全文获取类型
收费全文 | 56514篇 |
免费 | 980篇 |
国内免费 | 1014篇 |
专业分类
测绘学 | 1539篇 |
大气科学 | 4927篇 |
地球物理 | 10688篇 |
地质学 | 23411篇 |
海洋学 | 4197篇 |
天文学 | 10543篇 |
综合类 | 445篇 |
自然地理 | 2758篇 |
出版年
2021年 | 287篇 |
2020年 | 271篇 |
2019年 | 315篇 |
2018年 | 3712篇 |
2017年 | 3516篇 |
2016年 | 2461篇 |
2015年 | 677篇 |
2014年 | 856篇 |
2013年 | 1538篇 |
2012年 | 1988篇 |
2011年 | 3902篇 |
2010年 | 3677篇 |
2009年 | 4005篇 |
2008年 | 3222篇 |
2007年 | 3779篇 |
2006年 | 1156篇 |
2005年 | 1448篇 |
2004年 | 1267篇 |
2003年 | 1389篇 |
2002年 | 1158篇 |
2001年 | 820篇 |
2000年 | 890篇 |
1999年 | 770篇 |
1998年 | 721篇 |
1997年 | 755篇 |
1996年 | 661篇 |
1995年 | 636篇 |
1994年 | 548篇 |
1993年 | 488篇 |
1992年 | 461篇 |
1991年 | 444篇 |
1990年 | 443篇 |
1989年 | 422篇 |
1988年 | 401篇 |
1987年 | 477篇 |
1986年 | 447篇 |
1985年 | 473篇 |
1984年 | 563篇 |
1983年 | 569篇 |
1982年 | 506篇 |
1981年 | 505篇 |
1980年 | 464篇 |
1979年 | 434篇 |
1978年 | 447篇 |
1977年 | 394篇 |
1976年 | 359篇 |
1975年 | 355篇 |
1974年 | 405篇 |
1973年 | 389篇 |
1972年 | 245篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Analytical study of ground motion caused by seismic wave propagation across faulted rock masses
下载免费PDF全文
![点击此处可从《国际地质力学数值与分析法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Qp and Qs. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions. 相似文献
3.
4.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
5.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
6.
7.
8.
9.
H. A. Harutyunian 《Astrophysics》1996,39(4):370-374
The Voigt function and its derivatives are represented by means of series in Hermite polynomials. The equations obtained can be used both for numerical calculations of these functions and for analytical research.Translated from Astrofizika, Vol. 39, No. 4, pp. 619–625, October–December, 1996. 相似文献
10.
M. J. Freyberg H. Bräuninger W. Burkert G. D. Hartner O. Citterio F. Mazzoleni G. Pareschi D. Spiga S. Romaine P. Gorenstein B. D. Ramsey 《Experimental Astronomy》2005,20(1-3):405-412
The Max-Planck-Institut für extraterrestrische Physik (MPE) in Garching, Germany, uses its large X-ray beam line facility PANTER for testing X-ray astronomical instrumentation. A number of telescopes, gratings, filters, and detectors, e.g. for astronomical satellite missions like Exosat, ROSAT, Chandra (LETG), BeppoSAX, SOHO (CDS), XMM-Newton, ABRIXAS, Swift (XRT), have been successfully calibrated in the soft X-ray energy range (< 15keV). Moreover, measurements with mirror test samples for new missions like ROSITA and XEUS have been carried out at PANTER. Here we report on an extension of the energy range, enabling calibrations of hard X-ray optics over the energy range 15–50 keV. Several future X-ray astronomy missions (e.g., Simbol-X, Constellation-X, XEUS) have been proposed, which make use of hard X-ray optics based on multilayer coatings. Such optics are currently being developed by the Osservatorio Astronomico di Brera (OAB), Milano, Italy, and the Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, MA, USA. These optics have been tested at the PANTER facility with a broad energy band beam (up to 50 keV) using the XMM-Newton EPIC-pn flight spare CCD camera with its good intrinsic energy resolution, and also with monochromatic X-rays between C-K (0.277 keV) and Cu-Kα (8.04 keV).
PACS: 95.55.Ka, 95.55.Aq, 41 50.+h, 07.85.Fv 相似文献