全文获取类型
收费全文 | 155144篇 |
免费 | 22284篇 |
国内免费 | 31175篇 |
专业分类
测绘学 | 17928篇 |
大气科学 | 16035篇 |
地球物理 | 29480篇 |
地质学 | 80967篇 |
海洋学 | 22483篇 |
天文学 | 17388篇 |
综合类 | 7399篇 |
自然地理 | 16923篇 |
出版年
2024年 | 666篇 |
2023年 | 1940篇 |
2022年 | 5348篇 |
2021年 | 6840篇 |
2020年 | 5641篇 |
2019年 | 6922篇 |
2018年 | 7100篇 |
2017年 | 6712篇 |
2016年 | 7025篇 |
2015年 | 7333篇 |
2014年 | 8028篇 |
2013年 | 10913篇 |
2012年 | 10145篇 |
2011年 | 11084篇 |
2010年 | 10451篇 |
2009年 | 10829篇 |
2008年 | 10788篇 |
2007年 | 10157篇 |
2006年 | 9736篇 |
2005年 | 8219篇 |
2004年 | 6709篇 |
2003年 | 5130篇 |
2002年 | 5043篇 |
2001年 | 4572篇 |
2000年 | 4006篇 |
1999年 | 2352篇 |
1998年 | 1827篇 |
1997年 | 1634篇 |
1996年 | 1287篇 |
1995年 | 1271篇 |
1994年 | 1063篇 |
1993年 | 949篇 |
1992年 | 968篇 |
1991年 | 808篇 |
1990年 | 951篇 |
1989年 | 764篇 |
1988年 | 672篇 |
1987年 | 861篇 |
1986年 | 717篇 |
1985年 | 908篇 |
1984年 | 989篇 |
1983年 | 908篇 |
1982年 | 872篇 |
1981年 | 738篇 |
1980年 | 680篇 |
1979年 | 653篇 |
1978年 | 628篇 |
1977年 | 572篇 |
1976年 | 558篇 |
1974年 | 519篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
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
42.
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
43.
西秦岭温泉花岗岩体岩石学特征及岩浆混合标志 总被引:14,自引:5,他引:9
温泉花岗岩体由酸性端元的寄主岩石和暗色微细粒镁铁质包体群及基性岩墙群组成。无岩浆混合作用或岩浆混合作用较弱区段,寄主岩石以似斑状二长花岗岩为主.显示正常的花岗岩结构构造岩浆混合作用强烈区段。岩石的异常结构构造十分发育.矿物之间自形程度差异显著.常见包晶反应、包含结构、交代边、熔蚀边、交代蚕食的港湾状结构构造及交代缝合线、矿物镶边、斜长石异常环带和矿物残留等,多见指示岩浆混合的标志性矿物针状磷灰石。暗色微粒包体中多见寄主二长花岗岩中的捕掳晶。包体的形态、结构构造以及与寄主岩石强烈地成分交换等均是岩浆混合作用的标志。 相似文献
44.
45.
46.
47.
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
48.
The auriferous veins at Jinniushan occurs within the Jinniushan faulted zone in the Kunyushan Granite. Optical observation reveals that gold ore body formed during the main stage of hydrothermal activity. Detailed geothermometric studies of fluid inclusions from the veins show that the forming temperature ranges between 130℃ and 370℃ and the salinity is from 4.01 to 15.21 wvt percent NaCl. The ore-forming fluid is featured by low to moderate salinity, and low to moderate temperature. According to investigations of the values of vapor/liquid and temperatures of the ore-forming fluids, we propose that the boiling fluid inclusions exist in the main mineralization stages. Fluid boiling is suggested as a mechanism for the precipitation of gold from the hydrothermal fluid in the Jinniushan gold deposit. 相似文献
49.
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
50.
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