全文获取类型
收费全文 | 47386篇 |
免费 | 2042篇 |
国内免费 | 1101篇 |
专业分类
测绘学 | 1234篇 |
大气科学 | 3671篇 |
地球物理 | 11281篇 |
地质学 | 17621篇 |
海洋学 | 3919篇 |
天文学 | 9575篇 |
综合类 | 272篇 |
自然地理 | 2956篇 |
出版年
2022年 | 341篇 |
2021年 | 634篇 |
2020年 | 667篇 |
2019年 | 796篇 |
2018年 | 1538篇 |
2017年 | 1501篇 |
2016年 | 1722篇 |
2015年 | 1287篇 |
2014年 | 1719篇 |
2013年 | 2732篇 |
2012年 | 1983篇 |
2011年 | 2435篇 |
2010年 | 2161篇 |
2009年 | 2578篇 |
2008年 | 2174篇 |
2007年 | 2129篇 |
2006年 | 2020篇 |
2005年 | 1523篇 |
2004年 | 1422篇 |
2003年 | 1295篇 |
2002年 | 1244篇 |
2001年 | 1031篇 |
2000年 | 993篇 |
1999年 | 765篇 |
1998年 | 802篇 |
1997年 | 785篇 |
1996年 | 638篇 |
1995年 | 626篇 |
1994年 | 542篇 |
1993年 | 467篇 |
1992年 | 461篇 |
1991年 | 420篇 |
1990年 | 511篇 |
1989年 | 412篇 |
1988年 | 386篇 |
1987年 | 483篇 |
1986年 | 380篇 |
1985年 | 465篇 |
1984年 | 571篇 |
1983年 | 480篇 |
1982年 | 483篇 |
1981年 | 443篇 |
1980年 | 438篇 |
1979年 | 382篇 |
1978年 | 363篇 |
1977年 | 362篇 |
1976年 | 319篇 |
1975年 | 315篇 |
1974年 | 327篇 |
1973年 | 358篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
S. L. Bridle I. Zehavi A. Dekel O. Lahav M. P. Hobson A. N. Lasenby 《Monthly notices of the Royal Astronomical Society》2001,321(2):333-340
We compare and combine likelihood functions of the cosmological parameters Ωm , h and σ 8 , from peculiar velocities, cosmic microwave background (CMB) and type Ia supernovae. These three data sets directly probe the mass in the Universe, without the need to relate the galaxy distribution to the underlying mass via a 'biasing' relation. We include the recent results from the CMB experiments BOOMERANG and MAXIMA-1. Our analysis assumes a flat Λ cold dark matter (ΛCDM) cosmology with a scale-invariant adiabatic initial power spectrum and baryonic fraction as inferred from big-bang nucleosynthesis. We find that all three data sets agree well, overlapping significantly at the 2 σ level. This therefore justifies a joint analysis, in which we find a joint best-fitting point and 95 per cent confidence limits of (0.17,0.39), (0.64,0.86) and (0.98,1.37). In terms of the natural parameter combinations for these data (0.40,0.73), (0.16,0.27). Also for the best-fitting point, and the age of the Universe is 13.2 Gyr. 相似文献
952.
Slyuta E. N. Vysochkin V. V. Ivanov V. V. Makovchuk V. Yu. Nazarov A. I. Pogonin V. I. Roskina E. A. Safronov V. V. Tatsiy L. P. 《Solar System Research》2021,55(5):437-445
Solar System Research - The ionization-type cosmic dust detector METEOR-L is being developed for the lunar orbiter Luna-26 and is designed to study the distribution of meteoric bodies in space by... 相似文献
953.
Slyuta E. N. Marov M. Ya. Dunchenko A. G. Makovchuk V. Yu. Morozov O. V. Nazarov A. I. Ivanov V. V. Pogonin V. I. Roskina E. G. Safronov V. V. Kharlov B. N. Tatsiy L. P. 《Solar System Research》2021,55(5):446-466
Solar System Research - The device is being developed for the TERMO-LR experiment on the Luna-27 lunar lander; it is intended for contact geophysical measurements of various properties of the lunar... 相似文献
954.
Zaznobin I. A. Burenin R. A. Lyapin A. R. Khorunzhev G. A. Afanasiev V. L. Grokhovskaya A. A. Dodonov S. N. Eselevich M. V. Uklein R. I. Bikmaev I. F. Khamitov I. M. Gilfanov M. R. Lyskova N. S. Medvedev P. S. Sunyaev R. A. 《Astronomy Letters》2021,47(3):141-149
Astronomy Letters - We present the first results of our program of optical observations for galaxy clusters from the Lockman Hole X-ray survey with the eROSITA telescope onboard the SRG space... 相似文献
955.
Anthony L. Turkevich 《Earth, Moon, and Planets》1973,8(3):365-367
The available data on the chemical composition of the lunar surface at eleven sites (3 Surveyor, 5 Apollo and 3 Luna) are used to estimate the amounts of principal chemical elements (those present in more than about 0.5% by atom) in average lunar surface material. The terrae of the Moon differ from the maria in having much less iron and titanium and appreciably more aluminum and calcium.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973. 相似文献
956.
R.L. Millis 《Icarus》1973,19(2):247-286
UBV observations of Iapetus on 34 nights have revealed a 0.30-mag difference in the depths of two successive minima in the light curve of this satellite. The difference can be explained by a two-hemisphere model with the leading darker hemisphere having a much stronger variation in brightness with solar phase angle than the trailing brighter hemisphere. Aside from the variation in the depths of the minima, the general character of the light and color curves is similar to that reported by earlier investigators. 相似文献
957.
The Mariner 9 Ultraviolet Spectrometer has observed the 2550 Å ozone spectral absorption feature on Mars. This absorption was previously detected in the south polar region by Mariner 7 in 1969. Mariner 9 did not observe ozone at any time in the equatorial region, nor at the south polar cap during its summer season. However, ozone was found in the north polar region beginning at a latitude of 45°N and extending northward. Ozone later appeared in the southern hemisphere southward of 50°S as the Mars autumnal equinox approached. The presence of ozone on Mars seems to be coupled to the water vapor content of its atmosphere. 相似文献
958.
The radio emission from Jupiter at 10, 21 cm wavelength has been measured with a spatial resolution of the order of 1 Jupiter radius. This may be analytically reduced to the emission per cubic centimeter of source at each measured frequency. The theoretically predicted synchrotron emission of electrons as a function of frequency, magnetic field and electron energy can then be compared to the observed source emissivity to obtain the number density and ‘temperature’ of the electrons. Present observations taken at different epochs are not sufficiently reliable to infer peak energies within an order of magnitude. Nevertheless the present results indicate that electrons diffuse in rapidly (in a time of the order of months) conserving the first adiabatic invariant and reach a peak energy at about 2 Jupiter radii. The electron energy decreases rapidly nearer the planet because of energy lost to radiation in the large magnetic field close to the planet. 相似文献
959.
An analysis was performed on 29,574 densities derived from the drag of 10 satellites to determine simultaneously the parameters of the solar-activity effect in the thermosphere on the one hand, and the amplitude and shape of the diurnal-variation curve on the other. This paper reports on the study of the diurnal variation only.Although a considerable amount of smoothing is inherent in the drag method, it seemed useful to see whether we could detect any change in the shape of the diurnal-variation curve with height, latitude and solar activity. None was detected: the curve remains remarkably stable, symmetric, with a maximum at 14 hr 20 min L.S.T. and a minimum at 2 hr 20 min L.S.T. A systematic variation of the temperature range with height is observed when static models are used to derive it. 相似文献
960.
The type III carbonaceous chondrites Kainsaz and Efremovka have been analysed for eighteen major, minor and trace elements by X-ray fluorescence spectrometry. A comparison of the data on Kainsaz with four other Ornans sub-type carbonaceous chondrites reveals a remarkable degree of constancy of composition. Efremovka, together with Leoville and Coolidge, may be distinguished from the other Vigarano sub-type carbonaceous chondrites by their lower Na and K contents, variable Na/K ratios and relatively low Ca/Al ratios. Some observations are made on the ratio Na/K in various types of stony meteorite; the magnitude of the ratio in the basaltic achondrites appears to be more similar to that in the carbonaceous chondrites than in the ordinary chondrites. 相似文献