全文获取类型
收费全文 | 6491篇 |
免费 | 251篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 132篇 |
综合类 | 24篇 |
化学工业 | 799篇 |
金属工艺 | 110篇 |
机械仪表 | 198篇 |
建筑科学 | 346篇 |
矿业工程 | 3篇 |
能源动力 | 148篇 |
轻工业 | 298篇 |
水利工程 | 23篇 |
石油天然气 | 25篇 |
武器工业 | 3篇 |
无线电 | 1472篇 |
一般工业技术 | 1024篇 |
冶金工业 | 1118篇 |
原子能技术 | 33篇 |
自动化技术 | 1030篇 |
出版年
2023年 | 37篇 |
2022年 | 48篇 |
2021年 | 90篇 |
2020年 | 58篇 |
2019年 | 70篇 |
2018年 | 106篇 |
2017年 | 81篇 |
2016年 | 135篇 |
2015年 | 112篇 |
2014年 | 134篇 |
2013年 | 319篇 |
2012年 | 305篇 |
2011年 | 322篇 |
2010年 | 238篇 |
2009年 | 297篇 |
2008年 | 328篇 |
2007年 | 317篇 |
2006年 | 305篇 |
2005年 | 253篇 |
2004年 | 205篇 |
2003年 | 213篇 |
2002年 | 158篇 |
2001年 | 171篇 |
2000年 | 167篇 |
1999年 | 189篇 |
1998年 | 474篇 |
1997年 | 274篇 |
1996年 | 209篇 |
1995年 | 173篇 |
1994年 | 108篇 |
1993年 | 126篇 |
1992年 | 77篇 |
1991年 | 62篇 |
1990年 | 52篇 |
1989年 | 49篇 |
1988年 | 48篇 |
1987年 | 41篇 |
1986年 | 39篇 |
1985年 | 60篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 37篇 |
1981年 | 34篇 |
1980年 | 28篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 22篇 |
1976年 | 44篇 |
1975年 | 17篇 |
1973年 | 19篇 |
排序方式: 共有6786条查询结果,搜索用时 46 毫秒
111.
This paper presents a method of structuring the free space of a roving robot's environment into a set of overlapping convex regions ideally suited to path planning and navigation tasks. The structure of the free space environment is maintained as a hypergraph with each convex region represented by a hyperedge identifying the boundary walls of the region. A new methodology reveals the structure of free space and constructs the hypergraph representation through a directed search for a set of fundamental circits in an abstract graphical representation of the environment geometry. 相似文献
112.
Thermal stability behaviors of Cr(N,O)/CrN double-layered coatings by TGA/DTA analysis 总被引:1,自引:0,他引:1
In this study, Cr(N,O)/CrN double-layered coatings were synthesized using the cathodic arc deposition (CAD) process. CrN film was first deposited onto a substrate as an interlayer to ensure better adhesion, and Cr(N,O) film was subsequently deposited on top of the CrN layer as the surface layer. Variation in the Cr(N,O) coating composition was achieved through changing the O2/N2 flow ratio during the last stage of processing. Phase structure, chemical composition, and morphology of the resulting coatings were analyzed and observed using the X-ray diffractometer, Auger electron spectrometer and SEM. In addition, oxidation behavior of the coatings was investigated using TGA/DTA methods. The tests were carried out by increasing temperature up to 1000 °C in ambient air. With the introduction of oxygen gas during the CAD process, a superficial layer was produced in the Cr(N,O) constituent containing CrN and Cr2O3 phases. The formation of the oxide phase attributed to the reaction of chromium and oxygen was more favorable than that of chromium and nitrogen. The results also showed that Cr(N,O)/CrN double-layered coatings exhibited superior oxidation resistance at elevated temperature than that of CrN single-layer coated specimen (870 °C vs. 750 °C). 相似文献
113.
High-speed milling of titanium alloys using binderless CBN tools 总被引:4,自引:0,他引:4
Z. G. Wang Y. S. Wong M. Rahman 《International Journal of Machine Tools and Manufacture》2005,45(1):105-114
The performance of conventional tools is poor when used to machine titanium alloys. In this paper, a new tool material, which is binderless cubic boron nitride (BCBN), is used for high-speed milling of a widely used titanium alloy Ti–6Al–4V. The performance and the wear mechanism of the BCBN tool have been investigated when slot milling the titanium alloy in terms of cutting forces, tool life and wear mechanism. This type of tool manifests longer tool life at high cutting speeds. Observations based on the SEM and EDX suggest that adhesion of workpiece and attrition are the main wear mechanisms of the BCBN tool when used in high-speed milling of Ti–6Al–4V. 相似文献
114.
Tool wear and chatter detection using the coherence function of two crossed accelerations 总被引:1,自引:0,他引:1
X.Q. Li Y.S. Wong A.Y.C. Nee 《International Journal of Machine Tools and Manufacture》1997,37(4):425-435
Tool wear and chatter have been found to be the main causes of rejects in the machining of super alloys. A novel detection technique to identify both tool wear and chatter in turning a nickel-based super alloy is introduced. It uses the coherence function between two crossed accelerations from the bending vibration of the tool shank. The value of the coherence function at the chatter frequency reaches unity at the onset of chatter. Its values at the first natural frequencies of the tool shank approach unity in the severe tool wear stage. The results are interpreted using the analysis of the coherence function for a single input-two output model. The advantage of using this method is that the thresholds for detecting severe tool wear and chatter can be easily set, since values of coherence function are normalized to a range of between zero and unity, and are also not so susceptible to changing cutting conditions, because the value of the coherence function is close to unity at the onset of chatter and severe tool wear. 相似文献
115.
Direct laser sintering of a copper-based alloy for creating three-dimensional metal parts 总被引:12,自引:0,他引:12
Y. Tang H.T. Loh Y.S. Wong J.Y.H. Fuh L. Lu X. Wang 《Journal of Materials Processing Technology》2003,140(1-3):368-372
Direct laser sintering of metal, as one of the important developments in rapid prototyping technologies, is discussed in this paper. A special copper-based alloy is used for this rapid prototyping process. Experiments on the sintering conditions of this material had been conducted in a self-developed high temperature metal sintering machine. The mechanism of laser sintering for this kind of material was disclosed by SEM analysis of microstructures of sintered parts. The density, surface roughness and mechanical properties of the laser sintering parts due to variation of process parameters were measured and analysed. The effect of process parameters to the accuracy of sintered parts was also investigated. Thus, optimum parameters were obtained for direct laser sintering of three-dimensional metal parts. 相似文献
116.
The hydrodynamics of a two-dimensional gas–solid fluidized bed reactor were studied experimentally and computationally. Computational fluid dynamics (CFD) simulation results from a commercial CFD software package, Fluent, were compared to those obtained by experiments conducted in a fluidized bed containing spherical glass beads of 250– in diameter. A multifluid Eulerian model incorporating the kinetic theory for solid particles was applied in order to simulate the gas–solid flow. Momentum exchange coefficients were calculated using the Syamlal–O’Brien, Gidaspow, and Wen–Yu drag functions. The solid-phase kinetic energy fluctuation was characterized by varying the restitution coefficient values from 0.9 to 0.99. The modeling predictions compared reasonably well with experimental bed expansion ratio measurements and qualitative gas–solid flow patterns. Pressure drops predicted by the simulations were in relatively close agreement with experimental measurements at superficial gas velocities higher than the minimum fluidization velocity, Umf. Furthermore, the predicted instantaneous and time-average local voidage profiles showed similarities with the experimental results. Further experimental and modeling efforts are required in a comparable time and space resolutions for the validation of CFD models for fluidized bed reactors. 相似文献
117.
Woon Wong 《时间序列分析杂志》1997,18(2):181-194
A stationary multivariate time series { X t } is defined as linear if it can be written in the form X t = ∑∞ j =−∞ A j e t − j where A j are square matrices and e t are independent and identically distributed random vectors. If the e t } are normally distributed, then { X t is a multivariate Gaussian linear process. This paper is concerned with the testing of departures of a vector stationary process from multivariate Gaussianity and linearity using the bispectral approach. First the definition and properties of cumulants of random matrices are used to obtain the expressions for the higher-order cumulant and spectral vectors of a linear vector process as defined above. Then it is shown that linearity of a vector process implies constancy of the modulus square of its normalized higher-order spectra whereas the component of such a vector process does not necessarily have a linear representation. Finally, statistics for the testing of multivariate Gaussianity and linearity are proposed. 相似文献
118.
Nanoindentation of organomodified clay filled maleated polypropylene (MAPP) was investigated. The study aims to identify the relative increase in local stiffness in comparison to the increase in mechanical properties of the bulk in polypropylene-based nanocomposites. Such a study allows one to assess confined material property in addition to increased filler volume at the local scale. A mixture of highly intercalated and well exfoliated clay structures, when dispersed in MAPP matrix, was observed under transmission electron microscopy. The degree of exfoliation was found to increase with clay loading, which was attributed to the higher viscosity and mechanical shear forces during melt compounding. Instrumented indentation was performed on (1) clay aggregate supported by MAPP matrix, (2) clay-matrix boundary, and (3) the MAPP matrix. The clay aggregated region generally showed higher stiffness as compared to the matrix. And, the relative increase in indentation stiffness is substantially higher than the relative increase in tensile and compressive stiffnesses for clay reinforced systems. Polymer chain confinement and topological constraint appeared to be operative to enhance local stiffness in the clay aggregated region. Good correlation was, however, obtained between the change in macroscopic stiffness and the change in highly local indentation stiffness as a result of clay reinforcement. 相似文献
119.
Fluor公司开发的Fluor SOx净化工艺具有广泛多样的工艺布局,可以通过经济的方式定制脱除烟气中的有害组成。该工艺几乎能去除全部SOx并减少CO排放。Fluor SOx净化工艺的主要步骤已在多套工业装置中得到成功的证实。除技术可行、经济合理之外,Fluor SOx净化工艺不会产生任何有害副产物,也不会遇到与SOx有关的腐蚀问题。此外,该工艺生产高纯度可市售的元素硫。论述了Fluor SOx净化工艺的特征、技术和成本优势、设计和操作的简易性以及实施的便利性。 相似文献
120.
Fluor公司开发的Fluor SO_2净化工艺具有广泛多样的工艺布局,可以通过经济的方式定制脱除烟气中的有害组成。该工艺几乎能去除全部SO_2并减少CO排放。Fluor SO_x净化工艺的主要步骤已在多套工业装置中得到成功的证实。除技术可行、经济合理之外,Fluor SO_x净化工艺不会产生任何有害副产物,也不会遇到与SO_3 有关的腐蚀问题。此外,该工艺生产高纯度可市售的元素硫。论述了Fluor SO_x净化工艺的特征、技术和成本优势、设计和操作的简易性以及实施的便利性。 相似文献