全文获取类型
收费全文 | 25765篇 |
免费 | 5062篇 |
国内免费 | 6583篇 |
专业分类
测绘学 | 1776篇 |
大气科学 | 4220篇 |
地球物理 | 5432篇 |
地质学 | 14110篇 |
海洋学 | 3599篇 |
天文学 | 1134篇 |
综合类 | 1710篇 |
自然地理 | 5429篇 |
出版年
2024年 | 76篇 |
2023年 | 320篇 |
2022年 | 808篇 |
2021年 | 987篇 |
2020年 | 986篇 |
2019年 | 1217篇 |
2018年 | 1093篇 |
2017年 | 1074篇 |
2016年 | 1112篇 |
2015年 | 1222篇 |
2014年 | 1548篇 |
2013年 | 1498篇 |
2012年 | 1643篇 |
2011年 | 1593篇 |
2010年 | 1397篇 |
2009年 | 1798篇 |
2008年 | 1602篇 |
2007年 | 1923篇 |
2006年 | 1965篇 |
2005年 | 1671篇 |
2004年 | 1560篇 |
2003年 | 1491篇 |
2002年 | 1296篇 |
2001年 | 1125篇 |
2000年 | 944篇 |
1999年 | 822篇 |
1998年 | 733篇 |
1997年 | 623篇 |
1996年 | 608篇 |
1995年 | 512篇 |
1994年 | 446篇 |
1993年 | 389篇 |
1992年 | 327篇 |
1991年 | 262篇 |
1990年 | 172篇 |
1989年 | 220篇 |
1988年 | 109篇 |
1987年 | 78篇 |
1986年 | 43篇 |
1985年 | 22篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1954年 | 16篇 |
1877年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
I.A. Crawford 《Astrophysics and Space Science》2003,285(3-4):661-675
I review the recent discoveries of variable interstellar absorption lines, widely taken to imply the existence of very small
scale(10–100 AU) structure in the interstellar medium. Possible origins of this structure are discussed, and attention is
drawn to the fact that most known examples seem to be associated with interstellar shells and bubbles of various kinds. On
the other hand, in at least one case (κ Velorum),the variation appears to occur in the supposedly quiescent cold neutral medium,
consistent with earlier studies of small scale structure in atomic hydrogen probed at radio wavelengths. Further work is urgently
required to determine the prevalence, mode of formation, and the physical and chemical state of these enigmatic structures.
Only then will their implications for our wider understanding of the interstellar medium become apparent.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
72.
Nikolay Sidorenkov 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):27-38
Spectral analysis of the components of the relative atmospheric angular momentum vector is performed based on the series of these components for the 6 h intervals within the period of 1958–2000. These series have been computed in the Subbureau of the Atmospheric Angular Momentum of the International Earth Rotation Service using the NCEP/NCAR reanalysis of atmospheric observations. The basic harmonics of diurnal tides are determined. New results on the fortnight's and week's duration oscillations of the equatorial components of the atmospheric angular momentum are obtained. The zonal tides transformation mechanisms in the atmosphere are discussed. It is shown that the main mechanism of the zonal tides effect on the atmospheric variability is the amplitude modulation of daily oscillations of the relative atmospheric angular momentum. The effects of the atmospheric tides on the Earth rotation are discussed. 相似文献
73.
74.
本文论述了保安地区火山岩的地质、岩石、副矿物、岩石化学、微量元素、稀土元素、稳定同位素、火山岩相及火山机构等特征。并对其演化规律、形成机制与成矿作用的关系,作了初步探讨。 相似文献
75.
FUZZY COMPREHENSIVE EVALUATION OF CONTAINER TRANSPORTATION MODES ALONG THE CHANGJIANG RIVER MAIN LINE AND ITS DELTA AREA 总被引:1,自引:0,他引:1
ZHANGShi-yu XIAOHan-liang 《中国地理科学(英文版)》2003,13(3):259-261
The Changjiang River (Yangtze) is one of the fastest growth areas of container transportation in Chi-na. Rail, road and water transportation have competed against each other for container transportation in the Chang-jiang River main line and its delta area. It is of significance to assess these different transportation modes scientifi-cally in order to organize container transportation efficiently in this area and make decision for integral plan and construction of transportation system in this area. This paper outlines application of fuzzy comprehensive evaluation to appraise different modes of typical direction of containers. Twelve assessment indexes were decided. Membership functions were formulated. Evaluation results indicated that road transportation was optimal mode in the Changjiang River delta area, however water transportation was the primary way in the Changjiang River main line. 相似文献
76.
S.W. Allen 《Astrophysics and Space Science》2003,285(1):247-256
Chandra X-ray observations of rich, dynamically relaxed galaxy clusters allow the properties of the X-ray gas and the total
gravitating mass to be determined precisely. Here, we discuss how Chandra observations may be used as a powerful tool for
cosmological studies. By combining Chandra X-ray results on the X-ray gas mass fractions in clusters with independent measurements
of the Hubble constant and the mean baryonic matter density of the universe, we obtain a tight constraint on the mean total
matter density of the universe, Οm, and an interesting constraint on the cosmological constant, ΟΛ. Using these results, together with the observed local X-ray luminosity function of the most X-ray luminous galaxy clusters,
a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the
mass function predicted by numerical simulations, we obtain a precise constraint on the normalization of the power spectrum
of density fluctuations in the nearby universe,σ8. We compare our results with those obtained from other, independent methods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
77.
Darwin is a cornerstone mission of the Horizons 2000+ program of the European Space Agency. It has the express purpose of
carrying out the first direct search for terrestrial exoplanets, and to achieve unprecedented spatial resolution in the infrared wavelength region. The
detection and study of terrestrial exoplanets promises to usher in a new era in science and will affect a broad spectrum of
disciplines. Further, the time line for implementation of such an instrument is now likely to be of the close order of 10
years, leading to possible answers to one of mankind's most fundamental questions in the second decade of the 21st century.
It has been found that in order to realize am interferometer in space in the next 10–15 years, it is necessary to prepare
the way through a number of intermediary steps – both on the ground and in space. In this context, we here describe GENIE
– a ground based nulling interferometry experiment to be implemented at the VLTI in a partnership between ESA and ESO.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
78.
M. T. Murphy S. J. Curran J. K. Webb 《Monthly notices of the Royal Astronomical Society》2003,342(3):830-836
We describe initial results of a search for redshifted molecular absorption towards four millimetre-loud, optically faint quasars. A wide frequency bandwidth of up to 23 GHz per quasar was scanned using the Swedish–ESO Submillimetre Telescope at La Silla. Using a search list of commonly detected molecules, we obtained nearly complete redshift coverage up to z abs = 5 . The sensitivity of our data is adequate to have revealed absorption systems with characteristics similar to those seen in the four known redshifted millimetre-band absorption systems, but none were found. Our frequency-scan technique nevertheless demonstrates the value of wide-band correlator instruments for searches such as these. We suggest that a somewhat larger sample of similar observations should lead to the discovery of new millimetre-band absorption systems. 相似文献
79.
80.