全文获取类型
收费全文 | 557999篇 |
免费 | 7081篇 |
国内免费 | 984篇 |
学科分类
工业技术 | 566064篇 |
出版年
2021年 | 5215篇 |
2020年 | 4022篇 |
2019年 | 5278篇 |
2018年 | 9220篇 |
2017年 | 9427篇 |
2016年 | 9838篇 |
2015年 | 6035篇 |
2014年 | 10255篇 |
2013年 | 26121篇 |
2012年 | 15786篇 |
2011年 | 21099篇 |
2010年 | 16983篇 |
2009年 | 18840篇 |
2008年 | 19091篇 |
2007年 | 18778篇 |
2006年 | 16294篇 |
2005年 | 14748篇 |
2004年 | 13994篇 |
2003年 | 13568篇 |
2002年 | 12676篇 |
2001年 | 12222篇 |
2000年 | 11483篇 |
1999年 | 11287篇 |
1998年 | 26988篇 |
1997年 | 19471篇 |
1996年 | 14988篇 |
1995年 | 11915篇 |
1994年 | 10758篇 |
1993年 | 10511篇 |
1992年 | 8239篇 |
1991年 | 8018篇 |
1990年 | 7937篇 |
1989年 | 7670篇 |
1988年 | 7388篇 |
1987年 | 6658篇 |
1986年 | 6460篇 |
1985年 | 7328篇 |
1984年 | 6640篇 |
1983年 | 6358篇 |
1982年 | 5716篇 |
1981年 | 5845篇 |
1980年 | 5586篇 |
1979年 | 5690篇 |
1978年 | 5634篇 |
1977年 | 6149篇 |
1976年 | 7654篇 |
1975年 | 5070篇 |
1974年 | 4867篇 |
1973年 | 4943篇 |
1972年 | 4256篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Siyao Li Shoulei Xu Xiangyu Wang Daini Wang Bernard A. Goodman Xing Hong Wen Deng 《Ceramics International》2021,47(3):3346-3353
Cubic zirconia single crystals stabilized with yttria and doped with Gd2O3 (0.10–5.00 mol%) were prepared by the optical floating zone method, and characterized by a combination of X-ray diffraction (XRD), and Raman, electron paramagnetic resonance (EPR), ultraviolet–visible (UV–Vis), photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopic techniques. XRD and Raman spectroscopy showed that the crystal samples were all in the cubic phase, whereas the ceramic sample consisted of a mixture of monoclinic and cubic phases. The absorption spectrum showed four peaks at 245, 273, 308, and 314 nm in the ultraviolet region, and the optical band gap differed between samples with ≤3.00 mol% and those with >3.00 mol% Gd2O3. The emission spectrum showed a weak peak at 308 nm and a strong peak at 314 nm, which are attributed to the 6P5/2 → 8S7/2 and 6P7/2 → 8S7/2 transitions of Gd3+, respectively. The intensities of the peaks in the excitation and emission spectra increased with Gd3+ concentration, reached a maximum at 2.00 mol%, then decreased with higher concentrations. This quenching is considered to be the result of the electric dipole-dipole interactions, and this interpretation is supported by the Gd3+ EPR spectra, which showed progressive broadening with increasing Gd3+ concentration throughout the concentration range investigated. 相似文献
92.
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
93.
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
94.
Korotkov S. V. Kuznetsov A. S. Aristov Yu. V. 《Instruments and Experimental Techniques》2021,64(5):687-690
Instruments and Experimental Techniques - A generator of high-power nanosecond pulses is described that contains a high-voltage unit, which is based on a magnetic-compression circuit and a diode... 相似文献
95.
Patil Rupesh C. Jagdale Ashutosh A. Patil Uttam P. Ghodake Jeevan S. Mali Sawanta S. Hong Chang K. Patil Suresh S. 《Catalysis Letters》2021,151(12):3617-3631
Catalysis Letters - We converted agro-waste Custard Apple Peels (CAP) to ash via thermal treatment, on which Pd(OAc)2 was immobilized easily that produced a low-cost, highly efficient Pd/CAP-ash... 相似文献
96.
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
97.
Carolyn A. Grimley Stephen Funni Christopher Green Elizabeth C. Dickey 《Journal of the European Ceramic Society》2021,41(4):2807-2817
In flash sintering experiments, the thermal history of the sample is key to understanding the mechanisms underlying densification rate and final properties. By combining robust temperature measurements with current-ramp-rate control, this study examined the effects of the thermal profile on the flash sintering of yttria-stabilized zirconia, with experiments ranging from a few seconds to several hours. The final density was maximized at slower heating rates, although processes slower than a certain threshold led to grain growth. The amount of grain growth observed was comparable to a similar conventional thermal process. The bulk electrical conductivity correlated with the maximum temperature and cooling rate. The only property that exhibited behavior that could not be attributed to solely the thermal profile was the grain boundary conductivity, which was consistently higher than conventional in flash sintered samples. These results suggest that, during flash sintering, athermal electric field effects are relegated to the grain boundary. 相似文献
98.
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
99.
Dolmatov O. Yu. Kuznetsov M. S. Semenov A. O. Shamanin I. V. Verkhoturova V. V. 《Atomic Energy》2021,130(1):1-5
Atomic Energy - An implementation assessment of PSKD-600 type power reactors was made. It was established that the readiness level of all PSKD-600 nuclear fuel cycle technologies is no lower than... 相似文献
100.
Atomic Energy - An economic and mathematical model has been developed to determine the competitiveness of REMIX-A and -C uranium-plutonium fuel obtained by reprocessing spent fuel from thermal... 相似文献