首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3272篇
  免费   83篇
  国内免费   4篇
电工技术   32篇
综合类   10篇
化学工业   695篇
金属工艺   83篇
机械仪表   59篇
建筑科学   75篇
矿业工程   1篇
能源动力   100篇
轻工业   237篇
水利工程   12篇
石油天然气   4篇
无线电   467篇
一般工业技术   558篇
冶金工业   577篇
原子能技术   16篇
自动化技术   433篇
  2023年   17篇
  2022年   67篇
  2021年   70篇
  2020年   27篇
  2019年   32篇
  2018年   50篇
  2017年   45篇
  2016年   58篇
  2015年   67篇
  2014年   97篇
  2013年   229篇
  2012年   155篇
  2011年   221篇
  2010年   183篇
  2009年   205篇
  2008年   189篇
  2007年   196篇
  2006年   135篇
  2005年   127篇
  2004年   110篇
  2003年   83篇
  2002年   98篇
  2001年   67篇
  2000年   58篇
  1999年   54篇
  1998年   139篇
  1997年   84篇
  1996年   77篇
  1995年   42篇
  1994年   46篇
  1993年   35篇
  1992年   32篇
  1991年   34篇
  1990年   26篇
  1989年   25篇
  1988年   14篇
  1987年   13篇
  1986年   16篇
  1985年   14篇
  1984年   18篇
  1983年   7篇
  1982年   13篇
  1981年   14篇
  1980年   13篇
  1979年   11篇
  1978年   5篇
  1977年   7篇
  1976年   6篇
  1973年   5篇
  1971年   4篇
排序方式: 共有3359条查询结果,搜索用时 15 毫秒
151.
Optimum structure for HD-DVD optical disks containing Al–Ti/Si bi-layer recording system was identified by reflectivity simulation and dynamic test of disk samples. For the disk sample with optimized structure, the maximum partial response signal-to-noise ratio (PRSNR) of 19.1 dB, minimum simulated bit error rate (sbER) of 1.7 × 10?7 and modulation >0.6 were achieved at the writing power (Pw) = 11.2 mW. Transmission electron microscopy (TEM) revealed that the polycrystalline granular clusters constitute the recording marks. Subsequent analyses evidenced that element mixing/alloy reactions occur in between Si and Al–Ti layers and the formation of Al3.21Si0.47 crystalline phase is responsible for the signal recording in the disk samples.  相似文献   
152.
An oxygen concentration dependent metal–nonmetal (MN) transition was observed for Rb0.23WO y with 2.80 < y < 3.08. As 2.80 < y < 3.0, the room temperature resistivity (RT) of the Rb0.23WO y is about 5 × 10–4 cm. While in the case of y > 3.04, the RT of the Rb0.23WO y exhibits a four orders of magnitude increase with a value of 5 cm. Correspondingly, the lattice constant along c-direction slightly shortens as oxygen concentration increases from 2.80 to 3.08. The observed results suggest that the hybridization between W 5d (t2g) and O 2p orbitals might be responsible for the MN transition. In addition, similar measurements were performed for Rb x WO3.04 and Rb x WO2.85 with 0.19 < x < 0.27. No rubidium concentration dependent MN transition was observed, indicating the electronic structure of the host WO y is not modified significantly by varying the soluble rubidium concentration.  相似文献   
153.
Aqueous solutions of acetate-functionalized alumina nanoparticles (A-alumoxane), with an average particle size of 28 nm, have been used as alumina precursors for the surface infiltration and repair of porous and/or damaged alumina surfaces. SEM and AFM measurements indicate that treatment with a 1 wt% solution results in a reduction of surface roughness from >0.6 m to 100 nm for surface pores in the 100 nm to 1 m range. The use of 6 wt% solutions gives better infiltration repair for 50 m features, but surface cracking is observed. The surface hardness of the porous alumina substrate is increased upon infiltration. No spallation of the surface infiltration layer is observed after indentation measurements and grain dislodgment is overcome.  相似文献   
154.
Wu SP  Hsieh CS 《Applied ergonomics》2002,33(5):493-501
The culinary spatula (turning shovel) is one of the most common cooking tools used in the kitchen in Asia. However, the culinary spatula has seldom been ergonomically investigated. When a person uses a spatula to cook food, the operations involve repetitive bent-wrist motions, such as dorsiflexion, palmary flexion, and radial and ulnar deviations. These movements may cause cumulative trauma disorders in the upper extremities, and in particular carpal tunnel syndrome. A poorly designed culinary spatula will be ergonomically inefficient and cause injury to the hand and wrist. The purpose of this study was to investigate the effects of spatula handle length and lift angle on food-frying, food-turning, and food-shoveling performance. Eight female subjects were tested using 16 different culinary spatulas, with four different handle lengths (20, 25, 30 and 35 cm) and four different lift angles (15 degrees, 25 degrees, 35 degrees and 45 ). The criterion measures included cooking performance, and rating of perceived exertion. The subjects ranked their preference after all of the tasks in the tests were completed. The results showed that: (1) The handle length had a significant influence on the cooking performance, and rating of perceived exertion. The optimal handle lengths for frying food, turning food, and shoveling food were 20, 25 and 25 cm, respectively. (2) The lift angle significantly affected the cooking performance, and rating of perceived exertion. The optimal lift angles for frying food, turning food, and shoveling food were 15 degrees, 15 degrees and 25 degrees, respectively. (3) Both the handle length and lift angle had significant effects on subjective preference. For the handle length, the 20 cm length was the best. For the lift angle, the 25 angle was the best. (4) In general, a spatula with a 20 cm handle length and 25 degrees lift angle was the best. A spatula with a 25 cm handle length and 15 lift angle was the second most preferred. (5) However, to prevent subjects from touching the edge of a hot pan, a spatula with a 25 cm handle length and 25 lift angle is suggested.  相似文献   
155.
This study evaluated spinal loads associated with lifting and hanging heavy mining cable in a variety of postures. This electrical cable can weigh up to 10 kg per metre and is often lifted in restricted spaces in underground coal mines. Seven male subjects performed eight cable lifting and hanging tasks, while trunk kinematic data and trunk muscle electromyograms (EMGs) were obtained. The eight tasks were combinations of four postures (standing, stooping, kneeling on one knee, or kneeling on both knees) and two levels of cable load (0 N or 100 N load added to the existing cable weight). An EMG-assisted model was used to calculate forces and moments acting on the lumbar spine. A two-way split-plot ANOVA showed that increased load (p < 0.05) and changes in lifting posture (p < 0.05) independently affected trunk muscle recruitment and spinal loading. The increase in cable load resulted in higher EMG activity of all trunk muscles and increased axial and lateral bending moments on the spine (p < 0.05). Changes in posture caused more selective adjustments in muscle recruitment and affected the sagittal plane moment (p < 0.05). Despite the more selective nature of trunk EMG changes due to posture, the magnitude of changes in spinal loading was often quite dramatic. However, average compression values exceeded 3400 N for all cable lifting tasks.  相似文献   
156.
Abstract— A 3.5‐in. QVGA‐formatted driving‐circuit fully integrated LCD has been developed using low‐temperature poly‐Si (LTPS) technology. This display module, in which no external ICs are required, integrates all the driving circuits for a six‐bit RGB digital interface with an LTPS device called a “FASt LDD TFT” and achieves a high‐quality image, narrow frame width, and low power consumption. The LTPS process, device, and circuit technologies developed for system‐on‐glass LCD discussed. The development phase of LTPS circuit integration for system‐on‐glass LCDs is also reviewed.  相似文献   
157.

This paper presents a novel micro-fabricated formaldehyde gas sensor with enhanced sensitivity and detection resolution capabilities. The device comprises a quartz substrate with Pt heaters as a micro-hotplate and deposited formaldehyde-sensing layer on it. A sputtered NiO thin film is used as the formaldehyde-sensing layer. A specific orientation of NiO becomes more apparent as the substrate temperature increases in the sputtering process, which helps the formation of NiO material with a correct stoichiometric ratio. The gas sensor incorporates Pt heating resistors integrated with a micro-hotplate to provide a heating function and utilizes Au inter-digitated electrodes. When formaldehyde is present in the atmosphere, oxydation happens near the sensing layer with a high temperature caused by the micro-hotplate and causes a change in the electrical conductivity of the NiO film. Therefore, the measured resistance between the inter-digitated electrodes changes correspondingly. The application of a voltage to the Pt heaters causes the temperature of the micro-hotplate to increase, which in turn enhances the sensitivity of the sensor. The nanometer scale grain size of the sputtered oxide thin film is conducive to improving the sensitivity of the gas sensor. The experimental results indicate that the developed device has a high stability (0.23%), a low hysteresis value (0.18%), a quick response time (13.0 s), a high degree of sensitivity (0.14 Ω ppm−1), and a detection capability of less than 1.2 ppm.

  相似文献   
158.
We used spaceborne imaging spectroscopy provided by the Earth Observing-1 Hyperion sensor to quantify the relative importance of precipitation and substrate age that control ecosystem development and functioning in Metrosideros polymorpha rainforests of Hawaii. Four hyperspectral vegetation indices provided metrics of forest canopy structure, biochemistry and physiology to compare along gradients of annual rainfall (750 to > 6000 mm year 1) and substrate age (0 to 250,000 years). The canopy greenness index NDVI increased with annual precipitation and substrate age, but saturated in forests with rainfall of 3000 mm year 1. Precipitation and substrate age were roughly equal contributors to the observed greenness of the forests. A canopy water content index (NDWI) also increased with precipitation and substrate age, but did not reach a maximum until very wet (> 5000 mm year 1) forest conditions were encountered on the oldest substrates. The water index appears superior to the NDVI in capturing spatial and climate-substrate driven variations in canopy structure. The photochemical reflectance index (PRI) indicated highest light-use efficiency levels in canopies on the most developed substrates and at annual precipitation levels of 3-4500 mm year 1. A leaf carotenoid index (CRI) suggested a maximum canopy photosynthetic capacity at ∼ 4000 mm rainfall year 1 on the oldest substrates. These results quantify the sensitivity of rainforest canopies to changing precipitation and soil conditions, and they corroborate plot-scale analyses in native Hawaiian forests ecosystems. Structural and functional studies of remote rainforest regions are possible with spaceborne imaging spectroscopy, and could be used to understand the dynamics of rainforests with climate change.  相似文献   
159.
A microstrip open‐loop resonator oscillator operating at even modes is proposed. The even mode of the ring circuit can be predicted by using a simple transmission‐line model. The new oscillator has a characteristic similar to that of a push‐push oscillator. In addition, in comparison with the push‐push oscillator, the new oscillator with one active device can minimize the size and lower the cost. A voltage‐controlled piezoelectric transducer (PET) is used to vary the resonant frequencies of the ring resonator, which in turn tunes the oscillator with a good tuning range of 4.9% at around 12.1 GHz. This tuned oscillator should have many applications in wireless systems. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.  相似文献   
160.
A genetic fuzzy agent using ontology model for meeting scheduling system   总被引:1,自引:0,他引:1  
A Genetic Fuzzy Agent (GFA) using the ontology model for Meeting Scheduling System (MSS) is presented in this paper. The ontology model includes the Fuzzy Meeting Scheduling Ontology (FMSO) and the Fuzzy Personal Ontology (FPO) that can support to construct the knowledge base of the GFA. The FMSO is utilized to record and describe the meeting scheduling domain knowledge for the GFA. In addition, we implement a FMSO editor for generating the Web Ontology Language, OWL, that will be utilized by the GFA. Furthermore, the GFA will infer the suitable meeting time slots based on the ontology model. Moreover, it also adjusts the FMSO and FPO based on the results of the genetic learning mechanism for the next meeting. The experimental results show that our approach can effectively work for MSS.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号