全文获取类型
收费全文 | 690232篇 |
免费 | 7343篇 |
国内免费 | 1174篇 |
专业分类
电工技术 | 12317篇 |
综合类 | 525篇 |
化学工业 | 109525篇 |
金属工艺 | 30542篇 |
机械仪表 | 22506篇 |
建筑科学 | 15192篇 |
矿业工程 | 6007篇 |
能源动力 | 16884篇 |
轻工业 | 51731篇 |
水利工程 | 9034篇 |
石油天然气 | 20029篇 |
武器工业 | 48篇 |
无线电 | 70233篇 |
一般工业技术 | 146760篇 |
冶金工业 | 112408篇 |
原子能技术 | 18895篇 |
自动化技术 | 56113篇 |
出版年
2021年 | 6629篇 |
2019年 | 6298篇 |
2018年 | 11245篇 |
2017年 | 11416篇 |
2016年 | 11960篇 |
2015年 | 7328篇 |
2014年 | 12501篇 |
2013年 | 31252篇 |
2012年 | 19017篇 |
2011年 | 25302篇 |
2010年 | 20318篇 |
2009年 | 22712篇 |
2008年 | 23015篇 |
2007年 | 22578篇 |
2006年 | 19411篇 |
2005年 | 17505篇 |
2004年 | 16783篇 |
2003年 | 16450篇 |
2002年 | 15921篇 |
2001年 | 15381篇 |
2000年 | 14816篇 |
1999年 | 14336篇 |
1998年 | 32103篇 |
1997年 | 23526篇 |
1996年 | 18300篇 |
1995年 | 14148篇 |
1994年 | 12958篇 |
1993年 | 12687篇 |
1992年 | 9987篇 |
1991年 | 9816篇 |
1990年 | 9686篇 |
1989年 | 9380篇 |
1988年 | 9029篇 |
1987年 | 8335篇 |
1986年 | 8066篇 |
1985年 | 9024篇 |
1984年 | 8298篇 |
1983年 | 8027篇 |
1982年 | 7287篇 |
1981年 | 7440篇 |
1980年 | 7188篇 |
1979年 | 7406篇 |
1978年 | 7385篇 |
1977年 | 8043篇 |
1976年 | 9718篇 |
1975年 | 6669篇 |
1974年 | 6579篇 |
1973年 | 6646篇 |
1972年 | 5820篇 |
1971年 | 5399篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
851.
In this paper, we examine methods of characterizing somatosensory evoked potentials (SEP's) in both the time and frequency domains. We have found that the truncated impulse response (TIR) method produced an accurate time domain model of the SEP signals at model orders greatly reduced from the original state space matrix. The TIR method was valuable for smoothing signals that were slightly corrupted by noise. In this case, the simulated data sequence was close to the original data sequence in the mean squared error sense. For signals that were greatly corrupted by noise, the TIR method was not able to perform as well. Therefore, the TIR method was not a feature extraction method but was valuable for data simulation. In the frequency domain, we have used the autoregressive moving average model (ARMA) to parameterize the SEP signal. An overdetermined set of Yule-Walker equations was created to determine the autoregressive (AR) parameters of the original data with the model order established by the singular value decomposition. From these AR parameters, a residual time series was generated which was used to find the moving average parameters. The resulting ARMA model was used to produce a simulated data sequence. The frequency domain characteristics of the simulated sequence and the corresponding power spectral density of the ARMA filter were very close to the periodogram of the original data sequence. Accurate parameterization was achieved for the SEP waveforms at low filter lengths. 相似文献
852.
853.
Conclusions The chemical mutagenesis method is recommended for use in local purification installations for cleaning up of caprolactam-containing wastewater.Use of this method permits one to carry out a biochemical clean-up of wastewater having a caprolactam content up to 600 mg/liter while increasing the oxidative power of the aeration tank by a factor of two.Translated from Khimicheskie Volokna, No. 6, p. 46, November–December, 1985. 相似文献
854.
A coupled-mode theory of overmoded, cylindrical metal Bragg-reflectors is presented. The first-order Bragg coupling constants are derived for TE → TE, TM → TM, TE → TM, and TM → TE mode conversions. Reflectivities and transverse modeQ -factors are computed for a Bragg-reflector resonator. The results illustrate important competition effects between nearly-degenerate-transverse-modes occurring within both the Bragg-reflectors and the resonator. 相似文献
855.
Z. P. Shul'man B. M. Khusid I. L. Ryklina É. A. Zal'tsgendler O. R. Dornyak É. V. Ivashkevich Z. A. Shabunina 《Journal of Engineering Physics and Thermophysics》1987,53(5):1285-1291
Dynamic processes are studied in media with softly and hardly internal destroyable configurations. A method is examined for the measurement of properties of media with spatial separation of the chemical transformation stages and thermal hydrodynamic measurements.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 5, pp. 781–789, November, 1987. 相似文献
856.
857.
A. Bernasik J. Janowski W. Hirschwald F. Stolze J. Nowotny 《Journal of Materials Science》1991,26(9):2527-2532
Surface segregation of various impurities such as Mg, Si, Ca, Al and Cr were determined for the haematite phase (Fe2O3) annealed in two different gas compositions involving (1) air at 1173 K, and (2) a gas mixture containing sulphur at 773 K. The objective of work was to establish the effect of the gas-phase composition on segregation of lattice defects. The near-surface segregation profiles of the impurities were determined by secondary ion mass spectrometry. The depth profile analysis was made by sputtering using an Ar+ primary beam of energy 30 keV. The surface charge was neutralized by an electron gun. It was found that annealing Fe2O3 under a gas phase containing sulphur resulted in the formation of an Fe(SO4)3 surface layer. It was observed that the two surface treatment procedures applied (both with and without sulphur) result in Mg enrichment in the near-surface region of Fe2O3. Si and Ca exhibit an enrichment and impoverishment after the surface treatments 1 and 2, respectively. Finally, the near-surface layer is impoverished in Cr and Al after both types of surface treatment. Experimental results are discussed in terms of segregation driving forces of the respective elements and the possible effect of sulphur on the gas-solid heterogeneous kinetics. 相似文献
858.
Y. Rey-Tauriac J. Badoc B. Reynard R.A. Bianchi D. Lachenal A. Bravaix 《Microelectronics Reliability》2005,45(9-11):1349
This paper presents results of reliability investigation of 20 V N-Drift MOS transistor in 0.13 μm CMOS technology. Due to high performances required for CMOS applications, adding high voltage devices becomes a big challenge to guarantee the reliability criteria. In this context, new reliability approaches are needed. Safe Operating Area are defined for switch, Vds limited and Vgs limited applications in order to improve circuit designs. For Vds limited applications, deep doping dose effects in drift area are investigated in correlation to lifetime evaluations based on device parameter shifts under hot carrier stressing. To further determine the amount and locations of hot carriers injections, accurate 2D technological and electrical simulations are performed and permit to select the best compromise between performance and reliability for N-Drift MOS transistor. 相似文献
859.
860.
M. V. Zagidullin V. D. Nikolaev M. I. Svistun N. A. Khvatov 《Journal of Engineering Physics and Thermophysics》2007,80(3):555-562
The results of parametric tests of a centrifugal bubble singlet-oxygen generator based on the reaction of chlorine with an
alkaline hydrogen peroxide solution have been given. The utilization of chlorine grows with bubble-layer height, whereas the
relative content of O2(1Δ) remains constant. Growth in centrifugal acceleration leads to a more efficient utilization of chlorine. A specific oxygen
output of more than 1 mmole·cm−2·sec−1 from the bubble layer for a degree of chlorine utilization of ∼95% and a singlet-oxygen yield of more than 50% has been attained.
It has been shown that a centrifugal bubble singlet-oxygen generator is an efficient energy source for an oxygen-iodine laser.
__________
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 121–128, May–June, 2007. 相似文献