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   307474篇
  免费   2922篇
  国内免费   1010篇
化学   160771篇
晶体学   5030篇
力学   13554篇
综合类   10篇
数学   33494篇
物理学   98547篇
  2020年   2370篇
  2019年   2539篇
  2018年   3234篇
  2017年   3086篇
  2016年   4865篇
  2015年   3164篇
  2014年   4737篇
  2013年   13165篇
  2012年   10032篇
  2011年   12307篇
  2010年   8278篇
  2009年   7992篇
  2008年   11113篇
  2007年   11257篇
  2006年   10947篇
  2005年   10031篇
  2004年   9190篇
  2003年   8192篇
  2002年   7974篇
  2001年   9075篇
  2000年   7036篇
  1999年   5518篇
  1998年   4543篇
  1997年   4548篇
  1996年   4271篇
  1995年   4074篇
  1994年   3720篇
  1993年   3631篇
  1992年   4117篇
  1991年   4058篇
  1990年   3967篇
  1989年   3773篇
  1988年   3828篇
  1987年   3821篇
  1986年   3573篇
  1985年   4754篇
  1984年   5052篇
  1983年   4208篇
  1982年   4597篇
  1981年   4420篇
  1980年   4324篇
  1979年   4425篇
  1978年   4603篇
  1977年   4550篇
  1976年   4635篇
  1975年   4363篇
  1974年   4227篇
  1973年   4510篇
  1972年   2861篇
  1971年   2201篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
An interconnection strategy with built-in adaptive controllersis presented which achieves synchronization of scalar linearsystems: the closed-loop network forces all outputs to followthe same signal asymptotically while maintaining the open-loopcharacteristics. In the design of the output feedback controllers,no knowledge of system parameters is assumed, but each systemmust have the same poles and be high-gain-stable. The proofof the main theorem relies critically on derived systems-theoreticresults and the special system topology as a network of interconnectedsystems. The topology is explained by first solving the simplerproblem of signal synchronization.  相似文献   
82.
A formulation of an implicit characteristic-flux-averaging method for the unsteady Euler equations with real gas effects is presented. Incorporation of a real gas into a general equation of state is achieved by considering the pressure as a function of density and specific internal energy. The Ricmann solver as well as the flux-split algorithm are modified by introducing the pressure derivatives with respect to density and internal energy. Expressions for calculating the values of the flow variables for a real gas at the cell faces are derived. The Jacobian matrices and the eigenvectors are defined for a general equation of state. The solution of the system of equations is obtained by using a mesh-sequencing method for acceleration of the convergence. Finally, a test case for a simple form of equation of state displays the differences from the corresponding solution for an ideal gas.  相似文献   
83.
This section appears from time to time. Contributions are invited, and should be submitted to R. C. Thompson, Mathematics Department, University of California, Santa Barbara, CA 93106.  相似文献   
84.
85.
86.
New polyimidates were prepared from bisphenols and mono- and dicarboxylic acid imidoyl chlorides. The structures of the polymers were determined, and their physicochemical, chemical, and thermal properties were studied. The possibility of preparing film and compression materials with good mechanical characteristics from these polymers was examined.  相似文献   
87.
 Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation while for inclination angle larger than 10, the average Nusselt number can be correlated into an elegant correlation. Received on 18 April 2001 / Published online: 29 November 2001  相似文献   
88.
Monomial ideals     
In this paper, we study the numeric characteristics (the Hilbert function and graded Betti numbers) of monomial ideals in the polynomial ring and in the exterior algebra. __________ Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 30, Algebra, 2005.  相似文献   
89.
Finite element solutions of the Euler and Navier-Stokes equations are presented, using a simple dissipation model. The discretization is based on the weak-Galerkin weighted residual method and equal interpolation functions for all the unknowns are permitted. The nonlinearity is iterated upon using a Newton method and at each iteration the linear algebraic system is solved by a direct solver with all unknowns fully coupled. Results are presented for two-dimensional transonic inviscid flows and two- and three-dimensional incompressible viscous flows. Convergence of the algorithm is shown to be quadratic, reaching machine accuracy in very few iterations. The inviscid results demonstrate the existence of nonunique numerical solutions to the steady Euler equations.  相似文献   
90.
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