全文获取类型
收费全文 | 2138篇 |
免费 | 92篇 |
国内免费 | 375篇 |
专业分类
测绘学 | 58篇 |
大气科学 | 705篇 |
地球物理 | 211篇 |
地质学 | 1308篇 |
海洋学 | 87篇 |
天文学 | 110篇 |
综合类 | 33篇 |
自然地理 | 93篇 |
出版年
2023年 | 34篇 |
2022年 | 27篇 |
2021年 | 92篇 |
2020年 | 63篇 |
2019年 | 83篇 |
2018年 | 88篇 |
2017年 | 83篇 |
2016年 | 95篇 |
2015年 | 44篇 |
2014年 | 26篇 |
2013年 | 51篇 |
2012年 | 46篇 |
2011年 | 146篇 |
2010年 | 139篇 |
2009年 | 95篇 |
2008年 | 91篇 |
2007年 | 132篇 |
2006年 | 65篇 |
2005年 | 35篇 |
2004年 | 18篇 |
2003年 | 22篇 |
2002年 | 43篇 |
2001年 | 95篇 |
2000年 | 288篇 |
1999年 | 62篇 |
1998年 | 65篇 |
1997年 | 58篇 |
1996年 | 40篇 |
1995年 | 31篇 |
1994年 | 25篇 |
1993年 | 61篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 24篇 |
1987年 | 21篇 |
1986年 | 10篇 |
1985年 | 22篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 17篇 |
1973年 | 11篇 |
排序方式: 共有2605条查询结果,搜索用时 0 毫秒
1.
2.
Philippe CARREZ Karine DEMYK Patrick CORDIER Lon GENGEMBRE Jean GRIMBLOT Louis D'HENDECOURT Anthony P. JONES Hugues LEROUX 《Meteoritics & planetary science》2002,37(11):1599-1614
Abstract— We present the results of irradiation experiments aimed at understanding the structural and chemical evolution of silicate grains in the interstellar medium. A series of He+ irradiation experiments have been performed on ultra‐thin olivine, (Mg,Fe)2SiO4, samples having a high surface/volume (S/V) ratio, comparable to the expected S/V ratio of interstellar dust. The energies and fluences of the helium ions used in this study have been chosen to simulate the irradiation of interstellar dust grains in supernovae shock waves. The samples were mainly studied using analytical transmission electron microscopy. Our results show that olivine is amorphized by low‐energy ion irradiation. Changes in composition are also observed. In particular, irradiation leads to a decrease of the atomic ratios O/Si and Mg/Si as determined by x‐ray photoelectron spectroscopy and by x‐ray energy dispersive spectroscopy. This chemical evolution is due to the differential sputtering of atoms near the surfaces. We also observe a reduction process resulting in the formation of metallic iron. The use of very thin samples emphasizes the role of surface/volume ratio and thus the importance of the particle size in the irradiation‐induced effects. These results allow us to account qualitatively for the observed properties of interstellar grains in different environments, that is, at different stages of their evolution: chemical and structural evolution in the interstellar medium, from olivine to pyroxene‐type and from crystalline to amorphous silicates, porosity of cometary grains as well as the formation of metallic inclusions in silicates. 相似文献
3.
4.
5.
H. Flanquart C. Meur-Férec Ph. Deboudt V. Morel A.-P. Hellequin et al. 《GeoJournal》1991,24(2):223-223
Reports
Littoral '92 相似文献6.
Charles H. Nelson Douglas S. Hall Francis C. Fekel Robert E. Fried Richard E. Lines Helen C. Lines 《Astrophysics and Space Science》1991,182(1):1-17
Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27d.07±0d.07, which is slightly different from the 27d.5384±0d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R
h=2.58R
,R
c=12.28R
,M
h=1.40M
,M
c=1.46M
,i=80o.61 and velocity semi-amplitudesK
c=48.36 km s–1±0.79 km s–1, andK
h=50.50 km s–1±0.33 km s–1. The apparent magnitudes areV
h=9
m
.73 andV
c=8
m
.48. The distance to HD 155638 was estimated to be 310 parsecs. 相似文献
7.
The prevalence of dermal neoplasia among neotenic tiger salamanders (Ambystoma tigrinum) collected from the Reese Air Force Base sewage lagoon far exceeded that among salamanders from nearby uncontaminated lagoons. Perylene was the predominant pglycyclic aromatic hydrocarbon contaminant in this lagoon. Perylene was shown to be a substrate for monooxygenases in skin and liver homogenates and formed DNA-binding metabolites. Perylene exposure appeared to augment subsequent perylene metabolism by dermal enzymes but it was not a strong inducer of hepatic monooxygenases. Aroclor 1254 induced benzo(a)pyrene and perylene metabolism by both skin and liver enzymes. However, perylene apparently was not activated by salamander enzymes, as suggested by its lack of in vitro mutagenicity and failure to induce tumors. 相似文献
8.
9.
An extremely simple CFD tool is used to compare the calm-water drags of a series of hull forms and to define ‘optimized’ monohull ships for which the total (friction+wave) calm-water drag is minimized. The friction drag is estimated using the classical ITTC formula. The wave drag is predicted using the zeroth-order slender-ship approximation. Comparisons of theoretical predictions and experimental measurements for a series of eight hull forms show that—despite the extreme simplicity of the method that is used here to estimate the friction drag and the wave drag—the method is able to rank the drags of a series of hull forms roughly in accordance with experimental measurements. Thus, the method may be used, with appropriate caution, as a practical hull form design and optimization tool. For purposes of illustration, optimized hull forms that have the same displacement and waterplane transverse moment of inertia as the classical Wigley hull, taken as initial hull in the optimization process, are determined for three speeds and for a speed range. 相似文献