全文获取类型
收费全文 | 8093篇 |
免费 | 1098篇 |
国内免费 | 1193篇 |
专业分类
化学 | 6340篇 |
晶体学 | 136篇 |
力学 | 388篇 |
综合类 | 140篇 |
数学 | 1003篇 |
物理学 | 2377篇 |
出版年
2023年 | 108篇 |
2022年 | 171篇 |
2021年 | 202篇 |
2020年 | 287篇 |
2019年 | 275篇 |
2018年 | 227篇 |
2017年 | 208篇 |
2016年 | 377篇 |
2015年 | 365篇 |
2014年 | 449篇 |
2013年 | 579篇 |
2012年 | 655篇 |
2011年 | 724篇 |
2010年 | 588篇 |
2009年 | 518篇 |
2008年 | 595篇 |
2007年 | 607篇 |
2006年 | 543篇 |
2005年 | 417篇 |
2004年 | 397篇 |
2003年 | 317篇 |
2002年 | 332篇 |
2001年 | 255篇 |
2000年 | 189篇 |
1999年 | 151篇 |
1998年 | 121篇 |
1997年 | 100篇 |
1996年 | 84篇 |
1995年 | 58篇 |
1994年 | 58篇 |
1993年 | 62篇 |
1992年 | 49篇 |
1991年 | 36篇 |
1990年 | 39篇 |
1989年 | 28篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 24篇 |
1984年 | 12篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1928年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
971.
972.
973.
974.
—本文提出了一种新的轴系相交度误差测试方法。该方法不存在测量基准安装偏心问题,更适合于大型转台轴系相交度误差的测量 相似文献
975.
本文选用考虑横向剪切效应的退化梁单元,引入几何非线性假设,对具粘弹性阻尼层的夹层梁动响应及其衰减效果进行了研究,得到了一些具有应用价值的结论。 相似文献
976.
Compact finite difference-Fourier spectral method for three-dimensional incompressible Navier-Stokes equations 总被引:1,自引:0,他引:1
A new compact finite difference-Fourier spectral hybrid method for solving the three dimensional incompressible Navier-Stokes
equations is developed in the present paper. The fifth-order upwind compact finite difference schemes for the nonlinear convection
terms in the physical space, and the sixth-order center compact schemes for the derivatives in spectral space are described,
respectively. The fourth-order compact schemes in a single nine-point cell for solving the Helmholtz equations satisfied by
the velocities and pressure in spectral space is derived and its preconditioned conjugate gradient iteration method is studied.
The treatment of pressure boundary conditions and the three dimensional non-reflecting outflow boundary conditions are presented.
Application to the vortex dislocation evolution in a three dimensional wake is also reported.
The project supported by the National Natural Science Foundation of China 相似文献
977.
978.
979.
980.
The problem investigated in this paper is that of calculating the eigenfrequencies of the bouncing-ball modes of oscillation of scalar waves in a three-dimensiol, arbitrarily shaped enclosure or resonator. With a view to future applications in seismology, we consider wave resonators limited above by a flat reflector—the earth's surface—and below by a curved one—the sediment/rock interface. The surface of the curved reflector is smooth but otherwise of arbitrary shape. The EBK (Einstein-Brillouin-Keller) method of semiclassical quantization is used to compute the eigenfrequencies. Conventional ray tracing is used to determine the trajectories of the rays in configuration space as well as in the Poincaré surfaces of section needed for the application of the method. For a prescribed set of mode numbers the EBK conditions produce a set of algebraic equations whose solution gives the required eigenfrequency and the corresponding eigentrajectory. Additionally, a system of four nonlinearly coupled ODE's is derived that simulates accurately the trajectories of the bouncing points of rays and can be used as a fast alternative to ray tracing. A variational method based upon the Rayleigh-Ritz formulation is used to obtain bounds on the eigenfrequencies and to determine the resonator's eigenfunctions. For separable and smooth nonseparable domains both approaches give consistent results. If the curvature of the reflector is convex towards the approaching ray, repeated reflections will result in highly unstable ray trajectories which ultimately becomne chaotic. In this case the EBK method fails. A brief discussion of the inherent tendency to chaotic behavior of the multiply reflecting ray system inside arbitrarily shaped enclosures is presented. 相似文献