全文获取类型
收费全文 | 29332篇 |
免费 | 391篇 |
国内免费 | 323篇 |
专业分类
测绘学 | 616篇 |
大气科学 | 1817篇 |
地球物理 | 5250篇 |
地质学 | 11270篇 |
海洋学 | 2966篇 |
天文学 | 6859篇 |
综合类 | 68篇 |
自然地理 | 1200篇 |
出版年
2022年 | 297篇 |
2021年 | 455篇 |
2020年 | 509篇 |
2019年 | 556篇 |
2018年 | 1091篇 |
2017年 | 1040篇 |
2016年 | 1146篇 |
2015年 | 545篇 |
2014年 | 1041篇 |
2013年 | 1687篇 |
2012年 | 1152篇 |
2011年 | 1434篇 |
2010年 | 1282篇 |
2009年 | 1557篇 |
2008年 | 1329篇 |
2007年 | 1396篇 |
2006年 | 1301篇 |
2005年 | 755篇 |
2004年 | 705篇 |
2003年 | 660篇 |
2002年 | 687篇 |
2001年 | 619篇 |
2000年 | 569篇 |
1999年 | 461篇 |
1998年 | 479篇 |
1997年 | 455篇 |
1996年 | 391篇 |
1995年 | 350篇 |
1994年 | 378篇 |
1993年 | 294篇 |
1992年 | 297篇 |
1991年 | 286篇 |
1990年 | 322篇 |
1989年 | 220篇 |
1988年 | 225篇 |
1987年 | 269篇 |
1986年 | 210篇 |
1985年 | 314篇 |
1984年 | 277篇 |
1983年 | 258篇 |
1982年 | 275篇 |
1981年 | 205篇 |
1980年 | 243篇 |
1979年 | 195篇 |
1978年 | 211篇 |
1977年 | 165篇 |
1976年 | 163篇 |
1975年 | 173篇 |
1974年 | 167篇 |
1973年 | 166篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
N. I. Bondar’ 《Astronomy Reports》2017,61(2):130-137
Photometric data covering 1994–2009, obtained at the Crimean Astrophysical Observatory or retrieved from the ASAS and SuperWASP catalogs, were used to analyze the brightness variations of the rapidly rotating star V833 Tau, whose activity level is close to saturation. Combined with previously published results, these data represent for the first time all stages in the development of the star’s 19- year activity cycle. The photometric period and rotational-modulation amplitude for different epochs are determined, and the qualitative pattern of the spots is considered. The photometric period is close to the orbital period, but always exceeds it, indicating that surface inhomogeneities are located far from the equatorial plane. With the high spottedness of the star, reaching 28% at the cycle maximum, the rotationalmodulation amplitude is 0.05?0.1 m , and increases during the growth and decline phases of the 19-year cycle. The rotational modulation is due to spots with higher latitudes than in the case of the Sun, and concentrating on active longitudes. 相似文献
102.
M.?A.?LevitanEmail author T.?N.?Gelvi K.?V.?Syromyatnikov K.?D.?Chekan 《Geochemistry International》2018,56(4):304-317
Lithofacies zoning is described for the first time for the Neo- and Eopleistocene of the Bering Sea. Four lithofacies sedimentation zones are distinguished: (I) terrigenous; (II) siliceous–terrigenous; (III) siliceous, and (IV) volcanoterrigenous ones. Corresponding maps were treated using Ronov volumetric method to quantify sedimentation parameters for distinguished lithofacies zones (subzones) and types of Pleistocene sediments. It was revealed that terrigenous sediments predominate over other sediments. Accumulation of the terrigenous sediments was more intense (by 1.4 times) in the Neopleistocene than in the Eopleistocene. The sedimentation rate of siliceous sediments of the Bowers Ridge in the Eopleistocene was two times higher than in the Neopleistocene. 相似文献
103.
S. N. Arteha 《Astrophysics and Space Science》1996,246(1):51-64
A self-consistent statistical approach to the problem of planetary and stellar magnetism is suggested. The mechanism of magnetic field generation in the astronomical objects, where the existence of fields is associated with the axial rotation of objects, is discussed. In the general case the light pressure, the centrifugal, gravitational and other forces produce partial -separation of the charges. As a result of the system rotation, the magnetic fields of the currents of these charges are not compensated. The influence of various factors on the magnetic field of some object is analysed. 相似文献
104.
105.
Summary Future research directions for agricultural geography were the subject of debate in Area in the late 1980s, and the subsequent application of political economy ideas undoubtedly revived interest in agricultural research. This paper argues that agricultural geography contains greater diversity than the dominant political economy discourse would suggest. It reviews 'other' areas of agricultural research such as policy, post- productivism, people, culture and animals, presenting future suggestions which should ensure that agricultural research continues revitalized rather than redundant into the next millennium. 相似文献
106.
Man's engineering activities are concentrated on the uppermost part of the earth's crust which is called engineering-geologic zone. This zone is characterized by a significant spatialtemporal variation of the physical properties status of rocks, and saturating waters. This variation determines the specificity of geophysical and, particularly, geoelectrical investigations. Planning of geoelectric investigations in the engineering-geologic zone and their subsequent interpretation requires a priori) geologic-geophysical information on the main peculiarities of the engineering-geologic and hydrogeologic conditions in the region under investigation. This information serves as a basis for the creation of an initial geoelectric model of the section. Following field investigations the model is used in interpretation. Formalization of this a priori) model can be achieved by the solution of direct geoelectric problems. An additional geologic-geophysical information realized in the model of the medium allows to diminish the effect of the “principle of equivalence” by introducing flexible limitations in the section's parameters. Further geophysical observations as well as the correlations between geophysical and engineering-geologic parameters of the section permit the following step in the specification of the geolectric model and its approximation to the real medium. Next correction of this model is made upon accumulation of additional information. The solution of inverse problems with the utilization of computer programs permits specification of the model in the general iterational cycle of interpretation. 相似文献
107.
A. E. Volvach A. A. Berezhnoi L. N. Volvach I. D. Strepka E. A. Volvach 《Bulletin of the Crimean Astrophysical Observatory》2011,107(1):122-124
Investigations on OH maser lines in comets have been performed with the RT-22 at CrAO. The results of observations of 9P/Temper1
and Lulin C/2007 N3 comets in the OH molecule line at a wavelength of 18 cm are presented. An original technique for observation
data analysis has been developed. The gas production rate of OH molecules in these comets is estimated. 相似文献
108.
Karaevskaya E. S. Demidov N. E. Kazantsev V. S. Elizarov I. M. Kaloshin A. G. Petrov A. L. Karlov D. S. Schirrmeister L. Belov A. A. Wetterich S. 《Izvestiya Atmospheric and Oceanic Physics》2021,57(10):1254-1270
Izvestiya, Atmospheric and Oceanic Physics - The archaeal composition of permafrost samples taken during the drilling of frozen marine sediments in the area of the Barentsburg coal mine on the east... 相似文献
109.
A. F. Morozov B. N. Khakhaev O. V. Petrov V. I. Gorbachev G. V. Tarkhanov L. D. Tsvetkov Yu. M. Erinchek A. M. Akhmedov V. A. Krupenik K. Yu. Sveshnikova 《Doklady Earth Sciences》2010,435(1):1483-1486
A thick (200 m) rock salt mass covering Late Archean granitoids was exposed for the first time in the Early Proterozoic volcanogenic-sedimentary
formations in the Onega trough of the east Baltic Shield by the Onega parametric well. The mineral composition of salts, their
geochemical features, and the isotopic composition of carbonate carbon and oxygen have been studied. After fluid inclusions
present in salts, their metamorphism temperature and isotopic composition of helium and argon were determined. The obtained
results give evidence of the fact that rock salts and magnesites associated with them were formed in an evaporate basin with
participation of deep crustal processes. The age of the underlying granitoids (2.716 ± 9 Ma) is determined using the Pb—Pb
method. 相似文献
110.
Doklady Earth Sciences - Distribution density functions for the sensitivity of a three-coil sounder are constructed as the weighted mean rock volume between the in-phase surfaces of running... 相似文献