全文获取类型
收费全文 | 43323篇 |
免费 | 4499篇 |
国内免费 | 3391篇 |
专业分类
电工技术 | 2374篇 |
综合类 | 3691篇 |
化学工业 | 2419篇 |
金属工艺 | 2370篇 |
机械仪表 | 4602篇 |
建筑科学 | 2214篇 |
矿业工程 | 1193篇 |
能源动力 | 564篇 |
轻工业 | 1495篇 |
水利工程 | 593篇 |
石油天然气 | 498篇 |
武器工业 | 528篇 |
无线电 | 8065篇 |
一般工业技术 | 5301篇 |
冶金工业 | 911篇 |
原子能技术 | 154篇 |
自动化技术 | 14241篇 |
出版年
2024年 | 190篇 |
2023年 | 615篇 |
2022年 | 949篇 |
2021年 | 1209篇 |
2020年 | 1274篇 |
2019年 | 1177篇 |
2018年 | 1096篇 |
2017年 | 1809篇 |
2016年 | 1947篇 |
2015年 | 2344篇 |
2014年 | 3126篇 |
2013年 | 2925篇 |
2012年 | 3676篇 |
2011年 | 3948篇 |
2010年 | 2693篇 |
2009年 | 2988篇 |
2008年 | 2857篇 |
2007年 | 3062篇 |
2006年 | 2491篇 |
2005年 | 1863篇 |
2004年 | 1491篇 |
2003年 | 1309篇 |
2002年 | 988篇 |
2001年 | 874篇 |
2000年 | 760篇 |
1999年 | 613篇 |
1998年 | 501篇 |
1997年 | 601篇 |
1996年 | 364篇 |
1995年 | 334篇 |
1994年 | 254篇 |
1993年 | 196篇 |
1992年 | 180篇 |
1991年 | 138篇 |
1990年 | 103篇 |
1989年 | 81篇 |
1988年 | 48篇 |
1987年 | 24篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1977年 | 3篇 |
1958年 | 1篇 |
1955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.
Optical studies of residual strain in cadmium telluride (CdTe) films grown using molecular beam epitaxy on gallium arsenide (GaAs) substrate have been performed using photoreflectance techniques. Measurements have been conducted to determine the fundamental transition energy, heavy-hole and light-hole transition energy critical-point parameters in a range of temperatures between 12 and 300 K. There are problems inherent in the fabrication of optoelectronic devices using high-quality CdTe films, due to strain effects resulting from both the lattice mismatch (CdTe: 14.6%) and the thermal expansion coefficient difference. The CdTe film exhibits compressive stress causing valence-band splitting for light and heavy holes. We have used different models to fit the obtained experimental data and, although the critical thickness for the CdTe has been surpassed, the strain due to the lattice mismatch is still significant. However, the strain due to the thermal expansion is dominant. We have found that the fundamental transition energy, E0, is affected by the compressive strain and the characteristic values are smaller than those reported. In addition, the total strain is compressive for the full measured range, since the strain due to the lattice mismatch is one order of magnitude higher than that calculated from the thermal expansion. 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.
5.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior. 相似文献
6.
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
7.
8.
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
9.
10.
Maenghyo Cho Hee Yuel Roh 《International journal for numerical methods in engineering》2003,56(1):81-115
In the present study first‐order shear deformable shell finite elements based on general curvilinear co‐ordinates are proposed. For the development of the present shell elements, a partial mixed variational functional with independently assumed strains is provided in order to avoid the severe locking troubles known as transverse shear and membrane lockings. Bubble functions are included in the shape function of displacement to improve the performance of the developed element. The proposed assumed strain four‐ and nine‐node elements based on the general tensor shell theory provide an efficient linkage framework for shell surface modelling and finite element analysis. In the several benchmark problems, the present shell elements with exact geometric representations demonstrate their performance compared to previously reported results. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献