首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   721篇
  免费   65篇
  国内免费   65篇
测绘学   44篇
大气科学   63篇
地球物理   159篇
地质学   175篇
海洋学   67篇
天文学   183篇
综合类   55篇
自然地理   105篇
  2024年   2篇
  2023年   1篇
  2022年   17篇
  2021年   9篇
  2020年   21篇
  2019年   16篇
  2018年   16篇
  2017年   18篇
  2016年   29篇
  2015年   21篇
  2014年   19篇
  2013年   30篇
  2012年   24篇
  2011年   25篇
  2010年   28篇
  2009年   33篇
  2008年   63篇
  2007年   37篇
  2006年   54篇
  2005年   53篇
  2004年   32篇
  2003年   30篇
  2002年   40篇
  2001年   24篇
  2000年   22篇
  1999年   23篇
  1998年   22篇
  1997年   18篇
  1996年   17篇
  1995年   15篇
  1994年   11篇
  1993年   18篇
  1992年   8篇
  1991年   14篇
  1990年   13篇
  1989年   7篇
  1988年   3篇
  1987年   5篇
  1986年   3篇
  1984年   1篇
  1983年   4篇
  1981年   1篇
  1978年   2篇
  1977年   2篇
排序方式: 共有851条查询结果,搜索用时 15 毫秒
91.
Although analytic solutions for the attitude motion of a rigid body are available for several special cases, a comprehensive theory does not exist in the literature for the more complicated problems found in spacecraft dynamics. In the present paper, analytic solutions in complex form are derived for the attitude motion of a near-symmetric rigid body under the influence of constant body-fixed torques. The solution is very compact, which enables efficient and rapid machine computation. Numerical simulations reveal that the solution is very accurate when applied to typical spinning spacecraft problems.  相似文献   
92.
The regions of quasi-periodic motion around non-symmetric periodic orbits in the vicinity of the triangular equilibrium points are studied numerically. First, for a value of the mass parameter less than Routh's critical value, the stability regions determined by quasi-periodic motion are examined around the existing families of short (Ls 4) and long (Ll 4) period solutions. Then, for two values of μ greater than the Routh value, the unified family Lsl 4, to which, in these cases, Ls 4 and Ll 4 merge, is considered. It is found that such regions surround in general the linearly stable segments of the corresponding families and become smaller as the mass ratio increases. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
93.
Dynamics of Two Planets in the 2/1 Mean-Motion Resonance   总被引:1,自引:1,他引:0  
The dynamics of two planets near a first-order mean-motion resonance is modeled in the domain of the general three-body planar problem. The system studied is the pair Uranus-Neptune (2/1 resonance). The phase space of the resonance and near-resonance regions is studied by means of surfaces of section and spectral analysis techniques. After a thorough investigation of the topology of the phase space, we find that several regimes of motion are possible for the Uranus-Neptune system, and the regions of transition between the regimes of motion are the seats of chaotic motion. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
94.
If a mine waste pile is left open, an active chemical reaction of oxidation is often found due to the commonly high content of pyritic materials. The oxidation of pyrites is an exothermic process and the released heat will promote the flow of fresh oxygen from the surrounding atmosphere into the waste dump. As a result, oxidation reaction will accelerate and temperature within the dump can increase to as high as 60°C above the ambient temperature. The oxidation process also releases sulphuric acid and hydrogen ions into ground water to cause water contamination. Low‐permeability covers such as clay liners have been recently proposed to abate the oxidation process in mine wastes. The effectiveness of using low‐permeability materials to cover mine wastes in order to suppress the pyrite oxidation is examined. By conducting the theoretical analysis of the onset of convective air flow within waste rocks, the conditions under which soil gas flow is significant are identified. By comparing the results with previous field measurements and theoretical analysis for the uncovered conditions, it is shown that low‐permeability covers can effectively suppress soil gas flow and slow down the pyrite oxidation process in mine wastes. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
95.
获得了一类一阶可变号非线性奇异初值问题的新结果。  相似文献   
96.
用正行列式作为工具,给出了瓶颈指派问题新的解法,并利用正行列式的值求出了瓶颈指派问题的全部最优解。最后通过一个实例说明该算法的实用和有效性。  相似文献   
97.
用正行列式作为工具,给出了瓶颈指派问题新的解法,并利用正行列式的值求出了瓶颈指派问题的全部最优解。最后通过一个实例说明该算法的实用和有效性。  相似文献   
98.
We study the existence of invariant tori in a neighbourhood of the collinear equilibrium points of the planar three-body problem. To this end some properties of the normal form of the Hamiltonian reduced to the 4D central manifold are proved. Using this normal form, we show that the nondegeneracy conditions of KAM theorem are satisfied for all positive masses, including the 2:1 resonance case. The evaluation of the conditions is done numerically.  相似文献   
99.
Orbits repeating their ground track on the surface of the earth are found to be members of periodic-orbit families (in a synodic frame) of the tesseral problem of the Earth artificial satellite. Families of repeat ground track orbits appear as vertical bifurcations of the equatorial family of periodic orbits, and they evolve from retrograde to direct motion throughout the 180 degrees of inclination. These bifurcations are always close to the resonances of the Earth's rotation rate and the mean motion of the orbiter.  相似文献   
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号