全文获取类型
收费全文 | 1536篇 |
免费 | 140篇 |
国内免费 | 225篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 89篇 |
地球物理 | 228篇 |
地质学 | 461篇 |
海洋学 | 228篇 |
天文学 | 727篇 |
综合类 | 68篇 |
自然地理 | 86篇 |
出版年
2024年 | 14篇 |
2023年 | 22篇 |
2022年 | 45篇 |
2021年 | 56篇 |
2020年 | 42篇 |
2019年 | 40篇 |
2018年 | 37篇 |
2017年 | 34篇 |
2016年 | 31篇 |
2015年 | 41篇 |
2014年 | 68篇 |
2013年 | 45篇 |
2012年 | 56篇 |
2011年 | 86篇 |
2010年 | 61篇 |
2009年 | 135篇 |
2008年 | 122篇 |
2007年 | 143篇 |
2006年 | 136篇 |
2005年 | 117篇 |
2004年 | 114篇 |
2003年 | 90篇 |
2002年 | 69篇 |
2001年 | 52篇 |
2000年 | 46篇 |
1999年 | 68篇 |
1998年 | 43篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1901条查询结果,搜索用时 15 毫秒
951.
We compare standard models of accretion discs around black holes (BHs) that include the appropriate zero-torque inner boundary condition and relativistic effects on the emission and propagation of radiation. The comparison is performed adopting the multicolour disc blackbody model (MCD) as reference and looking for the parameter space in which it is in statistical agreement with 'more physical' accretion disc models. We find simple 'recipes' that can be used for adjusting the estimates of the physical inner radius of the disc, the BH mass and the accretion rate inferred using the parameters of the MCD fits. We applied these results to four ultraluminous X-ray sources for which MCD spectral fits of their X-ray soft spectral components have been published and find that, in three cases (NGC 1313 X-1, X-2 and M 81 X-9), the BH masses inferred for a standard disc around a Schwarzschild BH are in the interval ∼100–200 M⊙ . Only if the BH is maximally rotating are the masses comparable to the much larger values previously derived in the literature. 相似文献
952.
B. Devecchi E. Rasia † M. Dotti M. Volonteri M. Colpi 《Monthly notices of the Royal Astronomical Society》2009,394(2):633-640
Anisotropic gravitational radiation from a coalescing black hole (BH) binary is known to impart recoil velocities of up to ∼1000 km s−1 to the remnant BH. In this context, we study the motion of a recoiling BH inside a galaxy modelled as a Hernquist sphere, and the signature that the hole imprints on the hot gas, using N -body/smoothed particle hydrodynamics simulations. Ejection of the BH results in a sudden expansion of the gas ending with the formation of a gaseous core, similarly to what is seen for the stars. A cometary tail of particles bound to the BH is initially released along its trail. As the BH moves on a return orbit, a nearly spherical swarm of hot gaseous particles forms at every apocentre: this feature can live up to ≈108 years. If the recoil velocity exceeds the sound speed initially, the BH shocks the gas in the form of a Mach cone in density near each supersonic pericentric passage. We find that the X-ray fingerprint of a recoiling BH can be detected in Chandra X-ray maps out to a distance of Virgo. For exceptionally massive BHs, the Mach cone and the wakes can be observed out to a few hundred of milliparsec. The detection of the Mach cone is of twofold importance as it can be a probe of high-velocity recoils, and an assessment of the scatter of the M BH − M bulge relation at large BH masses. 相似文献
953.
954.
955.
S. Mondal P. Basu S. K. Chakrabarti † 《Monthly notices of the Royal Astronomical Society》2009,396(2):1038-1045
In the present communication of our series of papers dealing with the accretion flows in the pseudo-Kerr geometry, we discuss the effects of viscosity on the accretion flow around a rotating black hole. We find the solution topologies and give special attention to the solutions containing shocks. We draw the parameter space where standing shocks are possible and where the shocks could be oscillating and could produce quasi-periodic oscillations (QPOs) of X-rays observed from black hole candidates. In this model, the extreme locations of the shocks give the upper limits of the QPO frequencies (νQPO ) which could be observed. We show that both the viscosity of the flow and the spin of the black hole a increase the QPO frequency while, as expected, the black hole mass reduces the QPO frequencies. Our major conclusion is that the highest observed frequency gives a strict lower limit of the spin. For instance, a black hole exhibiting νQPO ∼ 400 and 700 Hz must have the spin parameters of a > 0.25 and >0.75 , respectively, provided viscosity of the flow is small. We discuss the implications of our results in the light of observations of QPOs from black hole candidates. 相似文献
956.
F. Capitanio T. Belloni M. Del Santo P. Ubertini 《Monthly notices of the Royal Astronomical Society》2009,398(3):1194-1200
We report on a campaign of X-ray and soft γ-ray observations of the black hole candidate (BHC) H1743−322 (also named IGR J17464-3213), performed with the RXTE , INTEGRAL and Swift satellites. The source was observed during a short outburst between 2008 October 03 and November 16. The evolution of the hardness–intensity diagram throughout the outburst is peculiar, in that it does not follow the canonical pattern through all the spectral states (the so-called q-track pattern) seen during the outburst of black hole transients. On the contrary, the source only makes a transition from the hard state to the hard–intermediate state. After this transition, the source decreases in luminosity and its spectrum hardens again. This behaviour is confirmed by both spectral and timing analyses. This kind of outburst has been rarely observed before in a transient BHC. 相似文献
957.
958.
黑碳气溶胶直接辐射强迫及其对中国夏季降水影响的模拟研究 总被引:8,自引:1,他引:7
利用NCAR的全球大气模式CAM3分析了黑碳气溶胶在大气顶和地表的直接辐射强迫分布及其季节变化,重点讨论了云对黑碳气溶胶直接辐射强迫的影响,以及黑碳气溶胶对中国夏季降水的影响。结果表明:黑碳气溶胶在大气顶和地表的直接辐射强迫分布范围和强度都具有明显的季节变化。有云条件下,黑碳气溶胶在大气顶产生正的直接辐射强迫,全球年平均强迫值为+0.33 W·m-2;在地表产生负的直接辐射强迫,全球年平均强迫值为-0.56 W·m-2。晴空条件下,黑碳气溶胶在大气顶和地表的全球年平均辐射强迫值分别为+0.21 和-0.71 W·m-2。云的存在对黑碳气溶胶的辐射强迫产生了很大的影响,使大气顶的正辐射强迫增加,地表的负辐射强迫减小。黑碳气溶胶导致夏季中国北方30°N~45°N之间区域降水明显增加;而中国长江以南地区除了海南和广西的部分城市外,降水明显减少。模拟结果表明,中国夏季近50年来经常发生的南涝北旱并非由黑碳气溶胶引起。 相似文献
959.
960.
Characteristics of Anthropogenic Sulfate and Carbonaceous Aerosols over East Asia: Regional Modeling and Observation 总被引:3,自引:0,他引:3
The authors present spatial and temporal characteristics of anthropogenic sulfate and carbonaceous aerosols over East Asia using a 3-D coupled regional climate-chemistry-aerosol model, and compare the simulation with the limited aerosol observations over the region. The aerosol module consists of SO2, SO4^2-, hydrophobic and hydrophilic black carbon (BC) and organic carbon compounds (OC), including emission, advections, dry and wet deposition, and chemical production and conversion. The simulated patterns of SO2 are closely tied to its emission rate, with sharp gradients between the highly polluted regions and more rural areas. Chemical conversion (especially in the aqueous phase) and dry deposition remove 60% and 30% of the total SO2 emission, respectively. The SO4^2- shows less horizontal gradient and seasonality than SO2, with wet deposition (60%) and export (27%) being two major sinks. Carbonaceous aerosols are spatially smoother than sulfur species. The aging process transforms more than 80% of hydrophobic BC and OC to hydrophilic components, which are removed by wet deposition (60%) and export (30%). The simulated spatial and seasonal SO4^2-, BC and OC aerosol concentrations and total aerosol optical depth are generally consistent with the observations in rural areas over East Asia, with lower bias in simulated OC aerosols, likely due to the underestimation of anthropogenic OC emissions and missing treatment of secondary organic carbon. The results suggest that our model is a useful tool for characterizing the anthropogenic aerosol cycle and for assessing its potential climatic and environmental effects in future studies. 相似文献