全文获取类型
收费全文 | 25612篇 |
免费 | 1751篇 |
国内免费 | 820篇 |
专业分类
电工技术 | 2100篇 |
综合类 | 1624篇 |
化学工业 | 3108篇 |
金属工艺 | 1434篇 |
机械仪表 | 1567篇 |
建筑科学 | 2472篇 |
矿业工程 | 1377篇 |
能源动力 | 1290篇 |
轻工业 | 1359篇 |
水利工程 | 784篇 |
石油天然气 | 1779篇 |
武器工业 | 100篇 |
无线电 | 1624篇 |
一般工业技术 | 3926篇 |
冶金工业 | 1392篇 |
原子能技术 | 532篇 |
自动化技术 | 1715篇 |
出版年
2024年 | 64篇 |
2023年 | 196篇 |
2022年 | 533篇 |
2021年 | 602篇 |
2020年 | 590篇 |
2019年 | 495篇 |
2018年 | 469篇 |
2017年 | 624篇 |
2016年 | 691篇 |
2015年 | 763篇 |
2014年 | 1440篇 |
2013年 | 1663篇 |
2012年 | 1850篇 |
2011年 | 2157篇 |
2010年 | 1513篇 |
2009年 | 1537篇 |
2008年 | 1327篇 |
2007年 | 1597篇 |
2006年 | 1489篇 |
2005年 | 1161篇 |
2004年 | 1105篇 |
2003年 | 1003篇 |
2002年 | 949篇 |
2001年 | 833篇 |
2000年 | 637篇 |
1999年 | 593篇 |
1998年 | 458篇 |
1997年 | 359篇 |
1996年 | 322篇 |
1995年 | 290篇 |
1994年 | 219篇 |
1993年 | 146篇 |
1992年 | 115篇 |
1991年 | 99篇 |
1990年 | 66篇 |
1989年 | 65篇 |
1988年 | 40篇 |
1987年 | 33篇 |
1986年 | 19篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
I. Hole T. Tybell J. K. Grepstad I. Wrnhus T. Grande K. Wiik 《Solid-state electronics》2003,47(12):2279
Heteroepitaxial LaFeO3(1 1 0) thin films with a thickness of 150 nm were grown on LaAlO3(0 0 1) by reactive sputtering in an inverted cylindrical magnetron geometry. Equilibrium conductivity was measured as a function of partial pressure of oxygen at T=1000 °C, and logσ plotted vs. logP(O2) showed a minimum in conductivity for P(O2)=10−11 atm and a linear response between 10−10 and 1 atm. This linear response makes thin films of LaFeO3 a promising material for oxygen sensor applications. We have also measured the time response of the film conductivity upon an abrupt change in the partial pressure of ambient oxygen from 10−2 to 10−3 atm, which was determined at 60 s for T=700 °C and <3.5 s at T=1000 °C. 相似文献
122.
123.
By integrating lithography and self‐assembly via electrohydrodynamic instabilities, Russel and co‐workers are able to guide initially flat polymer films to evolve into periodic arrays of pillars over regions much greater in extent than their natural domain sizes, as detailed on p. 1992. Novel structures that involve a combination of linear ridges and pillars are also produced, mainly as as result of the dynamic merging among preformed pillars. To pattern thin polymer films via electrohydrodynamic instabilities, we design and utilize two different kinds of mask patterns to guide pillars into alignment over regions much greater in extent than their natural domain sizes. First, narrow protruding ridges that intersect to form regular patterns on the mask trigger the growth of pillars beneath. Later, square and triangular packings of pillars develop in the regions enclosed by those ridges, preserving the registry from one domain to the next over a much larger area than within individual domains in unpatterned portions of the mask. Second, small square protrusions that are prealigned into a large regular array on the mask guide the formation of square packings of pillars in domains that conform to the mask, forming a large array of pillars. Novel structures involving a combination of linear ridges and pillars are also produced mainly due to the dynamic merging among preformed pillars. Finally, we find vertex symmetry of the mask pattern is necessary for generating and preserving ordered patterns on the polymer film. 相似文献
124.
William Kent 《Computer Standards & Interfaces》1991,13(1-3):201-206
OSQL is the object-oriented database language developed for the Iris object-oriented database management system at Hewlett-Packard Laboratories. Its three fundamental constructs are objects, types, and functions. This paper provides an overview of the underlying concepts and some important features of OSQL. 相似文献
125.
双辊式薄带连铸工艺研究 总被引:6,自引:0,他引:6
进行了双辊法薄带连铸的试验研究。阐述了双辊连铸机浇注系统的研究结果、工艺参数对连铸的影响,以及18—8不锈钢薄带坯的凝固组织和冷轧特性,该工作为薄带连铸的中间生产机组的研究奠定了基础。 相似文献
126.
When freshly etched samples of various types of copper were exposed in moderately acid, aerated chloride solutions, two phenomena were observed. First the corrosion potential and the pH of the solution decreased over a shorter time, then the potential increased over a long period (600-1500 min), following an s-shaped pattern. Increase in pH during the second stage was avoided using a pH-stat. The corrosion rate increased little or not at all over the entire period. A tentative interpretation of the short-term behaviour is presented with some reservation. The long-term development of the potential suggests phase formation or transformation following the Avrami pattern. By suitable derivations it was possible to fit the development of potentials to the Avrami equation. Subsequent examinations by Auger spectroscopy proved the presence of thin layers of Cu2O on the copper surfaces, increasing in thickness with exposure time. The dissolution kinetics can be described in terms of two parallel electrochemical reactions and a simultaneous non-electrochemical dissolution reaction. 相似文献
127.
Microstructural changes in concretes with sulfate exposure 总被引:1,自引:0,他引:1
In prior papers the responses of concretes to 50,000 ppm MgSO4 exposure depending on cement type, w/cm and the presence of slag were described. The present paper completes this analysis by examining the effects of immersion of concretes produced using slag blended cements, in solutions containing 50,000 ppm of sodium sulfate. The spatial evolution of microstructure associated with carbonation and sulfate attack show differences which can be related to the nature of the cation associated with the sulfate, the cement type, and the w/cm ratio. 相似文献
128.
用热失重法确定水合粘土水分含量及存在形式 总被引:1,自引:1,他引:0
文章以蒙脱土为例,采用热失重法定性定量确定了水合粘土中结合水类型、界限及其相对含量,并与等温吸附法结果进行了对比。结果表明,用该方法得到的水合蒙脱土中各种水分的相对含量及总含水量与等温吸附实验结果相一致。热失重(25~250 ℃)分析结果表明,水合蒙脱土中水分子主要存在自由水、松散吸附结合水、紧密吸附水(强吸附结合水)3种状态,分别对应于25~75 ℃、75~120 ℃、120~230 ℃区间里的失水。从热失重(25~250 ℃)规律来看,仍存在两个明显的转折点p/ps=0.9、0.98,它们为粘土-水体系的两个特征湿度,前者为粘土表面强结合水与松散结合水(渗透结合水)之间的界限,后者为松散结合水与自由水之间的界限,这验证了等温吸附法确定的两个特征湿度及对粘土表面结合水界限划分的正确性。 相似文献
129.
Hong-hui YuJohn W Hutchinson 《Thin solid films》2003,423(1):54-63
Delamination of residually stressed thin film strips is analyzed to expose the dependence on strip width and film/substrate elastic mismatch. Isotropic films and substrates are assumed. The residual stress in the film is tensile and assumed to originate from mismatch due to thermal expansion or epitaxial deposition. Full and partial delamination modes are explored. In full delamination, the interface crack extends across the entire width of the strip and releases all the elastic energy stored in the strip as the crack propagates along the interface. The energy release rate available to propagate the interface crack is a strong function of the strip width and the elastic modulus of the film relative to that of the substrate. The energy release rate associated with full delamination is determined as a function of the interface crack length from initiation to steady-state, revealing a progression of behavior depending in an essential way on the three dimensionality of the strip. The dependence of the energy release rate on the remaining ligament as the interface crack converges with the strip end has also been calculated, and the results provide an effective means for inferring interface toughness from crack arrest position. A partial delamination propagates along the strip leaving a narrow width of strip attached to the substrate. In this case, the entire elastic energy stored in the strip is not released because the strain component parallel to the strip is not relaxed. A special application is also considered, in which a residually stressed metal superlayer is deposited onto a polymer strip. The energy release rate for an interface crack propagating along the interface between the polymer and the substrate is determined in closed form. 相似文献
130.