全文获取类型
收费全文 | 30993篇 |
免费 | 424篇 |
国内免费 | 240篇 |
专业分类
测绘学 | 751篇 |
大气科学 | 2392篇 |
地球物理 | 6125篇 |
地质学 | 11399篇 |
海洋学 | 2663篇 |
天文学 | 6440篇 |
综合类 | 68篇 |
自然地理 | 1819篇 |
出版年
2021年 | 288篇 |
2020年 | 304篇 |
2019年 | 313篇 |
2018年 | 750篇 |
2017年 | 740篇 |
2016年 | 863篇 |
2015年 | 485篇 |
2014年 | 835篇 |
2013年 | 1598篇 |
2012年 | 957篇 |
2011年 | 1273篇 |
2010年 | 1089篇 |
2009年 | 1416篇 |
2008年 | 1236篇 |
2007年 | 1209篇 |
2006年 | 1206篇 |
2005年 | 878篇 |
2004年 | 873篇 |
2003年 | 797篇 |
2002年 | 809篇 |
2001年 | 730篇 |
2000年 | 722篇 |
1999年 | 567篇 |
1998年 | 546篇 |
1997年 | 614篇 |
1996年 | 486篇 |
1995年 | 496篇 |
1994年 | 482篇 |
1993年 | 398篇 |
1992年 | 389篇 |
1991年 | 369篇 |
1990年 | 389篇 |
1989年 | 356篇 |
1988年 | 353篇 |
1987年 | 383篇 |
1986年 | 337篇 |
1985年 | 446篇 |
1984年 | 434篇 |
1983年 | 471篇 |
1982年 | 433篇 |
1981年 | 382篇 |
1980年 | 416篇 |
1979年 | 345篇 |
1978年 | 320篇 |
1977年 | 312篇 |
1976年 | 281篇 |
1975年 | 275篇 |
1974年 | 280篇 |
1973年 | 270篇 |
1971年 | 183篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
The transition 111 ? 110 at 4.829 GHz of formaldehyde (H2CO) was the first one showing the anomalous absorption, i.e., the absorption against the cosmic microwave background. Anomalous absorption is an unusual phenomena. Structure of H2CC is very similar to that of H2CO and H2CS. Both H2CO and H2CS have already been identified in a number of cosmic objects. Though H2CC is not yet identified in the cosmic objects, we propose that H2CC may be identified in cool cosmic objects through its transition 111 ? 110 at 4.85 GHz in anomalous absorption. 相似文献
73.
A new protocol was devised to improve the efficiency of astrometric follow-up observations of Near Earth Asteroids for the
accurate determination of their orbits. It was implemented in the activities of the Spaceguard Central Node (SCN, a facility
of the Spaceguard Foundation, established with the support of the European Space Agency) in the form of a Priority List. Here
we describe this protocol and results obtained during five years of activity (2000–2004). 相似文献
74.
J. A. Vorpahl E. G. Gibson P. B. Landecker D. L. McKenzie J. H. Underwood 《Solar physics》1975,45(1):199-216
132 soft X-ray flare events have been observed with The Aerospace Corporation/Marshall Space Flight Center S-056 X-ray telescope that was part of the ATM complement of instruments aboard Skylab. Analyses of these data are reported in this paper. The observations are summarized and a detailed discussion of the X-ray flare structures is presented. The data indicated that soft X-rays emitted by a flare come primarily from an intense well-defined core surrounded by a region of fainter, more diffuse emission. Loop structures are found to constitute a fundamental characteristic of flare cores and arcades of loops are found to play a more important role in the flare phenomena than previously thought. Size distributions of these core features are presented and a classification scheme describing the brightest flare X-ray features is proposed. The data show no correlations between the size of core features and: (1) the peak X-ray intensity, as indicated by detectors on the SOLRAD satellite; (2) the rise time of the X-ray flare event, or (3) the presence of a nonthermal X-ray component. An analysis of flare evolution indicates evidence for preliminary heating and energy release prior to the main phase of the flare. Core features are found to be remarkably stable and retain their shape throughout a flare. Most changes in the overall configuration seem to be the result of the appearance, disappearance or change in brightness of individual features, rather than the restructuring or re-orientation of these features. Brief comparisons with several theories are presented. 相似文献
75.
I. B. Safarov 《Izvestiya Physics of the Solid Earth》2006,42(3):260-270
The elastic and density properties of rocks of the Shamakha-Ismailly seismogenic blocks are studied by the ultrasonic pulse method in quasi-hydrostatic high pressure apparatuses. An attempt is made to more accurately determine the upper crustal lithology of these blocks. The observed values of the elastic and density characteristics of the rocks at high pressures suggest that the upper layers in the Ismailly and Shamakha blocks can consist of sedimentary carbonate rocks such as marls, sandstones, mudstones, and limestones. The middle layers apparently consist of volcaniclastic rocks: lithoclastic tuffs, andesites, etc. The lower layer (basement) in both blocks is likely composed of basic rocks such as basalts, trachybasalts, etc. According to the values of elastic wave velocities and densities, gabbroid rocks may compose the fourth layer of the Buinuz intrusion, identified from seismic data. 相似文献
76.
Summary. The contributions from the oceanic and ionospheric dynamos, Lo and LI respectively, to the geomagnetic lunar daily variation, L , at Alibag, a coastal station in the Indian equatorial region, are calculated from the L harmonics derived from a 41–yr long series of observations. The analysis in the calendar months shows a steady and significant ocean dynamo contribution in the vertical component, Z, in all the months except April. Examination, by an analysis of the data year by year, of the association of Lo and LI with varying solar and magnetic activities reveals, surprisingly, a stable correlation between the magnetic activity index A P and the oceanic part in the horizontal and vertical components but not in declination, which probably indicates the influence of induced currents, along the latitudes, on L o . 相似文献
77.
In this paper we compute the rate of solar EUV heating in the upper atmosphere by photo-dissociation and photo-ionization, taking care to include properly the effects of oblique incidence of solar flux, sphericity of the atmosphere and ellipticity of the Earth's orbit. The time and latitudinal variations of the computed heat function are revealed by numerical Fourier analysis of the heat function into harmonics of the yearly cycle. It is shown that EUV absorption contains a ‘latitude independent’ semi-annual component of heating with the ‘proper phase’ to account for the semi-annual density variations. Further, the annual component of the heat function predicts the existence of ‘summer polar’ density increases in the northern and southern hemispheres. 相似文献
78.
79.
Summary All of the barium and marginal barium stars in the 1972 MacConnell, Frey, and Upgren (1972: MFU) list of such objects which
are located south of the celestial equator were examined for visual duplicity. Over 200 objects were observed, and a total
of six possible candidates for wide pair visual binaries were found. Of these, four are most likely optical in nature. These
data suggest that the incidence of wide binaries among barium stars is of the order of 1%. 相似文献
80.