全文获取类型
收费全文 | 21126篇 |
免费 | 1573篇 |
国内免费 | 867篇 |
专业分类
电工技术 | 1285篇 |
技术理论 | 4篇 |
综合类 | 1133篇 |
化学工业 | 3784篇 |
金属工艺 | 998篇 |
机械仪表 | 1272篇 |
建筑科学 | 1479篇 |
矿业工程 | 546篇 |
能源动力 | 600篇 |
轻工业 | 1148篇 |
水利工程 | 331篇 |
石油天然气 | 1183篇 |
武器工业 | 137篇 |
无线电 | 2723篇 |
一般工业技术 | 2756篇 |
冶金工业 | 1062篇 |
原子能技术 | 181篇 |
自动化技术 | 2944篇 |
出版年
2024年 | 68篇 |
2023年 | 315篇 |
2022年 | 576篇 |
2021年 | 836篇 |
2020年 | 608篇 |
2019年 | 554篇 |
2018年 | 608篇 |
2017年 | 620篇 |
2016年 | 595篇 |
2015年 | 733篇 |
2014年 | 965篇 |
2013年 | 1295篇 |
2012年 | 1224篇 |
2011年 | 1350篇 |
2010年 | 1064篇 |
2009年 | 1137篇 |
2008年 | 1077篇 |
2007年 | 1033篇 |
2006年 | 1090篇 |
2005年 | 973篇 |
2004年 | 651篇 |
2003年 | 632篇 |
2002年 | 551篇 |
2001年 | 476篇 |
2000年 | 561篇 |
1999年 | 630篇 |
1998年 | 558篇 |
1997年 | 483篇 |
1996年 | 462篇 |
1995年 | 334篇 |
1994年 | 312篇 |
1993年 | 228篇 |
1992年 | 183篇 |
1991年 | 149篇 |
1990年 | 134篇 |
1989年 | 103篇 |
1988年 | 81篇 |
1987年 | 57篇 |
1986年 | 45篇 |
1985年 | 36篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 31篇 |
1981年 | 22篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Although the good appearance and biocompatibility of dental porcelains, failures are still of considerable concern because of the limited properties to all ceramic system. Physical properties that might be considered ideal include high strength, resistance to abrasion, and resistance to the hostile oral environment. Porcelain has been considered by many of its physical characteristic are similar to those of enamel. In 1983 a new modality of treatment, the etched porcelain restoration was introduced by Simonsen and Calamia. Numerous investigations have shown the strength of the etched porcelain bonded to composite resin and also the clinical success of this porcelain to be used as laminated veneers and etched inlays and onlays. 相似文献
82.
83.
Tan Fu Lei Tang Po Chen Horng-Chih Lin Chun-Yen Chang 《Electron Devices, IEEE Transactions on》1995,42(12):2104-2110
A new material, Si-B, is proposed as a solid diffusion source for fabrication of poly-Si contacted p+-n shallow junctions. The junction depth of the Si-B source diode has been measured and compared with that of a BF2+-implanted poly-Si source diode. It was found that the Si-B source diode had a much shallower junction and was less sensitive to thermal budget than the BF2+ source diode. This was attributed to the smaller surface concentration and diffusivity of boron in the silicon in Si-B source diodes. Regarding electrical characteristics of diodes with a junction depth over 500 Å, a forward ideality factor of better than 1.01 over 8 decades and a reverse-current density lower than 0.5 nA/cm2 at -5 V were obtained. As the junction depth shrank to 300 Å, the ideality factor and reverse current density of diodes increased slightly to 1.05 and 1.16 nA/cm2, respectively. These results demonstrated that a uniform ultrashallow p+-n junction can be obtained by using a thin Si-B layer as a diffusion source 相似文献
84.
85.
W.K ChiuS.T Tan 《Computer aided design》2002,34(13):997-1010
In many applications the location of the centre of gravity of a mechanical part is an important factor that a designer must consider. If it is not in a desired location, a part might not work properly, e.g. unbalanced force might be generated in a rotational part. After a part is modeled, its centre of gravity cannot be altered unless its external shape or internal mass distribution is changed. However, the external shape is usually constrained by other design considerations. In this paper, an algorithm is proposed for controlling the centre of gravity of a hollowed part. Using this algorithm, the location of the centre of gravity of a part is controlled by changing its internal mass distribution. 相似文献
86.
混合冷媒气液相充注对冷媒成分的影响 总被引:1,自引:0,他引:1
申广玉 《制冷与空调(北京)》2002,2(5):51-53
R40 7C、R5 0 7A、R40 4A和R410A混合冷媒按气、液相方式进行充注时 ,冷媒容器内的冷媒成分会或多或少地随着冷媒容器移充填率的变化而变化。因此 ,本文建议充注任何混合冷媒时 ,都应该采用液相方式进行充注 ,同时为了将冷媒成分变化控制在 2 %以内 ,R40 7C冷媒容器中最后的 10 %冷媒剩余量不应再进行充注 ,R5 0 7A、R40 4A和R410A冷媒容器中的最后冷媒剩余量可控制在 5 %。 相似文献
87.
Dasgupta U. Wooi Gan Yeoh Chun Geik Tan Sheng Jau Wong Mori H. Singh R. Itoh M. 《Microwave Theory and Techniques》2002,50(11):2443-2452
An implementation of the IF section of WCDMA mobile transceivers with a set of two chips fabricated in an inexpensive 0.35-/spl mu/m two-poly three-metal CMOS process is presented. The transmit/receive chip set integrates quadrature modulators and demodulators, wide dynamic range automatic gain control (AGC) amplifiers, with linear-in-decibel gain control, and associated circuitry. This paper describes the problems encountered and the solutions envisaged to meet stringent specifications, with process and temperature variations, thus overcoming the limitations of CMOS devices, while operating at frequencies in the range of 100 MHz-1 GHz. Detailed measurement results corroborating successful application of the new techniques are reported. A receive AGC dynamic range of 73 dB with linearity error of less than /spl plusmn/2 dB and spread of less than 5 dB for a temperature range of -30/spl deg/C to +85/spl deg/C in the gain control characteristic has been measured. The modulator measurement shows a carrier suppression of 35 dB and sideband/third harmonic suppression of over 46 dB. The core die area of each chip is 1.5 mm/sup 2/. 相似文献
88.
89.
90.
空间桁架结构拓扑优化设计的线性规划方法 总被引:1,自引:0,他引:1
本文以杆件内力为设计变量,构造了多工况作用下空间桁架结构拓扑优化的线性规划模型,考虑了应力和位移约束,能够避免奇异最优拓扑和不稳定结构的产生。 相似文献