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91.
Hyun?Tae?Jang Sang?Bum?KimEmail author Wang?Seog?Cha Sung?Chang?Hong Dong?Sup?Doh 《Korean Journal of Chemical Engineering》2003,20(1):138-144
The combustion characteristics of a mixture of anthracite and bituminous coal were studied in a 0.155 m i.d. fluidized bed
combustor (FBC). The properties of the pressure fluctuation for the bed such as the standard deviation, cross-correlation
function, dominant frequency and the power spectral density function were obtained through statistical analysis. To interpret
the combustion characteristics in the FBC with uniform or multi-sized particles of anthracitebituminous coal mixture, the
properties of pressure fluctuation were determined as a function of the particle size distribution and anthracite mixing fraction.
In the present work, it is known that the combustion region could be obtained from the analysis of pressure fluctuation properties,
and the mixed-firing of anthracite-bituminous coal is related to the reaction models of both coals and particle size distribution.
Moreover, the relation between coal size distribution and static mean pressure, and the ignition region could be obtained
from the mean pressure profile. 相似文献
92.
Young-Sang Jeon Jukyung Cha Sangwook Nam 《Microwave Theory and Techniques》2007,55(4):690-696
A novel bias-switching scheme for a high-efficiency power amplifier is proposed. Two voltage levels for the drain bias of the RF power amplifier are generated using a combination of a class E dc/ac inverter and a class E rectifier with offset voltage. When signal peaks occur, the output of the class E dc/ac inverter is rectified and the rectified dc is added to the offset voltage by the class E rectifier, which boosts the drain bias of the RF power amplifier. Except during peaks, the drain bias of the RF power amplifier is connected to the offset voltage directly. Since the efficiency when there are no peaks is very high due to the direct connection between the offset voltage and drain bias, the overall efficiency of the RF power amplifier can be improved dramatically in high peak-to-average power ratio (PAPR) systems. The measured results show that the drain bias of the RF power amplifier is boosted up to approximately 1.8 times the offset voltage when the RF peaks generate. The overall efficiency of the proposed bias-switching amplifier is improved by 62% compared to that of the fixed bias amplifier in high PAPR systems 相似文献
93.
Nam I. Kyudon Choi Joonhee Lee Hyouk-Kyu Cha Bo-Ik Seo Kwon K. Kwyro Lee 《Microwave Theory and Techniques》2007,55(4):682-689
In this paper, a low-power low-IF receiver and a direct-conversion transmitter (DCT) suitable for the IEEE standard 802.15.4 radio system at the 2.4-GHz band are presented in 0.18-mum deep n-well CMOS technology. By using vertical NPN (V-NPN) bipolar junction transistors in the baseband analog circuits of the low-IF receiver, the image rejection performance is improved and the power consumption is reduced. In addition, by applying the V-NPN current mirrored technique in a DCT, the carrier leakage is reduced and the linearity performance is improved. The receiver has 10 dB of noise figure, -15 dBm of third-order input intercept point, and 35 dBc of image rejection. The transmitter has more than -2 dBm of transmit output power, -35 dBc of local oscillator leakage, and -46 dBc of the transmit third harmonic component. The receiver and transmitter dissipate 6 and 9 mA from a 1.8-V supply, respectively 相似文献
94.
Junho Cha Yasuo Kuga Akira Ishimaru Sangil Lee 《Antennas and Propagation, IEEE Transactions on》2007,55(2):290-297
A simple steerable array antenna is designed and developed using a movable dielectric phase shifter. The change of effective dielectric constant at different dielectric slab positions on a coplanar waveguide is used as the phase shifter. The impedance matching and desired phase shift conditions are satisfied at two slab heights, and the reflection is designed to be minimized at these slab positions. The low-loss dielectric material is used as the dielectric slab and is placed close to a coplanar transmission line with airgap. The 4times4 steerable array antenna with the phase shifters is designed and fabricated at 20 GHz. The H-plane radiation patterns are measured at different phase shift positions and compared with the expected results 相似文献
95.
The system of (1 − y)(Mg0.6Zn0.4)1−xCoxTiO3-yCaTiO3 was investigated to optimize its microwave dielectric properties by adopting appropriate contents of Co and Ca and by controlling sintering conditions. The effect of Co substitution was to enhance densification and Qf value, while the addition of CaTiO3 resulted in increases of dielectric constant and TCF. As an optimal compositions, 0.93(Mg0.6Zn0.4)0.95Co0.05TiO3-0.07CaTiO3 successfully demonstrated a dielectric constant of 23.04, a Qf of 79,460 GHz and a TCF value of +1.4 ppm/°C after firing at a relatively lower sintering temperature of 1200 °C. The increase of sintering temperature beyond 1200 °C tended to degrade overall microwave dielectric properties presumably due to Zn volatilization as evidenced by the presence of a Zn-deficient phase (MgTi2O5) at 1400 °C. An attempt to establish the correlation between microstructure characteristics and dielectric properties was made in this dielectric system where the extensive range of firing temperature up to 1400 °C was evaluated. 相似文献
96.
Dong-Hoon Kim Jun-Yeob Song Seung-Ho Lee Suk-Keun Cha 《International Journal of Precision Engineering and Manufacturing》2009,10(5):53-57
This study aims at securing technology to develop a multisensor and complex position-tracking Zigbee node module for USN (ubiquitous
sensor network). In a concrete way, it aims at developing military (invader detection module and system) and industrial (transformer-tracking
and thermo-measurement module and system) Zigbee telecommunication node module, and developing wireless monitoring and tracking
technology based on such modules. In addition, it aims at building up the foundation of interface test for various sensors
(thermo sensors, pressure sensors, vibration sensors and vision sensors) and the foundation of a comprehensive interlocking
device to which GIS (Geographic Information System) and GPS (Global Positioning System) were applied, for industrial devices
are mostly installed in mountains. Moreover, it aims at developing a roaming-type variable Zigbee node module to the end that
it stands against unfavorable conditions (extreme temperatures, dust, winds, electromagnetism, noise, etc.). In case such
aims are achieved, Zigbee communications will not be limited to normal and stable conditions (home networks, building automation,
etc.) but will be applied to the industrial field under noises and unfavorable conditions. In such a case, the application
of Zigbee node modules is expected to be unlimited. 相似文献
97.
G S Cha D Liu M E Meyerhoff H C Cantor A R Midgley H D Goldberg R B Brown 《Analytical chemistry》1991,63(17):1666-1672
Ammonium and potassium ion-selective membranes formulated with PVC/hydroxylated PVC, polyurethane/hydroxylated PVC, and moisture-curable silicone rubber matrices are studied in an effort to extend the lifetime of solid-state ion sensors through improved membrane adhesion. The PVC/membranes exhibit electrochemical performance equivalent to that of conventional PVC membranes in terms of slope, detection limit, and selectivity. The polyurethane- and silicone-rubber-based membranes have better adhesion to silicon nitride than do PVC or hydroxylated PVC matrices. Incorporating a silanizing reagent (silicon tetrachloride) significantly improves the adhesion of the polyurethane matrix. The use of silicon tetrachloride in membrane matrices also enhances the electrochemical stability of the interfacial potential between ion-selective polymer-matrix membranes and silver epoxy inner reference electrodes of solid-state sensors. The biocompatibility of the polymer matrices is examined via radiotracer protein adsorption studies and whole blood clotting time measurements. The polyurethane- and silicone-rubber-based membranes exhibit less overall nonspecific protein adsorption than the PVC or hydroxylated PVC matrices. 相似文献
98.
Electrolyte design for Li ion batteries was approached by means of comparison of faradaic and non-faradaic currents. The faradaic
current by the movement of Li+ ions was dependent on the composition of the electrolyte and was related to the battery capacity; the higher the capacity,
the greater the current by the faradaic reaction. The open circuit potential of the electrode with a greater faradaic current
decreased at a slower rate than that of the electrode with a smaller faradaic current. This analysis method can be used to
prepare an optimal electrolyte of an actual Li ion battery, especially when developing batteries with excellent high-rate
discharge capabilities and low temperature discharge properties. 相似文献
99.
SW Kim SS Cha HS Cho JS Kim NC Ha MJ Cho S Joo KK Kim KY Choi BH Oh 《Canadian Metallurgical Quarterly》1997,36(46):14030-14036
Bacterial Delta5-3-ketosteroid isomerase (KSI) catalyzes a stereospecific isomerization of steroid substrates at an extremely fast rate, overcoming a large disparity of pKa values between a catalytic residue and its target. The crystal structures of KSI from Pseudomonas putida and of the enzyme in complex with equilenin, an analogue of the reaction intermediate, have been determined at 1.9 and 2.5 A resolution, respectively. The structures reveal that the side chains of Tyr14 and Asp99 (a newly identified catalytic residue) form hydrogen bonds directly with the oxyanion of the bound inhibitor in a completely apolar milieu of the active site. No water molecule is found at the active site, and the access of bulk solvent is blocked by a layer of apolar residues. Asp99 is surrounded by six apolar residues, and consequently, its pKa appears to be elevated as high as 9.5 to be consistent with early studies. No interaction was found between the bound inhibitor and the residue 101 (phenylalanine in Pseudomonas testosteroni and methionine in P. putida KSI) which was suggested to contribute significantly to the rate enhancement based on mutational analysis. This observation excludes the residue 101 as a potential catalytic residue and requires that the rate enhancement should be explained solely by Tyr14 and Asp99. Kinetic analyses of Y14F and D99L mutant enzymes demonstrate that Tyr14 contributes much more significantly to the rate enhancement than Asp99. Previous studies and the structural analysis strongly suggest that the low-barrier hydrogen bond of Tyr14 (>7.1 kcal/mol), along with a moderate strength hydrogen bond of Asp99 ( approximately 4 kcal/mol), accounts for the required energy of 11 kcal/mol for the transition-state stabilization. 相似文献
100.
Cher Liang Cha Eng Fong Chor Hao Gong An Qing Zhang Lap Chan 《Semiconductor Manufacturing, IEEE Transactions on》2000,13(3):386-389
The breakdown time of flash memory oxide/nitride/oxide (ONO) layer tbd under positive constant current stressing has been found to be closely related to the cumulative extent of (over)etch of the tungsten silicide, control polysilicon, and ONO layers, i.e., Σ(ΛOE). An empirical first-order relation between tbd and Σ(ΛOE) has been derived to facilitate the plasma etch recipe optimization. This has led to a four-fold increase in the average tbd across a 200-mm wafer to 208 s. More importantly, the spread in tbd has been tightened to ~5%, which is down from ~54% 相似文献