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71.
Zirconia-mullite composites were prepared byin situ reaction between zircon and alumina. Stabilizers like yttria and magnesium carbonate were used. Almost vitrified bodies were
obtained by sintering at 1465–1535°C. Flexural strength increased on annealing at 1040°C. 相似文献
72.
73.
Redefining clustering for high-dimensional applications 总被引:1,自引:0,他引:1
Clustering problems are well-known in the database literature for their use in numerous applications, such as customer segmentation, classification, and trend analysis. High-dimensional data has always been a challenge for clustering algorithms because of the inherent sparsity of the points. Recent research results indicate that, in high-dimensional data, even the concept of proximity or clustering may not be meaningful. We introduce a very general concept of projected clustering which is able to construct clusters in arbitrarily aligned subspaces of lower dimensionality. The subspaces are specific to the clusters themselves. This definition is substantially more general and realistic than the currently available techniques which limit the method to only projections from the original set of attributes. The generalized projected clustering technique may also be viewed as a way of trying to redefine clustering for high-dimensional applications by searching for hidden subspaces with clusters which are created by interattribute correlations. We provide a new concept of using extended cluster feature vectors in order to make the algorithm scalable for very large databases. The running time and space requirements of the algorithm are adjustable and are likely to trade-off with better accuracy 相似文献
74.
K. K. Aggarwal 《Sadhana》1987,11(1-2):155-165
The complexity of computer communication networks has taken a dramatic upswing, following significant developments in electronic
technology such as medium and large scale integrated circuits and microprocessors. Although components of a computer communication
network are broadly classified into software, hardware and communications, the most important problem is that of ensuring
the reliable flow of information from source to destination.
An important parameter in the analysis of these networks is to find the probability of obtaining a situation in which each
node in the network communicates with all other remaining communication centres (nodes). This probability, termed as overall
reliability, can be determined using the concept of spanning trees.
As the exact reliability evaluation becomes unmanageable even for a reasonable sized system, we present an approximate technique
using clustering methods. It has been shown that when component reliability ⩾ 0.9, the suggested technique gives results quite
close to those obtained by exact methods with an enormous saving in computation time and memory usage.
For still quicker reliability analysis while designing the topological configuration of real-time computer systems, an empirical
form of the reliability index is proposed which serves as a fairly good indicator of overall reliability and can be easily
incorporated in a design procedure, such as local search, to design maximally reliable computer communication network. 相似文献
75.
76.
F. Kochary M. D. Aggarwal A. K. Batra R. Hawrami D. Lianos A. Burger 《Journal of Materials Science: Materials in Electronics》2008,19(11):1058-1063
The lead magnesium niobate-lead titanate is one of the new generations of piezoelectric materials with outstanding properties.
Single crystals of 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-PT) show superior properties as compared to piezoelectric ceramics and piezoelectric films in device applications. Large
size crystals are required for specific applications. Previously, transparent and high quality PMN-PT single crystals have
been grown in our laboratory using the high temperature flux method. The size of the obtained crystals was small and varied
from 2 to 8 mm3, mostly showing regular prismatic shape. In present attempt, PMN-PT crystals are grown from the vertical gradient freeze
method with no flux using congruent melt. Processing conditions and growth parameters have been optimized to increase the
size and yield of the perovskite crystals including cooling rate, soak time and soak temperature. The size of the grown crystals
obtained by this method is very large relatively and varied from 5 to 30 mm3. The microstructure of the as grown single crystals is investigated by scanning electron microscopy. Piezoelectric properties
of the grown crystals are also investigated. PMN-PT plates show excellent piezoelectric properties. Samples were poled under
an applied electric field of 5 kV/cm. Dielectric properties at a frequency of 1 kHz are examined. Finally, the variation of
pyroelectric coefficient with temperature is studied. The grown PMN-PT crystals show typical relaxor dielectric properties. 相似文献
77.
In this paper, the thermodynamic properties of lithium nitrate-ammonia mixtures are presented. The vapour pressure-temperature correlations are developed by fitting the experimental P-T-x data. The enthalpy of solution, the latent heat of vaporization, the integral heat of solution and the differential heat of solution are presented in appropriate tabular and graphical forms. 相似文献
78.
A differential feeder protection that utilizes voltage and current signals is described. This approach obviates the need for relay bias to compensate for capacitance spill current, thus improving the relay sensitivity. From a practical point of view, the scheme has been designed to simplify the digital hardware requirements and reduce the bandwidth requirements for signal transmission over a fiber-optic link 相似文献
79.
Heavy metal fluoride (HMF) glass optical fibres were spliced by fusing the two ends of fibres using a DC arc. An average optical loss of 0.08 dB per splice and strengths of up to 600 MPa were achieved for fusion splices using an inert gas purge during splicing. Estimates are made to determine the feasibility of achieving a splice loss of 0.005 dB for single-mode (HMF) fibres.<> 相似文献
80.
Chappell MA Laird DA Thompson ML Li H Teppen BJ Aggarwal V Johnston CT Boyd SA 《Environmental science & technology》2005,39(9):3150-3156
Smectites, clay minerals commonly found in soils and sediments, vary widely in their ability to adsorb organic chemicals. Recent research has demonstrated the importance of surface charge density and properties of exchangeable cations in controlling the affinity of smectites for organic molecules. In this study, we induced hysteresis in the crystalline swelling of smectites to test the hypothesis that the extent of crystalline swelling (or interlayer hydration status) has a large influence on the ability of smectites to adsorb atrazine from aqueous systems. Air-dried K-saturated Panther Creek (PC) smectite swelled less (d(001) = 1.38 nm) than never-dried K-PC (d(001) = 1.7 nm) when rehydrated in 20 mM KCl. Correspondingly, the air-dried-rehydrated K-PC had an order of magnitude greater affinity for atrazine relative to the never-dried K-PC. Both air-dried-rehydrated and never-dried Ca-PC expanded to approximately 2.0 nm in 10 mM CaCl2 and both samples had similar affinities for atrazine that were slightly lower than that of never-dried K-PC. The importance of interlayer hydration status in controlling sorption affinity was confirmed by molecular modeling, which revealed much greater interaction between interlayer water molecules and atrazine in a three-layer hydrate relative to a one-layer hydrate. The entropy change on moving atrazine from a fully hydrated state in the bulk solution to a partially hydrated state in the smectite interlayers is believed to be a major factor influencing sorption affinity. In an application test, choice of background solution (20 mM KCl versus 10 mM CaCl2) and air-drying treatments significantly affected atrazine sorption affinities for three-smectitic soils; however, the trends were not consistent with those observed for the reference smectite. Further, extending the initial rehydration time from 24 to 240 h (prior to adding atrazine) significantly decreased the soil's sorption affinity for atrazine. We conclude that interlayer hydration status has a large influence on the affinity of smectites for atrazine and that air-drying treatments have the potential to modify the sorption affinity of smectitic soils for organic molecules such as atrazine. 相似文献