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1.
Pushing popular contents to the edge of the network can meet the growing demand for data traffic, reduce latency and relieve the pressure of the backhaul. However, considering the limited storage space of the base stations, it is impossible to cache all the contents, especially in ultra-dense network ( UDN). Furthermore, the uneven distribution of mobile users results in load imbalance among small base stations (SBSs) in both time and space, which also affects the caching strategy. To overcome these shortcoming, the impact of the changing load imbalance in UDN was investigated, and then a dynamic hierarchical collaborative caching (DHCC) scheme was proposed to optimize latency and caching hit rate. The storage of the SBS is logically divided into the independent caching layer and the collaborative caching layer. The independent caching layer caches the most popular contents for local users爷interest, and the collaborative caching layer caches contents as much as possible for the benefit of content diversity in the region. Different SBSs have respective storage space layer division ratios, according to their real-time traffic load. For SBSs with heavy load, the independent caching layers are allocated with more space. Otherwise, the collaborative caching layers could store more contents with larger space. The simulation results show that, DHCC improved both transmission latency and hit rate compared with existing caching schemes. 相似文献
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Urban PM2.5 (particulate matter with aerodynamic diameter smaller than 2.5 microm) is associated with excess mortality and other health effects. Stationary sources are regulated and considerable effort is being put into developing low-pollution vehicles and environment-friendly transportation systems. While waiting for technological breakthroughs in emission controls, the current work assesses the exposure reductions achievable by a complementary means: efficient filtration of supply air in buildings. For this purpose infiltration factors for buildings of different ages are quantified using Exposures of Adult Urban Populations in Europe Study (EXPOLIS) measurements of indoor and outdoor concentrations in a population-based probability sample of residential and occupational buildings in Helsinki, Finland. These are entered as inputs into an evaluated simulation model to compare exposures in the current scenario with an alternative scenario, where the distribution of ambient PM2.5 infiltration factors in all residential and occupational buildings are assumed to be similar to the subset of existing occupational buildings using supply air filters. In the alternative scenario exposures to ambient PM2.5 were reduced by 27%. Compared with source controls, a significant additional benefit is that infiltration affects particles from all outdoor sources. The large fraction of time spent indoors makes the reduction larger than what probably can be achieved by local transport policies or other emission controls in the near future. PRACTICAL IMPLICATIONS: It has been suggested that indoor concentrations of ambient particles and the associated health risks can be reduced by using mechanical ventilation systems with supply air filtering in buildings. The current work quantifies the effects of these concentration reductions on population exposures using population-based data from Helsinki and an exposure model. The estimated exposure reductions suggest that correctly defined building codes may reduce annual premature mortality by hundreds in Finland and by tens of thousands in the developed world altogether. 相似文献
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ABSTRACTIn just one decade, social media have moved from being marginal phenomena to having three billion active monthly users globally in 2017. We use a large representative sample to study which company characteristics are associated with the early adoption of social media. Our findings suggest that digital orientation (outside social media), innovativeness, external collaboration in marketing and sales, and orientation towards consumer markets all increase a company’s probability of adopting social media. In addition, larger and younger companies are more likely to be early movers. Overall, business use of social media has only reached its early maturity; thus, it still has plenty of room to grow. 相似文献
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Indoor inhalation intake fractions of fine particulate matter: review of influencing factors 下载免费PDF全文
N. Hodas M. Loh H.‐M. Shin D. Li D. Bennett T. E. McKone O. Jolliet C. J. Weschler M. Jantunen P. Fantke 《Indoor air》2016,26(6):836-856
Exposure to fine particulate matter (PM2.5) is a major contributor to the global human disease burden. The indoor environment is of particular importance when considering the health effects associated with PM2.5 exposures because people spend the majority of their time indoors and PM2.5 exposures per unit mass emitted indoors are two to three orders of magnitude larger than exposures to outdoor emissions. Variability in indoor PM2.5 intake fraction (iFin,total), which is defined as the integrated cumulative intake of PM2.5 per unit of emission, is driven by a combination of building‐specific, human‐specific, and pollutant‐specific factors. Due to a limited availability of data characterizing these factors, however, indoor emissions and intake of PM2.5 are not commonly considered when evaluating the environmental performance of product life cycles. With the aim of addressing this barrier, a literature review was conducted and data characterizing factors influencing iFin,total were compiled. In addition to providing data for the calculation of iFin,total in various indoor environments and for a range of geographic regions, this paper discusses remaining limitations to the incorporation of PM2.5‐derived health impacts into life cycle assessments and makes recommendations regarding future research. 相似文献
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Pirjo Koskela Merja Teirikangas Ari Alastalo Johanna Forsman Jari Juuti Unto Tapper Ari Auvinen Heikki Seppä Heli Jantunen Jorma Jokiniemi 《Advanced Powder Technology》2011,22(5):649-656
Metallic cobalt nanoparticles were synthesized by hydrogen reduction method. Particles were coated in situ with carbon by adding ethene to reaction flow. Particles were characterized by transmission electron microscopy, energy dispersive X-ray emission, X-ray diffraction, X-ray fluorescence and BET method. The observed cobalt particle size distributions in different cobalt batches produced with unvarying reaction parameters was reproducible: The mean diameter of primary cobalt particle varied only 5% from the mean value of 76 nm in different batches. Increased carbon precursor concentration decreased mean diameter of cobalt particles to 17 nm. The produced nanoparticles were used as filler material in 0–3 type metal–polymer composites. Composite samples with varying filler loading were fabricated with mixing extrusion and injection moulding techniques. The magnetic properties of the fabricated composites were measured up to 1 GHz. In order to analyse the particle distribution in composite matrix and its effect on magnetic properties the microstructure was studied. 相似文献
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Heli Koivuluoto Ville Matikainen Jussi Larjo Petri Vuoristo 《Journal of Thermal Spray Technology》2018,27(3):423-432
In cold spraying, powder particles are accelerated by preheated supersonic gas stream to high velocities and sprayed on a substrate. The particle velocities depend on the equipment design and process parameters, e.g., on the type of the process gas and its pressure and temperature. These, in turn, affect the coating structure and the properties. The particle velocities in cold spraying are high, and the particle temperatures are low, which can, therefore, be a challenge for the diagnostic methods. A novel optical online diagnostic system, HiWatch HR, will open new possibilities for measuring particle in-flight properties in cold spray processes. The system employs an imaging measurement technique called S-PTV (sizing-particle tracking velocimetry), first introduced in this research. This technique enables an accurate particle size measurement also for small diameter particles with a large powder volume. The aim of this study was to evaluate the velocities of metallic particles sprayed with HPCS and LPCS systems and with varying process parameters. The measured in-flight particle properties were further linked to the resulting coating properties. Furthermore, the camera was able to provide information about variations during the spraying, e.g., fluctuating powder feeding, which is important from the process control and quality control point of view. 相似文献
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