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311.
Abraham Achterberg Yves A. Gallant John G. Kirk Axel W. Guthmann 《Monthly notices of the Royal Astronomical Society》2001,328(2):393-408
We consider the acceleration of charged particles near ultrarelativistic shocks, with Lorentz factor . We present simulations of the acceleration process and compare these with results from semi-analytical calculations. We show that the spectrum that results from acceleration near ultrarelativistic shocks is a power law, , with a nearly universal value for the slope of this power law.
We confirm that the ultrarelativistic equivalent of the Fermi acceleration at a shock differs from its non-relativistic counterpart by the occurrence of large anisotropies in the distribution of the accelerated particles near the shock. In the rest frame of the upstream fluid, particles can only outrun the shock when their direction of motion lies within a small loss cone of opening angle around the shock normal.
We also show that all physically plausible deflection or scattering mechanisms can change the upstream flight direction of relativistic particles originating from downstream by only a small amount: . This limits the energy change per shock crossing cycle to , except for the first cycle where particles originate upstream. In that case the upstream energy is boosted by a factor for those particles that are scattered back across the shock into the upstream region. 相似文献
We confirm that the ultrarelativistic equivalent of the Fermi acceleration at a shock differs from its non-relativistic counterpart by the occurrence of large anisotropies in the distribution of the accelerated particles near the shock. In the rest frame of the upstream fluid, particles can only outrun the shock when their direction of motion lies within a small loss cone of opening angle around the shock normal.
We also show that all physically plausible deflection or scattering mechanisms can change the upstream flight direction of relativistic particles originating from downstream by only a small amount: . This limits the energy change per shock crossing cycle to , except for the first cycle where particles originate upstream. In that case the upstream energy is boosted by a factor for those particles that are scattered back across the shock into the upstream region. 相似文献
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315.
空中人工触发闪电试验及特性分析 总被引:12,自引:10,他引:2
利用1996年南昌人工引雷试验观察测资料,分析了空中触发电的放电特征,估算了火箭上升时的电参数。结果表明:空中触发闪电的触发高度比地面触发闪电的蟹良高速度约大2倍。在火箭上升阶段,空中触发闪电在地面引起的电场变化为负,地面触发闪电在地面引直民的电场变化为正。 相似文献
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Zhang Guo-fan Chang Ya-qing Song Jian Ding Jun Shen Jin-kai Wang Yong-ping 《中国海洋湖沼学报》1998,16(3):249-255
Zygotes of Pacific oyster (Crassostrea gigas) were treated for triploid induction with caffeine (10 mmol/L, 15mmol/L and 20mmol/L) in combination with thermal shocks
(at 40 minute post-fertilization) lasting for 5 and 10 minutes. The highest yield of triploids, 41.5%, was obtained from the
treatment with 20 mmol/L caffeine at 34°C lasting 10 minutes. The triploid levels were less than 30.0% in other treatments.
Triploid induction was more effective in treatment with 15–20 mmol/L caffeine at 34–38 °C than with lower concentrations of
caffeine at temperatures below 32 °C. Our results suggest that triploid induction with caffeine in combination with thermal
shocks is less efficient than some other methods reported previously. 相似文献
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This paper presents global solutions of adiabatic accretion flows with isothermal shocks in Kerr black hole geometry. It is known that in the previously studied cases, where the flow including the shock is either entirely adiabatic or entirely isothermal, there can be no more than one stable shock solution, and the solution can only be of α –x type. However, the solution topology in the present case shows remarkable new characteristics: for the same flow parameters there can be two stable shock solutions satisfying physical boundary conditions, and the solution can be of three types, namely α– x , x –α and α–α type. In addition, shocks in the present case occur for a parameter region different from that for Rankine–Hugoniot shocks. These results greatly increase the possibilities of shock formation in astrophysical flows. It is also significant that the effects of frame-dragging of a rapid Kerr black hole on the shock formation are discovered. Finally, a brief comparison is made between shocked inviscid flows and two types of shock-free viscous flows, namely those of Shakura & Sunyaev and Narayan & Yi, and some comments are made about the fact that numerous authors who have studied transonic global solutions of accretion flows have found no shocks. 相似文献
320.
Cantó Espresate Raga & D'Alessio 《Monthly notices of the Royal Astronomical Society》1998,296(4):1041-1044
The 'plasmon' solution of De Young & Axford describes the interaction between a high-velocity clump and the surrounding medium. Even though this solution is probably too simplistic, it has proven to be most useful in the study of diverse astrophysical flows. In the present paper, we discuss a more detailed solution of the plasmon problem, which includes the centrifugal effects of the environmental material flowing around the plasmon. We derive both numerical and approximate analytic solutions of this problem, and compare them with the analytic solution of De Young & Axford. 相似文献