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991.
A generalised kinematically admissible velocity field is derived for axisymmetric extrusion through curved dies by employing rigid-plastic boundaries expressed in terms of arbitrarily chosen continuous functions. The corresponding upper-bound extrusion pressure is related directly to boundary functions for the plastically deforming region when the die shape, lubrication condition and material characteristics of the billet are given. The proposed method of analysis makes it possible to predict the deformation pattern as well as extrusion pressure. In computation a third-order polynomial is chosen for the die boundary and the bounding function for the plastic region is chosen to be a fourth-order polynomial. The workhardening effect is considered in the formulation. The plastic boundaries as well as stream lines are affected by various process parameters. The theory predicts the relatively faster axial flow at the center than near the die boundary for greater friction factor even with the same die shape. The effects of area reduction and die length are also discussed in relation to extrusion pressure and deformation. Experiments are carried out for steel billets at room temperature. Deformation patterns are measured for several area reductions by the photoetching technique and the extrusion pressure is measured using a load-cell. The predicted extrusion pressure is in excellent agreement with the value computed by the finite element method. The deformation patterns agree well with the experimental observation. 相似文献
992.
Professor Andrew Kusiak Gun Ho Lee 《The International Journal of Advanced Manufacturing Technology》1997,13(1):67-76
The design of parts and manufacturing systems can be viewed from different perspectives. This paper discusses the design of parts and manufacturing systems from reliability and maintainability perspectives. A convenient method of considering reliability and maintainability is through the use of design rules which are based on empirical and theoretical knowledge. Four design rules for improvement of reliability and maintainability of systems are presented. The design rules are proven and substantiated with numerical results. The relationship between the design for reliability and maintainability rules and design for manufacturing process rules is discussed. 相似文献
993.
M. R. Driels C. C. Lee 《The International Journal of Advanced Manufacturing Technology》1988,3(4):3-32
In this paper, three successive feature reduction methods are employed to select good features for the automatic visual inspection
of solder joints. This reduction strategy includes (1) a stability test to remove the features with unstable performance,
(2) a separability examination to select the features with good classification capabilities, (3) a correlation analysis to
delete the redundant features. Three sets of features are implemented in this feature reduction work: (1) a circular sub-area
feature set is related to the intensity conditions within distinct areas in the joint image, (2) a moment of inertia feature
set is based upon the intensity of pixels and their relative position in the image plane, (3) a surface curvature feature
set analyses the three-dimensional joint topology. Initially 50 features are formulated based on the above strategy. The reduction
technique deletes 39 features from this set because of instability, poor performance, and high correlation with other features.
Finally, the remaining 11 feature are tested and shown to be superior to state-of-the-art identification methods. 相似文献
994.
E. S. Lee J. K. Won Y. J. Chun M. W. Cho W. S. Cho J. H. Lee 《The International Journal of Advanced Manufacturing Technology》2007,31(11-12):1101-1108
The machinable ceramic Si3N4-BN is a material which is increasingly being employed for automobile bearings and machinable ceramics. This material is very hard and has high resistance against volatile temperature and wear. It's efficient quality and accurate surfaces have always been of high demand for many applications in the industrial field. Besides, this material is varied by the percentage of BN contained in it, and the characteristics of lapping also varies according to this percentage of BN. Hence, in-process electrolytic dressing for ultra-precision lapping was introduced and used to experiment with the differing BN percentages in machinable ceramic Si3 N4. Metal-bonded super-abrasive diamond lapping wheels have superior qualities such as high bond strength, high stability and high machinability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the cast-iron bonded diamond lapping wheel and, therefore, dressing should be considered. In this respect, in-process electrolytic dressing (IED) is proposed as an effective method regarding continuous protruding abrasives on the surface of wheels, whereby loading and glazing phenomena can apparently disappear. In this paper, the machining characteristics of machinable ceramic Si3N4-BN have been studied by adapting the IED lapping process in terms of the percentage of h-BN material. 相似文献
995.
Hyunpung Park Kwan H. Lee 《The International Journal of Advanced Manufacturing Technology》2005,27(3-4):313-320
Parametric modeling technology is difficult to apply to freeform mesh models since there is no efficient way to impose geometric
constraints. In this paper, we propose a novel method to control freeform mesh models parametrically. Our approach is to construct
a control mesh that surrounds an object model and then impose constraints on it. The control mesh is parametrically controlled
and the shape of the object model is modified by using an existing freeform deformation method.
This paper is mainly concerned with automated construction of a control mesh and treatment of geometric constraints. Procedures
for creating a control mesh are as follows: 1) determine the optimal orientation of the model, 2) project the model along
three axes and extract contours, 3) create 2D control polygons for the contours, and 4) construct the 3D control mesh from
the 2D control polygons. Geometric constraints are imposed on the edges and faces of a control mesh. Types of constraints
are given by either a relative relationship between elements or an absolute displacement. A new control mesh is calculated
by solving these constraints and the original model is modified accordingly. We tested our algorithms for two freeform models. 相似文献
996.
本文在特定条件下,通过对阶跃输入下FvRO15G7S-4EX输出响应特性的分析和实际观测,提出了它的传递函数的数学模型和等效结构图。 相似文献
997.
Jinkeun Oh W. C. Lee Sung Gyu Pyo Woojin Park Sunghak Lee Nack J. Kim 《Metallurgical and Materials Transactions A》2002,33(12):3649-3659
This study is concerned with the microstructural analysis of multilayered or bulk Ti aluminide sheets fabricated by the self-propagating
high-temperature synthesis (SHS) reaction using hot rolling and heat treatment. Multilayered Ti/Al sheets were prepared by
stacking thin Ti and Al sheets alternately, and a good Ti/Al interfacial bonding was achieved after rolling at 500 °C. When
these sheets were held at 1000 °C, spheroidal TiAl3 phases were formed by the SHS reaction at Ti/Al interfaces and inside Al layers. Microstructural analysis on the hot-rolled,
multilayered Ti/TiAl3 sheets revealed that intermetallic phases such as TiAl2, TiAl, and Ti3Al were formed at Ti/TiAl3 interfaces due to interaction between Ti and TiAl3 and that pores formed in the TiAl3 layer were significantly reduced during hot rolling. When multilayered Ti/Ti aluminide sheets were heat treated at 1000 °C,
Ti3Al, TiAl, and TiAl2 were grown as Ti and TiAl3 were consumed. As the heat treatment proceeded, TiAl grew further, eventually leading to the fabrication of multilayered
sheets composed of Ti3Al and TiAl. Bulk Ti aluminide sheets, having a lamellar structure of Ti3Al and TiAl, instead of multilayered sheets, were also fabricated successfully by heat treatment at 1400 °C. This fabrication
method of the bulk sheets had several advantages over the method by hot forging or rolling of conventional cast Ti aluminides.
From these findings, an idea to fabricate multilayered or bulk Ti aluminide sheets by hot rolling and heat treatment is suggested
as an economical and continuous fabrication method, and the formation and growth mechanisms of interfacial phases are elucidated
in this study. 相似文献
998.
Lewis Melissa A.; Hove M. Christina; Whiteside Ursula; Lee Christine M.; Kirkeby Benjamin S.; Oster-Aaland Laura; Neighbors Clayton; Larimer Mary E. 《Canadian Metallurgical Quarterly》2008,22(1):58
The present research was conducted to clarify the relationships among social anxiety, alcohol consumption, alcohol-related problems, and negative-reinforcement drinking motives among college students. Heavy drinking students (N = 316, 53.80% female) completed self-report measures of social anxiety, alcohol consumption, alcohol-related problems, and drinking motives. Findings indicated that students higher in social anxiety consumed less alcohol but experienced more negative consequences. Moreover, the relationship between social anxiety and negative consequences was mediated by coping and conformity drinking motives in addition to alcohol consumption. In the context of social anxiety, the current research demonstrates the importance of examining problematic drinking as distinct constructs: alcohol consumption and negative consequences. Findings are also discussed in terms of implications for interventions with socially anxious students. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
1000.
Tai Sik Lee Dong Wook Lee Hyeeun Lee Hee Sun Park 《Canadian Metallurgical Quarterly》2005,21(4):159-163
The Leader–Member Exchange (LMX) relationship quality between superiors and subordinates in Korean civil engineering companies were empirically examined for superiors’ feedback-seeking behaviors. The results showed that for superiors, affect, loyalty, and contribution toward subordinates were positively related to seeking negative as well as positive feedback from subordinates. From subordinates’ point of view, affect, contribution, and professional respect toward their superiors were positively related to superiors’ negative feedback seeking, but affect was negatively related to superiors’ positive feedback seeking. It was also found that superiors and subordinates were not consensual in LMX and superiors’ feedback-seeking behaviors. For example, for superiors, all of the four LMX dimensions were positively related to superiors’ asking subordinates directly for feedback, whereas for subordinates, none of the LMX dimensions were significantly related to superiors’ asking subordinates directly for feedback. These and other findings are discussed in detail, and implications for the findings are provided. 相似文献