全文获取类型
收费全文 | 3671篇 |
免费 | 327篇 |
国内免费 | 106篇 |
专业分类
电工技术 | 167篇 |
综合类 | 481篇 |
化学工业 | 244篇 |
金属工艺 | 100篇 |
机械仪表 | 111篇 |
建筑科学 | 1125篇 |
矿业工程 | 264篇 |
能源动力 | 178篇 |
轻工业 | 257篇 |
水利工程 | 268篇 |
石油天然气 | 155篇 |
武器工业 | 23篇 |
无线电 | 84篇 |
一般工业技术 | 269篇 |
冶金工业 | 174篇 |
原子能技术 | 39篇 |
自动化技术 | 165篇 |
出版年
2024年 | 3篇 |
2023年 | 35篇 |
2022年 | 105篇 |
2021年 | 117篇 |
2020年 | 125篇 |
2019年 | 76篇 |
2018年 | 59篇 |
2017年 | 73篇 |
2016年 | 99篇 |
2015年 | 107篇 |
2014年 | 239篇 |
2013年 | 200篇 |
2012年 | 261篇 |
2011年 | 298篇 |
2010年 | 217篇 |
2009年 | 219篇 |
2008年 | 195篇 |
2007年 | 250篇 |
2006年 | 238篇 |
2005年 | 203篇 |
2004年 | 185篇 |
2003年 | 153篇 |
2002年 | 130篇 |
2001年 | 121篇 |
2000年 | 84篇 |
1999年 | 69篇 |
1998年 | 56篇 |
1997年 | 37篇 |
1996年 | 25篇 |
1995年 | 29篇 |
1994年 | 24篇 |
1993年 | 13篇 |
1992年 | 23篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1965年 | 1篇 |
1961年 | 2篇 |
1960年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4104条查询结果,搜索用时 15 毫秒
81.
Candida Antarctica lipase B (CALB), a specific enzyme to catalyze the hydrolysis of esters, can be a good candidate for acetylcholine (ACh) hydrolysis instead of acetylcholinesterase. The catalytic mechanism of the CALB acylation, as the first stage in the hydrolysis reaction, with ACh and methylcaprylate (MEC) has been examined by using density functional theory technique. The significant emphasis of this article is on the free energy barriers for the acylation step of hydrolysis reactions. Computed free energy barriers of the first step are 9.2 and 15.9 kcal mol−1, but for the second step are 7.9 and 11.6 kcal mol−1 for MEC and ACh respectively. Activation free energies are in the comparable and acceptable range and imply both of two reactions are theoretically possible. The stability role of the adjacent amino acids was examined by using two applied tools. It is exposed that the oxyanion hole residues decrease energy barriers by stabilizing the transition state structures. 相似文献
82.
随着我国社会经济和科学技术的迅速发展,电力业扩报装工作取得了明显的进步。但是,在业扩报装工作中依然存在许多问题,例如业扩报装的工作时间长、收费的公开度低、工作环节多等,这些问题不仅成为电力用户关注的焦点,对电力企业的售电量也产生了重要的影响。 相似文献
83.
84.
《Journal of the European Ceramic Society》2019,39(14):4255-4263
Structural and microstructural investigation of solution precursor plasma sprayed copper-doped hydroxyapatite coatings with different Cu dopant concentration was carried out. Scanning electron micrographs did not show any significant morphological changes at the surface and cross-section of the coatings as copper content increases. X-ray diffraction results showed the decrease in the HA phase content from 93 wt.% to 14 wt.% and its degree of crystallinity from 94% to 85% with increasing copper concentration. Raman and IR spectra revealed the broadening and red-shifting of the phosphate bands due to the distortion of the HA structure caused by possible insertion of copper. X-ray photoelectron spectroscopy identified Cu and Cu2+ as copper species incorporated in HA. Rietveld refinement showed an increase in the lattice a and c parameter and expansion of the unit cell volume associated to an interstitial insertion of Cu along the hexagonal channel of the HA structure. 相似文献
85.
《Soils and Foundations》2014,54(4):621-638
The collapse of a filling occurred due to heavy rain in Higashi-Hiroshima City׳s Shiwa District at about 5:30 am July 25th, 2009. The filling was made of surplus soils, and it contained a mass of water supplied from rainfall and ground water flow of a permeable layer at the bottom of the filling. The collapsed soil flowed down and destroyed a house. In this paper, the cause of this disaster is discussed. The site of the disaster was used as the dumping site of surplus soils, after several changes of ground formation. The history of the geographical change was reconstructed by the image processing of old map, aerial photographs, result of 3-dimentional laser survey carried out after collapse and the measurement of thickness of collapsed soil by dynamic cone penetration test. According to the result of processing, the shape and the size of the filling before collapse was reconstructed. The relationship between the rainfall and the groundwater in the river sediments layer over which the filling was constructed was determined. A stability analysis of the filling was conducted considering the rise of the groundwater level in the filling and the laboratory measured strength parameters. The results of the stability analysis showed that the collapse would have taken place when the groundwater level rose by about 9 m due to the supply of groundwater through the river sediments layer. 相似文献
86.
Due to increasing use of clay/epoxy nanocomposites in industry, investigation of mechanical properties of clay nanocomposites has become of great interest. While the stiffening mechanism of clay nanocomposites is well documented, there is still not a clear understanding about how addition of clays affect the fracture behavior of clay/epoxy nanocomposites. The main aim of this paper is to measure and explain the effect of clays on ductility reduction of these nanocomposites. First, epoxy and clay/epoxy nanocomposites with different clay weight ratio were built. Then, the damage parameters of epoxy and clay/epoxy nanocomposites were measured by variation of the elasticity modulus. Based on loading–unloading experiments, the Lemaitre damage parameters for epoxy and clay/epoxy nanocomposites were extracted. Crack initiation and propagation in dog-bone sample were simulated for epoxy and clay/epoxy nanocomposites using the eXtended Finite Element Method (XFEM). The comparison between experimental and numerical results shows that the proposed method can predict the crack initiation location and propagation path in clay/epoxy nanocomposites. 相似文献
87.
88.
李兰英 《金属材料与冶金工程》2014,(2):17-19,35
对类气煤、气煤、瘦煤、贫瘦煤等弱粘结性炼焦煤进行煤质分析及配用研究,并在工业生产中得到很好的应用。 相似文献
89.
90.
《Thin》2015
This paper presents an experimental investigation on behaviour and design of built-up cold-formed steel section battened columns. The built-up columns were pin-ended and consisted of two cold-formed steel channels placed back-to-back at varied spacing of intersection. The two channels were connected using batten plates, with varying longitudinal spacing. The cold-formed steel channel sections were manufactured by brake-pressing flat strips having a plate thickness of 2 mm. The built-up cold-formed steel section battened columns had different slenderness and geometries but had the same nominal length of 2200 mm. The column strengths, load–axial shortening, load–lateral displacement and load–axial strain relationships were measured in the tests. In addition, the failure modes and deformed shapes at failure were observed in the tests and reported in this paper. Overall, the built-up column tests provided valuable experimental data regarding the column behaviour that compensated the lack of information on this form of construction as well as used to develop nonlinear 3-D finite element models. The column strengths measured experimentally were compared against design strengths calculated using the North American Specification, Australian/New Zealand Standard and European Code for cold-formed steel columns. Generally, it is shown that the specifications were unconservative for the built-up cold-formed steel section battened columns failing mainly by local buckling, while the specifications were conservative for the built-up columns failing mainly by elastic flexural buckling. 相似文献