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91.
Raghavan A. Venkataraman S. Banerjee B. Youngsuk Suh Deukhyoun Heo Laskar J. 《Solid-State Circuits, IEEE Journal of》2003,38(9):1443-1450
A new empirical InGaP/GaAs heterojunction bipolar transistor (HBT) large-signal model including self-heating effects is presented. The model accounts for the inherent temperature dependence of the device characteristics due to ambient-temperature variation as well as self-heating. The model is accompanied by a simple extraction process, which requires only dc current-voltage (I-V) and multibias-point small-signal S-parameter measurements. All the current-source model parameters, including the self-heating parameters, are directly extracted from measured forward I-V data at different ambient temperatures. The distributed base-collector capacitance and base resistance are extracted from measured S-parameters using a new technique. The extraction procedure is fast, accurate, and inherently minimizes the average squared-error between measured and modeled data, thereby eliminating the need for further optimization following parameter extraction. This modeling methodology is successfully applied to predict the dc, small-signal S-parameter, and output fundamental and harmonic power characteristics of an InGaP/GaAs HBT, over a wide range of temperatures. 相似文献
92.
PURPOSE: To use fluorophotometry to measure corneal epithelial barrier function after excimer laser photorefractive keratectomy (PRK). SETTING: Seoul National University Hospital, Seoul, Korea. METHODS: Twenty-five eyes of 21 patients (13 women, 8 men) had PRK to correct myopia. Corneal epithelial healing time was measured and corneal epithelial permeability to sodium fluorescein evaluated by fluorophotometry 1, 2, and 3 weeks after surgery. RESULTS: Epithelial permeability showed a statistically significant increase 1 week after surgery and returned to its preoperative level 1 week later. Comparative studies according to epithelial healing day and corrected diopter showed results that were not statistically significant (P > .05). CONCLUSION: These results suggest that PRK delays complete reconstruction of corneal epithelial barrier function. In humans, the corneal epithelium regained its normal barrier function 2 weeks after PRK. Thus, at least during these weeks, care should be taken to minimize further epithelial trauma. 相似文献
93.
AIMS: To investigate the relationship in patients with heart failure between BP response to the first dose of ACE inhibitor and (1) plasma drug concentration and (2) baseline clinical and laboratory variables. METHODS: We studied individual placebo-corrected BP responses to initiation of treatment with one of a number ACE inhibitor preparations in 132 patients with mild to moderate CHF. Various pharmacokinetic/pharmacodynamic models were compared. We assessed the strength of association between baseline physiological and laboratory variables and the BP response as assessed directly from the AUC(0,10 h) and indirectly from the slope of the PK/PD relationship. Predictive models for response variables were developing using regression analysis. RESULTS: BP response was primarily related to plasma drug concentration. The association between the fall in BP and baseline variables was weak. The strongest single predictor of BP response was baseline mean arterial pressure (r2 = 5.8%, P = 0.02). The best combinations of predictor variables contained mean arterial pressure, plasma renin activity, creatinine concentration and age (r2 = 14.4%, P = 0.37). When the choice of ACE inhibitor was added, the predictive power of the model increased (r = 23.6%, P < 0.01) but left the majority of the variability in response unexplained. CONCLUSIONS: The first-dose blood pressure response to ACE inhibition cannot be accurately predicted from baseline pathophysiological variables in patients with mild to moderate CHF. The choice of ACE inhibitor accounts for a small proportion of the variability in response but wide inter-individual variability exists in the response to each treatment. 相似文献
94.
This paper considers a TMN‐based management system for the management of public ATM switching networks using a four‐level hierarchical structure consisting of one network management system, several element management systems, and several agent‐ATM switch pairs. Using Jackson's queuing model, we analyze the effects of one TMN command on the performance of the component ATM switch in processing local calls. The TMN command considered is the permanent virtual call connection. We analyze four performance measures of ATM switches—utilization, mean queue length and mean waiting time for the processor directly interfacing with the subscriber lines and trunks, and the call setup delay of the ATM switch—and compare the results with those from Jackson's queuing model. 相似文献
95.
N. H. Heo 《Metallurgical and Materials Transactions A》1996,27(10):3059-3065
Nonequilibrium segregation kinetics of alloying elements and a ductile-brittle-ductile transition behavior have been investigated
in an Fe-8.4Mn-7.4Ni-l.7Ti alloy. The alloy experienced a ductilebrittle-ductile (DBD) transition during isothermal aging.
In the brittle region, the alloy showed a decrease in intergranular fracture strength and a subsequent increase with aging
time. This is due to the segregation of titanium to the grain boundaries and its desegregation into the matrix. The intergranular
fracture strength was higher on the zero tensile elongation finish curve than on the start curve. This is because the grain-boundary
segregation level of titanium is relatively lower on the finish curve. The lowest intergranular fracture strength increased
with increasing aging temperature, which was attributed to a lower grain-boundary segregation level of titanium at higher
temperature. Manganese caused an overall reduction in intergranular fracture strength and, as a result, the delayed occurrence
of the zero tensile elongation (ZTE) finish curve in a temperature and log-time plot.
formerly Graduate Student, Department of Metallurgical Engineering, Seoul National University, Seoul, 151-742 Korea 相似文献
96.
A mechanical approach to the nuclear fuel fretting problem is studied in this paper to find a possible and efficient way of a wear restraint. Two different contours of the spacer grid spring and dimple were developed to increase the contact area. Fretting wear experiments were carried out for the developed springs and tube specimens. Contact forces of 10 and 30 N, and slip displacements of 50–100 μm were applied under the environment of air as well as water at room temperature. Wear scars on the rods were examined to observe the effect of the mechanical approach on the wear. Especially, the influence of a contour deviation which occurred during fabrication and the wear particle accumulation in the clearance region were investigated in detail. It was found that the contact shape influenced the feature and the behavior of the length, width and volumetric shape of the wear. For the model of fuel fretting wear, equivalent depth (De) is suggested as a new parameter that can represent the wear severity. 相似文献
97.
Yongtaek Hwang Kyuyoung Heo Chang Hwan Chang Man Kil Joo Moonhor Ree 《Thin solid films》2006,510(1-2):159-163
High dielectric constant (high-k) gate dielectric alumina films were prepared with nanoscale thicknesses on p-type silicon substrates by atomic layer deposition (ALD) with alternating pulses of trimethyl aluminum, nitrogen, ozone and nitrogen, and some of them were further thermally annealed. These high-k gate dielectric films were characterized by synchrotron X-ray reflectivity (XR), and the XR data were quantitatively analyzed, providing the following structural parameters of each gate dielectric film: the surface roughness and interfacial roughness, the electron density profile, the number of layers, and the thickness of individual layers. These structural characteristics were then analyzed in detail by considering the ALD processing conditions and post-thermal annealing history. 相似文献
98.
Dae-Oh Kang Kihong Park Seung-Jin Heo Young-Il Ryu Jay Il Jeong 《International Journal of Precision Engineering and Manufacturing》2010,11(2):265-272
A Virtual Proving Ground (VPG) is a vehicle simulation environment used for evaluating durability of the suspension elements.
Among the components that comprise the VPG system, the tire model with its complex nonlinear characteristics has most significant
impact on the credibility of the estimated durability. This research proposes a method for generating an equivalent road profile
as a way to compensate for the limits involved in modeling details of the tire characteristics. The method first identifies
the frequency response function from the road heights to the spindle forces, which would contain rich information on the tire’s
effect on the vehicle dynamics. Then it back-calculates a road profile using this model and the spindle force measurement.
Finally the solution is updated iteratively until it yields the spindle forces close to their measured values. Using the proposed
method, an equivalent road profile was successfully generated from a spindle force measurement collected from a physical durability
test. In order to investigate validity of the proposed method, durability analysis was performed for a suspension component
— a lower control arm. From the preliminary VPG simulation results, it was confirmed that the estimated fatigue life agreed
well with the estimation based upon the force measurement. 相似文献
99.
Jun Ho Kim Wan Sik Jung Gui Seck Bae Ho Jin Heo Dae-Ok Kim Jin A. Yoon Sangho Kim Young Jun Kim 《Food science and biotechnology》2010,19(1):267-270
This study was designed to evaluate the effect of the oral administration of fruit extracts (lemon and Japanese apricot) combined
with red-ginseng on the endurance and availability of metabolic substrates in ICR mice. Administration of the fruit extracts
and red-ginseng (RG) (1:1) significantly increased swimming capacity, by 40%, with increased expenditures of non-esterified
fatty acids and triglycerides in the plasma of the mice after 1 week of feeding. There was no significant increase in swimming
capacity with the fruit extract alone. These results suggest that the fruit extract could synergistically elevate the effects
of red-ginseng on swimming capacity in the mice by increasing fat utilization and reducing the consumption of stored glucose. 相似文献
100.
Chao Liu Jong Heo Woon Jin Chung Xiujian Zhao 《International Journal of Applied Glass Science》2013,4(1):5-8
A method is reported that uses visible continuous-wave laser to directly fabricate micropatterns in glasses containing silver (Ag) nanoparticles. Ag nanoparticles were formed in the glass using thermal treatment. Upon laser irradiation, Ag nanoparticles with their surface plasmon in resonance with the laser beam were partially melted and decreased in size due to the temperature increase induced by the excited Ag nanoparticles. Three-dimensional patterns were achieved by scanning the laser beam through the thickness of the glass. 相似文献