全文获取类型
收费全文 | 71998篇 |
免费 | 1167篇 |
国内免费 | 665篇 |
专业分类
测绘学 | 1740篇 |
大气科学 | 5084篇 |
地球物理 | 14400篇 |
地质学 | 25484篇 |
海洋学 | 6256篇 |
天文学 | 16407篇 |
综合类 | 213篇 |
自然地理 | 4246篇 |
出版年
2022年 | 401篇 |
2021年 | 715篇 |
2020年 | 799篇 |
2019年 | 843篇 |
2018年 | 1919篇 |
2017年 | 1793篇 |
2016年 | 2268篇 |
2015年 | 1348篇 |
2014年 | 2213篇 |
2013年 | 3823篇 |
2012年 | 2318篇 |
2011年 | 3185篇 |
2010年 | 2638篇 |
2009年 | 3543篇 |
2008年 | 3303篇 |
2007年 | 3078篇 |
2006年 | 2902篇 |
2005年 | 2379篇 |
2004年 | 2287篇 |
2003年 | 2142篇 |
2002年 | 1960篇 |
2001年 | 1811篇 |
2000年 | 1726篇 |
1999年 | 1388篇 |
1998年 | 1479篇 |
1997年 | 1391篇 |
1996年 | 1104篇 |
1995年 | 1147篇 |
1994年 | 968篇 |
1993年 | 879篇 |
1992年 | 859篇 |
1991年 | 763篇 |
1990年 | 859篇 |
1989年 | 720篇 |
1988年 | 660篇 |
1987年 | 818篇 |
1986年 | 665篇 |
1985年 | 858篇 |
1984年 | 924篇 |
1983年 | 862篇 |
1982年 | 833篇 |
1981年 | 708篇 |
1980年 | 664篇 |
1979年 | 609篇 |
1978年 | 603篇 |
1977年 | 555篇 |
1976年 | 539篇 |
1975年 | 499篇 |
1974年 | 507篇 |
1973年 | 470篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
M. V. Belyaeva A. S. Drofa V. N. Ivanov 《Izvestiya Atmospheric and Oceanic Physics》2013,49(2):154-161
Comparative estimates of the efficiency of hygroscopic reagents for the seeding of convective clouds to obtain additional precipitation are performed based on numerical simulation. It is shown that the use of polydisperse salt powders has many benefits over other known hygroscopic reagents. The effect of seeding with salt powders manifests itself at mass concentrations of hygroscopic particles an order of magnitude less than when pyrotechnic flares are used. With salt-powder seeding, it is possible to obtain precipitation from warm convective clouds of moderate thickness from which precipitation does not typically fall. In this case the effect of “reseeding” of clouds, which can be observed in seeding with hygroscopic reagents having narrow size distributions of particles, does not reveal itself. 相似文献
995.
K. SchroederA.C. Haza A. Griffa T.M. Özgökmen P.M. PoulainR. Gerin G. PeggionM. Rixen 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(3):209-228
Relative dispersion in the Liguro-Provençal basin (a subregion of the Mediterranean Sea) is investigated using clusters of surface drifters deployed during two Marine Rapid Environment Assessment (MREA) experiments covering different months in 2007 and 2008, respectively. The clusters have initial radii of less than 1 km, or an order of magnitude below a typical deformation radius (approximately 10-20 km). The data set consists of 45 original pairs and more than 50 total pairs (including chance ones) in the spatial range between 1 and 200 km. Relative dispersion is estimated using the mean square separation of particle pairs and the Finite Scale Lyapunov Exponents (FSLEs). The two metrics show broadly consistent results, indicating in particular a clear exponential behaviour with an e-folding time scale between 0.5 and 1 days, or Lyapunov exponent ?? in the range of 0.7-1 days−1. The exponential phase extends for 4-7 days in time and between 1 and 10-20 km in separation space. To our knowledge, this is only the third time that an exponential regime is observed in the world ocean from drifter data. This result suggests that relative dispersion in the Liguro-Provençal basin is nonlocal, namely controlled mainly by mesoscale dynamics, and that the effects of the sub-mesoscale motions are negligible in comparison. NCOM model results are used to complement the data and to quantify errors arising from the sparse sampling in the observations. 相似文献
996.
Oceanology - The kinetic energy of six jets of the Antarctic Circumpolar Current (ACC) and of the cyclonic and anticyclonic mesoscale eddies generated by these jets is studied in application to the... 相似文献
997.
998.
Multiple magnetic clouds in interplanetary space 总被引:7,自引:0,他引:7
An interplanetary magnetic cloud (MC) is usually considered the byproduct of a coronal mass ejection (CME). Due to the frequent occurrence of CMEs, multiple magnetic clouds (multi-MCs), in which one MC catches up with another, should be a relatively common phenomenon. A simple flux rope model is used to get the primary magnetic field features of multi-MCs. Results indicate that the magnetic field configuration of multi-MCs mainly depends on the magnetic field characteristics of each member of multi-MCs. It may be entirely different in another situation. Moreover, we fit the data from the Wind spacecraft by using this model. Comparing the model with the observations, we verify the existence of multi-MCs, and propose some suggestions for further work. 相似文献
999.
It is the purpose of this paper to present evidence concerning the appearance of a sunspot in A.D. 939 observed by Arabs from
the Iberian Peninsula. The sunspot record appears in the Arab source known as al-Muqtabis V. 相似文献
1000.
The physics of scattering of electromagnetic waves by media in which the particles are in contact, such as planetary regoliths, has been thought to be relatively well understood when the particles are larger than the wavelength. However, this is not true when the particles are comparable with or smaller than the wavelength. We have measured the scattering parameters of planetary regolith analogs consisting of suites of well-sorted abrasives whose particles ranged from larger to smaller than the wavelength. We measured the variation of reflectance as the phase angle varied from 0.05° to 140°. The following parameters of the media were then deduced: the single scattering albedo, single scattering phase function, transport mean free path, and scattering, absorption, and extinction coefficients. A scattering model based on the equation of radiative transfer was empirically able to describe quantitatively the variation of intensity with angle for each sample. Thus, such models can be used to characterize scattering from regoliths even when the particles are smaller than the wavelength. The scattering parameters were remarkably insensitive to particle size. These results are contrary to theoretical predictions, but are consistent with earlier measurements of alumina abrasives that were restricted to small phase angles. They imply that a basic assumption made by virtually all regolith scattering models, that the regolith particles are the fundamental scattering units of the medium, is incorrect. Our understanding of scattering by regoliths appears to be incomplete, even when the particles are larger than the wavelength. 相似文献