全文获取类型
收费全文 | 6735篇 |
免费 | 669篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 58篇 |
综合类 | 6篇 |
化学工业 | 1843篇 |
金属工艺 | 261篇 |
机械仪表 | 413篇 |
建筑科学 | 119篇 |
矿业工程 | 1篇 |
能源动力 | 278篇 |
轻工业 | 784篇 |
水利工程 | 30篇 |
石油天然气 | 6篇 |
无线电 | 1143篇 |
一般工业技术 | 1484篇 |
冶金工业 | 239篇 |
原子能技术 | 100篇 |
自动化技术 | 660篇 |
出版年
2024年 | 8篇 |
2023年 | 109篇 |
2022年 | 152篇 |
2021年 | 269篇 |
2020年 | 189篇 |
2019年 | 216篇 |
2018年 | 260篇 |
2017年 | 286篇 |
2016年 | 336篇 |
2015年 | 276篇 |
2014年 | 386篇 |
2013年 | 467篇 |
2012年 | 509篇 |
2011年 | 666篇 |
2010年 | 455篇 |
2009年 | 391篇 |
2008年 | 355篇 |
2007年 | 283篇 |
2006年 | 253篇 |
2005年 | 218篇 |
2004年 | 163篇 |
2003年 | 188篇 |
2002年 | 158篇 |
2001年 | 126篇 |
2000年 | 109篇 |
1999年 | 98篇 |
1998年 | 136篇 |
1997年 | 68篇 |
1996年 | 62篇 |
1995年 | 41篇 |
1994年 | 32篇 |
1993年 | 22篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有7425条查询结果,搜索用时 15 毫秒
151.
Young-Soo Seo Weui-Bong Jeong Wan-Suk Yoo Ho-Kyeong Jeong 《Journal of Mechanical Science and Technology》2005,19(2):625-633
A finite element vibration analysis of thin-watled cylindrical shells conveying fluid with uniform velocity is presented The
dynamic behavior of thin-walled shell is based on the Sanders’ theory and the fluid in cyhndrical shell is considered as inviscid
and incompressible so that it satisfies the Laplace’s equation A beam-like shell element is used to reduce the number of degrees-of-freedom
by restricting to the circumferential modes of cylindrical shell An estimation of frequency response function of the pipe
considering of the coupled effects of the internal fluid is presented A dynamic coupling condition of the interface between
the fluid and the structure is used The effective thickness of fluid according to circumferential modes is also discussed
The influence of fluid velocity on the frequency response function is illustrated and discussed The results by this method
are compared with published lesults and those by commercial tools 相似文献
152.
Nak?Yong?KoEmail author Dong?Jin?Seo Koung?Suk?Kim 《Journal of Mechanical Science and Technology》2004,18(1):132-144
This paper presents a new method driving multiple robots to their goal position without collision. To consider the movement
of the robots in a work area, we adopt the concept of avoidability measure. The avoidability measure figures the degree of
how easily a robot can avoid other robots considering the velocity of the robots. To implement the concept to avoid collision
among multiple robots, relative distance between the robots is proposed. The relative distance is a virtual distance between
robots indicating the threat of collision between the robots. Based on the relative distance, the method calculates repulsive
force against a robot from the other robots. Also, attractive force toward the goal position is calculated in terms of the
relative distance. These repulsive force and attractive force are added to form the driving force for robot motion. The proposed
method is simulated for several cases. The results show that the proposed method steers robots to open space anticipating
the approach of other robots. In contrast, since the usual potential field method initiates avoidance motion later than the
proposed method, it sometimes fails preventing collision or causes hasty motion to avoid other robots. The proposed method
works as a local collision-free motion coordination method in conjunction with higher level of task planning and path planning
method for multiple robots to do a collaborative job. 相似文献
153.
Suárez-Orozco Carola; Gaytán Francisco X.; Bang Hee Jin; Pakes Juliana; O'Connor Erin; Rhodes Jean 《Canadian Metallurgical Quarterly》2010,46(3):602
Immigration to the United States presents both challenges and opportunities that affect students' academic achievement. Using a 5-year longitudinal, mixed-methods approach, we identified varying academic trajectories of newcomer immigrant students from Central America, China, the Dominican Republic, Haiti, and Mexico. Latent class growth curve analysis revealed that although some newcomer students performed at high or improving levels over time, others showed diminishing performance. Multinomial logistic regressions identified significant group differences in academic trajectories, particularly between the high-achieving youth and the other groups. In keeping with ecological–developmental and stage–environment fit theories, School Characteristics (school segregation rate, school poverty rate, and student perceptions of school violence), Family Characteristics (maternal education, parental employment, and household structure), and Individual Characteristics (academic English proficiency, academic engagement, psychological symptoms, gender, and 2 age-related risk factors, number of school transitions and being overaged for grade placement) were associated with different trajectories of academic performance. A series of case studies triangulate many of the quantitative findings as well as illuminate patterns that were not detected in the quantitative data. Thus, the mixed-methods approach sheds light on the cumulative developmental challenges that immigrant students face as they adjust to their new educational settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
154.
The fully lamellar microstructure of powder metallurgy Ti-48Al-2W after cooling from the α region to 1280 °C, followed by air cooling and aging at 950 °C for up to 96 hours, is presented. Aging times as short as
5 hours result in acicular-shaped precipitates of W-rich β
0 along lamellar interfaces, with the β
0 size increasing with aging time. The β
0 precipitates nucleate and grow in the α
2 lamellae. Concurrently, with the formation of β
0, the α
2 decomposes into discontinuous lamellae. Aging to precipitate β
0 along lamellar interfaces increases the 760 °C tensile strength (with a slight reduction of ductility) and reduces the instantaneous
creep strain, since β
0 precipitates at lamellar interfaces hinder interface dislocation mobility. The deformed microstructures from interrupted
creep tests at 140 to 276 MPa at 760 °C indicate that the precipitation of β
0 along interfaces substantially reduces the primary creep strain, primarily due to the influence of β
0 on interface dislocation emission and motion. These results are discussed in terms of the influence of lamellar morphology
on the instantaneous creep strain and primary creep transient, and the possible creep mechanisms are highlighted.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee of Mechanical Behavior of Materials. 相似文献
155.
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
156.
This paper deals with verb-verb morphological disambiguation of two different verbs that have the same inflected form. The verb-verb morphological ambiguity (VVMA) is one of the critical Korean parts of speech (POS) tagging issues. The recognition of verb base forms related to ambiguous words highly depends on the lexical information in their surrounding contexts and the domains they occur in. However, current probabilistic morpheme-based POS tagging systems cannot handle VVMA adequately since most of them have a limitation to reflect a broad context of word level, and they are trained on too small amount of labeled training data to represent sufficient lexical information required for VVMA disambiguation.In this study, we suggest a classifier based on a large pool of raw text that contains sufficient lexical information to handle the VVMA. The underlying idea is that we automatically generate the annotated training set applicable to the ambiguity problem such as VVMA resolution via unlabeled unambiguous instances which belong to the same class. This enables to label ambiguous instances with the knowledge that can be induced from unambiguous instances. Since the unambiguous instances have only one label, the automatic generation of their annotated corpus are possible with unlabeled data.In our problem, since all conjugations of irregular verbs do not lead to the spelling changes that cause the VVMA, a training data for the VVMA disambiguation are generated via the instances of unambiguous conjugations related to each possible verb base form of ambiguous words. This approach does not require an additional annotation process for an initial training data set or a selection process for good seeds to iteratively augment a labeling set which are important issues in bootstrapping methods using unlabeled data. Thus, this can be strength against previous related works using unlabeled data. Furthermore, a plenty of confident seeds that are unambiguous and can show enough coverage for learning process are assured as well.We also suggest a strategy to extend the context information incrementally with web counts only to selected test examples that are difficult to predict using the current classifier or that are highly different from the pre-trained data set.As a result, automatic data generation and knowledge acquisition from unlabeled text for the VVMA resolution improved the overall tagging accuracy (token-level) by 0.04%. In practice, 9-10% out of verb-related tagging errors are fixed by the VVMA resolution whose accuracy was about 98% by using the Naïve Bayes classifier coupled with selective web counts. 相似文献
157.
The performance of access methods and the underlying disk system is a significant factor in determining the performance of database applications, especially with large sets of data. While modern hard disks are manufactured with multiple physical zones, where seek times and data transfer rates vary significantly across the zones, there has been little consideration of this important disk characteristic in designing access methods (indexing schemes). Instead, conventional access methods have been developed based on a traditional disk model that comes with many simplifying assumptions such as an average seek time and a single data transfer rate. The paper proposes novel partitioning techniques that can be applied to any tree-like access methods, both dynamic and static, fully utilizing zoning characteristics of hard disks. The index pages are allocated to disk zones in such a way that more frequently accessed index pages are stored in a faster disk zone. On top of the zoned data placement, a localized query processing technique is proposed to significantly improve the query performance by reducing page retrieval times from the hard disk. 相似文献
158.
Effect of substrate temperature on structural, optical and electrical properties of ZnO thin films deposited by pulsed laser deposition 总被引:3,自引:0,他引:3
Seong Jun Kang Yang Hee Joung Hyun Ho Shin Yung Sup Yoon 《Journal of Materials Science: Materials in Electronics》2008,19(11):1073-1078
ZnO thin films were grown by the pulse laser deposition (PLD) method using Si (100) substrates at various substrate temperatures.
The influence of the substrate temperature on the structural, optical, and electrical properties of the ZnO thin films was
investigated. All of the thin films showed c-axis growth perpendicular to the substrate surface. At a substrate temperature of 500 °C, the ZnO thin film showed the highest
(002) peak with a full width at half maximum (FWHM) of 0.39°. The X-ray Photoelectron Spectroscopy (XPS) study showed that
Zn was in excess irrespective of the substrate temperature and that the thin film had a nearly stoichiometrical composition
at a substrate temperature of 500 °C. The photoluminescence (PL) investigation showed that the narrowest UV FWHM of 15.8 nm
and the largest ratio of the UV peak to the deep-level peak of 32.9 were observed at 500 °C. Hall effect measurement systems
provided information about the carrier concentration, mobility and resistivity. At a substrate temperature of 500 °C, the
Hall mobility was the value of 37.4 cm2/Vs with carrier concentration of 1.36 × 1018 cm−3 and resistivity of 2.08 × 10−1 Ω cm. 相似文献
159.
Plasmon Enhanced Fluorescence Based on Porphyrin–Peptoid Hybridized Gold Nanoparticle Platform 下载免费PDF全文
Younghye Kim Boyeong Kang Hyo‐Yong Ahn Jiwon Seo Ki Tae Nam 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(26)
A porphyrin–peptoid‐hybridized silica‐coated gold nanoparticle is developed, which is inspired by the protein–chlorophyll ensemble found in photosynthetic antenna. In the natural antenna, chlorophylls are integrated into dense assemblies that are supported by frameworks of proteins, which ensure optimal pigment arrangement for effective light harvesting. In the subject platform, porphyrins are conjugated to the peptoid helix scaffold in a structurally well‐defined alignments and subsequently immobilized on the surface of nanoparticles. This prevents intermolecular aggregation among porphyrins and allows high resolution analysis of the effect of porphyrin configuration on the optical properties of the system. Interestingly, under the influence of plasmon from the gold nanoparticle core, the fluorescence of porphyrin is enhanced up to 24‐fold at the wavelength where the plasmon resonance matches the porphyrin excitation wavelength. In addition, differences in porphyrin configuration result in spectral modification of their fluorescence emissions. Particularly, the peptoid bearing two porphyrins at a distance of 6 Å shows the most significant alteration in fluorescence. The platform can facilitate extensive studies on the relationship between porphyrin arrangement design and their photophysical interaction in antenna complexes. 相似文献
160.
Lee CY Kim GS Lee SY Kim TH Seo DW Lee SK 《Journal of nanoscience and nanotechnology》2011,11(8):6946-6952
Single crystalline silicon nanowires (SiNWs) were grown on Si(100) substrate using a gold (Au)-catalyzed vapor-liquid-solid (VLS) approach. The dependence of the growth time (i.e., the time of exposure to the Si source) on the density and surface evolution of the grown SiNWs is considered. It was observed that the density of grown SiNWs on Si substrate increased with increasing growth time. The highest density (approximately 1.1 x 10(6) mm(-2)) was reached at 4 hr. Upon further exposure to the Si source, we observed that the density was maintained for up to 9 hr. We suggest that the increased Si chemical potential in Au-Si droplets with increased growth time enhanced the SiNW growth rate at the interfaces between Au-Si droplets and SiNWs, and enhanced the transition of the NWs from the existing Au-Si droplets onto Si substrate. This allows the SiNW density to increase with increased growth time of up to 4 hr. Moreover, we examined the influence of the growth time on surface evolution including Au diffusion, facet and taper formation, and vapor-solid (VS) growth of the SiNWs. To explain the behavior of the grown SiNWs in the VLS process, we propose a combined model using the VLS and VS growth mechanisms. 相似文献