全文获取类型
收费全文 | 72212篇 |
免费 | 820篇 |
国内免费 | 503篇 |
专业分类
测绘学 | 1595篇 |
大气科学 | 4334篇 |
地球物理 | 14049篇 |
地质学 | 26189篇 |
海洋学 | 6716篇 |
天文学 | 16997篇 |
综合类 | 160篇 |
自然地理 | 3495篇 |
出版年
2022年 | 574篇 |
2021年 | 934篇 |
2020年 | 979篇 |
2019年 | 1111篇 |
2018年 | 2275篇 |
2017年 | 2081篇 |
2016年 | 2420篇 |
2015年 | 1126篇 |
2014年 | 2142篇 |
2013年 | 3754篇 |
2012年 | 2469篇 |
2011年 | 3168篇 |
2010年 | 2952篇 |
2009年 | 3606篇 |
2008年 | 3131篇 |
2007年 | 3335篇 |
2006年 | 3017篇 |
2005年 | 2049篇 |
2004年 | 1936篇 |
2003年 | 1897篇 |
2002年 | 1810篇 |
2001年 | 1699篇 |
2000年 | 1512篇 |
1999年 | 1150篇 |
1998年 | 1181篇 |
1997年 | 1222篇 |
1996年 | 957篇 |
1995年 | 962篇 |
1994年 | 906篇 |
1993年 | 811篇 |
1992年 | 777篇 |
1991年 | 761篇 |
1990年 | 799篇 |
1989年 | 740篇 |
1988年 | 705篇 |
1987年 | 780篇 |
1986年 | 658篇 |
1985年 | 871篇 |
1984年 | 927篇 |
1983年 | 848篇 |
1982年 | 768篇 |
1981年 | 791篇 |
1980年 | 702篇 |
1979年 | 624篇 |
1978年 | 656篇 |
1977年 | 621篇 |
1976年 | 551篇 |
1975年 | 542篇 |
1974年 | 535篇 |
1973年 | 571篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
A special system of canonical variables is considered. An algorithm for expanding the principal functions of Keplerian motion in new elements is presented. The advantage of the proposed system is a relatively small number of terms in the classical expansions of the unperturbed two-body problem. A method for expanding the time derivatives of the rectangular coordinates is proposed. Some estimates of the number of terms in the presented expansions have been obtained through numerical experiments. 相似文献
102.
Assuming that a disk galaxy is composed of an ambient pervasive gas, small clouds, molecular clouds and stars, its evolution is studied through examining the interchange processes among them. Main results obtained are: (1) The star formation rate is directed by the formation process of molecular clouds. (2) Depending upon the parameters there may be three or four types of evolution of disk galaxies: the no star formation case, the active in the past and inactive at present star formation case, the burst-like star formation case and the very active in star formation case.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan between 30 September–6 October, 1984. 相似文献
103.
104.
E.?S.?KazakEmail author E.?G.?Kalitina N.?A.?Kharitonova G.?A.?Chelnokov E.?V.?Elovskii I.?V.?Bragin 《Moscow University Geology Bulletin》2018,73(3):287-294
This paper reports the results of the experimental determination of the coefficient of sorption of rare-earth elements and yttrium (REY) under conditions of acidic pH using several strains of heterotrophic bacteria (Microbacterium sp., Curtobacterium sp., Bacillus subtilis, Pseudomonas putida, and Bacillus pumilis) that are widespread in natural and technogenic waters of the Far East (Russia). Insignificant fractionation between heavy and light rare-earth elements, negative cerium and dysprosium anomalies, and a positive europium anomaly were revealed. The selectivity of REY biosorption by gram-positive and gram-negative bacteria, as well as inertia of the biosorption process under more acidic conditions of the medium, were shown. 相似文献
105.
106.
The first small active regions of the last two new cycles seem to be formed, in its very first, preparatory stage, close to the equator with uncertain magnetic orientation, and as secondary products at the periphery of equatorial `magnetic bubbles' of the new magnetic flux still belonging to the old cycle. At the real beginning of the new cycle, at the periphery of its higher-latitude `magnetic bubbles', the opposite applies to the secondary regions of the ending cycle. It seems that two modes of magnetic flux supply the visible layers of the photosphere during the cycle transition phase: the emergence of the magnetic flux from the depth of the convective zone, and the mutual interaction of the earlier emerging fluxes, or the action of the `local dynamo', giving rise to the new local magnetic field concentrations. 相似文献
107.
The population and distribution of carbon-oxidizing and sulfate-reducing bacteria in the soils of the Mozhaisk Reservoir are studied. 相似文献
108.
109.
M. D. Sharma 《Geophysical Journal International》2008,174(3):971-977
Out of the four waves in an anisotropic poroelastic medium, two are termed as quasi-transverse waves. The prefix 'quasi' refers to their polarizations being nearly, but not exactly, perpendicular to direction of propagation. In this composite medium, unlike perfectly elastic medium, the propagation of a longitudinal wave along a phase direction may not be accompanied by transverse waves. The existence of a transverse wave in anisotropic poroelastic media is ensured by the two equations restricting the choice of elastic coefficients of porous aggregate as well as fluid–solid coupling. Necessary and sufficient conditions for the existence of transverse waves along the coordinate axes and in the coordinate planes for general anisotropy are discussed. The discussion is extended to the case of orthotropic materials and existence for few specific phase directions is also explored. The conditions for the transverse waves decided on the basis of their apparent polarizations, that is, particle motion being perpendicular to ray direction, are also discussed. For a particular numerical model, the existence of these apparent transverse waves is solved numerically for phase directions in coordinate planes. For general directions of phase propagation, the existence of these transverse waves is checked graphically for the chosen numerical model. 相似文献
110.
The eleventh list of faint late M and carbon type stars detected on the plates of the First Byurakan Spectral Survey in zone -7° -3° and covering about 1000 square degrees is presented. From 126 detected stars, 88 are newly discovered objects: they are 6 carbon stars, 8 carbon star candidates, and 74 M-type stars; among the latter 38 (26 PSC + 12 FSC) are unclassified IRAS sources, and one object is an unclassified ROSAT source. Distances to the 6 newly discovered early-type carbon stars are estimated. Equatorial coordinates, red magnitudes, and spectral classes determined from the Palomar E-charts are provided. The lack of optical counterparts on Palomar O and E maps for two detected late M-type stars indicates a large variability in brightnesses of these objects (amplitude not smaller than 7.0 magnitude). 相似文献