全文获取类型
收费全文 | 31946篇 |
免费 | 431篇 |
国内免费 | 371篇 |
专业分类
测绘学 | 697篇 |
大气科学 | 2134篇 |
地球物理 | 5819篇 |
地质学 | 12155篇 |
海洋学 | 3099篇 |
天文学 | 7448篇 |
综合类 | 82篇 |
自然地理 | 1314篇 |
出版年
2022年 | 303篇 |
2021年 | 468篇 |
2020年 | 521篇 |
2019年 | 575篇 |
2018年 | 1137篇 |
2017年 | 1074篇 |
2016年 | 1192篇 |
2015年 | 576篇 |
2014年 | 1094篇 |
2013年 | 1787篇 |
2012年 | 1224篇 |
2011年 | 1537篇 |
2010年 | 1362篇 |
2009年 | 1663篇 |
2008年 | 1451篇 |
2007年 | 1497篇 |
2006年 | 1380篇 |
2005年 | 865篇 |
2004年 | 790篇 |
2003年 | 733篇 |
2002年 | 772篇 |
2001年 | 689篇 |
2000年 | 637篇 |
1999年 | 542篇 |
1998年 | 561篇 |
1997年 | 520篇 |
1996年 | 457篇 |
1995年 | 418篇 |
1994年 | 424篇 |
1993年 | 345篇 |
1992年 | 341篇 |
1991年 | 334篇 |
1990年 | 357篇 |
1989年 | 261篇 |
1988年 | 244篇 |
1987年 | 295篇 |
1986年 | 243篇 |
1985年 | 344篇 |
1984年 | 327篇 |
1983年 | 287篇 |
1982年 | 311篇 |
1981年 | 242篇 |
1980年 | 280篇 |
1979年 | 228篇 |
1978年 | 241篇 |
1977年 | 185篇 |
1976年 | 189篇 |
1975年 | 184篇 |
1974年 | 195篇 |
1973年 | 183篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
131.
Current and future wide field surveys in infrared passbands present opportunities for ultra low‐mass stellar sample selection via proper motions, as well as or instead of purely photometric techniques. Furthermore, proper motion measurements yield additional clues as to candidate membership of cluster or field (kinematic) populations. In this paper we review some recent results and speculate as to the possibilities afforded by the next generation of wide‐field infrared surveys. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
132.
133.
The photometric U orbital variations of the symbiotic binary AG Peg, caused by occultation of a bright gaseous region by the
M giant in this system, are used to determine the geometry of this region whose existence is explained in the framework of
the colliding winds model. The emission of the bright region varies and a particular value of its mean density of 2–3 1010 cm-3 has been derived. The causes for the irregular variations of the light in the orbital minimum and maximum are discussed.
It is also obtained, when the mass-loss rate of the hot companion of the system decreases to about 5 10-10
Ms
⊙ yr-1, this bright region will disappear.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
134.
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
135.
西藏山地淋溶土系列与大骨节病分布的关系 总被引:3,自引:0,他引:3
通过西藏大骨节病县与非病县棕壤与暗棕壤各土属、土种的分布面积的对比分析对西藏耕型棕壤和暗棕壤分布与西藏大骨节病区分布的关系进行研究.结果表明,西藏大骨节病的分布与棕壤、暗棕壤为主的耕型淋溶土壤的分布有一定的联系,但土壤母质和发育程度不同,对大骨节病的分布影响不同.对于残坡积土壤,病区趋于分布在泥质土壤环境,而麻砂质土壤基本是大骨节病的非病区.同样的母质环境,大骨节病区趋于分布在土壤厚度较小,发育程度较低的地区;就洪积土壤来说,其与大骨节病分布的关系似乎与土壤质地有一定的联系,底部砾石含量高的土壤多集中在大骨节病地区.总体而言,山地棕壤、暗棕壤环境是西藏大骨节病区的主要土壤类型之一,西藏未开发的自然棕壤和暗棕壤环境将是大骨节病潜在危险区,因此系统研究西藏典型大骨节病区的土壤分异对探讨未来西藏大骨节病的分布与流行有重要意义. 相似文献
136.
"A modification of the population potential model is used to analyze the structure of the potential of population for cities of the Moscow region, to develop a relationship between population potential and city size, and to use this procedure to forecast future population change in Moscow Oblast cities." Cities in the region with a population of 50,000 or more at the censuses of 1959, 1970, and 1979 are included. 相似文献
137.
Summary. Particle-motion plots of shear waves have been studied for the section FG of the FENNOLORA seismic experiment. Shear-wave splitting is observed on some records and the polarization of the first arriving shear waves show two peaks at about N35°W and N65°E. These results can be interpreted as being due to crack-induced anisotropy with the crack direction dominated by a (dominant) horizontal stress around N35°W. This is consistent with in situ stress measurements and focal mechanism studies in Scandinavia. the results show that seismic refraction experiments may be useful in providing evidence of crack-induced anisotropy in the stable continental crust. 相似文献
138.
Summary. The contributions from the oceanic and ionospheric dynamos, Lo and LI respectively, to the geomagnetic lunar daily variation, L , at Alibag, a coastal station in the Indian equatorial region, are calculated from the L harmonics derived from a 41–yr long series of observations. The analysis in the calendar months shows a steady and significant ocean dynamo contribution in the vertical component, Z, in all the months except April. Examination, by an analysis of the data year by year, of the association of Lo and LI with varying solar and magnetic activities reveals, surprisingly, a stable correlation between the magnetic activity index A P and the oceanic part in the horizontal and vertical components but not in declination, which probably indicates the influence of induced currents, along the latitudes, on L o . 相似文献
139.
The geochemical study of the suspended matter in the waters of the Amazon River and its tributaries revealed that the chemical composition of this material ranges widely; however, generally, it is similar to the average composition of the suspended matter in the rivers and clayey sedimentary rocks around the world. Against this background, an essential regional Hg enrichment due to the anthropogenic factor is distinguished. The suspensions from the so-called clear waters from the tributaries of the Amazon River—Xingu and Trombetas—demonstrate the local enrichment in Pb, Sn, Zn, and organic carbon indicating the ore mineralization of the drainage basin, and points to the presence of metal-organic complexes. 相似文献
140.
N. Voglis P. Tsoutsis C. Efthymiopoulos 《Monthly notices of the Royal Astronomical Society》2006,373(1):280-294
In the presence of a strong m = 2 component in a rotating galaxy, the phase-space structure near corotation is shaped to a large extent by the invariant manifolds of the short-period family of unstable periodic orbits terminating at L 1 or L 2 . The main effect of these manifolds is to create robust phase correlations among a number of chaotic orbits large enough to support a spiral density wave outside corotation. The phenomenon is described theoretically by soliton-like solutions of a Sine–Gordon equation. Numerical examples are given in an N -body simulation of a barred spiral galaxy. In these examples, we demonstrate how the projection of unstable manifolds in configuration space reproduces essentially the entire observed bar–spiral pattern. 相似文献