全文获取类型
收费全文 | 783篇 |
免费 | 8篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 60篇 |
大气科学 | 28篇 |
地球物理 | 137篇 |
地质学 | 304篇 |
海洋学 | 23篇 |
天文学 | 210篇 |
综合类 | 6篇 |
自然地理 | 29篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 18篇 |
2020年 | 15篇 |
2019年 | 7篇 |
2018年 | 59篇 |
2017年 | 42篇 |
2016年 | 42篇 |
2015年 | 24篇 |
2014年 | 25篇 |
2013年 | 44篇 |
2012年 | 34篇 |
2011年 | 32篇 |
2010年 | 30篇 |
2009年 | 38篇 |
2008年 | 29篇 |
2007年 | 26篇 |
2006年 | 17篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 16篇 |
2002年 | 17篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1972年 | 3篇 |
1971年 | 9篇 |
1970年 | 2篇 |
排序方式: 共有797条查询结果,搜索用时 0 毫秒
61.
Jayanta K. Bhattacharjee Atri Bhattacharya Tapas K. Das Arnab K. Ray 《Monthly notices of the Royal Astronomical Society》2009,398(2):841-852
In a novel approach to studying viscous accretion flows, viscosity has been introduced as a perturbative effect, involving a first-order correction in the α-viscosity parameter. This method reduces the problem of solving a second-order non-linear differential equation (Navier–Stokes equation) to that of an effective first-order equation. Viscosity breaks down the invariance of the equilibrium conditions for stationary inflow and outflow solutions, and distinguishes accretion from wind. Under a dynamical systems classification, the only feasible critical points of this 'quasi-viscous' flow are saddle points and spirals. On large spatial scales of the disc, where a linearized and radially propagating time-dependent perturbation is known to cause a secular instability, the velocity evolution equation of the quasi-viscous flow has been transformed to bear a formal closeness with Schrödinger's equation with a repulsive potential. Compatible with the transport of angular momentum to the outer regions of the disc, a viscosity-limited length-scale has been defined for the full spatial extent over which the accretion process would be viable. 相似文献
62.
63.
X-ray emissions from Young Stellar Objects (YSO) are detected by many X-ray missions that are providing important information about their properties. However, their emission processes are not fully understood. In this research note, we propose a model for the generation of emissions from a YSO on the basis of a simple interaction between the YSO and its surrounding circumstellar accretion disc containing neutral gas and charged dust. It is assumed that the YSO has a weak dipole type magnetic field and its field lines are threaded into the circumstellar disc. Considering the motion of ions and charged dust particles in the presence of neutral gas, we show that the sheared dust-neutral gas velocities can lead to a current along the direction of ambient magnetic field. Magnitude of this current can become large and is capable of generating an electric field along the magnetic field lines. It is shown how the particles can gain energy up to MeV range and above, which can produce high-energy radiations from the YSO. 相似文献
64.
In this work, we consider the formation of electrostatic, dust-acoustic solitary structure in a unmagnetized plasma with Lorentzian electrons (kappa-distributed) and more than one species of thermal ions (Maxwellian). The work is inspired by results of different space-based observations of electrostatic solitary waves (ESW) in the near-earth and magnetospheric plasmas and recent experimental realization of existence of superthermal electron component in various space plasmas. We have, in this work, shown that existence of compressive potential structure is possible only with more than one species of thermal ions. Besides, formation of compressive double layers is also possible which depends on the amount of deviation of the electron thermal velocities from a Maxwellian distribution. We show that both dust-temperature and super-thermal electrons lead to a decrease in the soliton amplitude. 相似文献
65.
Biswajit Sahu 《Astrophysics and Space Science》2012,338(2):251-257
The nonlinear wave structures of ion acoustic waves (IAWs) in an unmagnetized plasma consisting of nonextensive electrons
and thermal positrons are studied in bounded nonplanar geometry. Using reductive perturbation technique we have derived cylindrical
and spherical Korteweg-de Vries-Burgers’ (KdVB) equations for IAWs. The presence of nonextensive q-distributed electrons is shown to influence the solitary and shock waves. Furthermore, in the existence of ion kinematic
viscosity, the shock wave structure appears. Also, the effects of nonextensivity of electrons, ion kinematic viscosities,
positron concentration on the properties of ion acoustic shock waves (IASWs) are discussed in nonplanar geometry. It is found
that both compressive and rarefactive type solitons or shock waves are obtained depending on the plasma parameter. 相似文献
66.
Behera Rashmisikha Kar Abhipsa Das Manas Ranjan Panda Prachi Prava 《Natural Hazards》2019,96(2):731-751
Natural Hazards - The 485-km-long coastline of Odisha, a state in the northeastern part of the Indian peninsula, is potentially vulnerable to several disaster events that take place frequently. In... 相似文献
67.
Tapas K. Das 《Monthly notices of the Royal Astronomical Society》1999,308(1):201-206
We compute the mass outflow rate R m˙ from relativistic matter that is accreting quasi-spherically on to the Schwarzschild black holes. Taking the pair-plasma pressure-mediated shock surface as the effective boundary layer (of the black hole) from where the bulk of the outflow is assumed to be generated, computation of this rate is done using combinations of exact transonic inflow and outflow solutions. We find that R m˙ depends on the initial parameters of the flow, the polytropic index of matter, the degree of compression of matter near the shock surface and the location of the shock surface itself. We thus not only study the variation of the mass outflow rate as a function of various physical parameters governing the problem, but also provide a sufficiently plausible estimation of this rate. 相似文献
68.
Das Ratul 《Water Resources》2020,47(2):222-230
Water Resources - Sediment mobility in stream corroborates many significant mechanisms in terms of interactions of transported particles in the carrier fluid flows. In general, the sediment... 相似文献
69.
Hriday Mani Kalita Das Rajdeep Hajong Atul Kumar Neeraj Kharnaior Donly Dkhar Heart Casingh 《Water Resources》2019,46(6):934-943
Water Resources - This paper reports a series of experimental studies done to simulate the flow behavior over crump and ogee type of weirs. The transition of subcritical to supercritical flow, as... 相似文献
70.