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61.
To characterize the role of spatially heterogeneous signaling in cellular function, methods are required for differentially exposing distinct regions of individual cells to externally applied reagents. Although a range of standard approaches exists for generating localized chemical gradients in culture, including puffer pipet spritzing and photolytic release of caged effectors, each is limited in key respects. Here, we report development of a cell-dosing strategy that addresses these limitations, providing the means to create steep gradients of any aqueous-miscible compound at essentially unlimited numbers of sites in parallel. In this approach, cells are cultured on a micrometer-thick polymer membrane that serves as a barrier between two stacked laminar-flow channels: one containing the cell culture and the other serving as a reagent flow cell. By focusing a pulsed laser beam onto one or more selected membrane positions, micrometer-diameter pores can be ablated upstream of desired cellular targets. Nascent pores thus serve as ports of entry into the culture environment for reagent streams capable of modifying subcellular features at positions potentially hundreds of micrometers from ablation sites. Importantly, individual reagent streams also can be rapidly eliminated by photo-cross-linking a protein plug over a selected pore. This versatile strategy for dynamically reshaping the chemical microenvironments in which cells reside should be useful in a variety of cell biology applications, ranging from neurotrophic modulation of neurite pathfinding to stimulation of cellular networks.  相似文献   
62.
In this article, the microstructures of Zn-55Al-1.6Si coating spangles on steel were examined using optical microscopy and the crystallographic orientations of the spangles analyzed using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). It was found that ??-Al dendrite arms forming the spangles grew along straight lines with uniform size, uniform dendrite arm spacing, and in most sectors in directions parallel to their border lines. It was also found that (111) and (100) were the most common orientations in the coating. The likely preferred dendrite arm growth directions for the spangles having the (111) orientation were [110] or [112], whereas both [100] and [110] were possible growth directions when the spangles had (100) orientations. The [320] directions suggested in the literature were unlikely to be the growth directions in any of the spangles examined.  相似文献   
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Most plastic packaging products are discarded after a single use resulting in an abundant supply of waste plastics. Natural fibres are light in weight, abundant and inexpensive. The stiffness and strength of polymers have been shown to improve with the incorporation of natural fibres. Hence, composite materials made of natural fibres and waste plastics would result in the reduction of plastic wastes and the use of fibres from renewable resources. Composite specimens and sheets consisting of fibres from the New Zealand flax plant, phormium tenax or Harakeke as it is known in Maori, and waste plastics have been produced through screwless extrusion followed by injection moulding. The tensile and impact properties of these composites have been determined. The formability of these composites has been assessed through thermoforming.  相似文献   
65.
This high-resolution study of the latest Holocene dinoflagellate cyst record from Gullmar Fjord, on the west coast of Sweden, provides evidence for the recognition of two major dinoflagellate communities within the fjord over the last 85 years. These communities may have their origins with the history of cultural eutrophication within the region, but are more likely to be associated with the wider phenomenon of the North Atlantic Oscillation and/or the complex hydrographical response of the fjord to various changing climatic environments between 1915 and 1999. The changing dinoflagellate cyst populations are compared in detail with the many hydrographical parameters available from this well studied fjord with its long instrumental records. Indeed the dinoflagellate cysts fail to demonstrate a convincing ongoing eutrophication record for the fjord but do show a major change in the cyst assemblages at about 1969/1970 at a time when the NAO was changing from a negative phase to the present-day positive phase. Gullmar Fjord is important in the history of dinoflagellate cyst studies, being the site of the 1954 study by Erdtman in which viable cysts, produced within the phytoplankton, were first documented within the water column.  相似文献   
66.
A new optical pumping method is demonstrated for creating a population inversion in GaN micropillar cavities with circular symmetry. This approach employs an axicon lens to produce a ring-shaped optical beam and provides for independent control of ring thickness and diameter. By bringing the pump beam into coincidence with whispering gallery modes confined near the outer rim of the cavity, we achieve a significant reduction in the threshold pump intensity for room-temperature operation of GaN micropillar lasers  相似文献   
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As hierarchically controlled computer-integrated manufacturing systems growthey tend to become complex and their designability, maintainability, expandability and fault tolerance deteriorate. As an alternative, herterarchical control architectures offer prospects of reduced compexity, reduced software development costs, high modularity, high flexibility, and improved fault tolerance. By locating decision making where information originates, global information is reduced to a minimum, scheduling becomes dynamic, machines and parts become “intelligent” entities that cooperatively interact, and the overall system is decomposed into functionally simplified, modular parts.Three flexible machining cell control systems have been constructed at the University of Wisconsin-Madison and are described in this paper: a centralized controller, a hierarchical controller with dynamic scheduling, and a fully distributed heterarchical controller with “intelligent parts”. Comparative results are reported showing that the heterarchical approach possesses a number of advantages including increased fault-tolerance, inherent adaptability and reconfigurability, decreased complexity, and reduced software development cost.  相似文献   
69.
Wireless Personal Communications - Bean which is botanically called Phaseolus vulgaris L. belongs to the Fabaceae family. Unnecessary economic losses arise during bean disease identification due to...  相似文献   
70.
Recent national and international actions regarding atmosphere warming mitigation, clean technology, and technology transfer have emphasized the need for a method for unambiguous greenhouse gas emissions analysis for comparing technologies, documentation of application of the method, and proof of applicability. We have developed and applied such an approach to production of methanol fuel from woody biomass. The entire approach is detailed, whereby the system was defined, its emissions for its entire lifetime delineated, and the atmospheric warming forcing calculated for that lifetime plus after effects. The results are presented with material and energy balances including ancillary equipment, external energy subsidies and invested quantities. These extend the analysis considerably beyond those possible using the global warming potential (GWP). For wood input of 283 mg day−1, 70 mg of methanol are produced. System carbon dioxide emissions are 3.18 tonne/tonne methanol produced, with another 1.37 mg emitted when that tonne methanol is burned in a vehicle. System energy usage efficiency was 41.2%, and 41.1% with inclusion of energy to construct the system. In essence, more than two Joules of carbon must be produced in wood for every Joule burned in the vehicle.  相似文献   
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