全文获取类型
收费全文 | 245520篇 |
免费 | 3396篇 |
国内免费 | 440篇 |
专业分类
电工技术 | 4341篇 |
综合类 | 261篇 |
化学工业 | 38934篇 |
金属工艺 | 9427篇 |
机械仪表 | 7486篇 |
建筑科学 | 5832篇 |
矿业工程 | 1415篇 |
能源动力 | 5417篇 |
轻工业 | 25040篇 |
水利工程 | 2545篇 |
石油天然气 | 4982篇 |
武器工业 | 32篇 |
无线电 | 25531篇 |
一般工业技术 | 46046篇 |
冶金工业 | 46410篇 |
原子能技术 | 5982篇 |
自动化技术 | 19675篇 |
出版年
2021年 | 2178篇 |
2019年 | 2210篇 |
2018年 | 3707篇 |
2017年 | 3643篇 |
2016年 | 3916篇 |
2015年 | 2439篇 |
2014年 | 4209篇 |
2013年 | 10805篇 |
2012年 | 6641篇 |
2011年 | 8998篇 |
2010年 | 7014篇 |
2009年 | 7665篇 |
2008年 | 8111篇 |
2007年 | 8173篇 |
2006年 | 7280篇 |
2005年 | 6389篇 |
2004年 | 6107篇 |
2003年 | 5831篇 |
2002年 | 5671篇 |
2001年 | 5411篇 |
2000年 | 5117篇 |
1999年 | 5092篇 |
1998年 | 12402篇 |
1997年 | 8783篇 |
1996年 | 6711篇 |
1995年 | 5381篇 |
1994年 | 4761篇 |
1993年 | 4636篇 |
1992年 | 3660篇 |
1991年 | 3387篇 |
1990年 | 3614篇 |
1989年 | 3471篇 |
1988年 | 3274篇 |
1987年 | 2892篇 |
1986年 | 2935篇 |
1985年 | 3374篇 |
1984年 | 3226篇 |
1983年 | 2913篇 |
1982年 | 2735篇 |
1981年 | 2807篇 |
1980年 | 2708篇 |
1979年 | 2626篇 |
1978年 | 2679篇 |
1977年 | 2939篇 |
1976年 | 3799篇 |
1975年 | 2366篇 |
1974年 | 2237篇 |
1973年 | 2361篇 |
1972年 | 1964篇 |
1971年 | 1839篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Golubev N. V. Ignat’eva E. S. Maurus A. A. Ziyatdinova M. Z. Lopatina E. V. Lorenzi R. Paleari A. Sigaev V. N. 《Glass and Ceramics》2021,77(11-12):415-418
Glass and Ceramics - The influence of Al2O3 as an additive and the heat-treatment regime on the luminescence spectra of gallate glass-ceramics was investigated. It is shown that its luminescence... 相似文献
42.
As immersive virtual reality (IVR) systems proliferate in classrooms, it is important to understand how they affect learning outcomes and the underlying affective and cognitive processes that may cause these outcomes. Proponents argue that IVR could improve learning by increasing positive affective and cognitive processing, thereby supporting improved performance on tests of learning outcome, whereas opponents of IVR contend that it could hurt learning by increasing distraction, thereby disrupting cognitive learning processes and leading to poorer learning outcomes. In a media comparison study, students viewed a biology lesson either as an interactive animated journey in IVR or as a slideshow on a desktop monitor. Those who viewed the IVR lesson performed significantly worse on transfer tests, reported higher emotional arousal, reported more extraneous cognitive load and showed less engagement based on EEG measures than those who viewed the slideshow lesson, with or without practice questions added to the lessons. Mediational analyses showed that the lower retention scores for the IVR lesson were related to an increase in self-reported extraneous cognitive load and emotional arousal. These results support the notion that immersive environments create high affective and cognitive distraction, which leads to poorer learning outcomes than desktop environments. 相似文献
43.
S.S. Choudhari S.R. Wadgane Bharatratna P. Gaikwad S.S. Satpute Khalid Mujasam Batoo Omar M. Aldossary Sagar E. Shirsath R.H. Kadam 《Ceramics International》2021,47(5):6496-6504
Materials with magneto-electric (ME) properties are of great importance because of their demand in electronic industries. Three dimensional nano-particles of the ME-composites having the general formula (1-x)CoCr0.3Fe1.7O4(CCFO)+(x)BaTiO3(BTO) (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were obtained by comprising the piezoelectric-BTO and piezomagnetic-CCFO phases. The individual phases of CCFO and BTO were synthesized separately by ultrasonic irradiation assisted sonochemical and sol-gel routs. X-ray diffraction patterns (XRD) confirmed the well-crystalline nature of both the phases. BTO and CCFO phases were under tensile strain as confirmed by the variation in lattice constants with varying proportion of BTO and CCFO. An energy-dispersive X-ray spectroscopy spectrum confirmed the phase purity of the samples and stoichiometric concentration of elements. Magnetic properties were investigated by M ? H loop measurements and dielectric properties by using RF impedance analyzer. Dielectric constant increased with the increasing percentage of BTO. The maximum value of ME coefficient (24.7 mV/cm?Oe) is observed for the 60%CCFO+40%BTO sample. The obtained results were discussed in the light of grain size, strain and the basic properties of the individual phases. The prepared materials can be applicable in electronic devices where high magneto-electric coefficient is desirable. 相似文献
44.
M.A. Darwish H.F. Abosheiasha A.T. Morchenko V.G. Kostishyn V.A. Turchenko E.L. Trukhanova K.A. Astapovich A.V. Trukhanov 《Ceramics International》2021,47(12):16752-16761
Rapid developments in information technologies and a large rise in electrical and electronic equipment have generated different forms of electronic environmental contamination. Microwave absorption materials are important to avoid the damage that can be caused by electromagnetic radiation. A necessary condition for the absorption of the most incoming radiation is balanced wave impedance at the air/shield interface, which depends on the studied materials' magnetic and electrical properties. The paper introduces the preparation of BaFe12-xZrxO19 (x = 0.1, 0.3, 0.6, 0.9, and 1.2) using a solid-state reaction technique. The studied samples were examined by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, and a vector network analyzer. The studied samples showed that controlling the grain size and the prepared samples' magnetic properties play an important role in enhancing the microwave radiation absorption. The examined samples can be a promising absorption material in electromagnetic shielding applications. 相似文献
45.
Spiridonova E. A. Rotko V. O. Samonin V. V. Podvyaznikov M. L. 《Protection of Metals and Physical Chemistry of Surfaces》2021,57(1):45-51
Protection of Metals and Physical Chemistry of Surfaces - In this work, a universal sorbent has been obtained that works according to the mechanisms of chemisorption and adsorption by impregnating... 相似文献
46.
Prof. Tsung-Shing Andrew Wang Ruo-Yu Wu Yu Hong Dr. Zhe-Chong Wang Dr. Tsung-Lin Li Dr. Jiun-Jie Shie Prof. Cheng-Chih Hsu 《Chembiochem : a European journal of chemical biology》2021,22(14):2415-2419
Secondary metabolites are structurally diverse natural products (NPs) and have been widely used for medical applications. Developing new tools to enrich NPs can be a promising solution to isolate novel NPs from the native and complex samples. Here, we developed native and deuterated chemoselective labeling probes to target phenol-containing glycopeptides by the ene-type labeling used in proteomic research. The clickable azido-linker was included for further biotin functionalization to facilitate the enrichment of labeled substrates. Afterward, our chemoselective method, in conjunction with LC-MS and MSn analysis, was demonstrated in bacterial cultures. A vancomycin-related phenol-containing glycopeptide was labeled and characterized by our labeling strategy, showing its potential in glycopeptide discovery in complex environments. 相似文献
47.
Macintosh Katrina A. McDowell Richard W. Wright-Stow Aslan E. Depree Craig Robinson Guy M. 《Nutrient Cycling in Agroecosystems》2021,120(2):121-129
Nutrient Cycling in Agroecosystems - Reducing agriculturally derived diffuse contaminant losses (via non-point sources) from land to water has proven difficult for decades. Owing to the diversity... 相似文献
48.
Andrew N. Kuhn Haidong Zhao Uzoma O. Nwabara Xiaofei Lu Mingyan Liu Yung-Tin Pan Wenjin Zhu Paul J. A. Kenis Hong Yang 《Advanced functional materials》2021,31(26):2101668
Copper catalysts are widely studied for the electroreduction of carbon dioxide (CO2) to value-added hydrocarbon products. Controlling the surface composition of copper nanomaterials may provide the electronic and structural properties necessary for carbon-carbon coupling, thus increasing the Faradaic efficiency (FE) towards ethylene and other multi-carbon (C2+) products. Synthesis and catalytic study of silver-coated copper nanoparticles (Cu@Ag NPs) for the reduction of CO2 are presented. Bimetallic CuAg NPs are typically difficult to produce due to the bulk immiscibility between these two metals. Slow injection of the silver precursor, concentrations of organic capping agents, and gas environment proved critical to control the size and metal distribution of the Cu@Ag NPs. The optimized Cu@Ag electrocatalyst exhibited a very low onset cell potential of −2.25 V for ethylene formation, reaching a FE towards C2+ products (FEC2+) of 43% at −2.50 V, which is 1.0 V lower than a reference Cu catalyst to reach a similar FEC2+. The high ethylene formation at low potentials is attributed to enhanced C C coupling on the Ag enriched shell of the Cu@Ag electrocatalysts. This study offers a new catalyst design towards increasing the efficiency for the electroreduction of CO2 to value-added chemicals. 相似文献
49.
Drinberg A. S. Ivakhnyuk G. K. Mametnabiev T. E. Nedvedskii G. R. 《Glass Physics and Chemistry》2022,48(1):50-53
Glass Physics and Chemistry - It is found that the chemical composition of the surface cannot fully provide superhydrophobicity, as a combination of a hydrophobic material with an appropriate... 相似文献
50.
Belov M. I. Anashin D. V. Kabdin N. E. Storchevoy V. F. Sudnik Yu. A. 《Russian Engineering Research》2022,42(11):1110-1116
Russian Engineering Research - The stability of robot-mower motion in a specific direction is considered. The direction is regulated by means of an angular sensor and a programmable controller... 相似文献