全文获取类型
收费全文 | 6240篇 |
免费 | 440篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 70篇 |
综合类 | 7篇 |
化学工业 | 1191篇 |
金属工艺 | 178篇 |
机械仪表 | 292篇 |
建筑科学 | 53篇 |
矿业工程 | 4篇 |
能源动力 | 169篇 |
轻工业 | 250篇 |
水利工程 | 36篇 |
无线电 | 766篇 |
一般工业技术 | 1139篇 |
冶金工业 | 2087篇 |
原子能技术 | 60篇 |
自动化技术 | 386篇 |
出版年
2023年 | 50篇 |
2022年 | 73篇 |
2021年 | 121篇 |
2020年 | 95篇 |
2019年 | 135篇 |
2018年 | 135篇 |
2017年 | 160篇 |
2016年 | 192篇 |
2015年 | 156篇 |
2014年 | 235篇 |
2013年 | 291篇 |
2012年 | 327篇 |
2011年 | 373篇 |
2010年 | 231篇 |
2009年 | 279篇 |
2008年 | 225篇 |
2007年 | 180篇 |
2006年 | 137篇 |
2005年 | 137篇 |
2004年 | 135篇 |
2003年 | 143篇 |
2002年 | 134篇 |
2001年 | 89篇 |
2000年 | 87篇 |
1999年 | 130篇 |
1998年 | 699篇 |
1997年 | 445篇 |
1996年 | 283篇 |
1995年 | 147篇 |
1994年 | 130篇 |
1993年 | 142篇 |
1992年 | 49篇 |
1991年 | 59篇 |
1990年 | 37篇 |
1989年 | 35篇 |
1988年 | 46篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 40篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 15篇 |
1980年 | 27篇 |
1979年 | 10篇 |
1977年 | 48篇 |
1976年 | 107篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1955年 | 4篇 |
排序方式: 共有6688条查询结果,搜索用时 15 毫秒
31.
Chul Kim Chul Woo Park 《The International Journal of Advanced Manufacturing Technology》2006,29(5-6):459-474
This paper deals with an automated computer-aided process planning and die design system by which the designer can determine
operation sequences even if they have little experience in process planning and die design for axisymmetric products. An attempt
is made to link programs incorporating a number of expert design rules with the process variables obtained by commercial FEM
softwares, DEFORM and ANSYS, to form a useful package. The system is composed of four main modules. The process planning and
the die design modules consider several factors, such as the complexities of preform geometry, punch and die profiles, specifications
of available multi-former, and the availability of standard parts. They can provide a flexible process based on either the
reduction in the number of forming sequences by combining the possible two processes in sequence, or the reduction of deviation
of the distribution on the level of the required forming loads by controlling the forming ratios. In the die design module
optimal design technique and the horizontal split of the die insert were investigated for determining appropriate dimensions
of components of the multi-former die set. It is suggested that the proposed method can be beneficial for improving the tool
life of the die set in practice. 相似文献
32.
In a previous paper [J. Nucl. Mater. 137 (1985) 7], the present authors have shown that void-lattice formation in crystals under irradiation is a non-equilibrium disorder-order phase transition that is intimately related to the existence of a one-dimensionally diffusing, metastable excited self-interstitial state (crowdion), as assumed in the two-interstitial model. In contrast to all other models of void-lattice formation, this theory explains in a natural way why void lattices possess the same structure and orientation as the host crystal lattices.
In the present work, the theory is extended to the evolution of void lattices after their formation. The three most characteristic features of void-lattice evolution, viz., the occurrence of void-growth saturation, the size uniformity of voids in a void lattice, and the displacive stability of void lattices within a wide range of the governing parameters, are not only predicted by the present theory but can be traced to a common cause — the existence of one-dimensionally migrating crowdions, previously shown to be the cause of void-lattice formation. 相似文献
33.
Chun Woo Young; Kruglanski Arie W.; Sleeth-Keppler David; Friedman Ronald S. 《Canadian Metallurgical Quarterly》2011,101(5):1124
This research examines the possibility that people's choices in the service of an explicit focal goal may also reflect their tendency to fulfill implicit background goals and in that sense are multifinal. We carried out 5 experimental studies to investigate this notion. In Experiment 1, a primed implicit goal affected individuals' choices even when those avowedly served an explicit “focal” goal. Experiment 2 replicated this finding with a different type of implicit goals. Experiment 3 found that primed implicit goals had no effect on choices where the options that served them undermined the explicit goal. Experiment 4 found that a primed implicit goal served by a multifinal option does not privilege it over a unifinal option if that goal had been already attained by a different means. Finally, Experiment 5, via 3 types of control groups, showed that choices were affected by both the explicit and implicit goals in isolation, and they shifted toward multifinality when these goals were conjointly present. The discussion considers the integrative potential of the multifinality framework and its implications for a variety of phenomena in the domain of motivated cognition. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
34.
Tae Woo Kim Hana Yoo In Young Kim Hyung‐Wook Ha Ah Reum Han Jong‐San Chang Ji Sun Lee Seong‐Ju Hwang 《Advanced functional materials》2011,21(12):2301-2310
Manganese oxide nanocrystals are combined with aluminum oxide nanocrystals to improve their crystallinity via calcination without a significant increase of crystal size. A nanocomposite, consisting of two metal oxides, can be synthesized by the reaction between permanganate anions and aluminum oxyhydroxide keggin cations. The as‐prepared manganese oxide–aluminum oxide nanocomposite is X‐ray amorphous whereas heat‐treatment gives rise to the crystallization of an α‐MnO2 phase at 600 °C and Mn3O4/Mn2O3 and γ‐Al2O3 phases at 800 °C. Electron microscopy and N2 adsorption‐desorption‐isotherm analysis clearly demonstrate that the as‐prepared nanocomposite is composed of a porous assembly of monodisperse primary particles with a size of ~20 nm and a surface area of >410 m2 g?1. Of particular interest is that the small particle size of the as‐prepared nanocomposite is well‐maintained up to 600 °C, a result of the prevention of the growth of manganate grains through nanoscale mixing with alumina grains. The calcined nanocomposite shows very‐high catalytic activity for the oxidation of cyclohexene with an extremely high conversion efficiency of >95% within 15 min. The present results show that the improvement of the crystallinity without significant crystal growth is very crucial for optimizing the catalytic activity of manganese oxide nanocrystals. 相似文献
35.
36.
Dong Kyun YimIn-Sun Cho Chan Woo LeeJun Hong Noh Hee Suk RohKug Sun Hong 《Optical Materials》2011,33(7):1036-1040
Novel whitish-blue phosphors based on a phosphate host matrix, γ-KCaPO4: Eu2+, were prepared by a conventional solid-state reaction method using slightly phosphorus deficient conditions and their photoluminescence properties were investigated. The concentration quenching process, temperature dependence of the luminescence and decay curve were also investigated. The γ-KCaPO4: Eu2+ phosphor was efficiently excited by UV-Visible light at wavelengths of 200-450 nm and exhibited a bright whitish-blue emission with a maximum peak wavelength of 473 nm. All of these characteristics suggest that the γ-KCaPO4: Eu2+ phosphors combined with red phosphors could be applicable to near UV-based white LEDs, i.e., only two kinds of phosphor powders are needed for the formation of white light. 相似文献
37.
The main goal of the present study is to optimise the precharge conditions such as the precharge location and dimensions that give significant effects on the mechanical performance of composite structures manufactured by the compression moulding process. As preliminary step of optimisation, we developed a manufacturing simulation program to predict the fibre volume fraction and fibre orientation. And coupled with this simulation program and a structural analysis program, a genetic algorithm (GA) is implemented to optimise the precharge conditions. The penalty function method and the repair algorithm are modified for handling constraints. The repair algorithm is applied to a symmetric structure and an arbitrary shape structure to find optimal precharge conditions. 相似文献
38.
Kee Do Woo Jae Hwang Kim Eui Pyo Kwon Min Seok Moon Hyun Bom Lee Tatsuo Sato Zhiguang Liu 《Metals and Materials International》2010,16(2):213-218
To fabricate an Al-V matrix composite reinforced with submicron-sized Al2O3 and AlxVy (Al3V, Al10V) phases, high energy mechanical milling (HEMM) and sintering were employed. By increasing the milling time, the size of mechanically milled powder was significantly reduced. In this study, the average powder size of 59 μm for Al, and 178 μm for V2O5 decreased with the formation of a new product, Al-Al2O3-AlxVy, with a size range from 1.3 μm to 2.6 μm formed by the in-situ combustion reaction during sintering of HEM milled Al and V2O5 composite powders. The in-situ reaction between Al and V2O5 during the HEMM and sintering transformed the Al2O3 and AlxVy (Al3V, Al10V) phases. Most of the reduced V reacted with excess the Al to form AlxVy (Al3V, Al10V) with very little V dissolved into Al matrix. By increasing the milling time and weight percentage of V2O5, the hardness of the Al-Al2O3-AlxVy composite sintered at 1173 K increased. The composite fabricated with the HEMM Al-20wt.%V2O5 composite powder and sintering at 1173 K for 2 h had the highest hardness. 相似文献
39.
基于级联卷积神经网络的疲劳检测 总被引:1,自引:0,他引:1
为了诊断热核聚变等离子体状态,研制了用于热 斑区等离子体诊断用的新型X射线光谱仪,能够同 时探测X射线光谱与聚爆靶图像信息。光谱检测功能由4块椭圆晶体分析器实现,材料分别 为α-石英(1010)、 α-石英(2023)、α-石英(1011)和Si(111),几乎能够覆盖2~20 keV能带范围内的X射线特 征光谱。光谱检测 结构为光源位于椭圆的一个焦点,其辐射光谱经过椭圆反射聚焦于椭圆另一焦点,由X射线 成像板(IP)接收。图 像检测功能由分幅相机匹配小孔阵列成像完成,理想状态能够得到20 幅不同时间的聚爆靶图像。在谱仪与 聚爆靶之间的调整台上设置厚为60μm的Be膜,以保护针孔与晶体避 免聚爆溅射碎片破坏。在中物院“神光- Ⅱ”升级装置上进行了打靶实验,获取了X射线光谱与聚爆靶图像信号。分析了光谱及图像 信息,并针对光谱 仪漏光问题改进了光谱仪结构,最后在神光-Ⅲ原型装置上进行了验证实验并获得比较理想 的图像信号,信噪比(SNR)数据达到15dB。 相似文献
40.
Reconstruction of conductivity and current density images using only one component of magnetic field measurements 总被引:5,自引:0,他引:5
Magnetic resonance current density imaging (MRCDI) is to provide current density images of a subject using a magnetic resonance imaging (MRI) scanner with a current injection apparatus. The injection current generates a magnetic field that we can measure from MR phase images. We obtain internal current density images from the measured magnetic flux densities via Ampere's law. However, we must rotate the subject to acquire all of the three components of the induced magnetic flux density. This subject rotation is impractical in clinical MRI scanners when the subject is a human body. In this paper, we propose a way to eliminate the requirement of subject rotation by careful mathematical analysis of the MRCDI problem. In our new MRCDI technique, we need to measure only one component of the induced magnetic flux density and reconstruct both cross-sectional conductivity and current density images without any subject rotation. 相似文献