全文获取类型
收费全文 | 149篇 |
免费 | 0篇 |
国内免费 | 3篇 |
专业分类
化学 | 68篇 |
力学 | 3篇 |
数学 | 9篇 |
物理学 | 72篇 |
出版年
2020年 | 3篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 2篇 |
2012年 | 5篇 |
2011年 | 14篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有152条查询结果,搜索用时 15 毫秒
101.
McDermott D.B. Balkcum A.J. Luhmann N.C. Jr. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1996,24(3):613-619
A 50-kV third-harmonic gyrotron is shown to be capable of high efficiency. Operation at the third harmonic allows the required magnetic field for 35 GHz generation to be supplied by a 4.5-kG permanent magnet. Two gyrotrons employing sliced circuits for mode control have been evaluated with a large-signal nonself-consistent particle-tracing simulation code and found to be capable of producing 25 kW continuously. The preliminary design of a third-harmonic TE41 gyrotron utilizing a magnetron injection electron gun is predicted to yield a device efficiency of 17%, which can potentially be increased to 46% with an ideal single-stage depressed collector, while an axis-encircling electron beam from a Cusp electron gun is predicted to drive a third-harmonic TE31 gyrotron with a device efficiency of 23%, which can theoretically be increased to 45% through the use of an ideal depressed collector 相似文献
102.
Chong C.K. McDermott D.B. Lin A.T. DeHope W.J. Wang Q.S. Luhmann N.C. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1996,24(3):735-743
A low-magnetic-field moderate-voltage gyrotron amplifier has been designed for stable high-performance operation at 95 GHz. A slotted interaction circuit is utilized to achieve strong amplification near the third cyclotron harmonic frequency. The start-oscillation conditions were determined by an analytical theory and confirmed by a multimode particle-in cell simulation code. The dominant threat to the amplifier's stability is from a third-harmonic peniotron backward-wave interaction. A slow-timescale particle-tracing simulation code predicts the three-section slotted third-harmonic gyro-TWT, which utilizes an 11.6-kG magnet and a 50-kV 3-A υ⊥/υz=1.4 axis-encircling electron beam with an axial velocity spread of 6% will yield an output power of 30 kW with an efficiency of 20%, a saturated gain of 40 dB, and a constant-drive bandwidth of 2% 相似文献
103.
104.
Philip J. McDermott Terry E. Krafft Jonathan D. Rich 《Journal of polymer science. Part A, Polymer chemistry》1991,29(12):1681-1689
Several synthetic routes to silicon polycarbonate copolymers utilizing aryl-terminated siloxanes have been examined. Anhydride capped siloxanes with varying polydimethylsiloxane units were prepared by the acid equilibration of 1,3-bis(4,4′-phthalicanhydride)tetramethyldisiloxane. These siloxanes were then imidized with aminophenol to the corresponding phenol capped siloxane. Reaction of these materials with 4,4′-isopropylidenediphenol (BPA) and phosgene (interfacially and non-interfacially) produced silicone polycarbonate copolymers. Similar copolymers were obtained by reaction with bis-chloroformate derivatives of 4,4′-isopropylidenediphenol (monomer and oligomers). The different synthetic routes significantly affect the thermal and mechanical properties as well as the composition of the new polymers. Materials synthesized by the bis-chloroformate route exhibit good hydrolytic and melt stabilities. Those made interfacially underwent phase separation in the melt. 相似文献
105.
106.
Leou K.C. McDermott D.B. Luhmann N.C. Jr. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(3):188-196
The bandwidth of a gyro-TWT (traveling-wave tube) can be widened by employing a dielectric-loaded waveguide to reduce the circuit's dispersion. Fast wave interaction allows the requirements on the beam's quality to be relaxed compared with slow wave interaction. A low-α (≡ν⊥/νz) electron beam is chosen to avoid the absolute instability and minimize the possibility of dielectric charging. This device is investigated using a self-consistent single-mode, large-signal simulation based on a slow time scale formulation. Simulation results show that a constant drive bandwidth of 20% can be achieved for a 100 kV, 5 A electron beam with a velocity ratio of α=0.59 and an axial velocity spread of 2.0%. The growth rate is relatively low because of the low α of the electron beam. The design of a proof-of-principle experiment is described. The tube is expected to deliver a power of 80 kW from 9 to 11 GHz with 15% efficiency and a saturated gain of 30 dB. The performance of a single-anode magnetron injection gun designed to produce the required high-quality electron beam has been studied through simulation 相似文献
107.
Michael J. Rozema Michael Fickes Maureen McLaughlin Bridget Rohde Todd McDermott 《Tetrahedron letters》2006,47(49):8765-8768
The stereoselective synthesis of A-345665.0 1, a novel farnesyl transferase inhibitor, is described. The key step involves a stereoselective addition of an imidazolyl Grignard reagent to aldehyde 8 in the presence of an external chiral auxiliary. Crystallization of the product as the dimeric zinc complex 12 facilitates the isolation of product in >98:2 er. The biaryl linkage is formed by the use of a Suzuki coupling, employing boronic acid 4 prepared by the directed ortho-lithiation of benzonitrile 6. The overall yield for the six step sequence is 21%. 相似文献
108.
109.
Vandali AE Sucher C Tsang DJ McKay CM Chew JW McDermott HJ 《The Journal of the Acoustical Society of America》2005,117(5):3126-3138
Pitch ranking of sung vowel stimuli, separated in fundamental frequency (F0) by half an octave, was measured with a group of eleven Nucleus 24 cochlear implant recipients using different sound coding strategies. In three consecutive studies, either two or three different sound coding strategies were compared to the Advanced Combinational Encoder (ACE) strategy. These strategies included Continuous Interleaved Sampling (CIS), Peak Derived Timing (PDT), Modulation Depth Enhancement (MDE), F0 Synchronized ACE (FOSync), and Multi-channel Envelope Modulation (MEM), the last four being experimental strategies. While pitch ranking results on average were poor compared to those expected for most normal hearing listeners, significantly higher scores were obtained using the MEM, MDE, and FOSync strategies compared to ACE. These strategies enhanced coding of temporal F0 cues by providing deeper modulation cues to F0 coincidentally in time across all activated electrodes. In the final study, speech recognition tests were also conducted using ACE, CIS, MDE, and MEM. Similar results among all strategies were obtained for word tests in quiet and between ACE and MEM for sentence tests in noise. These findings demonstrate that strategies such as MEM may aid perception of pitch and still adequately code segmental speech features as per existing coding strategies. 相似文献
110.
Yining Wang Michael P. McDermott 《Proceedings of the American Mathematical Society》2001,129(10):3091-3100
Let X be a -dimensional normal random vector with unknown mean and covariance matrix , where is a known matrix and an unknown parameter. This paper gives a test for the null hypothesis that lies either on the boundary or in the exterior of a closed, convex polyhedral cone versus the alternative hypothesis that lies in the interior of the cone. Our test is uniformly more powerful than the likelihood ratio test.