全文获取类型
收费全文 | 1185篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 101篇 |
化学工业 | 171篇 |
金属工艺 | 14篇 |
机械仪表 | 14篇 |
建筑科学 | 35篇 |
矿业工程 | 3篇 |
能源动力 | 26篇 |
轻工业 | 93篇 |
水利工程 | 24篇 |
石油天然气 | 4篇 |
无线电 | 152篇 |
一般工业技术 | 200篇 |
冶金工业 | 273篇 |
原子能技术 | 33篇 |
自动化技术 | 65篇 |
出版年
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 14篇 |
2014年 | 17篇 |
2013年 | 43篇 |
2012年 | 20篇 |
2011年 | 46篇 |
2010年 | 47篇 |
2009年 | 46篇 |
2008年 | 49篇 |
2007年 | 47篇 |
2006年 | 42篇 |
2005年 | 41篇 |
2004年 | 36篇 |
2003年 | 35篇 |
2002年 | 34篇 |
2001年 | 40篇 |
2000年 | 26篇 |
1999年 | 28篇 |
1998年 | 104篇 |
1997年 | 64篇 |
1996年 | 56篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 26篇 |
1992年 | 20篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 11篇 |
1974年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有1208条查询结果,搜索用时 31 毫秒
131.
132.
A technique of parallel connection of power devices by using current sharing reactors for pulsewidth modulated (PWM) inverters is reported in this paper. The proposed technique not only increases the current capacity but also decreases the output harmonic contents. The output voltage waveforms of the proposed inverter have certain voltage levels during their half cycles, thus it is anticipated that it will be difficult to analyze the output waveforms. For such waveforms, a frequency analysis approach is described, whose results are verified by experiments 相似文献
133.
M Sugimoto A Tanaka T Suzuki H Matsui S Nakamori H Takagi 《Canadian Metallurgical Quarterly》1997,61(10):1760-1762
The homoserine dehydrogenase (HD) genes from Brevibacterium lactofermentum lysine- and threonine-producing mutants were cloned, using the polymerase chain reaction, and sequenced. We found the amino acid substitutions, Val104Ile in the lysine-producing mutants in which HD may cause leaky mutation and Ser393Phe in the threonine-producing mutant with feedback-insensitive HD. 相似文献
134.
STUDY DESIGN: In this retrospective study, the long-term clinical results of lumbar intervertebral disc herniation in children less than 16 years of age were reviewed. OBJECTIVES: To evaluate the effectiveness of surgical treatment including posterior discectomy, extraperitoneal anterolateral discectomy, and anterior interbody fusion for lumbar intervertebral disc herniation in children less than 16 years of age. SUMMARY OF BACKGROUND DATA: Although previous follow-up studies on surgically managed lumbar intervertebral disc herniation in children and adolescents generally reveal good outcomes, few reports have focused on the time course of clinical findings and the long-term results. METHODS: The outcome of subjective symptoms, clinical signs, and time-related change of the intervertebral disc space in 11 patients were evaluated with an average follow-up period of 9 years (range, 5-12 years). RESULTS: The posterior discectomy procedure relieved clinical symptoms quickly. In the case of central herniation with or without intervertebral instability, extraperitoneal anterolateral discectomy or anterior interbody fusion led to favorable long-term results. Clinical symptoms (lower back pain, leg pain) and neurologic disturbance disappeared within 3 months after surgery. Recovery of normal straight leg raising test results (tight hamstrings), however, required much more time than recovery of other symptoms. Narrowing of the intervertebral disc space progressed up to 3-6 months after discectomy, but then disc space widening occurred. CONCLUSIONS: Satisfactory long-term clinical results and early return to school life were obtained with each surgical procedure. It is important to aim toward an early return to school via surgical treatment. 相似文献
135.
We investigated the role of the active form of vitamin D, 1,25-dihydroxyvitamin D3[1,25(OH)2D3], in promoting tumor cell invasiveness through the extracellular matrix, and showed that 1,25(OH)2D3-induced reduction of laminin production by the cells was correlated with the inhibitory effect of the hormone on tumor cell invasiveness. 1,25(OH)2D3 significantly inhibited invasiveness through the matrix, type IV collagenolytic and migratory activity, but not cell attachment to the matrix in human fibrosarcoma HT1080 cells. The 1,25(OH)2D3-induced inhibition showed the same dose dependency and magnitude for invasiveness as for the effects on type IV collagenolysis and cell migration. 1,25(OH)2D3 inhibited laminin production from the cells in a dose-dependent manner. The inhibitory effects of 1,25(OH)2D3 on the invasiveness, type IV collagenolysis and cell migration appeared to parallel the hormone-induced reduction of laminin production. Antilaminin monoclonal antibody, blocking the activity of laminin in the culture medium, inhibited HT1080 cell invasiveness. In the presence of exogenous laminin, 1,25(OH)2D3-induced inhibition of invasion was not observed. These findings suggest that 1,25(OH)2D3 acts on HT1080 cells, inhibiting the expression of laminin from the cells, and that the reduced laminin expression leads to the inhibition in the type IV collagenolytic and migratory activity of the cells, and consequently, to the inhibition of invasiveness through the extracellular matrix. 相似文献
136.
Arahira S. Kutsuzawa S. Matsui Y. Kunimatsu D. Ogawa Y. 《Photonics Technology Letters, IEEE》1998,10(2):209-211
We describe the generation of a synchronized, low-jitter, subterahertz optical pulse train by repetition-frequency multiplication of a subharmonic synchronous mode-locked semiconductor laser diode using the group-velocity dispersion (GVD) of optical fiber. A 49-196 GHz optical pulse train was generated with low intensity fluctuation and with low timing jitter, by adjusting fiber length in accordance with the mode-locking frequency and the fiber's GVD 相似文献
137.
1-Aminocyclopropane-1-carboxylate (ACC) deaminase catalyzes the cyclopropane ring fragmentation and deamination of ACC. Replacement of cysteine with alanine at a reactive thiol site, Cys-162, of ACC deaminase did not affect the enzyme activity, in spite of the previous result that modification of Cys-162 caused complete loss of the enzyme activity. Substitution of glycine or valine for the cysteine residue gave a higher Km for ACC without a significant change of the K0, indicating that changes of the amino acid side chain had structural effects on substrate binding. Replacement of lysine with alanine at the pyridoxal phosphate (PLP) binding site of the ACC deaminase caused a lower content of PLP and loss of detectable activity of ACC deamination. This mutant enzyme, K51A, showed absorption peaks at 330 nm and 405 nm. The peak at 405 nm was shifted to about 425 nm by the addition of ACC, D-, L-alanine, and D-, L-serine. The formation of aldimine complexes indicated by the spectral shift was reversible. It is suggested that lysine 51 affects the formation of holoenzyme and is important in catalysis. 相似文献
138.
Because of the introduction of deregulation and competition in the electricity supply industry, large numbers of IPPs (Independent Power Producers) will get into the market. It has become much more important to be able to determine which generators are supplying a particular load, which generator is responsible for transmission line congestion, and what is each generator's contribution to the system losses. In this paper, we propose a way to calculate these contributions automatically. The applicability of the proposed technique is demonstrated using the EAST 10 47‐bus power system. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(3): 28–35, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10181 相似文献
139.
A 100-1000 MHz range field strength standard using a short broadband dipole antenna has been developed for use in an anechoic chamber. The broad bandwidth of the standard antenna reduces calibration time and reduces the calibration differences which occur when the standard antennas must be changed for broadband calibration. The enclosure of the system in the anechoic chamber eliminates the interaction of the radiation with the neighboring environment, and ensures that the measurements are unaffected by weather. Error, due to reflection waves from each of the walls, the floor, and the ceiling of the chamber, was reduced by measuring the insertion loss with very closely spaced antennas, and by compensating the near-field effect theoretically. This frequency range is covered by only two standard antennas, and the field strength standard has been established with one-sigma uncertainty within ±1.6% 相似文献
140.
Matsui Y. Murai H. Arahira S. Ogawa Y. Suzuki A. 《Quantum Electronics, IEEE Journal of》1998,34(12):2340-2349
We present a theoretical analysis exploring the optimum design of high-speed multiple-quantum-well (MQW) lasers for 1.55-μm operation. Various combinations of well and barrier materials are examined for lattice-matched, strained-layered (SL), and strain-compensated (SC) MQW lasers with InGaAsP and InGaAlAs barriers. The gain characteristics are investigated for these MQW lasers with various barrier bandgap wavelengths and are used to evaluate the modulation characteristics based on the carrier dynamics model which includes a set of Poisson, continuity, and rate equations. The importance of band engineering aimed at simultaneously reducing the carrier transport effect and enhancing the differential gain is described. It is shown that SC-MQW lasers with InGaAlAs barriers have an advantage in reducing the density of states in the valence band by reducing the overlap integral between the heavy- and light-hole wave functions, which effect has previously been discarded as a minor correction in designing conventional InGaAsP-based MQW lasers. Furthermore, the hole transport rate across the barriers can be drastically reduced in SC-MQW lasers due to the reduced effective barrier height for the holes. Based on this novel design scheme, a 3-dB bandwidth approaching 70 GHz is expected for 20-well SC-MQW lasers with InGaAlAs barriers as a result of both the large differential gain and reduced transport effect 相似文献