全文获取类型
收费全文 | 264714篇 |
免费 | 5193篇 |
国内免费 | 3362篇 |
专业分类
测绘学 | 6975篇 |
大气科学 | 19521篇 |
地球物理 | 55314篇 |
地质学 | 92783篇 |
海洋学 | 22176篇 |
天文学 | 57365篇 |
综合类 | 1040篇 |
自然地理 | 18095篇 |
出版年
2021年 | 2244篇 |
2020年 | 2593篇 |
2019年 | 2857篇 |
2018年 | 4412篇 |
2017年 | 4146篇 |
2016年 | 6180篇 |
2015年 | 4219篇 |
2014年 | 6906篇 |
2013年 | 14183篇 |
2012年 | 6841篇 |
2011年 | 8622篇 |
2010年 | 7727篇 |
2009年 | 10240篇 |
2008年 | 8929篇 |
2007年 | 8618篇 |
2006年 | 9701篇 |
2005年 | 7906篇 |
2004年 | 7769篇 |
2003年 | 7257篇 |
2002年 | 6801篇 |
2001年 | 6016篇 |
2000年 | 5961篇 |
1999年 | 5219篇 |
1998年 | 5234篇 |
1997年 | 5030篇 |
1996年 | 4679篇 |
1995年 | 4431篇 |
1994年 | 4104篇 |
1993年 | 3854篇 |
1992年 | 3636篇 |
1991年 | 3591篇 |
1990年 | 3765篇 |
1989年 | 3521篇 |
1988年 | 3305篇 |
1987年 | 3848篇 |
1986年 | 3407篇 |
1985年 | 4224篇 |
1984年 | 4737篇 |
1983年 | 4406篇 |
1982年 | 4312篇 |
1981年 | 3928篇 |
1980年 | 3637篇 |
1979年 | 3508篇 |
1978年 | 3488篇 |
1977年 | 3280篇 |
1976年 | 3044篇 |
1975年 | 2960篇 |
1974年 | 2914篇 |
1973年 | 3077篇 |
1972年 | 2025篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
O.V.Chumak 《中国天文和天体物理学报》2003,3(2):175-182
We present a study of the relationship between integral area and corresponding total magnetic flux for solar active regions. It is shown that some of these relationships are satisfied to simple power laws. Fractal examination showed that some of these power laws can not be justified inside the simple models of stationary magnetic flux tube aggregation. All magnetic fluxes and corresponding areas were calculated using the data measured with the Solar Magnetic Field Telescope of the Huairou Solar Observing Station in Beijing. 相似文献
232.
E.A. Evstigneeva R.R. de Carvalho A.L. Ribeiro H.V. Capelato 《Astrophysics and Space Science》2003,284(2):487-490
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families
of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different
loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this
diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we
can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
233.
234.
S.J Weidenschilling 《Icarus》2003,165(2):438-442
For standard cosmic abundances of heavy elements, a layer of small particles in the central plane of the solar nebula cannot attain the critical density for gravitational instability. Youdin and Shu (2002, Astrophys. J. 580, 494-505) suggest that the local surface density of solids can be enhanced by radial migration of particles due to gas drag. However, they consider only motions of individual particles. Collective motion due to turbulent stress on the particle layer acts to inhibit such enhancement and may prevent gravitational instability. 相似文献
235.
Travis S. Metcalfe 《Astrophysics and Space Science》2003,284(1):141-151
A flood of reliable seismic data will soon arrive. The migration to largertelescopes on the ground may free up 4-m class instruments for multi-sitecampaigns, and several forthcoming satellite missions promise to yieldnearly uninterrupted long-term coverage of many pulsating stars. We willthen face the challenge of determining the fundamental properties of thesestars from the data, by trying to match them with the output of ourcomputer models. The traditional approach to this task is to make informedguesses for each of the model parameters, and then adjust them iterativelyuntil an adequate match is found. The trouble is: how do we know that oursolution is unique, or that some other combination of parameters will notdo even better? Computers are now sufficiently powerful and inexpensivethat we can produce large grids of models and simply compare all ofthem to the observations. The question then becomes: what range ofparameters do we want to consider, and how many models do we want tocalculate? This can minimize the subjective nature of the process, but itmay not be the most efficient approach and it may give us a false sense ofsecurity that the final result is correct, when it is really justoptimal. I discuss these issues in the context of recent advances inthe asteroseismological analysis of white dwarf stars. 相似文献
236.
237.
Green Lake Landslide is an ancient giant rock slide in gneiss and granodiorite located in the deeply glaciated Fiordland region of New Zealand. The landslide covers an area of 45 km2 and has a volume of about 27 km3. It is believed to be New Zealand's largest landslide, and possibly the largest landslide of its type on Earth. It is one of 39 known very large (106–107 m3) and giant (≥108 m3) postglacial landslides in Fiordland discussed in the paper. Green Lake Landslide resulted in the collapse of a 9 km segment of the southern Hunter Mountains. Slide debris moved up to 2.5 km laterally and 700 m vertically, and formed a landslide dam about 800 m high, impounding a lake about 11 km long that was eventually infilled with sediments. Geomorphic evidence supported by radiocarbon dating indicates that Green Lake Landslide probably occurred 12 000–13 000 years ago, near the end of the last (Otira) glaciation. The landslide is described, and its geomorphic significance, age, failure mechanism, cause, and relevance in the region are discussed, in relation to other large landslides and recent earthquake-induced landslides in Fiordland. The slope failure occurred on a low-angle fault zone undercut by glacial erosion, and was probably triggered by strong shaking (MM IX–X) associated with a large (≥ M 7.5–8) earthquake, on the Alpine Fault c. 80 km to the northwest. Geology was a major factor that controlled the style and size of Green Lake landslide, and in that respect it is significantly different from most other gigantic landslides. Future large earthquakes on the Alpine Fault in Fiordland are likely to trigger more very large and giant landslides across the region, causing ground damage and devastation on a scale that has not occurred during the last 160 years, with potentially disastrous effects on towns, tourist centres, roads, and infrastructure. The probability of such an event occurring within the next 50 years may be as high as 45%. 相似文献
238.
Takuya Matsumoto Masahiko Honda Ian McDougall Igor Yatsevich Suzanne Y. O'Reilly 《地学学报》2004,16(1):23-26
Using a Rayleigh distillation fractionation model, we calculate that the maximum isotope fractionation potentially achievable is less than 5% during the early stages of gas release from a sample. Our calculation corrects the erroneous conclusions of Gautheron and Moreira (2003), who re‐interpreted the plume‐like neon isotopic compositions found in metasomatic apatite from a south‐eastern Australian xenolith (Matsumoto et al., 1997) to be the result of Rayleigh‐type isotope fractionation of originally MORB‐type neon during stepheating gas extraction. We stress that the modelling of neon isotopic fractionation by Gautheron and Moreira (2003) is incorrect, and that the finding of a plume‐like neon isotopic composition in the apatite by Matsumoto et al. (1997) remains a quite valid and robust conclusion. 相似文献
239.
V. G. Gorbatskii 《Astrophysics》1990,32(2):149-154
Leningrad State University. Translated from Astrofizika, Vol. 32, No. 2, pp. 267–275, March–April, 1990. 相似文献
240.
This paper describes a wide-field survey made at 34.5 MHz using GEETEE,1 the low frequency telescope at Gauribidanur (latitude
13°36′12′′N). This telescope was used in the transit mode and by per forming 1-D synthesis along the north-south direction
the entire observable sky was mapped in a single day. This minimized the problems that hinder wide-field low-frequency mapping.
This survey covers the declination range of-50° to + 70° (- 33° to +61° without aliasing) and the complete 24 hours of right
ascension. The synthesized beam has a resolution of 26′ x 42′ sec (δ- 14°. 1). The sensitivity of the survey is 5 Jy/beam (1σ). Special care has been taken to ensure that the antenna responds
to all angular scale structures and is suitable for studies of both point sources and extended objects
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Roman Research Institute, Bangalore. 相似文献