全文获取类型
收费全文 | 334974篇 |
免费 | 3741篇 |
国内免费 | 1037篇 |
专业分类
电工技术 | 5581篇 |
综合类 | 2475篇 |
化学工业 | 46203篇 |
金属工艺 | 17664篇 |
机械仪表 | 14052篇 |
建筑科学 | 7876篇 |
矿业工程 | 2485篇 |
能源动力 | 6762篇 |
轻工业 | 20944篇 |
水利工程 | 4161篇 |
石油天然气 | 5675篇 |
武器工业 | 9篇 |
无线电 | 37037篇 |
一般工业技术 | 70246篇 |
冶金工业 | 44985篇 |
原子能技术 | 6246篇 |
自动化技术 | 47351篇 |
出版年
2021年 | 1672篇 |
2019年 | 1622篇 |
2018年 | 22147篇 |
2017年 | 21756篇 |
2016年 | 15234篇 |
2015年 | 2827篇 |
2014年 | 3424篇 |
2013年 | 9333篇 |
2012年 | 9903篇 |
2011年 | 22040篇 |
2010年 | 19294篇 |
2009年 | 17081篇 |
2008年 | 17708篇 |
2007年 | 20282篇 |
2006年 | 5853篇 |
2005年 | 9524篇 |
2004年 | 7721篇 |
2003年 | 7349篇 |
2002年 | 5616篇 |
2001年 | 4875篇 |
2000年 | 4893篇 |
1999年 | 4876篇 |
1998年 | 11583篇 |
1997年 | 8246篇 |
1996年 | 6539篇 |
1995年 | 4752篇 |
1994年 | 4374篇 |
1993年 | 4183篇 |
1992年 | 3307篇 |
1991年 | 3178篇 |
1990年 | 2924篇 |
1989年 | 3012篇 |
1988年 | 2888篇 |
1987年 | 2437篇 |
1986年 | 2347篇 |
1985年 | 2765篇 |
1984年 | 2548篇 |
1983年 | 2383篇 |
1982年 | 2120篇 |
1981年 | 2243篇 |
1980年 | 2062篇 |
1979年 | 2150篇 |
1978年 | 2147篇 |
1977年 | 2402篇 |
1976年 | 3232篇 |
1975年 | 1852篇 |
1974年 | 1780篇 |
1973年 | 1801篇 |
1972年 | 1452篇 |
1971年 | 1351篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Antti Voss Niko Hänninen Mohammad Pour-Ghaz Marko Vauhkonen Aku Seppänen 《Materials and Structures》2018,51(3):68
The development of visualizing tools to monitor unsaturated moisture flow in cement-based materials is of great importance, as most degradation processes in cement-based materials are connected to and take place in the presence moisture. This paper investigates the ability of electrical capacitance tomography (ECT) to image two-dimensional (2D) unsaturated moisture flow in cement-based materials. In ECT, the electrical permittivity distribution within an object is reconstructed based on measured capacitances between electrodes attached on the object’s surface. In a series of experiments, mortar specimens with and without discrete cracks were imaged with ECT during a 2D moisture ingress. The results show that ECT is able to monitor the evolution of the moisture flow, and to approximate the shape and position of the moisture front. These findings indicate that ECT is a viable method for monitoring and visualizing 2D unsaturated moisture flow in cement-based materials in the presence and absence of discrete cracks. 相似文献
122.
K.M. Srinivasamurthy Jagadeesha Angadi V S.P. Kubrin Shiddaling Matteppanavar D.A. Sarychev P. Mohan Kumar Haileeyesus Workineh Azale B. Rudraswamy 《Ceramics International》2018,44(8):9194-9203
Ferrites may contain single domain particles which gets converted into super-paramagnetic state near critical size. To explore the existence of these characteristic feature of ferrites, we have performed magnetization(M-H loop) and Mössbauer spectroscopic studies of Ni2+ substitution effect in Co1-xNixFe2O4 (where x?=?0, 0.25, 0.5, 0.75 and 1) nanoparticles were fabricated by solution combustion route using mixture of carbamide and glucose as fuels for the first time. As prepared samples exhibit spinel cubic structure with lattice parameters which decreases linearly with increase in Ni2+ concentration. The M-H loops reveals that saturation magnetization(Ms), coercive field(Hc) remanence magnetization(Mr) and magnetron number(ηB) decreases significantly with increasing Ni2+ substitution. The variation of saturation magnetization has been explained on the basis of Neel's molecular field theory. The coercive field(Hc) is found strongly dependent on the concentration of Ni2+ and decrease of coercivity suggests that the particles have single domain and exhibits superparamagnetic behavior. The Mössbauer spectroscopy shows two ferrimagnetically relaxed Zeeman sextets distribution at room temperature. The dependence of Mössbauer parameters such as isomer shift, quadru pole splitting, line width and hyperfine magnetic field on Ni2+ concentration have been discussed. Hence our results suggest that synthesized materials are potential candidate for power transformer application. 相似文献
123.
An agriglass composition containing different oxides acts as a slow release for macro and micro nutrients and was chosen to improve maize yield under most important abiotic stresses which affecting agriculture development; salinity and drought. A field experiment was performed in salt affected soil (EC =?7.5 dSm??1) by using different water deficit rates (I1 = 100, I2 = 85 and I3 = 70% of maize water requirements). Irrigation levels were located in main plots. Every main-plot divided into six sub-plots contained glassy fertilizer treatments [F1 = 55 kg fed?1 with 1/2 mm diameter of agriglass (fed. =?4200 m2), F2 = 55 kg fed?1 with 1 mm diameter, F3 = 80 kg fed?1 with 1/2 mm diameter, F4 = 80 kg fed?1 with 1 mm diameter, F5 = Recommendations of Ministry of Agriculture and F6 = control]. The experimental results demonstrated that, ears, straw, grains and biological yields increased with increasing both water and agriglass rates. Application of agriglass as a slow release fertilizer improved yield more than mineral fertilizer. Some growth parameters, water use efficiency (IWUE), macronutrients concentration and their relations were included. Other studies on residual effect of agriglass and the annual application rates to withstand salinity and drought stress by strategic crops are required. 相似文献
124.
125.
Advanced technologies and modern high-production machines for underground mining of thick gently dipping coal demand strict adherence to technological discipline, reduction in operational loss and selection of optimized ventilation modes. The authors analyze ventilation schemes used in working areas in thick gently dipping seams in order to reveal influence exerted by the schemes, methods and parameters of ventilation on distribution of air loss in mined-out areas. 相似文献
126.
Radiochemistry - Azathioprine, an antitumor agent, was labeled with 99mTc using stannous chloride dihydrate as a reducing agent. Factors such as the amounts of the reducing agent and substrate, pH,... 相似文献
127.
Ahmed Obaid M. Alzahrani M. Sh. Abdel-wahab Meshari Alayash M. S. Aida 《Journal of Materials Science: Materials in Electronics》2018,29(19):16317-16324
In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector. 相似文献
128.
Video transmission over IEEE 802.11e wireless networks still shows poor performance for large bandwidth demand and frequently changed environments. Thus, several enhancements of IEEE 802.11e were proposed. On the other hand, big frames and simultaneous sending of adjacent frames always cause packet dropping for buffer overflow. In the past, we proposed an IEEE 802.11e enhancement named DFAA and a content aware mechanism to solve the above problems. The motivation of this paper is to find a proper way to integrate these two mechanisms. A DFAA enhancement (DFAA-E) is proposed to make up the insufficiency of content aware mechanism. Experiments results show that the combination of DFAA-E and content aware mechanism improves the video decoded quality greatly. And its performance can be further enhanced by selecting the suitable settings of certain parameters. 相似文献
129.
A. E. Kudryashov Zh. V. Eremeeva E. A. Levashov V. Yu. Lopatin A. V. Sevost’yanova E. I. Zamulaeva 《Surface Engineering and Applied Electrochemistry》2018,54(5):437-445
Electrospark treatment of OT4-1 titanium alloy was performed sequentially with a STIM-20N hard-alloy electrode (TiC–20% Ni) and carbon-containing material (graphite and carbon-based composite materials). Kinetics of the mass transfer of the hard-alloy electrode was studied. The cathode mass loss during the first minute of the treatment was established. The kinetics results were processed using the methods of mathematical statistics. The erosion resistance of the applied carbon-containing materials was determined. Phase composition and relief of the coatings formed were analyzed. It was found that the application of the carbon-containing material increases the content of refractory phases in the coatings. Increase in the time of the treatment using the carbon-containing materials decreases the roughness of the coatings. 相似文献
130.
The patent literature concerning thermal spraying for biomedical applications is reviewed in this contribution. The patents were compiled from multiple databases search spanning the 2005-2018 period. For clarity and ease of reading, the results have been grouped into sections according to four individual material groups (apatites, titanium, oxide ceramics, other), with the secondary sorting criterion being related to the specific bioapplication areas (maxillofacial, orthopedic, methods). Lastly, the patents are grouped according to the selected thermal spray method within the individual subsections. In the paper, recent R&D trends in this field are further identified and briefly commented. 相似文献