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61.
Concurrency control is the activity of synchronizing operations issued by concurrent executing transactions on a shared database. The aim of this control is to provide an execution that has the same effect as a serial (non-interleaved) one. The optimistic concurrency control technique allows the transactions to execute without synchronization, relying on commit-time validation to ensure serializability. Effectiveness of the optimistic techniques depends on the conflict rate of transactions. Since different systems have various patterns of conflict and the patterns may also change over time, so applying the optimistic scheme to the entire system results in degradation of performance. In this paper, a novel algorithm is proposed that dynamically selects the optimistic or pessimistic approach based on the value of conflict rate. The proposed algorithm uses an adaptive resonance theory–based neural network in making decision for granting a lock or detection of the winner transaction. In addition, the parameters of this neural network are optimized by a modified gravitational search algorithm. On the other hand, in the real operational environments we know the writeset (WS) and readset (RS) only for a fraction of transactions set before execution. So, the proposed algorithm is designed based on optional knowledge about WS and RS of transactions. Experimental results show that the proposed hybrid concurrency control algorithm results in more than 35 % reduction in the number of aborts in high-transaction rates as compared to strict two-phase locking algorithm that is used in many commercial database systems. This improvement is 13 % as compared to pure-pessimistic approach and is more than 31 % as compared to pure-optimistic approach. 相似文献
62.
Low delay-code excited linear prediction (LD-CELP) is an attractive algorithm in implementing vocoders in voice over Internet protocol networks. This algorithm has been proposed for the coding of speech at 16 kbps with toll quality. However, operation at transmission rates lower than 16 kbps is desirable, so that traffic can be accommodated during system overload conditions. In this paper, an array of self-organizing maps (SOMs) is employed instead of traditional codebook search module, recommended in ITU-T G.728, to determine the optimum index value of shape codebook. It is noted that a modified supervised training algorithm is used for SOMs in which some of the training parameters are optimized using particle swarm optimization (PSO) algorithm. Based on the occurrence frequency characteristics of codevectors, six bits for shape codebook and two bits for gain codebook are used in this work to produce a vocoder with lower bit rate as compared with traditional ITU-T G.728 vocoder. The performance comparison of the proposed SOM array trained by PSO-optimized supervised algorithm as the codebook search module in the structure of LD-CELP with a conventional implementation of LD-CELP coder shows that execution time of the algorithm is reduced up to 44 %. However, the degradation of voice quality in terms of mean opinion score, perceived evaluation of speech quality and segmental signal-to-noise ratio (SNRseg) is acceptable. 相似文献
63.
Dr. M. F. Ramadan M. M. A. Amer Dr. H. T. Mansour Dr. K. M. Wahdan Dr. R. M. El-Sayed Dr. S. El-Sanhoty Dr. W. A. El-Gleel 《Journal für Verbraucherschutz und Lebensmittelsicherheit》2009,4(3-4):239-245
Fatty acids, sterols and tocopherols profile of Pulicaria incise, Diplotaxis harra and Avicennia marina grown wild in Egypt were investigated. Linoleic acid followed by palmitic and oleic acids were the major fatty acids in P. incise. Oleic followed by stearic were the main acids in D. harra, while palmitic followed by oleic were the major fatty acids found in A. marina. Sterol markers of P. incise were campesterol followed by stigmasterol and β-sitosterol. In D. harra β-sitosterol followed by stigmasterol and ?5-avensterol were the major sterols, while campesterol followed by β-sitosterol and ?7-avensterol were main sterols of A. marina. Tocopherols were also estimated in high levels, wherein δ-tocopherol was the main tocopherol in all plants. Antioxidant properties of methanolic extracts of the plants were compared with methanolic solution of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and ascorbic acid during thiocyanate assay. Moreover, methanolic extracts of the whole plants exhibited strong antiradical potential against DPPH radicals. Information provided by the present study is of importance for further investigations of P. incise, D. harra and A. marina and utilization of these plants as a raw material of bioactive compounds. 相似文献
64.
A. Mansour H. M. Ismail Mohamed Fawzy Ramadan G. Gyulai 《Journal für Verbraucherschutz und Lebensmittelsicherheit》2009,226(4):118-127
Tomato (Lycopersicon esculentum Mill) is considered as important and economic agricultural crop all over the world. For improving the yield and yield attributes,
varieties are often produced and evaluated under different growth condition. In the study presented morphological (growth
and yield parameters), biochemical (oil, moisture content and radical scavenging activity) and molecular diversity (RAPD and
ISSR) of eleven freshmarket tomato (L. esculentum) cultivars (Aledo VF, Carmeuco 201M, Castle-rock, Falkon, Money Maker, Peto 86, Red Star, Super Marmande, Super Queen, Super
Strain B, and UC97–3) were analyzed under heat stress in Egypt to assist breeders in selecting heat tolerant cultivars and
nutritional quality. Cultivars Aledo, Peto86 and Red Star were found to have the most vigorous growth habit, while cv. Super
Queen has the most significant average fruit weight, yield/plant and total yield/m2 under heat stress. For nutritional quality cv. Super marmande and cv. Aledo showed the highest oil content while cv. Aledo
and cv. Money Maker showed the highest radical scavenging activities (RSA). Molecular polymorphism among cultivars was detected
using two molecular markers systems, RAPD (random amplified polymorphic DNA) and ISSR (inter-simple sequence repeat), providing
further facilities for molecular comparison. 相似文献
65.
The aim of this article is to introduce a new technology for the production of Dead Sea potassium chloride. The new technology depends on using the power of ultrasound waves during a crystallization process to enhance potassium chloride precipitation and to improve the end-use properties of the produced crystals. This environmentally clean technology, which is called sonocrystallization, has received very intensive research in the past few years. It was used in this study to modify the crystallization process of potassium chloride from the decomposition of Dead Sea carnallite. Two crystallization runs were done; the first was performed without the application of ultrasound waves and the second was performed with this application. The effect of sonication on the crystallization process time and on crystal size distribution as well as on the purity of the crystals was studied. It was found that the required time for the un-sonicated process was about 150 min. This time was reduced to about 50 min when sonication was applied. The produced crystals were sieved, and the crystal size distribution (CSD) was determined for the two runs. For the sonicated process, finer but more uniform crystals were obtained with a mean average size of 0.2643 mm in comparison with 0.5727 mm for the un-sonicated process. The produced crystals were found to be of 96.07% KCl for the un-sonicated process and this purity was improved to 97.31% KCl by the application of ultrasound waves. Based on the results of this study, it seems to be feasible and economical to scale up the proposed technology for industrial applications. 相似文献
66.
Operators and users of robotic systems perform tasks which require close proximity to dangerous moving parts. Two experiments were performed to assess human perception of safe robot arm speed and idling times. Experiment 1 was designed to determine the maximum safe speed of robots. Subjects were asked to adjust the robot speeds. Perceived safe speeds were indicated for two different types of robots. Experiment 2 was designed to determine safe programmed idle time of robots. Subjects were asked to enter the robot work envelope when a programmed idle was perceived to be caused by a malfunction. Safe idle times were reported for two different robot speeds during operational cycles. 相似文献
67.
This paper deals with the problem of how motion control can be achieved in very simple systems under a minimal number of preconditions.
The system's design is therefore as minimal as possible, reflecting the basal reflex arc as observed in biological systems.
The model for the movement of the agent is a multiplicatively modified random walk, and thus does not represent a diffusion
process of the Langevin type. The mobile agent shows a fast, reliable homing behavior toward a defined area, and finally stays
in some defined neighborhood of this area. Moreover, obstacle avoidance is shown to be an immediate result of the system's
properties. 相似文献
68.
MA Mansour FN Littooy WC Watson KA Blumofe TJ Heilizer GF Steffen C Chmura SS Kang N Labropoulos HP Greisler SG Fisher WH Baker 《Canadian Metallurgical Quarterly》1999,29(2):217-25; discussion 225-7
PURPOSE: The incidence rate of disease progression and stroke after the diagnosis of a moderate (50% to 79%) carotid stenosis was determined by means of color-flow duplex scanning. METHODS: During a 4-year period, 344 male veterans with moderate internal carotid artery stenoses, on one or both sides, were examined at regular intervals for a mean period of 25 months. Carotid color-flow scans were obtained semiannually. Clinical follow-up was performed to determine the incidence rate of amaurosis fugax, transient ischemic attacks, nonhemispheric symptoms, and strokes. RESULTS: New neurologic symptoms developed in 75 patients (21.8%). Fifty-one (14.8%) had ipsilateral symptoms during follow-up: 18 amaurosis fugax (5.2%), 14 transient ischemic attacks (4%), 5 nonhemispheric symptoms (1.4%), and 14 strokes (4%). Twenty-four patients (6.9%) had contralateral symptoms: 20 strokes (5.8%) and 4 transient ischemic attacks (1.2%). Life-table analysis showed that the annual rate of ipsilateral neurologic events was 8.1%, and the annual rate of stroke was 2.1%. Seventy-five patients (22%) died in the follow-up period. Disease progression to 80% to 99% stenosis or occlusion occurred in 71 of 458 vessels (15.5%). The internal carotid arteries that showed evidence of disease progression had a significantly higher initial peak systolic velocity (251 vs 190 cm/s; P <.0001) and end diastolic velocity (74 vs 52 cm/s; P < 0.0001). Black patients and patients with ischemic heart disease were at a higher risk for disease progression. We could not identify any atherosclerotic risk factors that reliably predicted patients in whom future ipsilateral neurologic symptoms were more likely to develop. However, there was an increased risk of stroke associated with progression of disease. CONCLUSION: Patients who are asymptomatic and who have moderate carotid stenoses are at significant risk for neurologic symptoms and death, but have a relatively low incidence rate of ipsilateral events. The initial flow characteristics in the stenotic vessel are predictive of future disease progression, but they are not helpful in identifying patients in whom symptoms will develop. 相似文献
69.
Hamid Ansari Ardeh Masoud Shariatpanahi Mansour Nikkhah Bahrami 《Structural and Multidisciplinary Optimization》2008,37(2):203-214
This paper presents a new approach to the shape optimization of road speed humps. The proposed approach is based on multiobjective
genetic optimization of the hump profile while taking into account the separation phenomenon, which occurs when the front
tires of the vehicle momentarily lose contact with the road surface. The optimization is carried out for speeds up to twice
the authorized speed (throughout this article, the term authorized speed refers to speed limits enforced in speed reduction [bump] areas of the roads) rather than for illegally high speeds as adopted
by many of the previous works. A 6-degree of freedom non-linear dynamic model is used to identify the speeds at which separation
occurs, and hump profiles associated with these speeds are discarded as infeasible solutions. Three independent objective
functions are selected for optimization. They include the maximum vertical acceleration experienced by the driver when crossing
the hump below the authorized speed limit (to be minimized), the same vertical acceleration at speeds above the authorized
speed (to be maximized), and the ascending ratio of the “speed—vertical acceleration” curve (to be maximized). These objective
functions are evaluated for more than 10,000 humps of two popular profile types (sinusoidal and flat top with straight ramps)
and optimum profiles for three speed limits of 20, 25, and 30km/h are determined using the multiobjective nondominated sorting
genetic algorithm II. As a result, a Pareto front of at least ten optimal points is achieved for each of the two hump profile
types. Furthermore, to incorporate the economical aspects of the real-world problem, Pareto optimal points for the two profile
types were compared based on their lateral section areas (an indication of the manufacturing cost). The comparison shows that
sinusoidal humps more often than not outdo their flat top rivals economically. 相似文献
70.
Saeedkia D. Majedi A.H. Safavi-Naeini S. Mansour R.R. 《Microwave and Wireless Components Letters, IEEE》2005,15(8):510-512
The extended scattering parameters for linear time varying devices are used to model a high-temperature superconducting (HTS) bridge under time-harmonic optical irradiation. It is shown that this structure acts as a time-varying low-pass filter, which its transfer function characteristic changes periodically with time. This behavior makes this configuration ideal for applications where a time-varying filter is on demand. 相似文献