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 15 毫秒
21.
D.V.N. Harish A. Bharatish H.N. Narasimha Murthy B. Anand K.N. Subramanya 《Ceramics International》2021,47(3):3498-3513
Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model. 相似文献
22.
N.A. Zhuk M.G. Krzhizhanovskaya N.A. Sekushin V.V. Kharton B.A. Makeev V.A. Belyy R.I. Korolev 《Ceramics International》2021,47(14):19424-19433
The solid solutions based on the pyrochlore-type system Bi2MgNb2-xTaxO9 were formed in the compositional range х = 0–2.0 (Bi1·6Mg0·8Nb1.6-tTatO7.2, t = 0–1.6). The Rietveld method was used to refine the structure for Bi2MgNb2-xTaxO9 (x = 0, 1.0, 2.0). The increasing tantalum content led to the slight decrease in the cubic unit cell parameters from 10.56934 (4) Å for x = 0 and 10.54607 (3) Å for x = 2 (sp.gr. Fd-3m:2). At the same time, tantalum additions suppressed grain growth in the pyrochlore ceramics during sintering and made it possible to obtain materials with an average grain size of 1–2 μm (Bi1·6Mg0·8Ta1·6O7.2). The increase in the Ta5+ concentration led to the decrease in the dielectric permeability from 104 (Bi1·6Mg0·8Nb1·6O7.2) to 20 (Bi1·6Mg0·8Ta1·6O7.2) at room temperature, while the dielectric loss tangent remained lower than 0.002, which is due to the small grain size and the high porosity of the samples. An increase in temperature has practically no effect on the values of the dielectric permittivity in the entire frequency range. The samples have weak through conductivity. The activation energies of electrical conductivity varied in the range of 0.84–1.00 eV, and the less tantalum, the lower the activation energy. The electrical properties of the samples at 200 Hz to 1 MHz are described by the simplest parallel scheme. 相似文献
23.
Olga Yu Kurapova Sergey M. Shugurov Evgenia A. Vasil'eva Daniil A. Savelev Vladimir G. Konakov Sergey I. Lopatin 《Ceramics International》2021,47(8):11072-11079
Ceria-based solid solutions are important materials for high- and medium-temperature electrochemical applications. However, the stabilities of both binary and ternary ceria-based solid solutions are insufficient at elevated temperatures, which limits their application as solid electrolytes or SOFC cathodes. Data on the high-temperature stability of ceria-based ceramics are unavailable in the literature. In the present study, we report a thermodynamic stability investigation of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions. The thermal prehistories of binary and ternary systems were investigated using STA, XRD, and ESCA techniques. The vaporization processes were investigated in the temperature range of 1577–2227°С via the Knudsen effusion mass spectrometry technique. Using data on the component activity in solid-phase thermodynamic properties of Y2O3-CeO2 solid solutions, which is represented as the Gibbs energy, the excess Gibbs energy was calculated as a function of the ceria mol. %. It was shown that the reduction of Ce4+ to Ce3+ in Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions corresponds to less-negative Gibbs energy compared to ZrO2-CeO2 solid solutions. 相似文献
24.
Zhuchkov V. I. Nazansky S. L. Frolkova A. K. Ganina K. D. 《Theoretical Foundations of Chemical Engineering》2021,55(4):786-791
Theoretical Foundations of Chemical Engineering - Using gas–liquid chromatography, the activity coefficients upon the infinite dilution of the components of the reaction mixture for obtaining... 相似文献
25.
Abdallah M. Altass H. M. El-Sayed R. Al Gorair Arej S. Jahdaly B. A. AL Sobhi M. 《Protection of Metals and Physical Chemistry of Surfaces》2021,57(4):811-819
Protection of Metals and Physical Chemistry of Surfaces - Three nonionic surfactants molecules (NS) derived from a fused pyridine characterized by IR and 1HNMR spectra were synthesized and examined... 相似文献
26.
Combustion, Explosion, and Shock Waves - A VISAR multipoint laser interferometer is used to study a detonation wave structure in mixtures of tetranitromethane with methanol and nitrobenzene. A poor... 相似文献
27.
28.
Steblevskaya N. I. Medkov M. A. Belobeletskaya M. V. 《Theoretical Foundations of Chemical Engineering》2021,55(5):1086-1090
Theoretical Foundations of Chemical Engineering - A method for producing lanthanum–cerium phosphates activated by terbium of the compositions La0.8Ce0.15Tb0.05PO4 and La0.8Ce0.15Tb0.05(PO3)3... 相似文献
29.
Thomas R. Savage Fernando Almeida-Trasvina Ehecatl A. del-Rio Chanona Robin Smith Dondga Zhang 《American Institute of Chemical Engineers》2021,67(11):e17358
With liquefied natural gas becoming increasingly prevalent as a flexible source of energy, the design and optimization of industrial refrigeration cycles becomes even more important. In this article, we propose an integrated surrogate modeling and optimization framework to model and optimize the complex CryoMan Cascade refrigeration cycle. Dimensionality reduction techniques are used to reduce the large number of process decision variables which are subsequently supplied to an array of Gaussian processes, modeling both the process objective as well as feasibility constraints. Through iterative resampling of the rigorous model, this data-driven surrogate is continually refined and subsequently optimized. This approach was not only able to improve on the results of directly optimizing the process flow sheet but also located the set of optimal operating conditions in only 2 h as opposed to the original 3 weeks, facilitating its use in the operational optimization and enhanced process design of large-scale industrial chemical systems. 相似文献
30.
Khammatova V. V. Gainutdinov R. F. Khammatova E. A. Titova L. V. 《Fibre Chemistry》2021,53(3):204-207
Fibre Chemistry - An analysis of the aramid fiber market including the range of industrial textile materials containing chemical fibers for specialized protective clothing of metallurgical workers,... 相似文献