全文获取类型
收费全文 | 3345篇 |
免费 | 142篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 126篇 |
大气科学 | 221篇 |
地球物理 | 1188篇 |
地质学 | 1066篇 |
海洋学 | 205篇 |
天文学 | 486篇 |
综合类 | 20篇 |
自然地理 | 185篇 |
出版年
2022年 | 25篇 |
2021年 | 50篇 |
2020年 | 49篇 |
2019年 | 52篇 |
2018年 | 305篇 |
2017年 | 199篇 |
2016年 | 164篇 |
2015年 | 93篇 |
2014年 | 137篇 |
2013年 | 164篇 |
2012年 | 75篇 |
2011年 | 155篇 |
2010年 | 156篇 |
2009年 | 172篇 |
2008年 | 130篇 |
2007年 | 106篇 |
2006年 | 116篇 |
2005年 | 89篇 |
2004年 | 88篇 |
2003年 | 86篇 |
2002年 | 73篇 |
2001年 | 52篇 |
2000年 | 50篇 |
1999年 | 33篇 |
1998年 | 46篇 |
1997年 | 36篇 |
1996年 | 53篇 |
1995年 | 37篇 |
1994年 | 33篇 |
1993年 | 41篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 26篇 |
1989年 | 32篇 |
1988年 | 26篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 27篇 |
1984年 | 23篇 |
1983年 | 28篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 24篇 |
1979年 | 23篇 |
1978年 | 27篇 |
1977年 | 25篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1973年 | 17篇 |
1971年 | 21篇 |
排序方式: 共有3497条查询结果,搜索用时 250 毫秒
731.
J. Klačka 《Earth, Moon, and Planets》1992,59(3):211-218
The problem of the complete set of perturbation equations of celestial mechanics in application to the Poynting-Robertson effect is discussed. Differential equations and initial conditions for them are justified. Sudden beginning of operation of the Poynting-Robertson effect (e.g., sudden release of dust particle from comet) is taken into account. 相似文献
732.
The orbital evolution of model meteoroids ejected from the comet Encke has been investigated. The particles abandon the mother body with velocities 20 and 40 ms-1 perihelion within the interval of the past 10,000 years. Their 10,000 years old osculating orbits were numerically integrated forward, using a dynamical model of the solar system consisting of all planets. Forces from solar electromagnetic and corpuscular radiation effecting the particles are considered, too. Orbital dispersions of the model meteoroids are presented. The importance of nongravitational forces for a long-term orbital evolution of meteoroid streams is shown. 相似文献
733.
734.
Andrés E. Piatti Ata Sarajedini Doug Geisler Juan Seguel David Clark 《Monthly notices of the Royal Astronomical Society》2005,358(4):1215-1230
Colour–magnitude diagrams (CMDs) are presented for the first time for 10 star clusters projected on to the Small Magellanic Cloud (SMC). The photometry was carried out in the Washington system C and T 1 filters allowing the determination of ages by means of the magnitude difference between the red giant clump and the main-sequence turnoff (MSTO), and metallicities from the red giant branch (RGB) locus. The clusters all have ages in the range 1.5–4 Gyr and metallicities between −1.3 < [Fe/H] < −0.6 , with respective errors of ∼0.5 Gyr and 0.3 dex. This increases substantially the sample of intermediate-age clusters in the SMC with well-derived parameters. We combine our results with those for other clusters in the literature to derive as large and homogeneous a data base as possible (totalling 26 clusters) in order to study global effects. We find evidence for two peaks in the age distribution of SMC clusters, at ∼6.5 and 2.5 Gyr, in good agreement with previous hints involving smaller samples. The most recent peak occurs at a time that corresponds to a very close encounter between the Large Magellanic Cloud (LMC) and the SMC according to the recent dynamical models of Bekki et al. that they used to explain the enhancement of LMC clusters with this age. It appears cluster formation may have been similarly stimulated in the SMC by this encounter as well. We also find very good agreement between cluster ages and metallicities and the prediction from a bursting model from Pagel and Tautvaišienė with a burst that occurred 3 Gyr ago. These two lines of evidence together favour a bursting cluster formation history as opposed to a continuous one for the SMC. 相似文献
735.
The spectral coefficients of the selenoid have been obtained by inverting the potential series for lunar gravity. The reference value of the lunar level surface has been determined on the base of the mean radius of lunar topography. This enables to evaluate the parameters of the tri-axial reference ellipsoid best fitted to the lunar level surface. 相似文献
736.
737.
Tomás Soler 《Geophysical Journal International》1985,81(2):363-379
Summary. This paper introduces a new matrix computational approach to the local determination of gravity gradients, convenient for comparing with gradient signals from moving base gradiometer systems or calculating topographic effects at instrument heights. The method represents a practical alternative to the more conventional spherical harmonics formulation, primarily global in nature, and it may be considered as an extension to other previously used local representations, such as point masses. Important characteristics of the analytical development outlined herein are its conceptual simplicity and the possibility of obtaining at once, up to a certain order n , and in an arbitrary Cartesian coordinate system, the symmetric point gradient tensor of second rank. 相似文献
738.
739.
Study of groundwaters using the environmental tritium and hydrochemical data in the Belgrade region 总被引:2,自引:1,他引:1
M. Hadžišehović M Župančić N. Miljević D. Paligorić M. Komatina 《Environmental Geology》1990,15(1):13-29
A study of tritium content and some physicochemical parameters has been performed in order to investigate interconnection between surface and atmospheric waters and underground waters in Belgrade area. Samples of the precipitation at Zeleno Brdo-Belgrade meteorological station, the Danube and the Sava river water, and underground water (Ranney wells and piezometers) have been analyzed. The3H content, the content of dissolved ions, total hardness, and electrical conductivity have been measured. The tritium data show existence of two water strata in the aquifer. The upper stratum (about 16 m thick) contains older water (mean monthly3H concentration of 17 TU) and has weak interaction with the river and the precipitation. Below this stratum lies the principal water bearing stratum, strongly connected with the river with the3H concentration similar to that of surface water (mean monthly3H concentration of 50 TU) and spreading out through the entire aquifer. The contribution of the Sava river water and the two water layers at the Ranney well are calculated starting with the hydrological aquifer model, which supposes that three water components are mixed in the pumped Ranney well water. According to calculation results using the3H concentration and physicochemical characteristics as parameters, more than 70 percent of the water pumped by the Ranney well (in 1983) comes from the Sava with a time delay of less that 15 days.Properties of tritium distribution in precipitation, river waters, and underground water in the Belgrade region are established from the results of measurements of3H concentrations in the period 1976–1983. 相似文献
740.
A. Kučera J. Rybák M. Minarovjech D. Novocký M. Saniga 《Astrophysics and Space Science》1990,171(1-2):279-281
The construction and the optical design as well as the controlling electronic device and the spectrum recording of the new horizontal solar telescope with the spectrograph of the Astronomical Institute of Slovak Academy of Sciences are described. Also some of its adjustments and improvements are briefly mentioned.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献