全文获取类型
收费全文 | 58273篇 |
免费 | 2742篇 |
国内免费 | 201篇 |
专业分类
电工技术 | 867篇 |
综合类 | 96篇 |
化学工业 | 10847篇 |
金属工艺 | 2070篇 |
机械仪表 | 3068篇 |
建筑科学 | 1240篇 |
矿业工程 | 53篇 |
能源动力 | 2159篇 |
轻工业 | 4070篇 |
水利工程 | 265篇 |
石油天然气 | 216篇 |
武器工业 | 1篇 |
无线电 | 10021篇 |
一般工业技术 | 11237篇 |
冶金工业 | 7527篇 |
原子能技术 | 630篇 |
自动化技术 | 6849篇 |
出版年
2023年 | 531篇 |
2022年 | 834篇 |
2021年 | 1403篇 |
2020年 | 992篇 |
2019年 | 1009篇 |
2018年 | 1334篇 |
2017年 | 1326篇 |
2016年 | 1655篇 |
2015年 | 1308篇 |
2014年 | 2035篇 |
2013年 | 3485篇 |
2012年 | 3194篇 |
2011年 | 3906篇 |
2010年 | 2975篇 |
2009年 | 3166篇 |
2008年 | 2921篇 |
2007年 | 2464篇 |
2006年 | 2244篇 |
2005年 | 1942篇 |
2004年 | 1853篇 |
2003年 | 1703篇 |
2002年 | 1653篇 |
2001年 | 1292篇 |
2000年 | 1205篇 |
1999年 | 1232篇 |
1998年 | 2779篇 |
1997年 | 1697篇 |
1996年 | 1400篇 |
1995年 | 1060篇 |
1994年 | 814篇 |
1993年 | 796篇 |
1992年 | 498篇 |
1991年 | 513篇 |
1990年 | 445篇 |
1989年 | 435篇 |
1988年 | 353篇 |
1987年 | 301篇 |
1986年 | 269篇 |
1985年 | 245篇 |
1984年 | 200篇 |
1983年 | 154篇 |
1982年 | 155篇 |
1981年 | 141篇 |
1980年 | 142篇 |
1979年 | 102篇 |
1978年 | 95篇 |
1977年 | 147篇 |
1976年 | 259篇 |
1975年 | 80篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Chang-Hyun Park Jun-Hee Lee Jae-Hyuk Jeong Dong-Hoon Choi 《Structural and Multidisciplinary Optimization》2014,49(1):131-145
When a cleaning blade in a laser printer is excessively deformed, immoderate permanent set can result, leading to weaker nip pressure between the cleaning blade and OPC drum that worsens its cleaning performance and printing quality. In this study, the correlation of the permanent set with stress and strain was investigated through tensile tests with rubber test specimens. Based on the experimental results, the maximum von-Mises stress value was used to quantify the permanent set. A design optimization problem was formulated to minimize the maximum von-Mises stress while satisfying the design constraints for maintaining appropriate contact between the cleaning blade and the OPC drum. We employed metamodel-based design optimization using design of experiments, metamodeling and an optimization algorithm to circumvent the difficulty of structural analyses at some design points. Using the proposed design approach, the optimal maximum von-Mises stress was reduced by 40.2 % compared to the initial stress value while all the design constraints were satisfied. In order to verify the validity of our design optimization result, we manufactured the cleaning blades according to the optimum design solution and performed permanent set and printer tests. The test results clearly showed the validity of our design optimization result. 相似文献
992.
The Energy based topology optimization method has been used in the design of compliant mechanisms for many years. Although many successful examples from the energy based topology optimization method have been presented, optimized configurations of these designs are often very similar to their rigid linkage counterparts; except using compliant joints in place of rigid links. These complaint joints will endure large strain under the applied forces in order to perform the specified motions which are very undesirable in a compliant mechanism design. In this paper, a strain based topology optimization method is proposed to avoid a localized high strain of the compliant mechanism design, which is one of the drawbacks using strain energy formulation. Therefore, instead of minimizing the strain energy for structural rigidity, a global effective strain function is minimized. This is done in order to distribute the strain within the entire mechanism while maximizing the structural rigidity. Furthermore, the physical programming method is adopted to accommodate both flexibility and rigidity design objectives. Design examples from both the strain energy based topology optimization and the strain based method are presented and discussed. 相似文献
993.
Gil-Young Song Youngjoon Cheon Kihwang Lee Heuiseok Lim Kyung-Yong Chung Hae-Chang Rim 《Personal and Ubiquitous Computing》2014,18(6):1387-1403
As various forms of social media are spreading, we often witness that an idea of an individual user drives macroscopic changes. From the perspectives of product development and marketing, the opinions left by potential consumers in online social network can generate big ripple effects. This study analyzes the user opinions in online space to grasp preferences toward various products psychologically categorized by users. We also suggest an aspect of the market mentally configured by users using network modeling while following the framework of economic sociology. Existing analyses on online market place are mainly dealing with structural issues such as inter-actor relationships and status measurement. This study, however, analyzes complex preferences regarding diverse products and brands and derives a new model for inter-market connections. We expect that our study will provide important consequences on digital marketing and community design of corporations planning word of mouth effect in online space. 相似文献
994.
Jung-Gi Yang Jae-Kwon Kim Un-Gu Kang Young-Ho Lee 《Personal and Ubiquitous Computing》2014,18(6):1351-1362
Coronary heart disease is a great concern in the field of healthcare, and one of the main causes of death across the world. In the USA, as in Europe, it is responsible for the highest mortality rate. Although the risk of coronary heart disease has been recognized, few studies have been conducted on this topic. On the other hand, computer science has become an important part of our lives. The use of medicine and medical science-related artificial intelligence facilitating the diagnosis and analysis of diseases and health problems is attracting considerable attention. The present study focuses on the determination of the optimum method for using artificial intelligence in a clinical decision support system in order to provide a solution and diagnosis regarding the research and medical issues related to the application of such a system. In the present study, we have developed a prediction model capable of the risk assessment of coronary heart disease by optimizing an adaptive-network-based fuzzy inference system (ANFIS) and linear discriminant analysis (LDA) on the basis of the dataset of Korean National Health and Nutrition Examinations Survey V. The ANFIS–LDA method, which is optimized using a hybrid method, exhibits a high prediction rate of 80.2 % and is more efficient and effective than the existing methods. We expect that our study to contribute to the prevention of coronary heart disease. 相似文献
995.
This paper proposes a technique for the detection of head nod and shake gestures based on eye tracking and head motion decision. The eye tracking step is divided into face detection and eye location. Here, we apply a motion segmentation algorithm that examines differences in moving people’s faces. This system utilizes a Hidden Markov Model-based head detection module that carries out complete detection in the input images, followed by the eye tracking module that refines the search based on a candidate list provided by the preprocessing module. The novelty of this paper is derived from differences in real-time input images, preprocessing to remove noises (morphological operators and so on), detecting edge lines and restoration, finding the face area, and cutting the head candidate. Moreover, we adopt a K-means algorithm for finding the head region. Real-time eye tracking extracts the location of eyes from the detected face region and is performed at close to a pair of eyes. After eye tracking, the coordinates of the detected eyes are transformed into a normalized vector of x-coordinate and y-coordinate. Head nod and shake detector uses three hidden Markov models (HMMs). HMM representation of the head detection can estimate the underlying HMM states from a sequence of face images. Head nod and shake can be detected by three HMMs that are adapted by a directional vector. The directional vector represents the direction of the head movement. The vector is HMMs for determining neutral as well as head nod and shake. These techniques are implemented on images, and notable success is notified. 相似文献
996.
The concept and design of a new chemical vapor deposition (CVD) reactor is presented for both epitaxial and nonepitaxial film
deposition in semiconductor processing. The reactor is designed in such a way that a stagnant semiconductor source fluid of
uniform concentration is provided for the film deposition without causing free or forced convection. The supply of the source
gas for the deposition is by diffusion through a porous material such as quartz or graphite. Compared to the low pressure
CVD (LPCVD) reactor with mounted wafer configuration, the new reactor should give a better film thickness uniformity and about
an order of magnitude reduction in the amount of the source gas required. Further, at least for polycrystalline silicon deposition,
the deposition rate can be much higher than is currently practiced with the LPCVD reactor. Design equations for the reactor
are given. Details on the design for the polycrystalline silicon deposition are also given. 相似文献
997.
Ki Soo ParkMyung Hun Cho Sang Ho ParkKee Suk Nahm Yang Kook SunYun Sung Lee Masaki Yoshio 《Electrochimica acta》2002,47(18):2937-2942
Layered Li0.7[M1/6Mn5/6]O2 (M=Li, Ni) was synthesized using a sol-gel method. P2-Na0.7[M1/6Mn5/6]O2 precursor was first synthesized by a sol-gel method, and then O2-Li0.7[M1/6Mn5/6]O2 was prepared by an ion exchange of Li for Na in P2-Na0.7[M1/6Mn5/6]O2 precursor. From charge/discharge curves, it was seen that Li0.7[Li1/6Mn5/6]O2 has two plateaus similar to those observed from a spinel structure, but Li0.7[Ni1/6Mn5/6]O2 holds a single plateau as observed from a typical layered structure. It was considered that Li0.7[Li1/6Mn5/6]O2 undergoes a phase transformation from layered to spinel structure during the charge/discharge cycle, but Li0.7[Ni1/6Mn5/6]O2 maintains O2-layered structure after the cycles. Li0.7[Ni1/6Mn5/6]O2 was higher in discharge capacity and retention rate than Li0.7[Li1/6Mn5/6]O2. 相似文献
998.
A photopolymerization process at room temperature was devised to copolymerize vinyl acetate (VAc) and n‐butyl acrylate (BA) mainly to prepare rubber‐like damping sheet bearing pressure‐sensitive adhesive property in this study. The investigations using both the differential scanning calorimeter and rheometric dynamic analysis show the existence of two glass transition temperatures for each copolymer. The scanning electron microscopic pictures reveal that the degree of microphase separation increases with increasing annealing time at 70°C. It was suggested that the rubbery domain (formed by the PBA blocks) disperses in the glassy domain (constituted by the PVAc blocks), making an effective damping entity. Excellent damping was observed for the copolymer samples, with the tanδ peak values as high as 1.76–1.80 at a certain temperature range and with tanδ> 0.3 at quite wide temperature ranges. In addition, the copolymers containing more VAc tend to have the higher damping. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1396–1403, 2004 相似文献
999.
4-{1′-(2″-Methacryloyloxyethoxy)-5′-naphthyliminomethylidene}-4′-nitro-stilbene 6 was prepared by the reactions of methacryloyl chloride with 4-{1′-(2″-hydroxyethoxy)-5′-naphthyliminomethylidene}-4′-nitrostilbene
5. Compound 5 was synthesized from 4′-methyl-4-nitrostilbene by several reaction steps. Monomer 6 was polymerized with DTBP as a radical initiator to obtain polymer with 4-(1′-oxy-5′-naphthyliminomethylidene)-4′-nitrostilbene,
which is presumably effective chromophore for second-order nonlinear optical applications in the side chain. The resulting
polymethacrylate 7 showed a thermal stability up to 300 °C in TGA thermogram, and the Tg value obtained from DSC thermogram was 120 °C, which is acceptable for NLO device applications.
Received: 14 October 1996/Accepted: 11 December 1996 相似文献
1000.
The objective of this research was to evaluate the effectiveness of several different methods for controlling the pore size and pore size distribution in activated carbon fibers. Variables studied included fiber shape, activation time, and the addition of small amounts of silver nitrate. Pure isotropic pitch and the same isotropic pitch containing 1 wt.% silver were melt spun to form fibers with round and trilobal cross sections. These fibers were then stabilized, carbonized, and activated in carbon dioxide. Field emission scanning electron microscopy (FE SEM), electron dispersive spectra (EDS), and wavelength dispersive spectra (WDS) were used to monitor the size and distribution of the silver particles in the fibers before and after activation. Each of these analyses showed that the distribution of silver particles was extremely uniform before and after activation. The fibers were also weighed before and after activation to determine the percent burn-off. The BET specific surface areas of the activated fibers were determined from N2 adsorption isotherms measured at −196 °C. The results showed that round and trilobal fibers with equivalent cross-sectional areas yielded similar burn-off values and specific surface areas after activation. Also, activation rates were found to be independent of CO2 flow rate. The porosity of the activated fibers depended on the total time of activation and the cross-sectional area of fibers. The N2 adsorption measurements showed that the activated fibers had extremely high specific surface areas (greater than 3000 m2/g) and high degrees of meso- and macro-porosity. FE SEM was also used to investigate surface texture and size of pore openings on the surfaces of the activated fibers. The photos showed that silver particles generated surface macro- and mesopores, in agreement with the inferences from N2 adsorption measurements. 相似文献