全文获取类型
收费全文 | 55759篇 |
免费 | 5296篇 |
国内免费 | 3544篇 |
专业分类
电工技术 | 3368篇 |
综合类 | 5219篇 |
化学工业 | 3438篇 |
金属工艺 | 2807篇 |
机械仪表 | 7927篇 |
建筑科学 | 4319篇 |
矿业工程 | 1824篇 |
能源动力 | 803篇 |
轻工业 | 1536篇 |
水利工程 | 972篇 |
石油天然气 | 1217篇 |
武器工业 | 750篇 |
无线电 | 8401篇 |
一般工业技术 | 5351篇 |
冶金工业 | 1111篇 |
原子能技术 | 259篇 |
自动化技术 | 15297篇 |
出版年
2024年 | 231篇 |
2023年 | 707篇 |
2022年 | 1219篇 |
2021年 | 1526篇 |
2020年 | 1547篇 |
2019年 | 1379篇 |
2018年 | 1324篇 |
2017年 | 2146篇 |
2016年 | 2333篇 |
2015年 | 2815篇 |
2014年 | 3874篇 |
2013年 | 3633篇 |
2012年 | 4480篇 |
2011年 | 4892篇 |
2010年 | 3444篇 |
2009年 | 3659篇 |
2008年 | 3503篇 |
2007年 | 4050篇 |
2006年 | 3348篇 |
2005年 | 2507篇 |
2004年 | 2019篇 |
2003年 | 1812篇 |
2002年 | 1394篇 |
2001年 | 1194篇 |
2000年 | 1062篇 |
1999年 | 883篇 |
1998年 | 645篇 |
1997年 | 787篇 |
1996年 | 510篇 |
1995年 | 434篇 |
1994年 | 314篇 |
1993年 | 215篇 |
1992年 | 175篇 |
1991年 | 150篇 |
1990年 | 102篇 |
1989年 | 84篇 |
1988年 | 74篇 |
1987年 | 31篇 |
1986年 | 12篇 |
1985年 | 5篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1959年 | 3篇 |
1958年 | 2篇 |
1957年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions. 相似文献
3.
Central force optimization (CFO) is an efficient and powerful population-based intelligence algorithm for optimization problems. CFO is deterministic in nature, unlike the most widely used metaheuristics. CFO, however, is not completely free from the problems of premature convergence. One way to overcome local optimality is to utilize the multi-start strategy. By combining the respective advantages of CFO and the multi-start strategy, a multi-start central force optimization (MCFO) algorithm is proposed in this paper. The performance of the MCFO approach is evaluated on a comprehensive set of benchmark functions. The experimental results demonstrate that MCFO not only saves the computational cost, but also performs better than some state-of-the-art CFO algorithms. MCFO is also compared with representative evolutionary algorithms. The results show that MCFO is highly competitive, achieving promising performance. 相似文献
4.
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
5.
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
6.
大位移井钻柱振动规律研究与应用 总被引:5,自引:0,他引:5
在大位移井钻井工程中钻柱受着各种振动,当各种振动共振时,钻柱承受着非常大的动载,很容易受损,同时,钻柱的振动影响着井壁的稳定,严重威胁着井下的作业安全。以大位移井近井底的钻柱为研究对象,分析了钻柱振动行为所遵循的规律。采用线性分析法,获得了大位移井钻柱横向振动和扭转振动的频谱方程。同时获得了钻柱各种共振频率的分布。经分析表明:大位移井钻柱的横向振动和扭转振动的共振频率与实际钻井转速非常接近,应合理选择转速以减小钻柱共振的发生。文章的分析研究为大位移井钻柱动态行为的研究提供了理论依据。 相似文献
7.
Ph. D. Candidate:Chen Xue-fengState Key Laboratory of Offshore Coastal Engineering Dalian University of Technology Dalian China e-mail: cxfeng @ student dlut. edu.cn 《水动力学研究与进展(B辑)》2003,15(6)
The reflection coefficient of perforated caissons and the total horizontal forces acting on them were experimentally and numerically analyzed and discussed when wave propagates normally. To consider the viscosity effect of fluid and nonlinear action of waves on structures, the VOF (Volume Of Fluid) method combined with the k-ε turbulence model was used to simulate the interaction between waves and structures. Governing equations were solved with the finite difference method. Through 2D experimental study in the wave flume, the empirical relationship between the reflection coefficient of perforated caissons and the main affecting factors were obtained from the experimental data using the least square method. Also the correlation between the ratio of the total horizontal force acting on perforated caisson and the force acting on solid caisson and the main affecting factors were regressed from the experimental data. 相似文献
8.
9.
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
10.