全文获取类型
收费全文 | 39697篇 |
免费 | 496篇 |
国内免费 | 285篇 |
专业分类
测绘学 | 926篇 |
大气科学 | 2889篇 |
地球物理 | 7697篇 |
地质学 | 14766篇 |
海洋学 | 3554篇 |
天文学 | 8397篇 |
综合类 | 109篇 |
自然地理 | 2140篇 |
出版年
2022年 | 274篇 |
2021年 | 443篇 |
2020年 | 461篇 |
2019年 | 499篇 |
2018年 | 1164篇 |
2017年 | 1071篇 |
2016年 | 1234篇 |
2015年 | 622篇 |
2014年 | 1149篇 |
2013年 | 2079篇 |
2012年 | 1308篇 |
2011年 | 1695篇 |
2010年 | 1507篇 |
2009年 | 1910篇 |
2008年 | 1669篇 |
2007年 | 1648篇 |
2006年 | 1578篇 |
2005年 | 1117篇 |
2004年 | 1108篇 |
2003年 | 1012篇 |
2002年 | 998篇 |
2001年 | 924篇 |
2000年 | 914篇 |
1999年 | 682篇 |
1998年 | 674篇 |
1997年 | 741篇 |
1996年 | 565篇 |
1995年 | 589篇 |
1994年 | 572篇 |
1993年 | 470篇 |
1992年 | 444篇 |
1991年 | 446篇 |
1990年 | 458篇 |
1989年 | 402篇 |
1988年 | 416篇 |
1987年 | 457篇 |
1986年 | 398篇 |
1985年 | 525篇 |
1984年 | 497篇 |
1983年 | 543篇 |
1982年 | 490篇 |
1981年 | 436篇 |
1980年 | 483篇 |
1979年 | 405篇 |
1978年 | 383篇 |
1977年 | 365篇 |
1976年 | 320篇 |
1975年 | 323篇 |
1974年 | 331篇 |
1973年 | 315篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
271.
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
272.
T. Wong E. F. Ladd D. Brisbin M. G. Burton I. Bains M. R. Cunningham N. Lo P. A. Jones K. L. Thomas S. N. Longmore A. Vigan B. Mookerjea C. Kramer Y. Fukui A. Kawamura 《Monthly notices of the Royal Astronomical Society》2008,386(2):1069-1084
We present a fully sampled C18 O (1–0) map towards the southern giant molecular cloud (GMC) associated with the H ii region RCW 106, and use it in combination with previous 13 CO (1–0) mapping to estimate the gas column density as a function of position and velocity. We find localized regions of significant 13 CO optical depth in the northern part of the cloud, with several of the high-opacity clouds in this region likely associated with a limb-brightened shell around the H ii region G333.6−0.2. Optical depth corrections broaden the distribution of column densities in the cloud, yielding a lognormal distribution as predicted by simulations of turbulence. Decomposing the 13 CO and C18 O data cubes into clumps, we find relatively weak correlations between size and linewidth, and a more sensitive dependence of luminosity on size than would be predicted by a constant average column density. The clump mass spectrum has a slope near −1.7, consistent with previous studies. The most massive clumps appear to have gravitational binding energies well in excess of virial equilibrium; we discuss possible explanations, which include magnetic support and neglect of time-varying surface terms in the virial theorem. Unlike molecular clouds as a whole, the clumps within the RCW 106 GMC, while elongated, appear to show random orientations with respect to the Galactic plane. 相似文献
273.
274.
Hong Kong has undergone substantial economic transformations and developed into a sophisticated business and financial center in the Asia-Pacific region,since the return of sovereignty to China as a Special Administrative Region under the One Country Two Systems (OCTS) in 1997.This paper discusses and analyzes the industrial structural changes of Hong Kong in recent decades as well as its future challenges and opportunities.The data and finding reveal that even though Hong Kong will face fierce competition from the Mainland’s cities as the rise of China,the important role as a bridge between China and the rest of the world will brace Hong Kong itself under the OCTS for developing into a service hub for business and trade in the Asia-Pacific region. 相似文献
275.
Multispectral faint galaxy counts, including the deepest Hubble DeepField, are interpreted with the help of our evolution
model PEGASE(Fioc and Rocca-Volmerange, 1997). The best fits correspond to galaxyformations at high redshifts, a pure luminosity
evolution andclassical luminosity functions. The adopted cosmology is a flatuniverse with the matter density parameter ΩM =0.3 and acosmological constant ΩΛ =0.7. A solution with ΩM=0.01 (open universe) is also acceptable. But a flat universe withΩM =1 is clearly excluded. The star formation histories for galaxytypes are derived from scenarios of evolution. The comparison
with resultsalready published in the litterature, arises puzzling problems needinga further analysis of star formation tracers,
specifically for bright galaxies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
276.
277.
Ezio Caroli Natalia Auricchio Lorenzo Amati Yuriy Bezsmolnyy Carl Budtz-JøRgensen Rui M. Curado da Silva Filippo Frontera Alessandro Pisa Stefano Del Sordo John B. Stephen Giulio Ventura 《Experimental Astronomy》2005,20(1-3):341-351
The energy range above 60 keV is important for the study of many open problems in high energy astrophysics such as the role of Inverse Compton with respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and annihilation lines. Recently the development of high energy Laue lenses with broad energy bandpasses from 60 to 600keV have been proposed for a Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of celestial sources. The required focal plane detector should have high detection efficiency over the entire operative range, a spatial resolution of about 1mm, an energy resolution of a few keV at 500keV and a sensitivity to linear polarization. We describe a possible configuration of the focal plane detector based on several CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at high energy.
Each layer can operate both as a separate position sensitive detector and polarimeter or work with other layers to increase the overall photopeak efficiency. Each layer has a hexagonal shape in order to minimize the detector surface required to cover the lens field of view. The pixels would have the same geometry so as to provide the best coupling with the lens point spread function and to increase the symmetry for polarimetric studies. 相似文献
278.
B. R. Johnson M. E. Abroe P. Ade J. Bock J. Borrill J. S. Collins P. Ferreira S. Hanany A. H. Jaffe T. Jones A. T. Lee L. Levinson T. Matsumura B. Rabii T. Renbarger P. L. Richards G. F. Smoot R. Stompor H. T. Tran C. D. Winant 《New Astronomy Reviews》2003,47(11-12):1067
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10′ to 2°. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary dataset was collected during a 26 h turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress. 相似文献
279.
The dynamical evolution of meteoroid streams associated with cornets Encke, Halley, Machholz 1986 VIII and asteroid Phaethon is discussed. It is shown that the planetary perturbations can greatly increase the streams thickness and each stream may produce several couples of meteor showers active in different seasons of the year. The theoretical and observed data are in a satisfactory accordance. 相似文献
280.
A nonlinear process for the resonant generation of low-frequency fast magnetosonic kink waves in coronal loops is discussed. The efficiency of the process is strongly enhanced due to the existence of a nonlinearly selected frequency produced by a constant frequency difference in the dispersion curves in the short wavelength limit. The kink wave with the selected frequency interacts with high-frequency kink and sausage waves. The efficiency of such interaction does not require coherence in the interactive waves. In a loop of width 2 × 103 km, field strength 50 G and number density 5 × 1015 m–3, the nonlinearly selected frequency is of order 46 mHz (period 21.8 s), but this may range through 11 mHz to 184 mHz (periods 86.5 s to 5.4 s) for typical coronal conditions. 相似文献