全文获取类型
收费全文 | 72302篇 |
免费 | 12217篇 |
国内免费 | 9288篇 |
专业分类
化学 | 51018篇 |
晶体学 | 979篇 |
力学 | 4448篇 |
综合类 | 662篇 |
数学 | 8621篇 |
物理学 | 28079篇 |
出版年
2024年 | 218篇 |
2023年 | 1335篇 |
2022年 | 2570篇 |
2021年 | 2631篇 |
2020年 | 2867篇 |
2019年 | 2806篇 |
2018年 | 2447篇 |
2017年 | 2410篇 |
2016年 | 3487篇 |
2015年 | 3634篇 |
2014年 | 4314篇 |
2013年 | 5524篇 |
2012年 | 6450篇 |
2011年 | 6575篇 |
2010年 | 4784篇 |
2009年 | 4597篇 |
2008年 | 4951篇 |
2007年 | 4407篇 |
2006年 | 4089篇 |
2005年 | 3527篇 |
2004年 | 2753篇 |
2003年 | 2230篇 |
2002年 | 2203篇 |
2001年 | 1723篇 |
2000年 | 1463篇 |
1999年 | 1436篇 |
1998年 | 1120篇 |
1997年 | 1006篇 |
1996年 | 999篇 |
1995年 | 850篇 |
1994年 | 735篇 |
1993年 | 618篇 |
1992年 | 524篇 |
1991年 | 470篇 |
1990年 | 393篇 |
1989年 | 304篇 |
1988年 | 229篇 |
1987年 | 195篇 |
1986年 | 192篇 |
1985年 | 166篇 |
1984年 | 96篇 |
1983年 | 99篇 |
1982年 | 60篇 |
1981年 | 42篇 |
1980年 | 38篇 |
1979年 | 25篇 |
1978年 | 22篇 |
1977年 | 22篇 |
1976年 | 24篇 |
1975年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
The Iyengar Type Inequalities with Exact Estimations and the Chebyshev Central Algorithms of Integrals 总被引:3,自引:0,他引:3
Xing Hua WANG Shi Jun YANG 《数学学报(英文版)》2005,21(6):1361-1376
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated. 相似文献
122.
123.
In the ever fusion experiments in SWIP, pellet forming process was carried out through adjusting relative devices by staff member in site, which will make every pellet-forming process slight distinction and will result in pellet difference in shape, size and intensity. In the intervals of HL-2A discharges, staff member have to go site to accomplish the pellet-forming process, this wastes human power and increase the potential danger. So it is necessary to develop a remote control system to perform the pellet-forming process. The control system needs have the features of real-time, reliability and be easy to operate and maintain. 相似文献
124.
RUAN Manqi XU Gang & ZENG Jinyan Department of Physics Tsinghua University Beijing China Department of Physics Peking University Beijing China Correspondence should be addressed to Zeng Jinyan 《中国科学G辑(英文版)》2004,47(1):36-41
Foratwo-particle(spin1/2)systemthespinstateisdescribedusingavectorinafour-dimensionalHilbertspace.Inangularmomentumcouplingtheory[1],theangularmomentumuncouplingandcouplingrepresentationsareusuallyadopted.WhilethesimultaneouseigenstatesoftheCSCO(s1z,s2z),12,12,12and12,arechosenasthebasisofangularmomentumuncouplingscheme,thesimultaneouseigenstatesoftheCSCO(2,zSS),,SM(12=+Sss),arechosenasthebasisofangularmomentumcouplingscheme,1212100,2轾=-臌1212110,2轾=+臌121211,1,1.=-=Thefo… 相似文献
125.
YBa2Cu3O7-x (YBCO) bulk is one of the most important high temperature superconducting materials for magnetic levitation applications, because it has a high magnetic irreversibility field Hirr at liquid nitrogen temperature, and can grow into large grains. The levitation force of YBCO bulk is proportional to the critical current density (Jc) and grain radius (r)[1], so higher Jc and r are appreciated for YBCO bulks to achieve higher levitation force. Now single-domain YBCO bulks up to s… 相似文献
126.
127.
Deposition of Hydrogen-Free Silicon Nitride Thin Films by Microwave ECR plasma Enhanced Magnetron Sputtering at Room Temperature 下载免费PDF全文
Hydrogen-free silicon nitride (SiNx) films were deposited at room temperature by microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalance magnetron sputtering system. Both Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy are used to study the bonding type and the change of bonding structures of the silicon nitride films. The results indicate that the chemical structure and composition of SiNx films deposited by this technique depend strongly on the N2 flow rates, the stoichiometric SiNx film, which has the highest hardness of 22.9 GPa, could be obtained at lower N2 flow rate of 4 sccm. 相似文献
128.
129.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
130.
The first α‐diimine nickel(I) complex having a chloro bridge is reported. The centrosymmetric dinuclear structure of {[ArN?C(Me)C(Me)?NAr]NiCl}2[Ar?2,6?C6H3(i‐Pr)2] features two chelating α‐diimine ligands and two bridged chlorine atoms, so that a distorted tetrahedral N2Cl2 coordination geometry for nickel results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献