全文获取类型
收费全文 | 41775篇 |
免费 | 377篇 |
国内免费 | 272篇 |
专业分类
测绘学 | 829篇 |
大气科学 | 2110篇 |
地球物理 | 8005篇 |
地质学 | 16174篇 |
海洋学 | 3944篇 |
天文学 | 9640篇 |
综合类 | 110篇 |
自然地理 | 1612篇 |
出版年
2022年 | 499篇 |
2021年 | 756篇 |
2020年 | 807篇 |
2019年 | 898篇 |
2018年 | 1771篇 |
2017年 | 1622篇 |
2016年 | 1738篇 |
2015年 | 726篇 |
2014年 | 1521篇 |
2013年 | 2283篇 |
2012年 | 1765篇 |
2011年 | 2114篇 |
2010年 | 1975篇 |
2009年 | 2253篇 |
2008年 | 1955篇 |
2007年 | 2153篇 |
2006年 | 1901篇 |
2005年 | 1050篇 |
2004年 | 980篇 |
2003年 | 968篇 |
2002年 | 897篇 |
2001年 | 851篇 |
2000年 | 731篇 |
1999年 | 514篇 |
1998年 | 528篇 |
1997年 | 532篇 |
1996年 | 410篇 |
1995年 | 421篇 |
1994年 | 393篇 |
1993年 | 340篇 |
1992年 | 336篇 |
1991年 | 356篇 |
1990年 | 386篇 |
1989年 | 319篇 |
1988年 | 300篇 |
1987年 | 325篇 |
1986年 | 238篇 |
1985年 | 362篇 |
1984年 | 379篇 |
1983年 | 351篇 |
1982年 | 326篇 |
1981年 | 317篇 |
1980年 | 325篇 |
1979年 | 253篇 |
1978年 | 308篇 |
1977年 | 252篇 |
1976年 | 230篇 |
1975年 | 219篇 |
1974年 | 210篇 |
1973年 | 242篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
It is proposed that Saturn's electrostatic discharges (SED) might be generated in the planet's equatorial atmosphere, perhaps as lightning from a storm system. The 10h10m periodicity of the signal envelope duplicates that of Saturn's equatorial jet. The rings shield the atmosphere from solar EUV photons, and thereby substantially reduce the local ionospheric cutoff frequency to allow low-frequency SED to leak out. Many of the unusual properties of SED could be explained in terms of changes in the storm system, the relative spacecraft position in the beaming pattern of the source, local refraction of the signal by the highly disturbed ionosphere, and the influence of the ring particles on the highest frequency component of SED. A comparison of SED with planetary lightning on other planets shows that the two are similar in general character and some time behavior; the power output of SED may be higher than most planetary lightnings but that is unclear because of uncertainties in the measurements and variations in the signal's spectrum. Our simple discussion suggests that lightning could be a viable source for SED and that exotic ring mechanisms are not necessarily required. 相似文献
52.
M. V. Martynova 《Water Resources》2012,39(2):223-228
The causes of the high Mn concentration in the solid phase and pore solution of bottom sediments in the Mozhaisk Reservoir
are discussed. Regularities are identified in variations the concentrations of Mn forms in reservoir deposits from its upper
part to the dam. 相似文献
53.
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
54.
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
55.
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
56.
The population and distribution of carbon-oxidizing and sulfate-reducing bacteria in the soils of the Mozhaisk Reservoir are studied. 相似文献
57.
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
58.
59.
60.
Studia Geophysica et Geodaetica - 相似文献