全文获取类型
收费全文 | 26244篇 |
免费 | 4290篇 |
国内免费 | 3963篇 |
专业分类
化学 | 13656篇 |
晶体学 | 348篇 |
力学 | 1081篇 |
综合类 | 368篇 |
数学 | 2362篇 |
物理学 | 7245篇 |
无线电 | 9437篇 |
出版年
2024年 | 81篇 |
2023年 | 578篇 |
2022年 | 820篇 |
2021年 | 964篇 |
2020年 | 960篇 |
2019年 | 1013篇 |
2018年 | 803篇 |
2017年 | 898篇 |
2016年 | 1060篇 |
2015年 | 1270篇 |
2014年 | 1518篇 |
2013年 | 1943篇 |
2012年 | 2160篇 |
2011年 | 2223篇 |
2010年 | 1823篇 |
2009年 | 1908篇 |
2008年 | 1972篇 |
2007年 | 1723篇 |
2006年 | 1670篇 |
2005年 | 1316篇 |
2004年 | 1093篇 |
2003年 | 823篇 |
2002年 | 968篇 |
2001年 | 760篇 |
2000年 | 720篇 |
1999年 | 595篇 |
1998年 | 400篇 |
1997年 | 334篇 |
1996年 | 319篇 |
1995年 | 281篇 |
1994年 | 242篇 |
1993年 | 244篇 |
1992年 | 193篇 |
1991年 | 153篇 |
1990年 | 119篇 |
1989年 | 108篇 |
1988年 | 96篇 |
1987年 | 58篇 |
1986年 | 46篇 |
1985年 | 57篇 |
1984年 | 38篇 |
1983年 | 38篇 |
1982年 | 31篇 |
1981年 | 17篇 |
1980年 | 5篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
84.
On Dirichlet Characters of Polynomials 总被引:1,自引:0,他引:1
The main purpose of this paper is to use the properties of Gaussiansums and the analytic method to study the problem of calculatingone kind of character sums modulo q, and to give an interestingidentity. 2000 Mathematics Subject Classification 11L10, 11L40. 相似文献
85.
Analysis on the effectiveness of the 20-H rule for printed-circuit-board layout to reduce edge-radiated coupling 总被引:1,自引:0,他引:1
Montrose M.I. Er-Ping Li Hong-Fang Jin Wei-Liang Yuan 《Electromagnetic Compatibility, IEEE Transactions on》2005,47(2):227-233
This paper presents the quantified study of the electromagnetic radiation mechanism of the 20-H rule using a numerical approach that has not yet been systematically addressed. The 20-H rule is a rule-of-thumb layout technique recommended to minimize radiated fields propagating from the edges of a printed circuit board (PCB) coupling onto nearby structures. Propagating electromagnetic fields may corrupt adjacent cable assemblies, sheet metal enclosures, and aperture openings. The magnitude of this design rule is investigated using the full-wave finite-difference time-domain (FDTD) method. An analysis on whether benefits exist from use of this rule is examined and under what conditions the rule is valid when correctly implemented. The purpose of this paper is to provide insight into the validity of the 20-H rule, recognizing that every PCB will have different simulation results. FDTD is used to capture a snapshot view of field propagation. This view allows one to determine the validity of the 20-H rule at a single point of time within a dynamic structure and what may be expected when digital components are finally added to a PCB assembly, which generally negates simulated results. 相似文献
86.
ZENG Hao BAI Xingyu RAO Jun 《核工业西南物理研究院年报(英文版)》2004,(1):65-67
When we carry out lower hybrid wave heating and current driving plasma experiment at tokamak, we need mega-watt order of microwave power. The microwave signal at frequency of 2450 MHz is generated by a microwave exciter. According to the experiment's demands, the microwave exciter must provide output power of 1.5~ 2. 5 W with stabilized frequency and amplitude tobe used as the klystron input. Being amplified by the klystron, the microwave signal is transmitted through the transmitting system to the antenna and is emitted into the HL-2A tokamak. So we can see that the microwave exciter's function is very important to the lower hybrid wave heating and current driving plasma experiment. 相似文献
87.
88.
89.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献
90.
物理模型教学与创新能力的培养 总被引:1,自引:0,他引:1
现代教学以能力培养为重点.学生获得研究问题、探索问题的能力是十分重要的,物理模型的教学过程对培养学生研究问题、探索问题、发展创造思维、培养辩证唯物主义思想方法都极为有利,因此,必须重视物理模型教学. 相似文献