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排序方式: 共有380条查询结果,搜索用时 15 毫秒
1.
《Cement and Concrete Composites》2007,29(7):527-532
In internal curing, pre-wetted lightweight aggregates (LWA) serve as internal reservoirs to supply the extra water needed by the cementitious and pozzolanic components of the concrete during their hydration processes. Due to their porous nature and reasonably high absorption capacity, the LWA can also be filled with other materials, such as phase change materials (PCMs). In this paper, three potential applications of PCM-filled LWA in concrete technology are presented. In addition to the previously explored application of increasing the energy storage capacity of concrete in residential and commercial construction by using a PCM with a transition temperature near room temperature, applications for higher and lower temperature PCMs also exist. In the former case, a PCM can be used to reduce the temperature rise (and subsequent rate of temperature decrease) of a large concrete section during (semi)adiabatic curing, to minimize thermal cracking, etc. In the latter case, a PCM can perhaps reduce the number or intensity of freeze/thaw cycles experienced by a bridge deck or other concrete exposed to a winter environment. In this paper, these latter two applications are preliminarily explored from both experimental and modeling viewpoints. 相似文献
2.
S. Yang J.G. Yao 《Photonics Technology Letters, IEEE》1996,8(7):894-896
The size limitation of a semiconductor laser amplifier (SLA) based optical matrix-vector multiplier (MVM) switch structure arising from amplifier noise and crosstalk is investigated theoretically and experimentally. Computer simulation reveals that the number of input/output channels in such a switch structure may be limited to less than 60/spl times/60 if the contrast ratio of each SLA is 20 dB or lower. 相似文献
3.
Gian Luca Mariottini Stefano Scheggi Fabio Morbidi Domenico Prattichizzo 《Mechatronics》2012,22(4):398-409
Planar catadioptric vision sensors consist of a pinhole camera observing a scene being reflected on two (or more) planar mirrors. These systems have recently received an increasing attention because, unlike stereo cameras, can capture two views of the same scene without the need of hardware multi-camera synchronization and calibration. In this paper we explore the original scenario in which a robot manipulator, equipped with a pinhole camera on its end-effector, observes an unknown 3-D scene both directly and reflected through multiple mirrors. We present new multiple-view properties for this scenario and, based on these theoretical results, we present new image-based camera localization and new 3-D scene reconstruction algorithms. Extensive simulation and real-data experiments illustrate the theory and show the effectiveness of the proposed designs. 相似文献
4.
5.
Shu-Tao Xia Fang-Wei Fu 《Communications Letters, IEEE》2006,10(5):381-383
In this letter, the stopping sets and stopping distance of finite geometry LDPC (FG-LDPC) codes are studied. It is known that FG-LDPC codes are majority-logic decodable and a lower bound on the minimum distance can be thus obtained. It is shown in this letter that this lower bound on the minimum distance of FG-LDPC codes is also a lower bound on the stopping distance of FG-LDPC codes, which implies that FG-LDPC codes have considerably large stopping distance. This may explain in one respect why some FG-LDPC codes perform well with iterative decoding in spite of having many cycles of length 4 in their Tanner graphs. 相似文献
6.
7.
《Advanced Powder Technology》1999,10(1):51-64
An electrically conducting powder was produced by mixing bronze spheres with a small amount of carbon black powder. The potential difference across beds of this powder was measured under static conditions and vibration. The system was very sensitive and monitored changes during vibration cycles at rapid rates. Horizontal and vertical conductances were measured. Above a minimum vertical stress, the ratio of the two was constant. The conductance was related to vertical stress by a linear relationship with hysteresis, for both static conditions and vibration at small accelerations. A simple model has been proposed to describe this system. At high accelerations (< 10 m/s2) changes were much larger. There were permanent changes in conductance and the system was non-linear. The data demonstrate that the internal structure of a particle bed displays great sensitivity, hysteresis and a dependence upon stress history. 相似文献
8.
《NDT International》1988,21(4):247-257
The essential features of the acousto-ultrasonic (AU) technique are described, including the parameter known as the ‘stress-wave factor’ (SWF). AU measurements are comparative, so that a high degree of repeatability is required to provide adequate sensitivity for the detection of defects. Part I of the paper describes a systematic investigation into the effects of the principal experimental parameters upon the variability and sensitivity of SWF readings. Parameters studied are: transducer couplant and coupling pressure, inter-transducer spacing, injected pulse energy, amplifier gain, threshold and gate width. This work leads to the definition of optimum conditions for discriminating between the fibre and transverse directions of a unidirectional carbon-fibre/PEEK laminate. In Part II of the paper, these optimized instrument settings, and other, are applied to the detection of deliberately introduced defects in laminates of the same material. Defects had been introduced in moulding, also by impact, by crushing and by drilling through-thickness holes. Because of the scatter of replicate SWF readings, statistical methods are applied to establish the level of confidence with which various defects may be detected in comparisons with sound laminates. At the 0.1% significance level, the detection limit for holes was 4 mm in a 20-ply laminate approximately 300 mm square. Moulded-in defects 30 mm square, including missing areas of reinforcement and aluminium foil inclusions, could not be distinguished above the scatter. Impact damage, which has been shown in other work to be of the order of 15 mm diameter, was similarly undetectable. 相似文献
9.
《Current Opinion in Solid State & Materials Science》2001,5(6):497-502
Continuous random network (CRN) models are often used as models for elemental and binary tetrahedral semiconductors such as a-Si and a-GaAs. Here, we review algorithms to generate CRN models. We discuss their structural properties and compare with those models obtained via different computational approaches, as well as with experiment. Additionally, we discuss current results towards the generation of para-crystalline models. 相似文献
10.
《Water research》1986,20(7):871-876
The removal and inactivation of indigenous viruses for individual water treatment processes were investigated both in a pilot (3 m3 h−1) and a full-scale (4000 m3 h−1) plant, treating water from the Seine and Oise rivers respectively.Viruses were recovered by the previously described methods of adsorption-elution using electronegative Balston filters (Joret and Block, 1981) for the pilot plant study or alternatively using either electronegative or electropositive 1 MDS Cuno filters (Sobsey and Glass, 1981) for the full-scale water supply.Depending on the efficiency of filtration, the volumes of water samples concentrated directly in the field varied from 30 to 100 litres for raw, preozonated, stored river water and decanted water, and from 550 to 1000 litres for treated water downstream from the clarification step. BGM cells were used for virus detection by the plaque assay method.During this study, the initial virus concentration in the Seine river water entering the pilot plant, varied from 190 to 1420 PFU/1000 l. The virus removal observed after coagulation-flocculation with 35–50 g m−3 of water aluminum chloride (WAC) (a basic aluminum chloride) and settling, was 31–90% effective (130–390 PFU/1000 l. of decanted water), and did not exceed 1–2 logarithms after sand filtration at a rate of 5 m h−1 (83% of 600–800 samples were positive for viruses, maximum concentration = 80 PFU/1000 l.).The preozonation of river water (0.8 ppm during 2–3 min without residual oxidant) inactivated 64–97% of viruses (maximum viral concentration in preozonated water being 300 PFU/1000 l.). Under these conditions, no viruses could be isolated from samples of 550–1000 litres of sand filtered water.The treatment process for the industrial water supply located at Mery sur Oise was preozonation (0.5–1 ppm for 1 min), storage, coagulation-flocculation, settling, sand filtration, second stage ozonation (1.4–1.6 ppm for 10 min, residual oxidant: traces to 0.3 ppm), activated carbon filtration, postozonation (0.4 ppm free residual for 4 min) and chlorine dioxide (0.1 ppm). Nine series of samples were taken after various stages of treatment and tested for viruses. All samples of raw river water yielded positive results with relatively low numbers (10–146 PFU/1000 l.) compared with the number of enterovirus in the Seine river.The efficiency of preozonation before storage could not be evaluated in this study due to its intermittent operation. Enteroviruses were found in 83% of samples after storage (7–100 PFU/1000 l.), 77% after settling and 55% after sand filtration (3–10 PFU/1000 l.). Enteroviruses were not detected after the second stage ozonation in any of the nine samples. The subsequent postozonation and final treatment with chlorine dioxide serves as an additional barrier to ensure virologically safe drinking water.During studies on pilot and full scale water treatment plants, viral isolates are as follows: ECHO virus (49 and 37% respectively), coxsackie B virus (42 and 49% respectively) and poliomyelitis virus (9 and 14% respectively). 相似文献