全文获取类型
收费全文 | 849篇 |
免费 | 45篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 112篇 |
地球物理 | 265篇 |
地质学 | 262篇 |
海洋学 | 36篇 |
天文学 | 180篇 |
综合类 | 2篇 |
自然地理 | 20篇 |
出版年
2022年 | 7篇 |
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 33篇 |
2017年 | 36篇 |
2016年 | 60篇 |
2015年 | 44篇 |
2014年 | 55篇 |
2013年 | 49篇 |
2012年 | 22篇 |
2011年 | 29篇 |
2010年 | 41篇 |
2009年 | 37篇 |
2008年 | 19篇 |
2007年 | 28篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 14篇 |
2003年 | 13篇 |
2002年 | 19篇 |
2001年 | 9篇 |
2000年 | 13篇 |
1999年 | 7篇 |
1998年 | 18篇 |
1997年 | 11篇 |
1996年 | 18篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 10篇 |
1971年 | 12篇 |
1965年 | 5篇 |
排序方式: 共有896条查询结果,搜索用时 44 毫秒
101.
Karel Pěč Jana Pěčová Oldřich Praus Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1977,21(3-4):383-393
n ¶rt;a, n¶rt;mau 531 au ¶rt; u aum m u¶rt;uu n mumu ana¶rt;, ¶rt; u -m n, aauum ¶rt;um u u amuaa n¶rt;naa ma ua aama. uu nmam an¶rt;u ¶rt; u aum aam ¶rt;au cuu uP
n
m
, n¶rt;am mn n=1, 2, 3 u 5 (m n). u uua ¶rt;a¶rt;amu uu n¶rt;mauu uum au (a. 1) u u n aumam uu nmu, m n¶rt;mam u¶rt; am uuu ¶rt; u aum (u. 1–4). annuau 2
u 5
mn nm ma am mmmu m (u. 5, 6). ama uuu u m aam amu uu uma. 相似文献
102.
Summary Results of computing the anomalies of the variable magnetic field, generated by a harmonically variable field of the H1,0-type in the model of a spherical Earth with an expressive bulge in the well-conducting part of the mantle, are presented. It was found that not only the radial, but also the tangential component of the magnetic field is disturbed above the bulge. The largest amplitudes of these changes can be observed over the area of the largest slope of the conductivity boundary if the exciting magnetic field is perpendicular to the surface of the interface. 相似文献
103.
SummarySome Foundation Stability Problems of the Railway Bridge over the Mala Rijeka The authors presented an outlay of problems occurring in estimating the stability of rocky slopes loaded by large vertical forces. General attitudes, kept by the authors during the stability analysis for an actual case — foundation of piers No. 3 and 4 of the railway bridge across the Mala Rijeka, are also presented. The results of calculation as well as the advantages of the approach applied are outlined in the paper. Finally, general conclusions are drawn regarding the method to be kept in solving the stability of slopes loaded by large artificial loading.With 7 Figures 相似文献
104.
Summary As a result of investigating the energy flow, transmitted by short-period HM waves, the existence of a frequency limitation was found at the theoretical investigation of the propagation of these HM waves. 相似文献
105.
Implications for behavior of volatile elements during impacts—Zinc and copper systematics in sediments from the Ries impact structure and central European tektites 下载免费PDF全文
Zuzana Rodovská Tomáš Magna Karel Žák Chizu Kato Paul S. Savage Frédéric Moynier Roman Skála Josef Ježek 《Meteoritics & planetary science》2017,52(10):2178-2192
Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn (~10–20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ66Zn values between 1.7 and 3.7‰ (relative to JMC 3‐0749 Lyon) and δ65Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ66Zn = ?0.07 to +0.64‰; δ65Cu = ?0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ65Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen‐poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact‐induced high‐velocity jet of vapor and melts. 相似文献
106.
We propose a new formal definition of discovery for a Solar System object. It is based on an objective and mathematically
rigorous algorithm to assess when a set of observations is enough to constitute a discovery. When this definition is satisfied,
in almost all cases the orbit is defined well enough to establish the nature of the object discovered (Main Belt vs. Near
Earth Asteroid, Trans-Neptunian vs. long period comet). The frequency of occurrence of exceptions is estimated by a set of
numerical experiments.
The availability of a non-subjective definition of discovery allows some rules to be adopted for the assignment of discovery
credit with a minimum risk of dispute. Such rules should be fair, encourage good practice by the observers and acknowledge
the contribution of the orbit computers providing the identifications and the orbits, as well as the one of all the contributing
observers. 相似文献
107.
108.
109.
B. Novaković K. Tsiganis Z. Knežević 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):35-49
In this paper we present a comprehensive analysis of the dynamics in the region of the (3556) Lixiaohua asteroid family. The family lies in a particularly interesting region of the phase space, crossed by several two-body and three-body mean motion resonances. Also, members of this family can have close encounters with large asteroids, such as Ceres. We have identified the mean motion resonances which contribute to the long-term dynamical evolution of the family and our results confirm that the members of this family can be classified into a number of groups, exhibiting different dynamical behavior. We show for the first time that in the Lixiaohua region, apart from the chaotic diffusion in proper eccentricity and inclination (e p and I p ), there is at least one extended chaotic zone where several resonances overlap, thus giving rise to chaotic diffusion in proper semi-major axis (a p ) as well. Using a code of Monte Carlo type, we simulate the evolution of the family, according to the model which combines the chaotic diffusion (in a p , e p and I p ), Yarkovsky/YORP thermal effect and random walk in a p due to the close encounters with massive asteroids. These simulations show that all these effects should be taken into account in order to accurately explain the observed distribution of family members in the space of proper elements, although a “minimal” model that accounts for chaotic diffusion in (e p , I p ), Yarkovsky-induced drift in a p and random walk in a p due to the close encounters with the most massive asteroids is enough to grossly characterize the shape of the family. 相似文献
110.