全文获取类型
收费全文 | 120966篇 |
免费 | 2060篇 |
国内免费 | 1813篇 |
专业分类
测绘学 | 3745篇 |
大气科学 | 8818篇 |
地球物理 | 24119篇 |
地质学 | 45016篇 |
海洋学 | 9768篇 |
天文学 | 23857篇 |
综合类 | 2385篇 |
自然地理 | 7131篇 |
出版年
2022年 | 506篇 |
2021年 | 960篇 |
2020年 | 1057篇 |
2019年 | 1128篇 |
2018年 | 6752篇 |
2017年 | 5912篇 |
2016年 | 5272篇 |
2015年 | 1910篇 |
2014年 | 2866篇 |
2013年 | 5257篇 |
2012年 | 3858篇 |
2011年 | 6481篇 |
2010年 | 5350篇 |
2009年 | 6807篇 |
2008年 | 5908篇 |
2007年 | 6181篇 |
2006年 | 3918篇 |
2005年 | 3339篇 |
2004年 | 3487篇 |
2003年 | 3298篇 |
2002年 | 2986篇 |
2001年 | 2525篇 |
2000年 | 2421篇 |
1999年 | 1935篇 |
1998年 | 2046篇 |
1997年 | 1948篇 |
1996年 | 1594篇 |
1995年 | 1595篇 |
1994年 | 1390篇 |
1993年 | 1294篇 |
1992年 | 1231篇 |
1991年 | 1145篇 |
1990年 | 1219篇 |
1989年 | 1102篇 |
1988年 | 1016篇 |
1987年 | 1233篇 |
1986年 | 1053篇 |
1985年 | 1303篇 |
1984年 | 1420篇 |
1983年 | 1310篇 |
1982年 | 1252篇 |
1981年 | 1187篇 |
1980年 | 1047篇 |
1979年 | 972篇 |
1978年 | 955篇 |
1977年 | 909篇 |
1976年 | 859篇 |
1975年 | 815篇 |
1974年 | 817篇 |
1973年 | 794篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem. 相似文献
52.
W. H. Jefferys G. F. Benedict P. D. Hemenway P. J. Shelus R. L. Duncombe 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):299-305
The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed. 相似文献
53.
MohammedHazaea HUKe MohammedMattash CHENBing M.O.AI-JabaliAref MohammedAbdussalam 《东北亚地学研究》2004,7(2):181-184
The chemical composition of several thermal springs around Changbaishan area has been investigated. Cenozoic basaltic rocks are widely distributed in Northeast China and geothermal characteristics have been described. About one hundred hot springs exist around Changhaishan Volcano at the border between China and D.P.R.Korea with high temperature about 82~C. The pH values of the spring water range from 6.9 to 7.1 and the total flow rate is about 4.8 L/sec. The chemical composition of the thermal springs is sodium carbonate; the high-mineral contents of thermal water are believed to have medicinal properties. Bathhouses are already built along the hot springs to take the advantage of the supposed healing properties. The high quality of those hot springs is believed to be utilitized for mineral water. The chemical equilibrium temperatures were estimated at about 160℃ based on the Na-K-Ca geochemical thermometer. 相似文献
54.
55.
56.
57.
M. A. Mansour 《Astrophysics and Space Science》1990,166(2):269-275
The interaction of free convection with thermal radiation of the oscillatory flow past a vertical plate is studied. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. 相似文献
58.
59.
M.S. Hanner E. Tedesco A.T. Tokunaga G.J. Veeder D.F. Lester F.C. Witteborn J.D. Bregman J. Gradie L. Lebofsky 《Icarus》1985,64(1):11-19
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm. 相似文献
60.
A coupled continuum‐discrete hydromechanical model was employed to analyse the liquefaction of a saturated loose deposit of cohesionless particles when subjected to a dynamic base excitation. The pore fluid flow was idealized using averaged Navier–Stokes equations and the discrete element method was employed to model the solid phase particles. A well established semi‐empirical relationship was utilized to quantify the fluid–particle interactions. The conducted simulations revealed a number of salient micro‐mechanical mechanisms and response patterns associated with the deposit liquefaction. Space and time variation of porosity was a major factor which affected the coupled response of the solid and fluid phases. Pore fluid flow was within Darcy's regime. The predicted response exhibited macroscopic patterns consistent with experimental results and case histories of the liquefaction of granular soil deposits. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献