全文获取类型
收费全文 | 2690篇 |
免费 | 267篇 |
国内免费 | 305篇 |
专业分类
测绘学 | 249篇 |
大气科学 | 440篇 |
地球物理 | 437篇 |
地质学 | 362篇 |
海洋学 | 215篇 |
天文学 | 1275篇 |
综合类 | 118篇 |
自然地理 | 166篇 |
出版年
2024年 | 6篇 |
2023年 | 17篇 |
2022年 | 28篇 |
2021年 | 38篇 |
2020年 | 57篇 |
2019年 | 75篇 |
2018年 | 49篇 |
2017年 | 61篇 |
2016年 | 62篇 |
2015年 | 89篇 |
2014年 | 85篇 |
2013年 | 139篇 |
2012年 | 117篇 |
2011年 | 98篇 |
2010年 | 100篇 |
2009年 | 223篇 |
2008年 | 207篇 |
2007年 | 259篇 |
2006年 | 207篇 |
2005年 | 154篇 |
2004年 | 143篇 |
2003年 | 126篇 |
2002年 | 132篇 |
2001年 | 110篇 |
2000年 | 123篇 |
1999年 | 106篇 |
1998年 | 115篇 |
1997年 | 37篇 |
1996年 | 47篇 |
1995年 | 50篇 |
1994年 | 43篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 21篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有3262条查询结果,搜索用时 46 毫秒
331.
D. N. Rachkovsky T. T. Tsap V. G. Lozitsky 《Journal of Astrophysics and Astronomy》2005,26(4):435-445
We analyse different observational data related to the problem of intrinsic magnetic field strength in small-scale fluxtubes
outside sunspots. We conclude that the kG range of fluxtube fields follows from not only classical line ratio method, but
also from other old and new techniques. For the quiet regions on the Sun, the most probable mode of such fields has a magnetic
field strength of 1.2–1.5 kG assuming the rectangular field profile. To best interpret the observations, a weak background
field between fluxtubes should be assumed, and its magnetic field strength is expected to increase with the filling factor
of fluxtubes. The alternative point of view about subkilogauss fluxtube fields is critically examined, and possible sources
of different conclusions are presented. 相似文献
332.
333.
The behaviour of the magnetic field of a neutron star with a superconducting quark matter core is investigated in the framework of the Ginzburg-Landau theory. We take into account the simultaneous coupling of the diquark condensate field to the usual magnetic and to the gluomagnetic gauge fields. We solve the Ginzburg-Landau equations by properly taking into account the boundary conditions, in particular, the gluon confinement condition. We found the distribution of the magnetic field in both the quark and hadronic phases of the neutron star and show that the magnetic field penetrates into the quark core in the form of quark vortices due to the presence of Meissner currents. 相似文献
334.
Alejandra Kandus 《Monthly notices of the Royal Astronomical Society》2007,378(4):1356-1364
We study semi-analytically and in a consistent manner the generation of a mean velocity field by helical magnetohydrodynamical (MHD) turbulence, and the effect that this field can have on a mean field dynamo. Assuming a prescribed, maximally helical small-scale velocity field, we show that large-scale flows can be generated in MHD turbulent flows via small-scale Lorentz force. These flows back-react on the mean electromotive force of a mean field dynamo through new terms, leaving the original α and β terms explicitly unmodified. Cross-helicity plays the key role in interconnecting all the effects. In the minimal τ closure that we chose to work with, the effects are stronger for large relaxation times. 相似文献
335.
336.
We present first results of our simulations of magnetic fields in the formation of single and binary stars using a recently
developed method for incorporating Magnetohydrodynamics (MHD) into the Smoothed Particle Hydrodynamics (SPH) method. An overview
of the method is presented before discussing the effect of magnetic fields on the formation of circumstellar discs around
young stars. We find that the presence of magnetic fields during the disc formation process can lead to significantly smaller
and less massive discs which are much less prone to gravitational instability. Similarly in the case of binary star formation
we find that magnetic fields, overall, suppress fragmentation. However these effects are found to be largely driven by magnetic
pressure. The relative importance of magnetic tension is dependent on the orientation of the field with respect to the rotation
axis, but can, with the right orientation, lead to a dilution of the magnetic pressure-driven suppression of fragmentation. 相似文献
337.
338.
339.
Summary. (Part 1) Fourier analyses of mean monthly sea-level data from Belém, Fortaleza, Salvador and Imbituba, ports on the Brazilian coast, are made with simultaneous data of air temperature, sea surface atmospheric pressure, atmospheric precipitation and evaporation. Results show that the mean monthly sea-levels of ports below Recife's latitude show peaks in February-March and April-May which are apparently related to the seasonal temperature changes and the combined action of precipitation, winds and oceanographic large-scale changes. The port of Belém showed a stronger semi-annual seasonal component, which seems to be related to the alternate southern and northern hemispheres' influences of the atmospheric precipitation. (Part 2 of the paper presented at the Symposium concerned the longer term changes of sea-level, including an analysis of principal components. These subjects will be treated in a separate paper.) 相似文献
340.
Previously published dispersion fields on ternary diagrams have been constructed variously, and their derivations have not been well-specified. Here an explanation of their bases is provided through an algebraic method for calculating two related forms, designated thesilhouette dispersion field and thegirth dispersion field. Such dispersion estimates can be made more precise by specifying the percentage of samples that fall within the field. Because such fields represent a mechanistic rather than a probabilistic approach, their use in comparison of sample sets must be viewed with caution. 相似文献