全文获取类型
收费全文 | 60335篇 |
免费 | 1147篇 |
国内免费 | 439篇 |
专业分类
测绘学 | 1219篇 |
大气科学 | 4225篇 |
地球物理 | 12074篇 |
地质学 | 21688篇 |
海洋学 | 5299篇 |
天文学 | 13489篇 |
综合类 | 132篇 |
自然地理 | 3795篇 |
出版年
2021年 | 551篇 |
2020年 | 652篇 |
2019年 | 748篇 |
2018年 | 1414篇 |
2017年 | 1378篇 |
2016年 | 1555篇 |
2015年 | 960篇 |
2014年 | 1531篇 |
2013年 | 2877篇 |
2012年 | 1765篇 |
2011年 | 2434篇 |
2010年 | 2139篇 |
2009年 | 2760篇 |
2008年 | 2485篇 |
2007年 | 2550篇 |
2006年 | 2348篇 |
2005年 | 1739篇 |
2004年 | 1784篇 |
2003年 | 1769篇 |
2002年 | 1614篇 |
2001年 | 1432篇 |
2000年 | 1326篇 |
1999年 | 1206篇 |
1998年 | 1217篇 |
1997年 | 1208篇 |
1996年 | 966篇 |
1995年 | 923篇 |
1994年 | 818篇 |
1993年 | 747篇 |
1992年 | 678篇 |
1991年 | 661篇 |
1990年 | 705篇 |
1989年 | 635篇 |
1988年 | 578篇 |
1987年 | 669篇 |
1986年 | 646篇 |
1985年 | 815篇 |
1984年 | 886篇 |
1983年 | 859篇 |
1982年 | 782篇 |
1981年 | 717篇 |
1980年 | 688篇 |
1979年 | 646篇 |
1978年 | 649篇 |
1977年 | 609篇 |
1976年 | 576篇 |
1975年 | 587篇 |
1974年 | 546篇 |
1973年 | 572篇 |
1972年 | 375篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Electron impact excitation rates for transitions in the S v ion, calculated with theR-matrix code, are used to derive the electron temperature sensitive emission line ratiosR
1 =I(854.8 Å)/I(786.9 Å),R
2 =I(852.2 Å)/I(786.9 Å),R
3 =I(849.2 Å)/I(786.9 Å), andR
4 =I(1199.1 Å)/I(786.9 Å), which are found to be significantly different from previous estimates. A comparison of the present results with observational data for a sunspot obtained with the Harvard S-055 spectrometer on boardSkylab reveals generally good agreement between theory and experiment, except in the case ofR
1, which is probably due to blending in the 854.8 Å feature. The possible effects of Lyman continuum absorption on the observed line ratios is briefly discussed. 相似文献
42.
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
43.
44.
45.
46.
47.
E.A. Evstigneeva R.R. de Carvalho A.L. Ribeiro H.V. Capelato 《Astrophysics and Space Science》2003,284(2):487-490
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families
of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different
loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this
diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we
can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
48.
In this paper we analyse error-removing techniques used without sufficient theoretical support in a previous paper, where Chandrasekhar's higher-order perturbation theories were developed for either uniformly or differentially-rotating polytropic stars. 相似文献
49.
Virgil E. Barnes 《Meteoritics & planetary science》1990,25(3):149-159
Abstract— Fifty-odd years of tektite research are reviewed, proceeding from the discovery of the first North American tektites in 1936. This included the early recognition that tektites were terrestrial objects rather than meteorites and that the glassy particles in tektites were fused quartz (lechatelierite). Later, during National Science Foundation-supported research, it was found that some tektites appeared to have formed as puddles of melt, that the content and character of bubbles in lechatelierite can be used as a relative temperature scale, that rayed bubbles in tektites formed from hydrous minerals, that bubbles in tektites formed chiefly from water which was absorbed into the walls of the bubbles leaving vacuums, and that “fingers” in the surficial part of some tektites may have formed by differential volatilization. Some unpublished observations and adventures are briefly reported. 相似文献
50.