全文获取类型
收费全文 | 51534篇 |
免费 | 745篇 |
国内免费 | 332篇 |
专业分类
测绘学 | 1534篇 |
大气科学 | 3980篇 |
地球物理 | 9883篇 |
地质学 | 16997篇 |
海洋学 | 4290篇 |
天文学 | 12489篇 |
综合类 | 127篇 |
自然地理 | 3311篇 |
出版年
2020年 | 393篇 |
2019年 | 380篇 |
2018年 | 964篇 |
2017年 | 905篇 |
2016年 | 1194篇 |
2015年 | 828篇 |
2014年 | 1320篇 |
2013年 | 2618篇 |
2012年 | 1260篇 |
2011年 | 1687篇 |
2010年 | 1552篇 |
2009年 | 2040篇 |
2008年 | 1858篇 |
2007年 | 1840篇 |
2006年 | 1744篇 |
2005年 | 1588篇 |
2004年 | 1567篇 |
2003年 | 1450篇 |
2002年 | 1400篇 |
2001年 | 1265篇 |
2000年 | 1183篇 |
1999年 | 1136篇 |
1998年 | 1087篇 |
1997年 | 1081篇 |
1996年 | 860篇 |
1995年 | 854篇 |
1994年 | 815篇 |
1993年 | 745篇 |
1992年 | 723篇 |
1991年 | 691篇 |
1990年 | 788篇 |
1989年 | 680篇 |
1988年 | 657篇 |
1987年 | 746篇 |
1986年 | 623篇 |
1985年 | 833篇 |
1984年 | 950篇 |
1983年 | 920篇 |
1982年 | 870篇 |
1981年 | 822篇 |
1980年 | 731篇 |
1979年 | 700篇 |
1978年 | 698篇 |
1977年 | 631篇 |
1976年 | 596篇 |
1975年 | 521篇 |
1974年 | 598篇 |
1973年 | 586篇 |
1972年 | 369篇 |
1971年 | 336篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
M. Yu. Khlopov R. V. Konoplich R. Mignani S. G. Rubin A. S. Sakharov 《Astroparticle Physics》2000,12(4):367-372
The existence of macroscopic regions with antibaryon excess in the baryon asymmetric Universe with general baryon excess is the possible consequence of practically all models of baryosynthesis. Diffusion of matter and antimatter to the border of antimatter domains defines the minimal scale of the antimatter domains surviving to the present time. A model of diffused antiworld is considered, in which the density within the surviving antimatter domains is too low to form gravitationally bound objects. The possibility to test this model by measurements of cosmic gamma ray fluxes is discussed. The expected gamma ray flux is found to be acceptable for modern cosmic gamma ray detectors and for those planned for the near future. 相似文献
112.
H. S. de Römer 《International Journal of Earth Sciences》1962,51(1):268-280
An attempt is made to correlate and separate in terms of style and time two contrasting sets of structural elements in the northwestern part of the Appalachian Uplands in the Province of Quebec, Canada. There is sufficient evidence to indicate that a fold system with north-south trending axes is superimposed on a fold system with east-west axes. It is suggested that the two sets of structures represent pulses of one long-continued deformation accompanied by corresponding early and late phases of metamorphism.
Zusammenfassung Es wurde versucht, in den Appalachen des südöstlichen Teiles der Provinz Quebec, Kanada, zwei ungleichzeitige tektonische Systeme verschiedenen Baustils zu trennen. Die komplexen Kleinstrukturen zeigen, da\ Ost-West streichende Faltenachsen von einer jüngeren Nord-Süd-Faltung überprägt worden sind. Der Autor ist der Meinung, da\ die zwei tektonischen Systeme, die von einer frühen und späten Phase der Metamorphose begleitet werden, den zeitlich getrennten Verformungsstadien einer Orogenese entsprechen.相似文献
113.
Examination of schorlomite from ijolite at Magnet Cove (USA) and silicocarbonatite at Afrikanda (Russia), using electron-microprobe and hydrogen analyses, X-ray diffraction and Mössbauer spectroscopy, shows the complexity of substitution mechanisms operating in Ti-rich garnets. These substitutions involve incorporation of Na in the eightfold-coordinated X site, Fe2+ and Mg in the octahedrally coordinated Y site, and Fe3+, Al and Fe2+ in the tetrahedrally coordinated Z site. Substitutions Ti4+Fe3+Fe3+–1Si–1 and Ti4+Al3+Fe3+–1Si–1 are of major significance to the crystal chemistry of schorlomite, whereas Fe2+ enters the Z site in relatively minor quantities (<3% Fe). There is no evidence (either structural or indirect, such as discrepancies between the measured and calculated Fe2+ contents) for the presence of [6]Ti3+ or [4]Ti4+ in schorlomite. The simplified general formula of schorlomite can be written as Ca3Ti4+2[Si3-x(Fe3+,Al,Fe2+)xO12], keeping in mind that the notion of end-member composition is inapplicable to this mineral. In the published analyses of schorlomite with low to moderate Zr contents, x ranges from 0.6 to 1.0, i.e. Ti4+ in the Y site is <2 and accompanied by appreciable amounts of lower-charged cations (in particular, Fe3+, Fe2+ and Mg). For classification purposes, the mole percentage of schorlomite can be determined as the amount of [6]Ti4+, balanced by substitutions in the Z site, relative to the total occupancy in the Y site: ([6]Ti4+–[6]Fe2+–[6]Mg2+– [8]Na+)/2. In addition to the predominant schorlomite component, the crystals examined in this work contain significant (>15 mol.%) proportions of andradite (Ca3Fe3+2Si3O12), morimotoite (Ca3Fe2+TiSi3O12), and Ca3MgTiSi3O12. The importance of accurate quantitative determination and assignment of Fe, Ti and other cations to the crystallographic sites for petrogenetic studies is discussed.
相似文献
A. R. ChakhmouradianEmail: Phone: +1-204-4747278Fax: +1-204-4747623 |
114.
The mechanism of concentration on the shaking table is discussed and a fresh attempt is made to obtain the theoretical model describing the velocity of a fluid in depth and time when in contact with a symmetrically reciprocating surface.The significance of the many design and operational variables and their interrelationships are examined. The various areas where the shaking table plays its role are then considered.The relevant features of micropanner, superpanner and the subsequent macropanner and pulsepanner are also treated since they all, like the shaking table, have the differential motion in common. 相似文献
115.
The galactic distribution and physical nature of X-ray transient sources is investigated. Two types of transients are considered. The observational data on 41 X-ray transient sources are given, and the average parameters of hard and soft X-ray transients are estimated. 相似文献
116.
In this paper we report on the MEM power spectrum analysis of brightness temperature fluctuations observed at 2.8 GHz during the total solar eclipse of 16 February 1980. The observed periodicities range from 3.5 min to 64 min. These periodicities may arise due to spatial and/or temporal variations in the solar radio emission. The observed periodicities imply presence of scale sizes ranging from 70,000 to 600,000 km assuming that the brightness fluctuations arise because of spatial variation only. On the other hand, if these fluctuations are due to temporal variation, the observed periodicities correspond well to predicted modes of solar global oscillations. 相似文献
117.
118.
119.
120.