全文获取类型
收费全文 | 36771篇 |
免费 | 7211篇 |
国内免费 | 5953篇 |
专业分类
化学 | 27271篇 |
晶体学 | 595篇 |
力学 | 2409篇 |
综合类 | 447篇 |
数学 | 4113篇 |
物理学 | 15100篇 |
出版年
2024年 | 108篇 |
2023年 | 663篇 |
2022年 | 1330篇 |
2021年 | 1386篇 |
2020年 | 1496篇 |
2019年 | 1553篇 |
2018年 | 1344篇 |
2017年 | 1389篇 |
2016年 | 1813篇 |
2015年 | 2002篇 |
2014年 | 2434篇 |
2013年 | 3036篇 |
2012年 | 3541篇 |
2011年 | 3589篇 |
2010年 | 2695篇 |
2009年 | 2738篇 |
2008年 | 2957篇 |
2007年 | 2454篇 |
2006年 | 2290篇 |
2005年 | 1850篇 |
2004年 | 1391篇 |
2003年 | 1167篇 |
2002年 | 1169篇 |
2001年 | 969篇 |
2000年 | 788篇 |
1999年 | 630篇 |
1998年 | 449篇 |
1997年 | 412篇 |
1996年 | 361篇 |
1995年 | 296篇 |
1994年 | 300篇 |
1993年 | 237篇 |
1992年 | 182篇 |
1991年 | 149篇 |
1990年 | 144篇 |
1989年 | 94篇 |
1988年 | 87篇 |
1987年 | 65篇 |
1986年 | 74篇 |
1985年 | 50篇 |
1984年 | 24篇 |
1983年 | 29篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1979年 | 20篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1957年 | 8篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Dielectric effect on the rf characteristics of a helical groove travelling wave tube 总被引:1,自引:0,他引:1 下载免费PDF全文
A new type of partial-dielectric-loaded helical groove slow-wave structure (SWS) for millimetre wave travelling wave tube (TWT) is presented in this paper.The radio-frequency characteristics including the dispersion properties,the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analysed.The results show that the dispersion of the helical groove circuit is weakened,the phase velocity is reduced and the position of the maximum Ez is moved from the mouth to the inside of the groove after partially filling the dielectric materials in the helical groove SWS.Therefore,the dielectric-loaded helical groove SWS is suitable for a multi-beam TWT with broad band and high gain. 相似文献
92.
93.
Ho K. I. J. Leung J. Y. T. Wei W. D. 《Journal of Algorithms in Cognition, Informatics and Logic》1994,16(3)
We consider the problem of preemptively scheduling a set of imprecise computation tasks on m ≥ 1 identical processors, with each task Ti having two weights, wi and w′i. Two performance metrics are considered: (1) the maximum w′-weighted error; (2) the total w-weighted error subject to the constraint that the maximum w′-weighted error is minimized. For the problem of minimizing the maximum w′-weighted error, we give an algorithm which runs in O(n3 log2n) time for multiprocessors and O(n2) time for a single processor. For the problem of minimizing the total w-weighted error subject to the constraint that the maximum w′-weighted error is minimized, we give an algorithm which also has the same time complexity. 相似文献
94.
Based on the effective-field theory with self-spin correlations and the differential operator technique,physical properties of the spin-2 system with biaxial crystal field on the simple cubic, body-centered cubic, as well as faced-centered lattice have been studied. The influences of the external longitudinal magnetic field on the magnetization,internal energy, specific heat, and susceptibility have been discussed in detail. The phenomenon that the magnetization in the ground state shows quantum effects produced by the biaxial transverse crystal field has been found. 相似文献
95.
96.
Wei Wang Li-Ping Pang Zun-Quan Xia 《应用数学学报(英文版)》2007,23(1):29-38
In this paper,the UV-theory and P-differential calculus are employed to study second-order ex-pansion of a class of D.C.functions and minimization problems.Under certain conditions,some properties ofthe U-Lagrangian,the second-order expansion of this class of functions along some trajectories are formulated.Some first and second order optimality conditions for the class of D.C.optimization problems are given. 相似文献
97.
98.
99.
100.
Jiang Tongsong Liu Yonghui Wei Musheng 《高校应用数学学报(英文版)》2006,21(1):113-118
This paper derives a theorem of generalized singular value decomposition of quaternion matrices (QGSVD),studies the solution of general quaternion matrix equation AXB -CYD= E,and obtains quaternionic Roth's theorem. This paper also suggests sufficient and necessary conditions for the existence and uniqueness of solutions and explicit forms of the solutions of the equation. 相似文献