全文获取类型
收费全文 | 363篇 |
免费 | 6篇 |
专业分类
化学 | 121篇 |
晶体学 | 1篇 |
力学 | 17篇 |
数学 | 56篇 |
物理学 | 78篇 |
无线电 | 96篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 17篇 |
2012年 | 9篇 |
2011年 | 10篇 |
2010年 | 5篇 |
2009年 | 11篇 |
2008年 | 18篇 |
2007年 | 14篇 |
2006年 | 8篇 |
2005年 | 20篇 |
2004年 | 14篇 |
2003年 | 30篇 |
2002年 | 9篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1934年 | 2篇 |
1886年 | 1篇 |
排序方式: 共有369条查询结果,搜索用时 0 毫秒
351.
This paper describes a new approach to the detection of rotation rate using the optical fiber Sagnac interferometer. An inherently reciprocal heterodyne system gives the advantages in terms of signal-to-noise ratios (SNR's) of heterodyne detection, while independent electronic monitoring of each propagation path through the interferometer significantly enhances signal processing flexibility. The system may thus be used as a probe to evaluate fiber properties in a way compatible with other architectures, and these measurements should lead to advances in performance characteristics. A prototype system has exhibited noise levels in the region of 100°/h, and improvement to the signal processing will soon improve on this figure. 相似文献
352.
Ohne Zusammenfassung 相似文献
353.
Brillouin lasing in an all-fibre ring resonator made of polarisation-maintaining fibre using a semiconductor laser pump at 830 nm is reported. The stimulated Brillouin scattering (SBS) lasing threshold is 0.91 mW, and the Stokes output is polarised and exhibits linewidth narrowing.<> 相似文献
354.
The title compound with exclusively the E-geometry has been synthesized by two independent routes. When this compound was reacted with cerium (IV) ammonium nitrate, it was found that oxidative cyclisation to the corresponding 4-hydroxybenzo-pyrans did not occur. This further defines the structural parameters required for such oxidative cyclisations. 相似文献
355.
A fiber connectorized MEMS variable optical attenuator 总被引:3,自引:0,他引:3
Barber B. Giles C.R. Askyuk V. Ruel R. Stulz L. Bishop D. 《Photonics Technology Letters, IEEE》1998,10(9):1262-1264
A voltage-controlled moving-mirror microelectro-mechanical systems variable optical attenuator is described that has less than 1-dB fiber-to-fiber insertion loss at 1550-nm wavelength and greater than 50-dB dynamic range. The device was configured with a simple feedback circuit to operate as an optical power regulator capable of stabilizing the output power to within 0.26 dB for a 12-dB input power excursion 相似文献
356.
Wilson NM Ellis D Boyd AS Giles BT Macgregor SA Rosair GM Welch AJ 《Chemical communications (Cambridge, England)》2002,(5):464-465
Reaction of Na2[7,9-C2B10H12] or its C-dimethyl analogue with SnCl2 in THF affords 4,1,6-closo-SnC2B10H12 or 1,6-Me2-4,1,6-closo-SnC2B10H10 respectively, the first 13-vertex metallacarboranes involving p-block metals; spectroscopic, structural and theoretical studies, including an analysis of fluctionality in solution, are reported. 相似文献
357.
358.
359.
Bortoletto D Chen A Garren L Goldberg M Horwitz N Jawahery A Lubrano P Moneti GC Trahern CG van Hecke H Csorna SE Mestayer MD Panvini RS Word GB Yi X Bean A Ferguson T Avery P Bebek C Berkelman K Blucher E Cassel DG Copie T DeSalvo R DeWire JW Ehrlich R Galik RS Gilchriese MG Gittelman B Gray SW Halling AM Hartill DL Heltsley BK Holzner S Ito M Kandaswamy J Kowalewski R Kreinick DL Kubota Y Mistry NB Mueller J Nordberg E Ogg M Peterson D Perticone D Pisharody M Read K Riley D Silverman A 《Physical review letters》1986,56(8):800-803
360.
Parra-Robles J Dominguez Viqueira W Xu X Ouriadov A Santyr GE 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,192(1):85-91
In this work, computer modeling based on a finite element method is used to simulate the T2* relaxation of hyperpolarized noble gases (HNG) in the lungs. A physical model of lung airways consisting of a phantom constructed from micro-capillary fibers of diameters similar to the size of lung airways with semi-permeable walls is also presented. The fibers are surrounded by a liquid medium (water) of magnetic susceptibility similar to lung tissue. Theoretical predictions of the field strength dependence of T2* for 129Xe in the phantom and in vivo rat lung are presented. These predictions are in good agreement with experimental T2* values obtained from the phantoms and in vivo rat lungs (160, 19 and 8 ms) at three different field strengths (0.074, 1.89 and 3T, respectively) using hyperpolarized 129Xe. The strong dependence of T2* on field strength is consistent with the theoretical prediction that low fields may be optimal for HNG MR imaging of the lungs as the decreased T2* at high fields necessitates an increase in bandwidth for conventional MR imaging. 相似文献