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81.
82.
M Riad XK Tong S el Mestikawy M Hamon E Hamel L Descarries 《Canadian Metallurgical Quarterly》1998,86(4):1031-1035
In addition to triggering vasoconstriction of peripheral blood vessels, which led to its discovery as a circulating neurohormone 50 years ago, serotonin (5-hydroxytryptamine) acts as a neurotransmitter/ modulator in the central nervous system and regulates local cerebral blood flow and vascular permeability through direct and indirect effects on intraparenchymal microvessels. Among the various 5-hydroxytryptamine receptors which mediate these effects, particular attention has been paid to the 5-hydroxytryptamine1B and 5-hydroxytryptamine1D subtypes, as the preferred targets of modern antimigraine agents. Immunoelectron microscopic labeling of the 5-hydroxytryptamine1B receptor in rat brain parenchyma has revealed a distinct localization to the endothelium of microvessels, which was predominantly cytoplasmic as opposed to membrane-bound, contrary to that on preterminal unmyelinated axons [Riad et al. (1997) Soc. Neurosci. Abstr. 23, 1214]. Similar observations have now been made in human cortical tissue, in which the expected localization of the vascular 5-hydroxytryptamine1B receptor to periarteriolar myocytes was also confirmed. Such a dual localization in human brain microvessels suggests that the 5-hydroxytryptamine1B receptor might mediate opposite effects, vasodilatory and contractile, depending upon its activation by circulating or centrally released 5-hydroxytryptamine. It raises new possibilities as regards 5-hydroxytryptamine effects on human brain microvessels in health and disease, and notably the triggering of migraine headache. 相似文献
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85.
Samir N. Shoukry Gergis W. William Brian Downie Mourad Y. Riad 《Construction and Building Materials》2011,25(2):688-696
Concrete mechanical properties are determined under laboratory conditions of ideal air temperatures between 20 and 22 °C and relative humidity between 40% and 60%. This paper describes the development of concrete mechanical properties when cured under different environmental conditions. Tests to measure modulus of elasticity, compressive strength, and split tensile strength were conducted at varying temperatures and humidity conditions to examine their effects on normal concrete. An environmental chamber was constructed in the laboratory using available materials. The chamber works in conjunction with a freezer to provide chilled air and a heat gun to provide hot air. The heating and cooling functions were controlled via a microcontroller. The moisture content in the concrete specimens was controlled by massing the specimens. The results indicate that concrete strength and modulus of elasticity are inversely related to temperature as well as moisture content in the concrete. Concrete modulus of elasticity was directly related to concrete compressive strength in both temperature and moisture testing. Mathematical formulas were developed for modulus of elasticity, compressive strength, tensile strength, and Poisson’s ratio. 相似文献
86.
Heterojunction cells of p-MgPc/n-Si have been fabricated by thermal evaporation of MgPc thin films onto Si100 single crystal wafers. The devices exhibit strong photovoltaic characteristics with an open–circuit voltage of 0.35 V, a short–circuit current of 3.57 mA and a power conversion efficiency of 1.05%. These parameters have been estimated at room temperature and under a monochromatic illumination of 633 nm with an input power density of 50 mW/cm2. The activation energy of the charge carriers of 0.32 eV and the cell series resistance of 2 kΩ have been evaluated from the measurements of the dark I–V characteristics. A free–carrier concentration of 2.2×1016 cm−3 and a barrier width of 75 nm have been estimated from C–V measurements. The temperature dependence of photocurrent, at constant illumination, has been also investigated. 相似文献
87.
Several aluminum cast pistons used in fuel gas reciprocating compressors suffered from cracking during operation after a short time of service. The pistons were obtained from two manufacturing sources and the failure time was different. Metallurgical investigation was made on the failed pistons to identify the root cause of cracking. The investigation revealed that the cracks primarily existed at the top surfaces of the pistons and joined screwed plugs. The investigation also showed that the cracks had originated as fatigue cracks starting from the roots of broken threads in the body of the pistons. The root cause of failure was found to be the improper screwing of the plugs which resulted in the shear deformation of the threads and development of incipient microcracks. The difference in failure time was attributed to differences in materials properties and the amount of casting defects. 相似文献
88.
The effect of duplex stainless steel microstructure on its cavitation morphology in seawater 总被引:1,自引:0,他引:1
An ultrasonically induced cavitation facility was used to study the effect of a cast duplex stainless steel (DSS) microstructure on its corrosion behavior in seawater. Under cavitation conditions, small cavities initiated in the ferritic matrix and at the ferrite–austenite boundaries. With the progress of cavitation, the attack concentrated in the austenitic phase and then spread to the ferritic phase and was associated with cleavage-like facets, ductile tearing, river patterns and crystallographic steps at later stages. Cross-sections of specimens revealed microcracks initiating from the ferritic matrix at the bottom of cavities. Crack propagation into the matrix was impeded by the austenitic islands. 相似文献
89.
Mourad Y. Riad Samir N. Shoukry Eduardo M. Sosa Gergis W. William 《Construction and Building Materials》2011,25(4):1653-1662
Concrete bridge decks are cast in segments using multiple mix batches in a process that can extend up to an entire working day. Construction codes state that the initial concrete must stay plastic over the entire casting operation, however this requirement is practically impossible to achieve with regular casting and curing procedures. This paper reports the experimental evaluation of the performance of a suggested pouring sequence of class K concrete designed for bridge decks, where retarding and accelerating admixtures were used to achieve homogeneous thermo-mechanical concrete properties based on uniform setting and curing at early age. The proposed pouring sequence was investigated in both laboratory conditions as well as in outdoors environment. In order to optimize the resulting properties, the effects of different curing methods were investigated. Taking into consideration variation in environmental conditions at a regular construction season of late spring and summer in West Virginia, the suggested sequence was able to achieve uniform setting times as well as thermal properties while being placed along an entire working day. 相似文献
90.
Mobile ad hoc networks (MANET) are wireless network without infrastructure and suffering from low power battery. Therefore the main objective in finding
a route for traffic transfer from a given source to a given destination is to minimize the node energy consumption. This paper solves the problem of finding
a route satisfying the main objective of minimum energy consumption and other QoS requirements such as minimum delay and maximum packet delivery
ratio by using linear programming technique. Two cases are considered: 1. The traffic amount of a given request is transmitted into single path, and 2.
The traffic amount of a request can be distributed into parallel paths. A preprocessing step is done first for network topology design. This step leads to
formulate the first case as integer linear programming problem and the second case as linear programming and not mixed integer linear programming. The
two obtained solutions are evaluated in terms of three criteria: energy consumption, execution time, and packet delivery ratio using an experimental study.
The results show that the solution of second case is much better than the first case in terms of energy consumption and execution time. Packet delivery ratio
in the second case is 100% while in the first case is only 76%. 相似文献