全文获取类型
收费全文 | 52654篇 |
免费 | 2764篇 |
国内免费 | 154篇 |
专业分类
电工技术 | 708篇 |
综合类 | 67篇 |
化学工业 | 10586篇 |
金属工艺 | 2135篇 |
机械仪表 | 3242篇 |
建筑科学 | 1114篇 |
矿业工程 | 26篇 |
能源动力 | 2113篇 |
轻工业 | 3898篇 |
水利工程 | 271篇 |
石油天然气 | 88篇 |
武器工业 | 2篇 |
无线电 | 7811篇 |
一般工业技术 | 10669篇 |
冶金工业 | 7154篇 |
原子能技术 | 658篇 |
自动化技术 | 5030篇 |
出版年
2024年 | 24篇 |
2023年 | 539篇 |
2022年 | 859篇 |
2021年 | 1481篇 |
2020年 | 1071篇 |
2019年 | 1176篇 |
2018年 | 1431篇 |
2017年 | 1416篇 |
2016年 | 1751篇 |
2015年 | 1295篇 |
2014年 | 2091篇 |
2013年 | 3013篇 |
2012年 | 3265篇 |
2011年 | 3891篇 |
2010年 | 2816篇 |
2009年 | 2923篇 |
2008年 | 2812篇 |
2007年 | 2186篇 |
2006年 | 2036篇 |
2005年 | 1729篇 |
2004年 | 1575篇 |
2003年 | 1522篇 |
2002年 | 1333篇 |
2001年 | 1134篇 |
2000年 | 997篇 |
1999年 | 1029篇 |
1998年 | 2524篇 |
1997年 | 1571篇 |
1996年 | 1168篇 |
1995年 | 793篇 |
1994年 | 631篇 |
1993年 | 612篇 |
1992年 | 321篇 |
1991年 | 337篇 |
1990年 | 308篇 |
1989年 | 303篇 |
1988年 | 263篇 |
1987年 | 211篇 |
1986年 | 153篇 |
1985年 | 149篇 |
1984年 | 92篇 |
1983年 | 70篇 |
1982年 | 58篇 |
1981年 | 54篇 |
1980年 | 49篇 |
1979年 | 33篇 |
1978年 | 35篇 |
1977年 | 132篇 |
1976年 | 190篇 |
1975年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Sung-Ik Shim Yong-Soo Park Soon-Tae Kim Chi-Bok Song 《Metals and Materials International》2002,8(3):301-307
Austenitic stainless steels such as AISI 316L have been used in equipment in which fluid flows at high speeds which can induce cavitation erosion on metallic surfaces due to the collapse of cavities, where the collapse is caused by the sudden change of local pressure within the liquid. Usually AISI 316L is susceptible to cavitation erosion. This research focuses on developing a better material to replace the AISI 316L used in equipment with high speed fluid flow, such as impellers. The effects of Rare Earth Metal (REM) additions on the cavitation erosion-corrosion resistance of duplex stainless steels were studied using metallographic examination, the potentiodynamic anodic polarization test, the tensile test, the X-ray diffraction test and the ultrasonic cavitation erosion test. The experimental alloys were found to have superior mechanical properties due to interstitial solid solution strengthening, by adding high nitrogen (0.4%), as well as by the refinement of phases and grains induced by fine REM oxides and oxy-sulfides. Corrosion resistance decreases in a gentle gradient as the REM content increases. However, REM containing alloys show superior corrosion resistance compared with that of other commercial alloys (SAF 2507, AISI 316L). Owing to their excellent mechanical properties and corrosion resistance, the alloys containing REM have high cavitation erosion-corrosion resistance. 相似文献
992.
Young-Wook Kim Yong-Seong Chun Ji Yeon Park Woo Seog Ryu Dong-Soo Park 《Metals and Materials International》2007,13(3):197-200
A new process using SiC fiber fabrics and SiC tapes to produce dense 2D SiC fiber-SiC (SiC/SiC) composites is demonstrated.
The strategy for fabricating the SiC/SiC composites involves: (i) alternately stacking the SiC fiber fabrics and SiC tapes
at room temperature, (ii) pyrolyzing of the stacked composites, and (iii) hot-pressing the pyrolyzed composites. By controlling
the hot-pressing temperature, it is possible to obtain dense 2D SiC/SiC composites with relative densities of >98%. The 2D
SiC/SiC composites show no degradation of the SiC fibers and a higher mechanical strength. 相似文献
993.
This paper examines a new concept of corrosion surface damage analysis by using the digital image processing. Corrosion phenomena are analyzed using a digital value for morphological surface damages instead of electrochemical methods. Initial images are characterized by three categories: color, texture and shape features. To calculate corrosion surface damages color we use the interpretation of HIS model. For the texture attributes, the method of co-occurrence matrix is used. Five types of corrosion damage are examined. Multidimensional scaling procedure is used to define the classification plane. This study suggests a probabilistic method of decision-making. This analysis develops a method for automated identification system of corrosion damages and is supposed to be more advantageous than that of electrochemical techniques. 相似文献
994.
Development of the active balancing device for high-speed spindle system using influence coefficients 总被引:10,自引:0,他引:10
Jong-Duk Moon Bong-Suk Kim Soo-Hun Lee 《International Journal of Machine Tools and Manufacture》2006,46(9):978-987
A high-speed spindle can be very sensitive to rotating mass unbalance which has harmful effect on many types of rotating machinery. Therefore, the balancing procedure is certainly needed to reduce vibration in all high-speed rotating systems. In this study, an active balancing program using influence coefficient method and an active balancing device of an electro-magnetic type with both simple and reliable structures were applied to the developed high-speed spindle system. A gain scheduling control using influence coefficients of the reference model was proved to be effective in balancing the spindle system although its characteristics were changed. The stability of reference influence coefficients was verified by experiments with frequency response functions. The active balancing experiment of the manufactured spindle system using an active balancing program and device was also performed efficiently during the operation. As a result, controlled unbalance responses after balancing work were below the vibration limit at all rotating speed ranges including critical speeds. 相似文献
995.
Yoon -Suk Choi Sung -Joon Kim Ik -Min Park Kwang -Woo Kwon In -Suk Yoo 《Metals and Materials International》1997,3(2):118-124
Boron distribution in a low-alloy steel (15B26:0.25C-0.29Cr-0.03Ti-0.028Al-0.0016B) has been characterized employing Fission
Track Etching (FTE) method. The characteristics of boron distribution with variation of cooling rate after austenitization
and through case-hardened depth after carburization were analyzed. Hardenability of 15B26 steel was also evaluated through
Jominy-end-quench test and the results are as follows: It was observed that, in austenitized 15B26 steel, boron was distributed
uniformly over the whole area of specimen with a little segregation along the austenite grain boundaries at higher cooling
rates and boron precipitates were formed in the intergranular as well as transgranular regions at lower cooling rates. Jominy
equivalents (HRC 35) of 15B26 steel were fairly increased between the Jominy temperatures of 820°C and 850°C, which might
result from the increase of the amount of soluble boron in austenite due to the dissolution of borocarbides between 820°C
and 850°C. In carburized 15B26 steel, the different through thickness features of boron distribution from the carburized surface
were found; coarse nodular boron precipitates up to the depth of 150 μm; uniform distribution of dissolved boron between 150~650
μm; and segregation of boron atoms along grain boundaries in the regions deeper than 650 μm. 相似文献
996.
Galvanic coupling effect on the corrosion of SiC-reinforced aluminum alloy-matrix composites was investigated in a sodium chloride solution. The potentiodynamic polarization measurement indicated that pitting potentials of metal matrix composites (MMCs) and AA2124 matrix alloy were similar, and pitting potential of MMCs was almost same as corrosion potential, while pitting susceptibility of MMCs was higher than that of AA2124 alloy. Galvanic current by formation of galvanic couple between SiCw and matrix reveals very low value because of large cathodic polarization of SiC. However, by increasing potential of matrix to pitting potential by this galvanic couple and thus, forming pits easily at the weak passive film near SiC reinforcing phase preferentially, it is concluded that pitting susceptibility of MMCs increases highly than AA2124 alloy of matrix composition. 相似文献
997.
Hwan-Cheol Kim In-Jin Shon J.E. Garay Z.A. Munir 《International Journal of Refractory Metals and Hard Materials》2004,22(6):257-264
The rapid sintering of nano-structured WC hard materials in a short time is introduced with a focus on the manufacturing potential of this spark plasma sintering process. The advantage of this process allows very quick densification to near theoretical density and prohibition of grain growth in nano-structured materials. A dense pure WC hard material with a relative density of up to 97.6% was produced with simultaneous application of 60 MPa pressure and electric current of 2800 A within 2 min. A larger current caused a higher rate of temperature increase and therefore a higher densification rate of the WC powder. The finer the initial WC powder size the higher is the density and the better are the mechanical properties. The fracture toughness and hardness values obtained were 6.6 MPa m1/2 and 2480 kg/mm2, respectively under 60 MPa pressure and 2800 A using 0.4 μm WC powder. 相似文献
998.
Young?Ah?JeonEmail author Kwang?Soo?No Jong?Sung?Kim Young?Soo?Yoon 《Metals and Materials International》2003,9(4):383-387
ZnO films for electronic applications were deposited by radio-frequency (rf) sputtering onto various metal bottom electrodes
(Pt/Ti, W, Ni) to investigate such structural properties as crystallinity and surface morphology. The crystallinity, surface
morphology and composition of the as-deposited films were studied using X-ray diffraction (XRD), scanning electron microscopy
(SEM) and Rutherford back-scattering spectrometry (RBS), respectively. The preferred orientation and surface morphologies
were strongly influenced by the type of bottom electrodes. The ZnO films with (200) texturing deposited on Pt/Ti/SiO2/Si showed a smoother and smaller grain size than those deposited on W and Ni. The ZnO films on Pt and W electrodes exhibited
compressive residual stress.
This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials”,
organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei
University, Seoul, Korea on October 25–26, 2002. 相似文献
999.
A study has been made to investigate the superplastic deformation mechanisms of 7475 Al alloy in relation to the variation of grain size ranging between 5.5 μm and 13 μm. The strain-rate sensitivity (m) was increased with decreasing grain size in the superplastic deformation regime. Microstructural investigation after tension tests revealed that the dispersoid free zones were produced mostly at the grain boundaries normal to the tensile direction. A new model for describing the deformation behavior of the 7475 Al alloy has been proposed based on the assumption that the grain boundary sliding was accommodated by both diffusional flow and slip. This new model well predicts many aspects of experimental results. 相似文献
1000.
Gate location design in injection molding of an automobile junction box with integral hinges 总被引:5,自引:0,他引:5
Polymers such as polypropylene or polyethylene offer a unique feature of producing an integral or living hinge for automobiles, which can flex over a million times without causing a failure. However, due to increased fluidity resistance at hinges during molding, several defects such as short shot or premature failure can occur with the improper selection of gate locations. In this paper, a design guideline was induced by investigating resin flow patterns depending on several gate positions obtained by numerical analyses of a simple strip with a hinge. The analyses of the simple strip part showed that the resin at the hinge did not flow until the other side of the strip was filled. Once the resin at the hinge did not flow for a long time enough to be solidified, defects such as short shots or hesitation marks formed. For a practical application of the design guideline determined, four gate systems for an automobile junction box were designed. It was found that the properly determined gate location leads to better resin flow and shorter hesitation time. Finally, injection molding tryouts using a mold that was designed by one of the proposed gate systems were conducted. The experiments showed that hinges without defects could be produced by using the designed gate location to assure the induced design guideline to be reasonable. 相似文献