全文获取类型
收费全文 | 61487篇 |
免费 | 13737篇 |
国内免费 | 20401篇 |
专业分类
测绘学 | 10264篇 |
大气科学 | 8007篇 |
地球物理 | 11257篇 |
地质学 | 39192篇 |
海洋学 | 11160篇 |
天文学 | 2664篇 |
综合类 | 4646篇 |
自然地理 | 8435篇 |
出版年
2024年 | 446篇 |
2023年 | 1293篇 |
2022年 | 3347篇 |
2021年 | 4056篇 |
2020年 | 3313篇 |
2019年 | 4018篇 |
2018年 | 3684篇 |
2017年 | 3482篇 |
2016年 | 3455篇 |
2015年 | 4050篇 |
2014年 | 4018篇 |
2013年 | 5061篇 |
2012年 | 5332篇 |
2011年 | 5541篇 |
2010年 | 5376篇 |
2009年 | 5137篇 |
2008年 | 5165篇 |
2007年 | 4863篇 |
2006年 | 4663篇 |
2005年 | 3995篇 |
2004年 | 3106篇 |
2003年 | 2184篇 |
2002年 | 2157篇 |
2001年 | 1947篇 |
2000年 | 1640篇 |
1999年 | 812篇 |
1998年 | 396篇 |
1997年 | 291篇 |
1996年 | 263篇 |
1995年 | 210篇 |
1994年 | 176篇 |
1993年 | 143篇 |
1992年 | 141篇 |
1991年 | 117篇 |
1990年 | 143篇 |
1989年 | 104篇 |
1988年 | 72篇 |
1987年 | 129篇 |
1986年 | 92篇 |
1985年 | 91篇 |
1984年 | 101篇 |
1983年 | 94篇 |
1982年 | 90篇 |
1981年 | 82篇 |
1980年 | 57篇 |
1979年 | 78篇 |
1977年 | 57篇 |
1976年 | 56篇 |
1974年 | 43篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
中国虚拟天文台图像处理分析工具(VO_IMPAT),是由国家天文台虚拟天文台项目组开发的一项服务,它提供了对数字巡天图像数据(Digital Sky Survey,DSS)、天文星表以及其他数据库的交互访问。VO_IMPAT的设计目的是实现多波段天文数据的融合。可以将不同波段的星表叠加到DSS底图上,如光学波段的USNO星表、近红外波段的2MASS星表、射电波段的NVSS星表和X射线波段的RASS星表。同时VO_IMPAT还可以对图像进行放大、缩小、伪彩色、等高线、直方图、尖锐化、平滑化、旋转等处理,不同的星表数据可以采用不同的颜色和图标显示。 相似文献
52.
We present solutions for the effective stress induced by gas flow through a porous solid into a borehole resulting from sudden pressure reduction. Tensile effective stress that exceeds the strength of the solid will lead to borehole failure. This has applications to the intentional creation of cavities, relevant to the efficient recovery of coalbed methane, and the avoidance of borehole stability problems in conventional gas production. 相似文献
53.
Arnaud M. Aubourg E. Bareyre P. Br';ehin S. Caridroit R. de Kat J. Dispau G. Djidi K. Gros M. Lachièze-Rey M. Laigneau Y. Laurent B. Lesquoy E. Lavocat Ph. Magneville C. Mazeau B. Milsztajn A. Moscoso L. Pasquaud J. Paul B. Perrin P. Petibon J. Piret Y. Queinnec F. Rich J. Spiro M. de Trogoff J. Vigroux L. Zylberajch S. Ansari R. Cavalier F. Moniez M. Beaulieu J. P. Ferlet R. Grison Ph. Vidal-Madjar A. Adrianzyk G. Berger J. P. Burnage R. Delclite J. C. Kohler D. Magnan R. Richaud A. Guibert J. Moreau O. Tajahmady F. Baranne A. Maurice E. Prévôt L. Gry C. 《Experimental Astronomy》1994,4(3-4):265-278
A 20cm
2
CCD mosaic camera has been especially built to search for dark galactic halo objects by the gravitational microlensing effect. The sensitive area is made of 16 edge-buttable CCDs developped by Thomson-CTS, with 23×23 µm
2
pixels. The 35 kg camera housing and mechanical equipment is presented. The associated electronics and data acquisition system are described in a separate paper. The camera resides at the focal plane of a 40 cm, f/10, Ferson reflector. The instrument has been in operation since December 1991 at the La Silla Observatory (ESO). 相似文献
54.
本文在Thorne工作的基础上讨论了吸积盘中黑洞的有关参量的演化,以及由Schwarzschild黑洞吸积盘向Kerr黑洞吸积盘演化过程中对吸积盘辐射通量的影响,最后针对几个典型的辐射过程,分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性,并给出此类问题的热不稳定性的判据。 相似文献
55.
A wave-height meter using a simple microwave Doppler radar,simeq10 mW in power and 10.525 GHz in frequency, is proposed so that we can measure oceanic waves effectively while the ship is steaming. It was first applied to the measurement of the variation of water level generated in a wave tank, which suggested that it is adequately applicable to the measurement of oceanic waves. A field test was carried out off the cape of Nojimazaki by installing the Doppler radar 5 m above the sea level at the bow of the ship. The result agreed reasonably well with that measured simultaneously by the ultrasonic wave-height meter installed at the same position. Another test is running successfully on a larger ship with the wave-height meter installed at 9 m above the sea level. The significant wave height measured by the present meter is being compared with that observed visually by the navigation officers. 相似文献
56.
Expressions for the mass quadrupole moment tensor in the model for a wide variety of astrophysical objects are shown to be identical in form. This makes it possible to obtain analytical expressions for the gravitational radiation emitted by the sources, as well as the angular distribution, polarization dependence, and the wave forms of the radiation. 相似文献
57.
A unified model for outbursts of dwarf novae is proposed based on the disk instability model in cataclysmic variable stars. In this model, two different intrinsic instabilities (i.e., the thermal instability and the tidal instability) within accretion disks are considered in non-magnetic cataclysmic variable stars. It is suggested that all of three sub-classes of dwarf novae (i.e., U Gem-type, Z Cam-type and SU UMa-type dwarf novae) may be explained in terms of two model parameters of the orbital period of the binary and of the mass transfer rate within the framework of the disk instability model. 相似文献
58.
WANG Yachun 《东北亚地学研究》2002,(1)
The paper deals with the methods of formation pressure evaluation for a single well by using the very common ac-cepted parameters, such as drilling exponent , and flowline temperature , etc. which is part of compiling the end well report. 相似文献
59.
60.
Yu. G. Shkuratov K. Muinonen E. Bowell K. Lumme J. I. Peltoniemi M. A. Kreslavsky D. G. Stankevich V. P. Tishkovetz N. V. Opanasenko L. Y. Melkumova 《Earth, Moon, and Planets》1994,65(3):201-246
About a dozen physical mechanisms and models aspire to explain the negative polarization of light scattered by atmosphereless celestial bodies. This is too large a number for the reliable interpretation of observational data. Through a comparative analysis of the models, our main goal is to answer the question: Does any one model have an advantage over the others? Our analysis is based on new laboratory polarimetric and photometric data as well as on theoretical results. We show that the widely used models due to Hopfield and Wolff cannot realistically explain the phase-angle dependence of the degree of polarization observed at small phase angles. The so-called interference or coherent backscattering mechanism is the most promising model. Models based on that mechanism use well-defined physical parameters to explain both negative polarization and the opposition effect. They are supported by laboratory experiments, particularly those showing enhancement of negative polarization with decreasing particle size down to the wavelength of light. According to the interference mechanism, pronounced negative branches of polarization, like those of C-class asteroids, may indicate a high degree of optical inhomogeneity of light-scattering surfaces at small scales. The mechanism also seems appropriate for treating the negative polarization and opposition effects of cometary dust comae, planetary rings, and the zodiacal light. 相似文献