全文获取类型
收费全文 | 1645篇 |
免费 | 55篇 |
国内免费 | 1篇 |
专业分类
化学 | 895篇 |
晶体学 | 8篇 |
力学 | 42篇 |
数学 | 149篇 |
物理学 | 400篇 |
无线电 | 207篇 |
出版年
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 22篇 |
2017年 | 12篇 |
2016年 | 34篇 |
2015年 | 27篇 |
2014年 | 40篇 |
2013年 | 63篇 |
2012年 | 60篇 |
2011年 | 80篇 |
2010年 | 33篇 |
2009年 | 35篇 |
2008年 | 72篇 |
2007年 | 69篇 |
2006年 | 70篇 |
2005年 | 70篇 |
2004年 | 64篇 |
2003年 | 54篇 |
2002年 | 61篇 |
2001年 | 47篇 |
2000年 | 50篇 |
1999年 | 30篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 29篇 |
1995年 | 28篇 |
1994年 | 34篇 |
1993年 | 33篇 |
1992年 | 25篇 |
1991年 | 13篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 18篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 27篇 |
1980年 | 11篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 20篇 |
1976年 | 17篇 |
1975年 | 23篇 |
1974年 | 25篇 |
1973年 | 17篇 |
1972年 | 22篇 |
1967年 | 13篇 |
排序方式: 共有1701条查询结果,搜索用时 7 毫秒
91.
92.
93.
Quantitative analysis of the products formed in 1,1′-azoisobutane pyrolyses in the temperature range of 553°–602°K has shown that the major reactions of the iso-butyl radical are Analysis of initial rate data gave log10k4/(kc)1/2(cm?3/2.mol 1/2.sec?1/2) = 7.54±0.44 ? (136.5 + 4.8) kJ/mol/2.303RT, the Arrhenius parameters obtained being in good agreement with thermodynamic data for reaction (4). Measured values of ka/(kc)1/2 where ka is the rate constant of the reaction iC4H9 + AIB → iC4H10 +. AIB were consistent with published parameters determined by photolysis of 1,1′-azoisobutane. Combination of photolysis and pyrolysis data gave log10 ka/(kc)1/2(cm3/2.mol?1/22.sec?1/2) = 3.68 ± 0.15 ? (27.2 ± 1.2) kJ/mol/2.303RT. The crosscombination ratio for methyl and iso-butyl radicals has been found to be 0.25, indicating that the geometric mean rule does not hold for methyl and iso-butyl radicals. 相似文献
94.
James CD Spence AJ Dowell-Mesfin NM Hussain RJ Smith KL Craighead HG Isaacson MS Shain W Turner JN 《IEEE transactions on bio-medical engineering》2004,51(9):1640-1648
Neuronal cell networks have been reconstructed on planar microelectrode arrays (MEAs) from dissociated hippocampal pyramidal neurons. Microcontact printing (microCP) and a photoresist-liftoff method were used to selectively localize poly-L-lysine (PLL) on the surface of MEAs. Haptotaxis led to the organization of the neurons into networks localized adjacent to microelectrodes. Various grids of PLL with 2-25-microm-wide lines spaced by 50-200 microm with 15-25-microm nodes at intersection points were used to guide cell body attachment and neurite outgrowth. Bursting activity with spike amplitude attenuation was observed, and multichannel recordings detected instances of coincident firing activity. Finally, we present here an extracellular recording from a approximately 2 microm bundle of guided neurites. 相似文献
95.
96.
97.
Nonlinear optical properties of HgS have been of interest lately. The electrooptic effect has been measured in a natural crystal and values for the two independent coefficients are reported here at wavelengths of 0.63 and 3.39 microns. The results agree well with predictions of purely electronic theories, but the wavelength dependence indicates an appreciable contribution of ionic motion to the optical polarizability. 相似文献
98.
Zheng BS Zhang XY Zhu HW Luo SX Lindoy LF McMurtrie JC Turner P Wei G 《Dalton transactions (Cambridge, England : 2003)》2005,(8):1349-1351
Discrete cobalt(II) and nickel(II) complexes of type ML (where L is a bis(2,4-pentanedionate) derivative incorporating a -SCH2CH2S- bridge between the gamma-carbons of respective beta-diketone units) have been synthesised and represent the first examples in which a gamma-substituted, thioether-containing beta-diketone ligand coordinates via a sulfur and oxygen donor in preference to the classical coordination mode involving both beta-diketonate oxygens. 相似文献
99.
Single-mode plane-polarized ytterbium-doped large-core fiber laser with 633-W continuous-wave output power 总被引:3,自引:0,他引:3
Jeong Y Nilsson J Sahu JK Soh DB Dupriez P Codemard CA Baek S Payne DN Horley R Alvarez-Chavez JA Turner PW 《Optics letters》2005,30(9):955-957
We demonstrate a cladding-pumped single-mode plane-polarized ytterbium-doped fiber laser generating 633 W of continuous-wave output power at 1.1 microm with 67% slope efficiency and a polarization extinction ratio better than 16 dB. The laser is end pumped through both fiber ends and shows no evidence of roll-over, even at the highest output power, which is limited only by the available pump power. 相似文献
100.
Single-frequency, single-mode, plane-polarized ytterbium-doped fiber master oscillator power amplifier source with 264 W of output power 总被引:10,自引:0,他引:10
Jeong Y Nilsson J Sahu JK Soh DB Alegria C Dupriez P Codemard CA Payne DN Horley R Hickey LM Wanzcyk L Chryssou CE Alvarez-Chavez JA Turner PW 《Optics letters》2005,30(5):459-461
We present a single-frequency, single-mode, plane-polarized ytterbium-doped all-fiber master oscillator power amplifier source at 1060 nm generating 264 W of continuous-wave output power. The final-stage amplifier operated with a high gain of 19 dB and a high conversion efficiency of 68%. There was no evidence of rollover from stimulated Brillouin scattering even at the highest output power, and the maximum output was limited only by the available pump power. 相似文献