全文获取类型
收费全文 | 72629篇 |
免费 | 1709篇 |
国内免费 | 1317篇 |
专业分类
测绘学 | 1822篇 |
大气科学 | 5403篇 |
地球物理 | 14602篇 |
地质学 | 26034篇 |
海洋学 | 6659篇 |
天文学 | 16078篇 |
综合类 | 309篇 |
自然地理 | 4748篇 |
出版年
2022年 | 446篇 |
2021年 | 813篇 |
2020年 | 793篇 |
2019年 | 881篇 |
2018年 | 1700篇 |
2017年 | 1588篇 |
2016年 | 1969篇 |
2015年 | 1232篇 |
2014年 | 1876篇 |
2013年 | 3670篇 |
2012年 | 2290篇 |
2011年 | 3144篇 |
2010年 | 2809篇 |
2009年 | 3633篇 |
2008年 | 3055篇 |
2007年 | 3176篇 |
2006年 | 3029篇 |
2005年 | 2309篇 |
2004年 | 2223篇 |
2003年 | 2099篇 |
2002年 | 2016篇 |
2001年 | 1733篇 |
2000年 | 1653篇 |
1999年 | 1354篇 |
1998年 | 1405篇 |
1997年 | 1374篇 |
1996年 | 1138篇 |
1995年 | 1131篇 |
1994年 | 997篇 |
1993年 | 931篇 |
1992年 | 886篇 |
1991年 | 831篇 |
1990年 | 890篇 |
1989年 | 808篇 |
1988年 | 780篇 |
1987年 | 916篇 |
1986年 | 792篇 |
1985年 | 982篇 |
1984年 | 1120篇 |
1983年 | 997篇 |
1982年 | 932篇 |
1981年 | 926篇 |
1980年 | 830篇 |
1979年 | 765篇 |
1978年 | 739篇 |
1977年 | 731篇 |
1976年 | 656篇 |
1975年 | 631篇 |
1974年 | 659篇 |
1973年 | 690篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
241.
S. D. Doty R. A. Metzler M. L. Palotti 《Monthly notices of the Royal Astronomical Society》2005,362(2):737-747
We present a study of radiative transfer in dusty, clumpy star-forming regions. A series of self-consistent, 3D, continuum radiative transfer models are constructed for a grid of models parametrized by central luminosity, filling factor, clump radius and face-averaged optical depth. The temperature distribution within the clouds is studied as a function of this parametrization. Among our results, we find that: (i) the effective optical depth in clumpy regions is less than in equivalent homogeneous regions of the same average optical depth, leading to a deeper penetration of heating radiation in clumpy clouds, and temperatures higher by over 60 per cent; (ii) penetration of radiation is driven by the fraction of open sky (FOS) – which is a measure of the fraction of solid angle along which no clumps exist; (iii) FOS increases as clump radius increases and as filling factor decreases; (iv) for values of FOS >0.6–0.8 the sky is sufficiently 'open' that the temperature distribution is relatively insensitive to FOS; (v) the physical process by which radiation penetrates is preferentially through streaming of radiation between clumps as opposed to diffusion through clumps; (vi) filling factor always dominates the determination of the temperature distribution for large optical depths, and for small clump radii at smaller optical depths; (vii) at lower face-averaged optical depths, the temperature distribution is most sensitive to filling factors of 1–10 per cent, in accordance with many observations; (viii) direct shadowing by clumps can be important for distances approximately one clump radius behind a clump. 相似文献
242.
This paper presents two and three dimensional simulations of the interaction of shocks with media with large numbers of dense
inclusions. An approximate model of the interaction of a starburst wind with the surrounding galactic ISM illustrates issues
which must be addressed in global models of ISM dynamics. As a step towards developing the sub-grid model of multiphase turbulence,
we define and study a form of ‘multiphase Riemann problem’. This allows us to develop macroscopic characteristics of the flows
which may be compared to such subgrid models. 相似文献
243.
244.
D.L. Mickey 《Solar physics》2004,220(1):21-27
I describe a method for quickly and accurately determining the plate parallelism in a tunable Fabry-Pérot interferometer. The method takes advantage of the fact that our Fabry-Pérot is installed in a spectropolarimeter: we measure profiles of solar or telluric absorption lines in three differently polarized telescope subapertures and use the residual polarization profiles to determine the plate parallelism error. An example of the error as a function of time during the observing day is also shown; it changes in a consistent way with telescope hour angle but the drift is enough to require frequent adjustment. 相似文献
245.
Astronomy Letters - The acceleration of anomalous cosmic rays (ACRs) at the heliospheric termination shock and their influence on the shock structure and location are analyzed in terms of a... 相似文献
246.
Fred L. Whipple 《Earth, Moon, and Planets》1996,72(1-3):69-78
This study is based primarily on the calculations of comet orbits over ~ 106 years for 160 short-period comets by Harold F. Levison and Martin J. Duncan from which there are calculated “ablation AGES”. There are positive statistical correlations (having many deviations) with radial nongravitational forces, comet activity measures, and dust-to-gas ratios in the spectra, in the sense that comets of greater “AGES” tend to be less active and to show less dust in their spectra than comets of lesser “AGES”. 相似文献
247.
Current plate motions 总被引:57,自引:0,他引:57
248.
Measured time series were generated by small omnidirectional explosive sources in a shallow water area. A bottom-mounted hydrophone recorded sound signals that propagated over a sloping bottom. The time series in the 250-500 Hz band were analyzed with a broad-band adiabatic normal mode approach. The measured waveforms contain numerous bottom interacting multipaths that are complicated by the subbottom structure that contains high-velocity layers near the water-sediment interface. Several of the details of the geoacoustic structure and the depth of the water column at the receiver are inferred from comparisons of the measured data to simulated time series. The sensitivity of broad-band matched-field ambiguity surfaces in the range-depth plane for a single receiver to selected waveguide parameters is examined. A consistent analysis is made where the simulated time series are compared to the measured time series along with the single-receiver matched-field localization solutions for ranges out to 5 km. In this range interval, it was found that the peak cross-correlation between the measured and simulated time series varied between 0.84 and 0.69. The difference between the GPS range and the range obtained from the matched-field solution varied from 0 to 63 m. The geoacoustic structure obtained in the analysis consists of an 8-m low-velocity sediment layer over an 8-m high-velocity layer followed by a higher velocity, infinite half-space 相似文献
249.
A.G.G.M. Tielens L.B.F.M. Waters F.J. Molster K. Justtanont 《Astrophysics and Space Science》1997,255(1-2):415-426
This paper reviews spectra obtained with the SWS on board of ISO of dust shells around O-rich objects. These spectra reveal
the presence of many new emission features between 10 and 45 μm. These bands are generally much narrower than the well-known
10 and 20 μm silicates features. The strength of these features relative to the underlying broad continuum varies from source
to source (≅ 5-50%). The 10 μm region shows evidence for the presence of Al2O3 grains. At longer wavelength, the spectra are
dominated by features due to crystalline olivine and pyroxene. The exact peak position of these features shows that the emitting
grains consist of the Mg-rich end-members of these minerals with an Fe-content of < 10%. The underlying continuum is attributed
to amorphous silicate grains.
These observations of aluminum-rich and magnesium-rich compounds compare well with the thermodynamic condensation sequence
of minerals expected for O-rich outflows. The observations also imply that freeze out (ie., kinetics) of this condensation
sequence at different temperatures is an important characteristic of dust formation in these objects. It is suggested that
the absence of Fe-rich silicates is a natural consequence of the low temperature at which gaseous Fe reacts with Mg-rich silicates
in these outflows, resulting in amorphous grains with little characterizing spectral detail.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
250.
R. Wieler Th. Graf P. Signer S. Vogt G. F. Herzog C. Tuniz D. Fink L. K. Fifield J. Klein R. Middleton A. J. T. Jull P. Pellas J. Masarik G. Dreibus 《Meteoritics & planetary science》1996,31(2):265-272
Abstract— We determined He, Ne, Ar, 10Be, 26Al, 36Cl, and 14C concentrations, as well as cosmic-ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ~20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ~65 Ma. If the first-stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first-stage exposure ages when constructing two-stage histories. 相似文献