全文获取类型
收费全文 | 14110篇 |
免费 | 1208篇 |
国内免费 | 36篇 |
专业分类
电工技术 | 195篇 |
综合类 | 9篇 |
化学工业 | 3370篇 |
金属工艺 | 501篇 |
机械仪表 | 973篇 |
建筑科学 | 256篇 |
矿业工程 | 3篇 |
能源动力 | 639篇 |
轻工业 | 1051篇 |
水利工程 | 44篇 |
石油天然气 | 12篇 |
无线电 | 2697篇 |
一般工业技术 | 3266篇 |
冶金工业 | 765篇 |
原子能技术 | 203篇 |
自动化技术 | 1370篇 |
出版年
2024年 | 10篇 |
2023年 | 176篇 |
2022年 | 245篇 |
2021年 | 442篇 |
2020年 | 367篇 |
2019年 | 388篇 |
2018年 | 456篇 |
2017年 | 503篇 |
2016年 | 561篇 |
2015年 | 465篇 |
2014年 | 649篇 |
2013年 | 941篇 |
2012年 | 1024篇 |
2011年 | 1221篇 |
2010年 | 864篇 |
2009年 | 849篇 |
2008年 | 789篇 |
2007年 | 606篇 |
2006年 | 557篇 |
2005年 | 481篇 |
2004年 | 432篇 |
2003年 | 416篇 |
2002年 | 391篇 |
2001年 | 311篇 |
2000年 | 279篇 |
1999年 | 282篇 |
1998年 | 376篇 |
1997年 | 241篇 |
1996年 | 187篇 |
1995年 | 133篇 |
1994年 | 121篇 |
1993年 | 104篇 |
1992年 | 61篇 |
1991年 | 69篇 |
1990年 | 52篇 |
1989年 | 48篇 |
1988年 | 44篇 |
1987年 | 39篇 |
1986年 | 27篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1975年 | 3篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
H.S. Seo Y.G. Choi B.J. Park D.H. Cho K.H. Kim 《Photonics Technology Letters, IEEE》2003,15(9):1198-1200
A flat signal gain over in the entire C- and L-bands by erbium (Er) ions' radiative transition and stimulated Raman scattering in an Er-doped germano-silica fiber can be obtained if proper values of the concentration of Er and background loss in a fiber core are obtained during the fiber fabrication process. The optimized conditions for the flat C- and L-band gain are analyzed as functions of Er concentrations. Even for a low-gain value provided by a germano-silica core fiber with a low Er concentration and an optimum fiber length, a relatively low pump is required to obtain the flat gain band. 相似文献
32.
To determine three‐dimensional fiber orientation states in injection‐molded short‐fiber composites, a confocal laser scanning microscope (CLSM) is used. Since the CLSM optically sections the specimen, more than two images of the cross sections on and below the surface of the composite can be obtained. Three‐dimensional fiber orientation states can be determined by using geometric parameters of fiber images obtained from two parallel cross sections. For experiments, carbon‐fiber‐reinforced polystyrene is examined by the CLSM and geometric parameters of fibers on each cross‐sectional plane are measured by an image analysis. In order to describe fiber orientation states compactly, orientation tensors are determined at different positions of the prepared specimen. Three‐dimensional orientation states are obtained without any difficulty by determining the out‐of‐plane angles utilizing fiber images on two parallel planes acquired by the CLSM. Orientation states are different at different positions and show the shell–core structure along the thickness of the specimen. Fiber orientation tensors are predicted by a numerical analysis and the numerically predicted orientation states show good agreement with measured ones. However, some differences are found at the end of cavity. They may result from the fountain flow effects, which are not considered in the numerical analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 500–509, 2003 相似文献
33.
Maenghyo Cho Hee Yuel Roh 《International journal for numerical methods in engineering》2003,56(1):81-115
In the present study first‐order shear deformable shell finite elements based on general curvilinear co‐ordinates are proposed. For the development of the present shell elements, a partial mixed variational functional with independently assumed strains is provided in order to avoid the severe locking troubles known as transverse shear and membrane lockings. Bubble functions are included in the shape function of displacement to improve the performance of the developed element. The proposed assumed strain four‐ and nine‐node elements based on the general tensor shell theory provide an efficient linkage framework for shell surface modelling and finite element analysis. In the several benchmark problems, the present shell elements with exact geometric representations demonstrate their performance compared to previously reported results. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
34.
Dong-Soo Yoon Jae Sung Roh Sung-Man Lee Hong Koo Baik 《Journal of Electronic Materials》2003,32(8):890-898
The effect of a thin RuOx layer formed on the Ru/TiN/doped poly-Si/Si stack structure was compared with that on the RuOx/TiN/doped poly-Si/Si stack structure over the post-deposition annealing temperature ranges of 450–600°C. The Ru/TiN/poly-Si/Si
contact system exhibited linear behavior at forward bias with a small increase in the total resistance up to 600°C. The RuOx/TiN/poly-Si/Si contact system exhibited nonlinear characteristics under forward bias at 450°C, which is attributed to no
formation of a thin RuOx layer at the RuOx surface and porous-amorphous microstructure. In the former case, the addition of oxygen at the surface layer of the Ru film
by pre-annealing leads to the formation of a thin RuOx layer and chemically strong Ru-O bonds. This results from the retardation of oxygen diffusion caused by the discontinuity
of diffusion paths. In particular, the RuOx layer in a nonstoichiometric state is changed to the RuO2-crystalline phase in a stoichiometric state after post-deposition annealing; this phase can act as an oxygen-capture layer.
Therefore, it appears that the electrical properties of the Ru/TiN/poly-Si/Si contact system are better than those of the
RuOx/TiN/poly-Si/Si contact system. 相似文献
35.
Development of a recurrent Sigma-Pi neural network rainfall forecasting system in Hong Kong 总被引:1,自引:1,他引:0
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead. 相似文献
36.
Ki Hyun Kim Yong Hoon Kang Byoungho Lee 《Photonics Technology Letters, IEEE》1997,9(12):1610-1612
A photorefractive volume hologram was recorded and probed using light diffracted from a tapered optical fiber as a reference beam. A single-mode fiber (SMF) was chemically etched and tapered to give a complicated beam pattern, and it is shown that the tapered optical fiber can be utilized to increase the storage density of the volume hologram. Spatial selectivity of the volume hologram with this method was increased by two times compared to the normal SMF referencing, which is due to the fact that the complicated beam pattern has little correlation with its shifted version 相似文献
37.
Won Tae KimCheolho Bai Young I. Cho 《International Journal of Heat and Mass Transfer》2002,45(3):597-607
The present study introduces a new experimental method to visualize the fouling process of CaCO3. A mini-channel heat exchanger system with a microscopic imaging technique was developed for real-time visualization of the fouling process. The present study discussed how scale started initially, how scale formed thick layers, and how a small crystal grew into a large one, touching the adjacent one. Detail microscopic images of scale crystals and corresponding fouling resistances were obtained over the entire fouling process. The microscopic observation indicated that the fouling process could be divided into three stages: an induction period, a period of uniform generation of nuclei, and a period of uniform growth of scale. Sudden appearance of numerous small nuclei indicated the end of the induction period, a key event before the rapid increase in the fouling resistance. The present experimental method using microscopic images of the wet fouling process provides a valuable insight on the fouling mechanism. 相似文献
38.
39.
Bongkee Cho 《Polymer Engineering and Science》1985,25(18):1139-1144
40.
We have investigated the effect of extended dislocations (0.5-3 μm) on charge distribution in GaN epilayer grown by metalorganic chemical vapor deposition on (0001) sapphire using atomic force microscopy (AFM) and scanning surface potential microscopy (SSPM). It has been observed for the surface at the extended dislocations present in undoped GaN film to be negatively charged showing 0.04-0.2 V higher potential relative to regions that contain no dislocations. In addition to the higher potential at the dislocation core, the surrounding surfaces, including the edge of the dislocations, are also negatively charged in a symmetric way around the dislocations revealing crater-shaped higher potential regions (∼0.04 V) relative to surrounding dislocation-free area. The experimental results show that the protrusion-type of dislocation is also negatively charged and its potential is dependent on the size of dislocation. 相似文献