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排序方式: 共有743条查询结果,搜索用时 31 毫秒
661.
A procedure is proposed to calculate both pre-exponential reverse currents of the double-exponential model of a diode's current-voltage experimental characteristics from previously extracted reverse current and diode quality factor of the diode's single-exponential model. The procedure is illustrated by modelling the drain-body junction of a MOSFET including its parasitic series resistance 相似文献
662.
The objective of this paper is to describe a simple device for detecting the time of an impact and to demonstrate its efficiency in measuring the depth of surface-opening cracks in concrete. Surface-opening cracks in concrete are relatively deep so that a mechanical impact instead of an ultrasonic transmitter is used to generate stress waves with enough energy for successful evaluation. A technique called the time-of-flight diffraction technique with impact-generated stress waves is an efficient method for detection of surface-opening cracks in concrete. Because the initial time of the impact is unavailable in a mechanical impact device, two receivers are employed in the test. One of the receivers is used to determine the time of the impact indirectly. The present study developed a simple device to record the time of impact initiation. The device comprises a conductive impact device, a sensing film, and an auxiliary circuit. With the device, stress waves are generated and the time of impact is detected so that the evaluation work needs only a single receiver. Laboratory studies were carried out on concrete specimens containing cracks with depths of 0.158 and 0.90 m. Field studies were performed on a dam damaged by an earthquake. Experimental results show that the new device can be used to accurately determine the crack depth in concrete. Using the device, the cost and effort for evaluation and signal analysis are reduced, which largely enhances the evaluation efficiency. 相似文献
663.
664.
MJ Liou HS Huang JD Lin BY Huang C Hsueh LB Jeng KY Tzen 《Canadian Metallurgical Quarterly》1996,19(2):121-128
Pulsed xenon chloride excimer and holmium laser-tissue interaction is primarily based on tissue water vaporization. Consequently, each ablative laser pulse produces a rapidly expanding and imploding vapour bubble in blood or the target tissue. In experimental studies, explosive water vaporization is the major mechanical cause of observed tissue dissections. By reduction of the induced bubble volume, a reduction in experimentally and clinically observed dissections after coronary excimer laser angioplasty is to be expected. This reduction of mechanical damage, however, in combination with efficient and substantial plaque debulking is the major challenge in the development of laser angioplasty. 相似文献
665.
Metal lines on semiconductor devices and circuits sometimes show slow-wave phenomena. To determine signal transmission characteristics along the lines, the typical assumption that metal is perfectly conducting is not always valid. A simple and accurate means is used here to include metallic loss in spectral domain analysis of planar transmission lines built on multilayer semiconducting media. Experimental results with a modulation-doped field-effect transistor (MODFET) structure and comparison with the calculations are presented 相似文献
666.
Flexible multi‐colored electrochromic and volatile memory devices are fabricated from a solution‐processable electroactive aromatic polyimide with starburst triarylamine unit. The polyimide prepared by the chemical imidization was highly soluble in many organic solvents and showed useful levels of thermal stability associated with high glass‐transition temperatures. The polyimide with strong electron‐donating capability possesses static random access memory behavior and longer retention time than other 6FDA‐based polyimides. The differences of the highest‐occupied and lowest unoccupied molecular orbital levels among these polyimides with different electron‐donating moieties are investigated and the effect on the memory behavior is demonstrated. The polymer film shows reversible electrochemical oxidation and electrochromism with high contrast ratio both in the visible range and near‐infrared region, which also exhibits high coloration efficiency, low switching time, and the outstanding stability for long‐term electrochromic operation. The highly stable electrochromism and interesting volatile memory performance are promising properties for the practical flexible electronics applications in the future. 相似文献
667.
In the current rapid prototyping processes, a physical part of a computer model can be quickly produced for functional and dimensional verification. Most of the existing systems can only produce non-metal parts, and thus limit rapid prototyping applications. The laser-based metal forming process is a technique that has the potential to produce fully functional models directly from a CAD system and eliminate the need for an intermediate step. This paper presents a review of the state of the art laser metal forming (LMF) processes. LMF process hardware, software, and process parameters are discussed, including laser parameters, beam delivery systems, work table variables, metal deposition techniques, measurement, and control. Process limitations, materials, and costs are summarized. 相似文献
668.
Abstract Functional analytic methods have been applied to the analysis of the extended Graetz problem with prescribed wall flux and viscous dissipation between parallel plates. First, the non‐self‐adjoint elliptic energy equation is decomposed into a set of first order partial differential equations to obtain a self‐adjoint formulism. Next, the induced eigenvalue problems are solved by applying an approximation method in a Hilbert space, and an algebraic characteristic equation is obtained. In addition, the expansion coefficients of the solutions on upstream and downstream regions can be explicitly obtained and unnecessary to match at the entrance. 相似文献
669.
Liou K.-Y. Ohtsu M. Burrus C.A. Jr. Koren V. Koch T.L. 《Lightwave Technology, Journal of》1989,7(4):632-639
Measurements are presented along with a theoretical analysis of power partition fluctuations in a distributed feedback (DFB) laser operating in continuous wave with the two DFB degenerate modes as the only significant longitudinal modes. The power ratio of the two modes was varied from 1.1 to 2500:1 by electrical control using a two-electrode DFB laser. The laser was observed to exhibit (1) transient power dropouts and (2) two-mode relaxation oscillation. The dropout depths were less than 30% of the main-mode power in all cases, except when the laser was subjected to external optical feedback. The relaxation oscillations of the two-mode power are anticorrelated, which is different from the relaxation oscillation of the total power due to photon-carrier interaction. The calculated result based on a Fokker-Planck analysis agrees with the experiment, except for the two-mode relaxation oscillation, which was not considered in the theory 相似文献
670.
Lin CC Wang YC Chen JY Liou YJ Bai YM Lai IC Chen TT Chiu HW Li YC 《Computer methods and programs in biomedicine》2008,91(2):91-99
Although one third to one half of refractory schizophrenic patients responds to clozapine, however, there are few evidences currently that could predict clozapine response before the use of the medication. The present study aimed to train and validate artificial neural networks (ANN), using clinical and pharmacogenetic data, to predict clozapine response in schizophrenic patients. Five pharmacogenetic variables and five clinical variables were collated from 93 schizophrenic patients taking clozapine, including 26 responders. ANN analysis was carried out by training the network with data from 75% of cases and subsequently testing with data from 25% of unseen cases to determine the optimal ANN architecture. Then the leave-one-out method was used to examine the generalization of the models. The optimal ANN architecture was found to be a standard feed-forward, fully-connected, back-propagation multilayer perceptron. The overall accuracy rate of ANN was 83.3%, which is higher than that of logistic regression (LR) (70.8%). By using the area under the receiver operating characteristics curve as a measure of performance, the ANN outperformed the LR (0.821+/-0.054 versus 0.579+/-0.068; p<0.001). The ANN with only genetic variables outperformed the ANN with only clinical variables (0.805+/-0.056 versus 0.647+/-0.066; p=0.046). The gene polymorphisms should play an important role in the prediction. Further validation of ANN analysis is likely to provide decision support for predicting individual response. 相似文献