全文获取类型
收费全文 | 32872篇 |
免费 | 3314篇 |
国内免费 | 2501篇 |
专业分类
电工技术 | 2180篇 |
综合类 | 2556篇 |
化学工业 | 1371篇 |
金属工艺 | 664篇 |
机械仪表 | 3972篇 |
建筑科学 | 433篇 |
矿业工程 | 813篇 |
能源动力 | 389篇 |
轻工业 | 724篇 |
水利工程 | 230篇 |
石油天然气 | 325篇 |
武器工业 | 418篇 |
无线电 | 7516篇 |
一般工业技术 | 2409篇 |
冶金工业 | 254篇 |
原子能技术 | 83篇 |
自动化技术 | 14350篇 |
出版年
2024年 | 147篇 |
2023年 | 452篇 |
2022年 | 703篇 |
2021年 | 876篇 |
2020年 | 905篇 |
2019年 | 805篇 |
2018年 | 757篇 |
2017年 | 1357篇 |
2016年 | 1477篇 |
2015年 | 1911篇 |
2014年 | 2621篇 |
2013年 | 2272篇 |
2012年 | 2983篇 |
2011年 | 3212篇 |
2010年 | 2165篇 |
2009年 | 2351篇 |
2008年 | 2267篇 |
2007年 | 2432篇 |
2006年 | 1907篇 |
2005年 | 1341篇 |
2004年 | 1044篇 |
2003年 | 922篇 |
2002年 | 678篇 |
2001年 | 574篇 |
2000年 | 486篇 |
1999年 | 376篇 |
1998年 | 303篇 |
1997年 | 428篇 |
1996年 | 223篇 |
1995年 | 189篇 |
1994年 | 149篇 |
1993年 | 102篇 |
1992年 | 83篇 |
1991年 | 73篇 |
1990年 | 46篇 |
1989年 | 24篇 |
1988年 | 18篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1961年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Transportation demand of shipping container fluctuates due to the seasonality of international trade, thus, every 3–6 months, the liner company has to alter its current liner shipping service network, redeploy ships and design cargo routes with the objective of minimizing the total cost. To solve the problem, the paper presents a mixed integer linear program model. The proposed model incorporates several relevant constraints, such as weekly frequency, the transshipment of cargo between two or more service routes, and transport time. Extensive numerical experiments based on realistic date of Asia–Europe–Oceania shipping operations show that the proposed model can solve real-case problems efficiently by CPLEX. The results demonstrate that the model can reduce ship’s capacity consumption and raise ships’ capacity utilization. 相似文献
3.
Achieving highly sensitive magnetic sensors by means of Metal-DNA-Metal (MDM) structure is a key issue. DNA, being a genetic information carrier in living cells reveals tunable semiconducting response in the presence of external electric and magnetic fields, which is promising for molecular electronics. The influence of magnetic fields up to 1200 mT on the current–voltage (I–V) behavior of Gold-DNA-Gold (GDG) structure having variable gap sizes from 20–50 μm are reported in this work. These structures were fabricated using UV lithography, DC magnetron sputtering and thermal evaporation techniques. DNA strands were extracted from Boesenbergia rotunda plant via standard protocol. The acquired I–V characteristics display the semiconducting diode nature of DNA in GDG structures. The potential barrier for all the structures exhibit an increasing trend with the increase of externally imposed magnetic field irrespective of variable gap sizes. Furthermore, the potential barrier in GDG junction at higher magnetic field strengths (>1000 mT) is found to be considerably enhanced. This enhancement in the junction barrier height at elevated magnetic fields is attributed to the reduction of carrier mobility and augmentation of resistance. The achieved admirable features of magnetic sensitivity suggest the viability of using these GDG sandwiches as a prospective magnetic sensor. 相似文献
4.
Korolev I. A. Alekseenko N. N. Porodnov B. T. Sapunov V. A. Savel'ev D. V. 《Measurement Techniques》2003,46(9):865-871
The design of a sylphon bellows sensor and the basic circuits of an LC-generator and of a microprocessor unit are presented. An analytical pressure–frequency conversion function and a special method of adjusting the sensor ensure an error of less than 0.05%. The dynamic range is up to 105. The instruments developed cover the ranges 103, 104, and 105 Pa. 相似文献
5.
6.
钻井参数仪的模块化设计方法研究 总被引:1,自引:0,他引:1
文章以模块化设计原理为基础,讨论了钻井参数仪的模块划分,模块化设计准则和主要设计内容。采用模块化设计方法、现场设备网络的开放网络和现场总线解决方案设计的钻井参数仪,具有传输信号稳定、可靠性高、抑制噪声能力强、组建现场网络成本低等特点。 相似文献
7.
8.
9.
制作压力传感器时,在二氧化硅层上淀积多晶硅膜,既可利用优良的机械特性,又可保证压敏电阻与衬底间具有良好的绝缘性,由此可大大提高器件的温度特性。介绍了一种多晶硅压力传感器的原理和设计。实验结果表明,这类传感器具有灵敏度好,精度高等特点,电路工作范围为0-250℃,且具有良好的温度稳定性。 相似文献
10.
Gert van der Horn Johan H. Huijsing 《Analog Integrated Circuits and Signal Processing》1997,14(3):207-222
In many applications electronic sensors are used toimprove performance and reliability of measurement systems. Suchsensors should provide a correct transfer from the physical signalto be measured to the electrical output signal. One importantstep to achieve this, is to calibrate each sensor by applyingdifferent reference input signals and adjusting the sensor transferaccordingly. Besides expensive reference equipment the calibrationprocess takes much time and attention per individual sensor,which means a considerable increase in sensor production costs.By including at the sensor or sensor interface chip a programmablecalibration facility the calibration of such smart sensors caneasily be automated and can be executed for a batch of sensorsat a time, thus minimizing the calibration time and costs. Thispaper presents a calibration method and options for integrationin the smart sensor concept, in hardware as well as in software.An advantage of the proposed method is that it does not needa large matrix of calibration data, which needs to be storedin a look-up table or converted into a correction formula, butinstead it uses a step-by-step approach to correct the sensortransfer at each calibration measurement until the error is sufficientlysmall. 相似文献