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   18699篇
  免费   3056篇
  国内免费   2398篇
化学   14411篇
晶体学   188篇
力学   940篇
综合类   208篇
数学   2206篇
物理学   6200篇
  2024年   59篇
  2023年   388篇
  2022年   633篇
  2021年   665篇
  2020年   810篇
  2019年   885篇
  2018年   680篇
  2017年   565篇
  2016年   975篇
  2015年   977篇
  2014年   1133篇
  2013年   1354篇
  2012年   1641篇
  2011年   1586篇
  2010年   1151篇
  2009年   1064篇
  2008年   1208篇
  2007年   1060篇
  2006年   922篇
  2005年   833篇
  2004年   721篇
  2003年   698篇
  2002年   825篇
  2001年   738篇
  2000年   450篇
  1999年   398篇
  1998年   254篇
  1997年   211篇
  1996年   178篇
  1995年   169篇
  1994年   130篇
  1993年   106篇
  1992年   116篇
  1991年   128篇
  1990年   106篇
  1989年   57篇
  1988年   50篇
  1987年   35篇
  1986年   35篇
  1985年   39篇
  1984年   26篇
  1983年   14篇
  1982年   8篇
  1981年   10篇
  1980年   7篇
  1979年   8篇
  1978年   5篇
  1977年   5篇
  1971年   5篇
  1936年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Feng Xiao  Long Wang   《Physica A》2006,370(2):364-380
In this paper, we discuss the dynamic behavior of networks of dynamic agents with general communication topologies. We first analyze the basic case: systems with communication topologies that have spanning trees, i.e., the systems that solve consensus problems. We establish an algebraic condition to characterize each agent's contributions to the final state. And we also study the influence of time-delays on each agent's contributions. Then, we investigate the general case: systems with weakly connected topologies. By using matrix theory, we prove that the states of internal agents will converge to a convex combination of boundary agents in the absence or presence of communication time-delays, and we also show that the coefficients of the convex combination are independent of time-delays even if the delays are time-varying. These results have broad applications in other areas, e.g., study of swarm behavior, formation control of vehicles, etc.  相似文献   
62.
The influence of interdiffusion on eigenstates in an interdiffusion-induced GaAs/AlxGa1-xAs single-quantum-well structure is analysed numerically by the finite element method. In this approach, the confinement potential profile of the interdiffused quantum well structure is nonlinear and is modelled by an error function and, in particular, the nature of the effective mass of an electron is considered. The results show that the number of eigenstates and energy levels varies with the extent of the interdiffusion. Numerical results for the quasi-bound states in the quantum well structure with an applied electric field are also presented.  相似文献   
63.
Differentkindsofopenchaincrownethershavebeensynthesizedasthemodelcompoundsofionophoresandtheirinteractionswithsodium,potassiumandrareearthionshavealsobeenstudiedl'z.PanshowedCe(III)yieldedalf1complexwithl,8-bis(8'-quinolyloxy)-3,6-dioxaandtheCe(IIl)ioncoordinatedbothtoetheroxygenandquinolinenitrogenatoms3.TUmInleridentifiedtwolanthanidenitratecomplexeshavingastoichiometryof3:2(3RE:2L)'.InordertostUdythefunctionsofbothquinolineandbenzenering,introducedintothepolyetherchain,a1inearpolyether…  相似文献   
64.
We give a Euclidean wormhole solution in the vacuum Bergmann-Wagoner scalar-tensor gravitational theory. We show that this wormhole, unlike others, has complex charge and is a baby universe (half a wormhole).  相似文献   
65.
66.
Let g is a positive increasing function with 1?g(0). The existence of a unique solution of the Navier-Stokes flow associated with Kε,γ and the convergence of the solution to that of the Euler equations as the viscosity goes to zero are established.  相似文献   
67.
Excitation functions for the55Mn(p, p )55Mn,55Mn(p, n )55Fe and55Mn(p, )56Fe reactions are studied for proton beam energyE p=1·3–2 MeV. The excitation functions are established from yield functions for -rays emitted from the first excited states of final nuclei. Many resonances are observed and competition of their decay into all three output channels is analysed. Spin-parity assignment for some resonant states in the56Fe compound nucleus is deduced.Participated partly in the course of his work on a Thesis.The authors wish to thank the staff of the Van de Graaff accelerator at Charles University in Prague for the efficient operation of the machine and dr. I. Wilhelm for the valuable technical help in the early period of the experimental work. One of us (N. A. N.) acknowledges the staff of the Dept. of Nuclear Physics of Charles University in Prague for the excellent working conditions.  相似文献   
68.
69.
70.
Jacobsen‘s catalyst was immobilized onto SBA-15 by multi-step grafting, and this heterogenized catalyst exhibited comparable catalytic performance with the corresponding homogeneous counterpart for the epoxidation of alkenes, and the catalyst could be recycled effectively several times.  相似文献   
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