, although under typical conditions it is smaller than the beam-broadening effect. The predictions of this simple model are found to be consistent with observations from the VHP radar at White Sands Missile Range, NM. 相似文献
127.
128.
The paper presents the first quantitative results of a laboratory study of the velocity field in a two-arm spiral-wave pattern generated in a steady-state fashion by a hydrodynamical instability in a differentially rotating, thin layer of liquid. The liquid layer has a free surface, and the rotational profile includes an interval where the velocity drops abruptly, as in the gaseous disks of spiral galaxies. The properties of anticyclonic vortices observed between the arms of this pattern at the corotation radius are considered. 相似文献
129.