全文获取类型
收费全文 | 69篇 |
免费 | 0篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 4篇 |
金属工艺 | 2篇 |
机械仪表 | 1篇 |
建筑科学 | 2篇 |
能源动力 | 23篇 |
无线电 | 24篇 |
冶金工业 | 3篇 |
出版年
2020年 | 1篇 |
2013年 | 6篇 |
2011年 | 1篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1977年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有69条查询结果,搜索用时 15 毫秒
21.
Raja M.Y.A. Brueck S.R.J. Osinski M. Schaus C.F. McInerney J.G. Brennan T.M. Hammons B.L. 《Electronics letters》1988,24(18):1140-1142
An optimised design for optoelectronic devices which depends on the interaction between an electromagnetic standing wave and the carrier population is described. The structure consists of quantum well layers spaced at one-half the wavelength of a selected optical transition in quantum wells. This spatial periodicity allows the amplifying or absorbing medium (quantum wells) to coincide with the peaks of the standing wave optical field in the Fabry-Perot cavity. In such a periodic medium, the gain or absorption for the selected wavelength is enhanced by a factor of two compared to a uniform medium. This concept was applied to fabricate a surface-emitting semiconductor laser in the GaAs/AlGaAs system. Lasing was achieved with the shortest gain medium length (320 nm) ever reported 相似文献
22.
Ripple currents on the DC side of both HVDC synchronous and asynchronous links together with cleared HVDC and AC system disturbances can excite in some circumstances onerous torsional vibrations in large steam generator shafts. The problem has assumed importance in recent months on account of the HVDC link between Scotland and Northern Ireland going ahead, on account of the proposed Eire/Wales link, and because AC/DC/AC couplers are to be installed extensively to interconnect the East and West European grid systems. This paper discusses and analyses excitation of shaft torsional vibrations in steam turbine-generator-exciter shafts in close proximity to HVDC power converter substations by: (i) variable-frequency ripple currents superimposed on the DC currents in asynchronous links; and (ii) disturbances at bi-polar converter stations. Detailed simulation of the HVDC converter and generator is necessary for precise assessments of shaft torsional response following HVDC converter station faults. 500 MW, 660 MW, 1000 MW and 1300 MW machines are considered in the analyses that are made 相似文献
23.
A review is given of the geothermal electric power potential in Iceland which could economically be developed to supplement hydro power for the proposed HVDC power link to the United Kingdom and supply the power-intensive industries in Iceland which are currently envisioned for development. Technically harnessable energy for electricity generation, taking account of geothermal resources down to an assumed base depth, temperature distribution in the crust, probable geothermal recovery factor, and accessibility of the field, has been assessed. Nineteen known high-temperature fields and nine probable fields have been identified. Technically harnessable geoheat for various areas is indicated. Data on high-temperature fields suitable for geothermal electric power generation and on harnessable energy for electric power generation within volcanic zones are presented 相似文献
24.
Losses and heating in rotors of large synchronous generators are examined following sustained stator-terminal and HV busbar line-to-line short-circuits at full load and no load, three-phase (L-L-L) short-circuits on a weak line connected to the HV generator transformer busbar with clearance at fault current zeros where the generator either remains in synchronism or falls from synchronism, and worst-case malsynchronization. Comparisons are made with negative sequence losses in solid generator rotors following these disturbances. The analysis uses a phase-variable model of a synchronous generator with detailed and reduced damper representations to compute stator and rotor current following a severe electrical disturbance at either the machine terminals or the HV unit transformer busbar. Simulations at full load and no load for a variety of assumptions and approximations, with connection of a field discharge resistor on tripping the main generator breaker, are performed 相似文献
25.
H.Q. Hou H.C. Chui K.D. Choquette B.E. Hammons W.G. Breiland K.M. Geib 《Photonics Technology Letters, IEEE》1996,8(10):1285-1287
Vertical-cavity surface-emitting lasers (VCSELs) were grown by metalorganic vapor phase epitaxy. Excellent uniformity of Fabry-Perot cavity wavelength for VCSEL materials of /spl plusmn/0.2% across a 3-in diameter wafer was achieved. This results in excellent uniformity of the lasing wavelength and threshold current of VCSEL devices. Employing pregrowth calibrations on growth rates periodically with an in situ reflectometer, we obtained a run-to-run wavelength reproducibility for 770- and 850-nm VCSELs of /spl plusmn/0.3% over the course of more than a hundred runs. 相似文献
26.
When Hurricane Georges hit the Florida Keys in 1998, deflecting its course and putting Pascagoula, Mississippi, USA within its potential path, the local refinery implemented standard hurricane readiness plans. A shutdown of the refinery was initiated when the storm's forecasted path changed from landfall at the mouth of the Mississippi River to landfall to the east along the Mississippi Gulf Coast. All processes were brought to a halt, and the entire refinery was brought to a stop. The four primary buildings, including facility maintenance, were flooded in up to 64 in of salt water. The destruction and disruption was almost overwhelming. The next week was spent in an effort to access the scope of the damage and develop a strategy to recover from the disaster. Since nothing of this magnitude had ever been experienced, all existing planning was insufficient to undertake such a task. This paper discusses the development of the recovery plan and the scope of the work. Establishing priorities, equipment reliability, and economic considerations are discussed. Execution of the recovery plan is described including communication . The key points outlined in this article can be of great assistance identifying key areas in planning and executing a successful recovery. 相似文献
27.
Some environmental factors affecting free amino acid composition in six varieties of peanuts 总被引:1,自引:0,他引:1
Clyde T. Young G. R. Waller R. S. Matlock R. D. Morrison R. O. Hammons 《Journal of the American Oil Chemists' Society》1974,51(6):265-268
This study involved six Spanish type entries (five commercial varieties and a plant introduction) grown in the National Variety
Tests in Oklahoma and Georgia under both irrigated and nonirrigated conditions. Significant effects (Georgia vs Oklahoma)
were observed on aspartic acid, proline, glycine, valine, isoleucine, peptide, ammonia, and histidine. Significant differences
for irrigated vs nonirrigated in the two states for aspartic acid, threonine, proline, glutamic acid, isoleucine, leucine,
tyrosine, phenylalanine, peptide, ammonia, and histidine were observed. Significant differences among the six entries were
observed for glutamic acid, leucine, tyrosine, phenylalanine, ammonia, histidine, arginine, tryptophan, and total amino acids.
None of the treatments produced significant changes in measured amounts of serine, alanine, methionine, and lysine. Significant
differences for Georgia vs Oklahoma and irrigated vs nonirrigated for Kjeldahl nitrogen of the whole peanut were noted.
Presented at the AOCS Spring Meeting, New Orleans, May 1973.
Journal paper 2636 of the Oklahoma Agricultural Experiment Station.
ARS, USDA. 相似文献
28.
29.
This paper analyzes rectifier ripple current superimposed on the direct current of a 600 MW asynchronous bipolar link between Lithuania and Poland and a 600 MW asynchronous monopolar link between Poland and Sweden in evaluating possible torsional vibrations in steam turbine-generator-exciter shafts. The studies are performed for machines in Northeastern Poland and in Southern Sweden close to the inverter station which are most at risk. Analyses are performed for the generators in Poland for the Lithuania/Poland link and for the generators in Sweden for the Poland/Sweden link. The paper examines system scaling factors for the Lithuania/Poland Link. It then examines AC system scaling factors and generator scaling factors for modulation product harmonic currents impressed on generators connected to the Swedish Grid Network by the inverter. Amplitude of shaft torsional torque due to resonant excitation imposed by the link on the generators in Sweden is evaluated for different scenarios of system and generator load. First, theory which relates magnitude of harmonic AC current injected into the AC system by the inverter is summarized. Dispersion of the injected harmonic AC current to proportion the current to individual generators is then reviewed, considering impedance of the generators, loads, and other system elements. Significance of simple and detailed shaft train models of machine shafts as well as approximate (Id, Iq) and detailed (2d, 3q) generator damper models on resonant torques is reviewed. Then, effects of both power factor and generator load on generator scaling factors is illustrated 相似文献
30.
Lee L.-N. Hammons A.R. Jr. Feng-Wen Sun Eroz M. 《Vehicular Technology, IEEE Transactions on》2000,49(6):2198-2207
This paper addresses the application of turbo codes for third-generation wireless services. It describes the specific characteristics of high-rate data applications in third-generation wide-band code-division multiple-access (CDMA) systems that make turbo codes superior to convolutional codes. In particular, it shows the positive effect of fast power control employed in these systems on the relative performance of turbo codes with respect to convolutional codes. It also shows how turbo and convolutional codes behave differently when the figure of merit is changed to frame error rate from bit error rate for high-speed data services. Furthermore, it describes in detail how and why the standardized turbo code has been selected in the presence of other candidates, which were also based on iterative decoding. Details of turbo interleaving and trellis termination as specified in the standards are explained. Performance of turbo codes under wide-band CDMA operating conditions are presented. The suitability of turbo codes for low-rate data applications is discussed. Finally it is shown that the performance loss as a result of internal decoder parameter quantization is negligible 相似文献