全文获取类型
收费全文 | 26284篇 |
免费 | 3865篇 |
国内免费 | 1009篇 |
专业分类
化学 | 2835篇 |
晶体学 | 89篇 |
力学 | 1777篇 |
综合类 | 210篇 |
数学 | 4960篇 |
物理学 | 6033篇 |
无线电 | 15254篇 |
出版年
2024年 | 87篇 |
2023年 | 345篇 |
2022年 | 536篇 |
2021年 | 677篇 |
2020年 | 691篇 |
2019年 | 501篇 |
2018年 | 528篇 |
2017年 | 908篇 |
2016年 | 1108篇 |
2015年 | 1215篇 |
2014年 | 1974篇 |
2013年 | 1847篇 |
2012年 | 1930篇 |
2011年 | 1828篇 |
2010年 | 1426篇 |
2009年 | 1532篇 |
2008年 | 1735篇 |
2007年 | 1660篇 |
2006年 | 1541篇 |
2005年 | 1281篇 |
2004年 | 1126篇 |
2003年 | 1203篇 |
2002年 | 845篇 |
2001年 | 680篇 |
2000年 | 622篇 |
1999年 | 515篇 |
1998年 | 446篇 |
1997年 | 347篇 |
1996年 | 316篇 |
1995年 | 270篇 |
1994年 | 216篇 |
1993年 | 168篇 |
1992年 | 134篇 |
1991年 | 125篇 |
1990年 | 87篇 |
1989年 | 71篇 |
1988年 | 73篇 |
1987年 | 55篇 |
1986年 | 49篇 |
1985年 | 69篇 |
1984年 | 42篇 |
1983年 | 36篇 |
1982年 | 40篇 |
1981年 | 33篇 |
1980年 | 49篇 |
1979年 | 46篇 |
1978年 | 28篇 |
1977年 | 37篇 |
1976年 | 37篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
91.
WANG Mingwei LI Bo FENG Kun RAO Jun KANG Zihua LI Xiujuan LILi WANG Minghong FAN Mingjie 《核工业西南物理研究院年报(英文版)》2004,(1):77-79
in order to study non-indutive plasma current production, the lower hybrid current drive(LHCD) experiment on the HL-2A tokamak is carried out. Simultaneously a microcomputer has been used to control the whole LHCD system. During the experiment this year, we can monitor and protect the LHCD system by use of the microcomputer control system, which will imediately switch off the microwave power to be launched into the tokamak if the plasma is disrupted. All this ensure that the microwave is injected into the equipment correctly. 相似文献
92.
A group representation of radiation propagation in an anisotropic medium is developed. The system of wave equations for electromagnetic potentials, obtained from the Maxwell equations with account for the constitutive equations, has been factorized. It is shown that the linear differential operator of the factorized system is orthogonal in transparent crystals and unitary in gyrotropic ones and is represented through the momentum operator. On the basis of the commutation relations for the components of this operator, the eigenvalue problem has been solved and the expression for the change in the radiant energy in the crystal in the form of spherical waves has been obtained. The dependences of the ray and phase velocities and the polarization vectors of waves on the birefringence anisotropy and gyrotropy as well as on the angular momentum, displacement current, and bound charge determining them have been analyzed. It has been established that in the general case of gyrotropic crystals where the nonreciprocity phenomenon takes place and in magnetoelectrics Maxwell equations are represented in a form similar to the Dirac equations and the electromagnetic radiation is correctly described by means of bispinors and is quantized as fermions. 相似文献
93.
介绍了一个计算机远程控制系统的设计与实现,该系统采用客户机/服务器模式,实现远程屏幕的实时传输,采用LZW压缩算法对图像进行压缩传输,在接受方进行解码并且实现了远程文件创建和删除、显示被控制端的主机信息、发送实时消息等功能。采用鼠标,键盘的模拟方式对计算机进行实时控制。 相似文献
94.
Density functional method (DFT) (B3p86) of Gaussian98 has been used to optimize the structure of the Tc_2 molecule. The result shows that the ground state for Tc_2 molecule is an 11-multiple state and its electronic configuration is {}^{11}Σ_g^-, which shows the spin polarization effect of Tc_2 molecule of a transition metal element for the first time. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher energy states. So, that the ground state for Tc_2 molecule is an 11-multiple state is indicative of the spin polarization effect of Tc_2 molecule of a transition metal element: that is, there exist 10 parallel spin electrons. The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of Tc_2 molecule is minimized. It can be concluded that the effect of parallel spin of the Tc_2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell--Sorbie potential functions with the parameters for the ground state {}^{11}Σ_g^- and other states of Tc_2 molecule are derived. Dissociation energy D_e for the ground state of T_{c2} molecule is 2.266eV, equilibrium bond length R_e is 0.2841nm, vibration frequency ω_e is 178.52cm^{-1}. Its force constants f_2, f_3, and f_4 are 0.9200aJ·nm^{-2}, --3.5700aJ·nm^{-3}, 11.2748aJ·nm^{-4} respectively. The other spectroscopic data for the ground state of Tc_2 molecule ω_eχ_e, B_e, α_e are 0.5523cm^{-1}, 0.0426cm^{-1}, 1.6331×10^{-4}cm^{-1} respectively. 相似文献
95.
Frank Jochmann 《Journal of Differential Equations》2004,203(2):232-254
In this paper, Maxwell's equations involving generally nonlinear polarization and field-dependent currents are studied. The main objective is the asymptotic behavior of the solution for t→∞ if no damping term occurs in the equation governing the polarization field. 相似文献
96.
97.
98.
风力发电机组变速恒频控制系统研究 总被引:2,自引:0,他引:2
全面介绍了一种最新应用于风力发电中的新型电机—无刷双馈电机,并分析了这种新型电机作变速恒频运行的原理并对这种电机进行了动态特性仿真研究,给出了形式简洁的控制方程和易于实现的控制方案。 相似文献
99.
光突发交换的交换控制策略和光缓存配置 总被引:4,自引:2,他引:2
光突发交换是面向下一代互联网的光交换模式.讨论了异步光突发交换系统的交换控制策略以及相应光缓存的优化配置策略.除了传统预约模式的交换策略,还研究了非预约和改进型预约模式,它们的性能评估由计算机仿真给出.结果表明:在条件相当情况下,改进型预约模式具有最低的丢包率.同时光缓存的配置对上述几类交换控制策略的性能都有很大影响,仿真结果指出:光缓存的粒度对系统性能具有重要影响,所讨论的几类交换模式都存在最佳时延粒度,研究结果对光交换矩阵的设计有指导意义. 相似文献
100.