全文获取类型
收费全文 | 37783篇 |
免费 | 977篇 |
国内免费 | 418篇 |
专业分类
测绘学 | 974篇 |
大气科学 | 3504篇 |
地球物理 | 8196篇 |
地质学 | 13601篇 |
海洋学 | 2766篇 |
天文学 | 7855篇 |
综合类 | 98篇 |
自然地理 | 2184篇 |
出版年
2021年 | 277篇 |
2020年 | 315篇 |
2019年 | 299篇 |
2018年 | 820篇 |
2017年 | 828篇 |
2016年 | 1144篇 |
2015年 | 773篇 |
2014年 | 1055篇 |
2013年 | 1952篇 |
2012年 | 1155篇 |
2011年 | 1426篇 |
2010年 | 1263篇 |
2009年 | 1642篇 |
2008年 | 1345篇 |
2007年 | 1159篇 |
2006年 | 1260篇 |
2005年 | 1041篇 |
2004年 | 1032篇 |
2003年 | 1012篇 |
2002年 | 1013篇 |
2001年 | 858篇 |
2000年 | 882篇 |
1999年 | 737篇 |
1998年 | 708篇 |
1997年 | 761篇 |
1996年 | 633篇 |
1995年 | 618篇 |
1994年 | 549篇 |
1993年 | 474篇 |
1992年 | 451篇 |
1991年 | 451篇 |
1990年 | 481篇 |
1989年 | 426篇 |
1988年 | 405篇 |
1987年 | 509篇 |
1986年 | 465篇 |
1985年 | 504篇 |
1984年 | 605篇 |
1983年 | 600篇 |
1982年 | 550篇 |
1981年 | 547篇 |
1980年 | 474篇 |
1979年 | 468篇 |
1978年 | 476篇 |
1977年 | 420篇 |
1976年 | 373篇 |
1975年 | 382篇 |
1974年 | 425篇 |
1973年 | 410篇 |
1972年 | 267篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
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
12.
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
13.
A spectacular change in the lower corona on the south-west limb has been found in solar images taken by the Yohkoh soft X-ray telescope. The event is characterized by a large topological change in magnetic field and a large intensity decrease observed after the X1. 1/1B flare on 9 November, 1991. A coronal mass ejection (CME) was observed by the Mark III K-coronameter (MK3) at the HAO/Mauna Loa Observatory. Both the MK3 (white-light) and soft X-ray observations showed that one leg of this CME was located above the flare site. An interplanetary shock associated with this event was observed by Pioneer Venus Orbiter, and, possibly, by IMP-8.Also Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309, U.S.A. 相似文献
14.
What the Sunspot Record Tells Us About Space Climate 总被引:1,自引:0,他引:1
The records concerning the number, sizes, and positions of sunspots provide a direct means of characterizing solar activity
over nearly 400 years. Sunspot numbers are strongly correlated with modern measures of solar activity including: 10.7-cm radio
flux, total irradiance, X-ray flares, sunspot area, the baseline level of geomagnetic activity, and the flux of galactic cosmic
rays. The Group Sunspot Number provides information on 27 sunspot cycles, far more than any of the modern measures of solar
activity, and enough to provide important details about long-term variations in solar activity or “Space Climate.” The sunspot
record shows: 1) sunspot cycles have periods of 131± 14 months with a normal distribution; 2) sunspot cycles are asymmetric
with a fast rise and slow decline; 3) the rise time from minimum to maximum decreases with cycle amplitude; 4) large amplitude
cycles are preceded by short period cycles; 5) large amplitude cycles are preceded by high minima; 6) although the two hemispheres
remain linked in phase, there are significant asymmetries in the activity in each hemisphere; 7) the rate at which the active
latitudes drift toward the equator is anti-correlated with the cycle period; 8) the rate at which the active latitudes drift
toward the equator is positively correlated with the amplitude of the cycle after the next; 9) there has been a significant
secular increase in the amplitudes of the sunspot cycles since the end of the Maunder Minimum (1715); and 10) there is weak
evidence for a quasi-periodic variation in the sunspot cycle amplitudes with a period of about 90 years. These characteristics
indicate that the next solar cycle should have a maximum smoothed sunspot number of about 145 ± 30 in 2010 while the following
cycle should have a maximum of about 70 ± 30 in 2023. 相似文献
15.
16.
Column density profiles for CN, C3, C2 and NH have been determined from a long-slit CCD spectrum of periodic comet P/Schaumasse (1992x). Comparisons of these profiles with Haser models indicate that the ratios of the CN, C3 and C2 production rates are typical for a short-period comet. Although the scale lengths for NH and its parent species are uncertain, the results indicate that the production rate for NH is much greater than for either C2 or CN. 相似文献
17.
C. Beaugé 《Celestial Mechanics and Dynamical Astronomy》1996,64(4):313-350
Starting with a simple Taylor-based expansion of the inverse of the distance between two bodies, we are able to obtain a series expansion of the disturbing function of the three-body problem (planar elliptic case) which is valid for all points of the phase space outside the immediate vicinity of the collision points. In particular, the expansion is valid for very high values of the eccentricity of the perturbed body. Furthermore, in the case of an interior mean-motion resonant configuration, the above-mentioned expression is easily averaged with respect to the synodic period, yielding once again a global expansion of (R) valid for very high eccentricities.Comparisons between these results and the numerically computed exact function are presented for various resonances and values of the eccentricity. Maximum errors are determined in each case and their origin is established. Lastly, we discuss the applicability of the present expansion to practical problems. 相似文献
18.
Results of several fits of the lunar theory ELP 2000-82B and of Moons' theory of libration are presented. The theories are fitted both to JPL numerical integrations and to LLR observations 相似文献
19.
The orbits of (69230) Hermes and 2002 SY50 are similar and the Earth approaches both of them twice: at the end of October the local orbital minimum distances are smaller
than 0.007 AU, and at the end of April the distances are smaller than 0.04 AU. This gives us opportunities to observe the
meteors associated with these asteroids. Using the geocentric parameters of the orbital close encounters (the theoretical
radiants) and our D
N
distance function (Valsecchi et al. Mon. Not. R. Astron. Soc. 304 (1999) 743), we searched for meteoroids originated by Hermes and 2002 SY50. A search among 1830 good quality photographic meteors gave negative results: we found no meteor dynamically similar to Hermes
or 2002 SY50. In a second search, done in a set of 62150 radio meteors, we applied two methods (M1, M2) and in both cases we found two
streams; the streams found with the M1 method had 43 and 30 members, those found with the M2 method had 39 and 14 members.
However, these results do not look convincing, due to the small number of common members in the corresponding streams. We
therefore conclude that amongst the IAU meteors used in our search there are no compact streams associated with Hermes and
2002 SY50. 相似文献
20.
A highly automated moving object detection package 总被引:1,自引:0,他引:1