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51.
A new method for calculating the confinement loss of leaky modes in arbitrary microstructured optical fibers is presented. The full vector algorithm is based on a polar coordinate Fourier decomposition method with adjustable boundary conditions, capable of accurately determining the outward radiating fields of the waveguide. Example waveguides with circular and elliptical hole shapes and their leaky mode solutions are presented and discussed. 相似文献
52.
The influence of three different catalysts [triethylendiamine (TD), stannous octoate (SO), and dibutylindilaurate (DBTDL)] and their blends (TD + SO and TD + DBTDL) on the kinetics of a RIM formulation, based on a high functionality polyether–polyol and a polymeric MDI, has been studied using the adiabatic temperature rise method and Fourier transform infrared spectroscopy. The synergism observed in the DBTDL/TD systems is explained by means of complex formation between the amine-based and metal-based catalysts. Infrared spectroscopy data support this complex formation. The SO/TD systems do not exhibit synergetic behaviour, being the reaction rate controlled by the metal catalyst which complexes the isocyanate group. 相似文献
53.
This paper presents an investigation on the effects of construction loads and vibrations on typical newly poured reinforced concrete bridge decks. The main objective of this paper was to perform dynamic finite-element analyses of concrete bridge decks under construction loads and vibrations. Two types of bridges were modeled by effectively simulating the loads encountered during construction. Separate analyses were performed to simulate one truck as well as two side-by-side trucks. Additional analyses were performed to simulate the loads during construction and pouring sequence. The loads imposed by concrete mixer trucks, including the full concrete load and the load imposed by a trailer unit carrying the pump, were taken into consideration during the modeling of the bridges. The results obtained consisted of vibration modes and frequencies for each structure in addition to top and bottom stresses in each principal direction. A separate analysis was performed that took into account the sequence of pour to determine the effect of moving loads from adjacent traffic and construction loads on fresh concrete. The time history and dynamic analysis indicated that the sequence of pour has a significant effect on the deformation of the concrete at early ages. As a result, the first three mode shapes obtained by the finite-element analysis will be used to optimize sensor locations for future dynamic field testing. 相似文献
54.
This paper presents the establishment of a Bridge Rating Expert System (BRES) by using a knowledge-based computer artificial intelligent expert system for analysis and rating of existing short span prestressed concrete highway bridges. The rating methods considered were: Inventory Rating, Operation Rating, Rating Factor Rating and Sufficiency Rating. A strength rating is based on the evaluation of existing prestressed concrete bridges in accordance with the American Association of State Highway Transportation Officials (AASHTO) specifications, and inventory rating for all bridges according to the Federal Highway Administration (FHWA) guide for the Structure Inventory and Appraisal of the Nation's Bridges. The parameters considered were bridge type, dead loads, type of vehicle loading, bridge dimensions and cross-section, material properties, reinforcement details, and existing physical condition of the bridge. The results show that, through its runtime rule controller, user interface and linkage mechanisms, the BRES is a friendly user system for rating highway bridges. In addition, the EXSYSP shell provides an effective tool for other possible applications in civil engineering practice. 相似文献
55.
Francisco Lpez María P. Calcagno Jesús M. Contreras Zulay Torrellas Katania Felisola Franco M. Rabagliati Issa A. Katime 《Polymer International》1991,24(2):105-112
The diphenylzinc-butanone system was used as polymerization catalyst for some oxiranes in benzene solution at 60°C. This system is greatly influenced by the molar ratio of butanone to diphenylzinc, and the maximum catalytic activity for propylene oxide and ethylene oxide was found for a ratio of unity. GPC results strongly suggest the presence of more than one active species for the system. 13C NMR analysis indicates that the resulting poly(propylene oxide) has a head-to-tail arrangement. For the polymerization of propylene oxide with butanone/diphenylzinc = 1, after an initial induction period, the reaction was first-order with respect to monomer with k = 2·51 × 10?5 s?1. Ethylene oxide polymerizations using butanone/diphenylzinc = 1 and 5 were also first-order with respect to monomer after an initial induction period with k = 7·80 × 10?6 s?1 and k = 5·71 × 10?6 s?1, respectively. The diphenylzinc-butanone system was not an effective catalyst for styrene oxide polymerization. 相似文献
56.
A study has been made of the anodic behavior of lead oxide deposits containing 92, 80 and 60%α-PbO2. The non-porous deposits were prepared by electrodeposition from a plumbite bath containing different proportions of 30% formaldehyde solution, acting as a reductant in the cases of 80 and 60%α-PbO2. Measurements of the steady-state oxygen evolution reaction under constant surface conditions of the electrodes, were carried out galvanostatically within the current-density range 30–190μAcm?2. The oxygen overpotential values were found to increase with increasing the amount of superficially formedβ-PbO2 during anodization in sulphuric acid solution. In the proposed mechanism for the o.e.r, the rate determining step is an electron-transfer reaction. Tafel slopes having values of 220±10 mV dec?1 were obtained. Possible interpretation of these higher slopes is given which is based on the dual barrier model. Potential-time decay curves reveal a retarded oxygen diffusion process. 相似文献
57.
Copolymerization of dimethylaminoethylacrylate-methyl chloride and acrylamide in inverse emulsion 总被引:1,自引:0,他引:1
Irune?Inchausti Pedro?M.?Sasia Issa?KatimeEmail author 《Journal of Materials Science》2005,40(18):4833-4838
The inverse emulsion copolymerization of acrylamide (AM) with dimethylaminoethylacrylate methyl chloride (Q9) using redox
initiation with low surfactant concentration in an isoparaffinic solvent has been studied. The kinetics of conversions of
inverse-emulsion polymerizations were investigated by HPLC method. It was an interesting way to know rapidly the conversion
of each monomer with high reproducibility. In all experiments the monomer concentration was 25% respect the total weight or
higher and the experiments were carried out at 50∘C.
The effects of initiator concentration, composition of the monomer mixture and monomer concentration on the polymerization
conversion and viscosity of copolymers solutions have been examined. For copolymer characterization, the results of viscosity
were compared with commercial copolymer viscosities.
The formulations with 3,000 ppm of initiator were the most interesting of all copolymer compositions since they presented
very high conversions and their viscosities were higher than those of commercial copolymer solutions. The analysis of monomer
concentration was carried out with 3,000 ppm and the conversion and viscosity were higher when the monomer concentration was
increased. 相似文献
58.
The most prevalent microorganisms isolated from urine specimens of dogs (385) and cats (132) with clinical signs of urinary tract infections were Escherichia coli, Proteus spp., and Staphylococcus aureus. The results of quantitative urine-culturing methods showed 48.6% of the canine and 12.1% of the feline specimens had more than 10(5) organisms per ml of urine. The bacteria isolated appear to have a greater resistance to antibacterial agents than previously reported. 相似文献
59.
Wireless reprogramming of a sensor network is useful for uploading new code or for changing the functionality of existing code. Reprogramming may be done multiple times during a node’s lifetime and therefore a node has to remain receptive to future code updates. Existing reprogramming protocols, including Deluge, achieve this by bundling the reprogramming protocol and the application as one code image which is transferred through the network. The reprogramming protocol being complex, the overall size of the program image that needs to be transferred over the wireless medium increases, thereby increasing the time and energy required for reprogramming a network. We present a protocol called Stream that significantly reduces this bloat by using the facility of having multiple code images on the node. It pre-installs the reprogramming protocol as one image and equips the application program with the ability to listen to new code updates and switch to this image. For a sample application, the increase in size of the application image is 1 page (48 packets of 36 bytes each) for Stream and 11 pages for Deluge. Additionally, we design an opportunistic sleeping scheme whereby nodes can sleep during the period when reprogramming has been initiated but has not yet reached the neighborhood of the node. The savings become significant for large networks and for frequent reprogramming. We implement Stream on Mica2 motes and conduct testbed and simulation experiments to compare delay and energy consumption for different network sizes with respect to the state-of-the-art Deluge protocol. 相似文献
60.
Abeer Ahmed Kassem Doaa Ahmed Elsayed Issa Gehan Sherif Kotry 《Drug development and industrial pharmacy》2017,43(1):120-131
AbstractIntroduction: Periodontal disease broadly defines group of conditions in which the supportive structure of the tooth (periodontium) is destroyed. Recent studies suggested that the anti-diabetic drug metformin hydrochloride (MF) has an osteogenic effect and is beneficial for the management of periodontitis.Objective: Development of strong mucoadhesive multiple layer film loading small dose of MF for intra-pocket application.Methodology: Multiple layer film was developed by double casting followed by compression method. Either 6% carboxy methyl cellulose sodium (CMC) or sodium alginate (ALG) constituted the inner drug (0.6%) loaded layer. Thiolated sodium alginate (TSA; 2 or 4%) constituted the outer drug free layers to enhance mucoadhesion and achieve controlled drug release. Optimized formulation was assessed clinically on 20 subjects.Results: Films were uniform, thin and hard enough for easy insertion into periodontal pockets. Based on water uptake and in vitro drug release, CMC based film with 4% TSA as an outer layer was the optimized formulation with enhanced mucoadhesion and controlled drug release (83.73% over 12?h). SEM showed the effective fabrication of the triple layer film in which connective lines between the layers could be observed. FTIR examination suggests possibility of hydrogen bonding between the –NH groups of metformin and –OH groups of CMC. DSC revealed the presence of MF mainly in the amorphous form. Clinical results indicated improvement of all clinical parameters six months post treatment.Conclusion: The results suggested that local application of the mucoadhesive multiple layer films loaded with metformin hydrochloride was able to manage moderate chronic periodontitis. 相似文献