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排序方式: 共有859条查询结果,搜索用时 15 毫秒
51.
This research investigates the use of equal channel angular extrusion (ECAE) processing to produce a superplastic form of
the aluminum alloy 2098. The starting material was a hot-rolled and precipitation-hardened plate with elongated grains of
width 67–92 μm, and a composition in weight percent of 2.2% Li, 1.3% Cu, 0.73% Mg, 0.05% Zr, balance Al. Microstructural evolution
was investigated with optical and transmission electron microscopy (TEM) and microhardness measurements after each step of
a multipass ECAE process. ECAE produced a submicron grain structure with an average size of about 0.5 μm. The sub-grain microstructure
size was a function of the magnitude of the input strain and the extrusion temperature. Misorientation angles of the developed
submicron structure increase with increasing number of passes at warm working temperatures. Superplastic behavior of the ECAE-processed
alloy was achieved. However, the low zirconium content of the 2098 alloy resulted in grain growth of the refined structure
at the superplastic processing temperatures, placing a lower limit on the deformation rates that can be used. 相似文献
52.
Arturo Gomez Ortega Luis Corona Galvan Mehdi Salem Kamel Moussaoui Stephane Segonds Sébastien Rouquette 《Science & Technology of Welding & Joining》2013,18(6):538-547
ABSTRACT4043 aluminium deposits were elaborated using a 3D print device equipped with a Cold Metal Transfer welding source. Two sets of process parameters leading to different average powers were compared in order to establish the relations between the powers and energies produced and the geometrical characteristics of the deposits. The effects of the travel speed and layer superposition on the transfer mechanisms as well as on the geometrical characteristics of the deposits were discussed for both sets of parameters. Finally, the formed microstructures were analysed and the porosity defects were quantified and discussed with regard to the heat input characteristics and the solidification conditions. 相似文献
53.
D. R. Salem 《Polymer Engineering and Science》1999,39(12):2419-2430
We review some recent research developments on structure development during drawing of poly(ethylene terephthalate) film, and we report a study of constant-load drawing of amorphous PET film at temperatures of 120°C and 132°C, including the effects of redrawing high-temperature drawn film at lower temperature. To permit constant-load drawing at high temperature without inducing crystallization in the undrawn specimen, a drawing instrument was built that permits very rapid heating of the sample, and its operation is described. The initial stage of drawing at high temperatures is characterized by polymer flow where, owing to high rates of molecular relaxation, neither molecular orientation nor crystallization occurs. Strain-rate increases sharply in the course of the deformation, reducing the time available for relaxation, and the chains start to orient at a draw ratio that depends on temperature. Orientation rapidly reaches a saturation level, which is lower at the higher draw temperature. Crystallization onset seems to lag only slightly behind orientation onset because the critical orientation for inducing crystallization is very low at these temperatures. It appears that there is time for crystallization to proceed to pseudo-equilibrium values corresponding to a particular orientation level, which differs from previous results obtained from constant-force drawing at lower temperatures, and possible reasons for this are discussed. In two-stage drawing, where film drawn at 132°C was redrawn along the same axis at 100°C, high draw ratios were obtained despite the high strain rates, and the levels of noncrystalline orientation and crystallinity were similar to the levels expected from single stage drawing at 100°C. 相似文献
54.
SPARCL: an effective and efficient algorithm for mining arbitrary shape-based clusters 总被引:3,自引:3,他引:0
Vineet Chaoji Mohammad Al Hasan Saeed Salem Mohammed J. Zaki 《Knowledge and Information Systems》2009,21(2):201-229
Clustering is one of the fundamental data mining tasks. Many different clustering paradigms have been developed over the years,
which include partitional, hierarchical, mixture model based, density-based, spectral, subspace, and so on. The focus of this
paper is on full-dimensional, arbitrary shaped clusters. Existing methods for this problem suffer either in terms of the memory
or time complexity (quadratic or even cubic). This shortcoming has restricted these algorithms to datasets of moderate sizes.
In this paper we propose SPARCL, a simple and scalable algorithm for finding clusters with arbitrary shapes and sizes, and
it has linear space and time complexity. SPARCL consists of two stages—the first stage runs a carefully initialized version
of the Kmeans algorithm to generate many small seed clusters. The second stage iteratively merges the generated clusters to
obtain the final shape-based clusters. Experiments were conducted on a variety of datasets to highlight the effectiveness,
efficiency, and scalability of our approach. On the large datasets SPARCL is an order of magnitude faster than the best existing
approaches. 相似文献
55.
This paper presents a technical approach for electronic multilateral trade of electricity in competitive power industries. The trade involves strategic sharing of data among agents in an attempt to provide the opportunity to intelligently discover competitive behavior of peer suppliers. A trading logic is implemented as a specialized software module within the agent. The logic mimics intelligence of the human strategic trade. A time-bounded trade protocol has been introduced as a trading basis among rivalry trade agents in the market. The protocol limits the trade rounds in order to bind the trading process to specific deadlines. The protocol is coded as part of the automated trade server. The results of a generic 3-bus test system show that the electronic multilateral trade logic presented in this paper better distributes market sales, lowers prices and consequently provides higher social welfare compared to the standard Cournot economic model that may be used by the human decision-maker for market trading. Based on a set of test cases with different load profiles, it is noted that the electronic multilateral trade drives the market price closer to the marginal cost of generation supply and far away from the estimated Cournot price. 相似文献
56.
Noha M. Hassan Maher Y. Younan Hanadi G. Salem 《JOM Journal of the Minerals, Metals and Materials Society》2003,55(10):38-42
The deformation behaviors of an Al-Li-Cu alloy (Aluminum 8090) during uniaxial and biaxial stress states were modeled using
the nonlinear finite element analysis package ABAQUS 5.8. Two different material models were used for the purpose of comparison and to propose a valid and accurate superplastic material
deformation behavior. Using a power law strain hardening model, the material was modeled with either constant or variable
properties of strain-rate sensitivity and strain-hardening exponent. Results from the numerical models were compared to experimental
results by Chen and Huang, who investigated the uniaxial and biaxial states of stress. Experimental data were primarily used
to acquire the needed uniaxial material parameters for the model. The strain-rate sensitivity and strain-hardening exponent
were dependent on the strain and strain rates. Comparing the two material models for both stress states indicated that the
material model with variable properties better represented the true behavior of the material when compared to the experimental
results.
For more information, contact Noha M. Hassan, the American University in Cairo, 113 Kasr El Aini St., P.O. Box 2511, Cairo
11511, Egypt; +202-797-5336; fax +202-797-7565; e-mail nhassan@vt.edu. 相似文献
57.
N Salem P Richaud R Gaston B Chacon L Mauriac E Bussières 《Canadian Metallurgical Quarterly》1998,2(3):282-286
The effect of the dose of oyster mushroom in the diet (1.0, 2.5, and 5.0%) and of the period of application (8, 16, 28, and 52 wk) on cholesterol accumulation in blood and body organs was studied in weanling male Wistar rats fed a diet containing 0.3% cholesterol. Reduction of cholesterol in serum and body organs was found to be dependent on the amount of dietary oyster mushroom administered. A negative correlation between the mushroom dose and cholesterol level was found after 8 and 28 wk of feeding (r=-0.9821 and -0.9803, respectively; P < 0.02 for both cases). The dose of 1% oyster mushroom did not affect cholesterol levels in serum or body organs. A significant reduction of cholesterol levels was observed in serum (31-46%) and liver (25-30%) at a dose of 5% of oyster mushroom for all periods. Reduced cholesterol content in very low-density lipoproteins (VLDL) was also observed at this level. The highest dose of oyster mushroom induced a decrease in conjugated diene levels in erythrocytes and an increase in the levels of reduced glutathione in the liver and stimulated the activities of catalase and glutathione peroxidase in the liver in the final period of the experiment. 相似文献
58.
Results are presented of studies to assess the role of surface roughness in the friction of sliding contacts. A model of the surface roughness uses conical steel needles. A theoretical model based on the mechanics of interaction is included. Experimental and calculated results are discussed in relation to real engineering surfaces and the models compared 相似文献
59.
Generally, an intruder must perform several actions, organized in an intrusion scenario, to achieve his or her malicious objectives. Actions are modeled by their pre and post conditions, which are a set of logical predicates or negations of predicates. Pre conditions of an action correspond to conditions the system’s state must satisfy to perform the action. Post conditions correspond to the effects of executing the action on the system’s state. When an intruder begins his intrusion, we can deduce, from the alerts generated byidss (Intrusion Detection Systems), several possible scenarios, by correlating attacks, that lead to multiple intrusion objectives. However, with no further analysis, we are not able to decide which are the most plausible ones among the possible scenarios. We propose in this paper to define an order over the possible scenarios by weighting the correlation relations between successive attacks composing the scenarios. These weights reflect to what level executing some actions are necessary to execute some action B. We will see that to be satisfactory, the comparison operator between two scenarios must satisfy some properties. 相似文献
60.
In this article, we studied the effects of variable viscosity and variable thermal diffusivity on heat transfer about a fluid
underlying the axisymmetric spreading surface, taking into account the effect of an axial magnetic field. The governing fundamental
equations are approximated by a system of nonlinear ordinary differential equations and are solved numerically by using shooting
method. Numerical solutions are obtained for different values of variable viscosity, variable thermal diffusivity and the
surface temperature variation parameter. The numerical results show that, variable viscosity, variable thermal diffusivity
and the surface temperature variation parameter have significant influences on the velocity and temperature profiles, shear
stress, couple stress and Nusselt number. 相似文献