全文获取类型
收费全文 | 33426篇 |
免费 | 3765篇 |
国内免费 | 2498篇 |
专业分类
电工技术 | 2359篇 |
技术理论 | 7篇 |
综合类 | 4281篇 |
化学工业 | 1486篇 |
金属工艺 | 1755篇 |
机械仪表 | 2191篇 |
建筑科学 | 9220篇 |
矿业工程 | 598篇 |
能源动力 | 557篇 |
轻工业 | 723篇 |
水利工程 | 418篇 |
石油天然气 | 644篇 |
武器工业 | 365篇 |
无线电 | 3126篇 |
一般工业技术 | 3483篇 |
冶金工业 | 963篇 |
原子能技术 | 255篇 |
自动化技术 | 7258篇 |
出版年
2024年 | 118篇 |
2023年 | 441篇 |
2022年 | 744篇 |
2021年 | 903篇 |
2020年 | 969篇 |
2019年 | 837篇 |
2018年 | 827篇 |
2017年 | 979篇 |
2016年 | 1136篇 |
2015年 | 1239篇 |
2014年 | 2213篇 |
2013年 | 1995篇 |
2012年 | 2460篇 |
2011年 | 2688篇 |
2010年 | 2299篇 |
2009年 | 2298篇 |
2008年 | 2233篇 |
2007年 | 2575篇 |
2006年 | 2201篇 |
2005年 | 1781篇 |
2004年 | 1484篇 |
2003年 | 1225篇 |
2002年 | 1031篇 |
2001年 | 887篇 |
2000年 | 793篇 |
1999年 | 655篇 |
1998年 | 482篇 |
1997年 | 387篇 |
1996年 | 331篇 |
1995年 | 300篇 |
1994年 | 238篇 |
1993年 | 181篇 |
1992年 | 174篇 |
1991年 | 98篇 |
1990年 | 93篇 |
1989年 | 94篇 |
1988年 | 64篇 |
1987年 | 37篇 |
1986年 | 28篇 |
1985年 | 25篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1964年 | 4篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
31.
NiTi形状记忆薄膜的显微结构和力学性能 总被引:3,自引:0,他引:3
NiTi形状记忆合金薄膜具有形状记忆效应,极有希望用于制造高技术领域微电子机械系统中的微型激发器。NiTi形状记忆合金薄膜在制备和使用过程中需要高品质(衬)底材。本文利用高分辨电子显微学和高分辨分析电子显微学详细研究了硅底材NiTi形状记忆合金薄膜的NiTi/Si和NiTi/SiO2微结构体系,包括薄膜精细结构和界面反应。也研究了其显微结构和力学性能的关系。特别给出了NiTi形状记忆合金薄膜产生疲劳过程的微观过程的起因,通过高达十万个使用热循环前后样品显微结构变化的比较,发现纳米尺度上的TiNi3新相的形成导致疲劳过程的发生。如何抑制TiNi3新相形成的研究正在进行之中,这将为进一步提高NiTi形状记忆合金的使用寿命指出方向。 相似文献
32.
Ching-Liang Su 《Journal of Intelligent and Robotic Systems》2006,45(1):1-14
This research uses the object extracting technique to extract the index, middle and ring fingers from the hand images. The algorithm developed in this research can find the precise locations of the different fingers' fingertips and the finger-to-finger-valleys. After finding the positions of the fingertips and finger-valleys, the index, middle and ring fingers can be extracted from the hand images by using morphological technique. The extracted index, middle and ring fingers contain many useful geometry features. One can use these features to do the person's identification. The orientations of the index, middle and ring fingers are found in this research. Image rotating, image shifting, and image interpolating techniques are used to align different persons' index, middle and ring fingers. Image subtraction is used to exam the difference of two index, middle and ring finger images. In this research so far only use the index, middle and the ring fingers as the features to identify different persons.
★This work was supported by National Science Council under grant NSC 93-2213-E-212-011. 相似文献
33.
3D characterization and analysis of particle shape using X-ray microtomography (XMT) 总被引:2,自引:0,他引:2
C.L. Lin 《Powder Technology》2005,154(1):61-69
34.
基于地理信息系统的天津房地产管理数据库 总被引:1,自引:0,他引:1
从地理信息系统CIS的组成开始.提出该类系统的组织与管理方法,同时重点介绍了在现阶段开发该类系统时所使用的高端技术,最后对GIS系统的发展趋势作出分析与顶测。 相似文献
35.
Dongchang Sun Liyong Tong 《International journal for numerical methods in engineering》2004,60(11):1911-1932
A novel finite element model is presented for static and dynamic analysis of composite plates integrated with a laminated piezoelectric layer, a host laminated composite plate and an adhesive layer between them. A new adhesive element is developed which includes both peel and shear effects in the adhesive layer based on first‐order shear deformation plate theory. The thin adhesive layer between the piezoelectric layer and the host plate is modelled by assuming that it carries constant shear and peel strains throughout its thickness. In addition, a weighted static shape control scheme for finding the optimal voltage distribution for static shape control is given. By selecting different weighting matrices, a variety of items such as displacements, slopes, curvatures, strains and even generalized forces, can be included in finding the optimal actuating voltage for static shape control. The present model is validated by comparing with those results available in the literature. The numerical results show that the weighted linear least method can give a satisfactory voltage distribution to best match the desired shape. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
36.
Bedich ika Helena Bendov Ivan Macha
《Chemical Engineering and Processing: Process Intensification》2005,44(12):1312-1319
A procedure has been proposed for the estimation of the terminal falling velocity of non-spherical particles moving in a Carreau model fluid in the transition flow region. The procedure is based on a modification of the relationship formerly developed for the fall of spherical particles including the particle dynamic shape factor. The suitability of the proposed procedure has been confirmed by good agreement between experimental and calculated terminal falling velocity data. In the experiments, the terminal falling velocity of short cylinders and rectangular prisms in polymer solutions of different measure of shear thinning and elasticity has been measured. 相似文献
37.
38.
Teerapong Senjuntichai Yasothorn Sapsathiarn 《Canadian Metallurgical Quarterly》2003,129(11):1330-1341
This paper considers the vertical vibrations of an elastic circular plate in a multilayered poroelastic half space. The plate is subjected to axisymmetric time–harmonic vertical loading and its response is governed by the classical thin-plate theory. The contact surface between the plate and the multilayered half space is assumed to be smooth and either fully permeable or impermeable. The half space under consideration consists of a number of layers with different thicknesses and material properties and is governed by Biot’s poroelastodynamic theory. The vertical displacement of the plate is represented by an admissible function containing a set of generalized coordinates. Contact stress and pore pressure jump are established in terms of generalized coordinates through the solution of flexibility equations based on the influence functions corresponding to vertical and pore pressure loading. Solutions for generalized coordinates are obtained by establishing the equation of motion of the plate through the application of Lagrange’s equations of motion. Selected numerical results are presented to portray the influence of various parameters on dynamic interaction between an elastic plate and a multilayered poroelastic half space. 相似文献
39.
M. Guerioune Y. Amiour W. Bounour O. Guellati A. Benaldjia A. Amara N. E. Chakri M. Ali-Rachedi D. Vrel 《International Journal of Self-Propagating High-Temperature Synthesis》2008,17(1):41-48
Aiming at preparation of shape memory alloys (SMAs), we explored the SHS of Cu1 − x
Zn1 − y
Al1 − z
alloys (0.29 < x < 0.30, 0.74 < y < 0.75, and 0.83 < z < 0.96). The most pronounced shape memory effect was exhibited by the alloys of the following compositions (wt %): (1) Cu(70.6)Zn(25.4)Al(4.0),
(2) Cu(70.1)Zn(25.9)Al(4.0), and (3) Cu(69.9)Zn(26.1)Al(4.0). The effect of process parameters on the synthesis of CuZnAl
alloys was studied by XRD, optical microscopy, and scanning electron microscopy (SEM). The grain size of CuZnAl was found
to depend on the relative amount of the primary CuZn and AlZn phases. Changes in the transformation temperature and heat of
transformation are discussed in terms of ignition intensity and compaction. Mechanism of the process depends on the level
of the temperature attained relative to the melting point of components. At the melting point of AlZn, the process is controlled
by the solid-state diffusion of AlZn into a product layer. The ignition temperature for this system depends on the temperature
of the austenite-martensite transformation in CuZnAl alloys. The composition and structure of the products was found to markedly
depend on process parameters. The SHS technique has been successfully used to prepare a variety of SMAs.
相似文献
40.
Many problems consist in splitting a set of objects into different groups so that each group verifies some properties. In practice, a partitioning is often encoded by an array mapping each object to its group numbering. In fact, the group number of an object does not really matter, and one can simply rename each group to obtain a new encoding. That is what we call the symmetry of the search space in a partitioning problem. This property may be prejudicial for optimization methods such as evolutionary algorithms (EA) which require some diversity during the search. 相似文献