全文获取类型
收费全文 | 21485篇 |
免费 | 1360篇 |
国内免费 | 531篇 |
专业分类
电工技术 | 543篇 |
综合类 | 1810篇 |
化学工业 | 2570篇 |
金属工艺 | 771篇 |
机械仪表 | 541篇 |
建筑科学 | 9091篇 |
矿业工程 | 1332篇 |
能源动力 | 825篇 |
轻工业 | 792篇 |
水利工程 | 1721篇 |
石油天然气 | 382篇 |
武器工业 | 42篇 |
无线电 | 326篇 |
一般工业技术 | 1456篇 |
冶金工业 | 601篇 |
原子能技术 | 220篇 |
自动化技术 | 353篇 |
出版年
2024年 | 19篇 |
2023年 | 175篇 |
2022年 | 429篇 |
2021年 | 531篇 |
2020年 | 477篇 |
2019年 | 348篇 |
2018年 | 398篇 |
2017年 | 490篇 |
2016年 | 554篇 |
2015年 | 676篇 |
2014年 | 1432篇 |
2013年 | 1121篇 |
2012年 | 1539篇 |
2011年 | 1826篇 |
2010年 | 1436篇 |
2009年 | 1418篇 |
2008年 | 1251篇 |
2007年 | 1537篇 |
2006年 | 1356篇 |
2005年 | 1186篇 |
2004年 | 843篇 |
2003年 | 780篇 |
2002年 | 668篇 |
2001年 | 571篇 |
2000年 | 497篇 |
1999年 | 390篇 |
1998年 | 289篇 |
1997年 | 249篇 |
1996年 | 182篇 |
1995年 | 161篇 |
1994年 | 131篇 |
1993年 | 95篇 |
1992年 | 71篇 |
1991年 | 48篇 |
1990年 | 26篇 |
1989年 | 38篇 |
1988年 | 30篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 19篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1959年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
《Ceramics International》2020,46(1):186-195
The Al2O3/SiO2–B2O3–Al2O3–Na2O glass/Al2O3 joints reinforced cooperatively by glass matrix and in-situ Al4B2O9 whiskers were obtained via a low-melting borosilicate glass braze. The composition of glass seam transformed from SiO2–B2O3–Na2O to SiO2–B2O3–Al2O3–Na2O due to continuous diffusion and dissolution of Al2O3. An appropriate amount of [AlO4] units introduced into the glass braze played a vital role in strengthening the glass network structure resulting to considerably improved mechanical strength of the glass seam. Meanwhile, plenty of in-situ Al4B2O9 whiskers growing from the Al2O3/glass braze interface to the center of glass seam in various directions generated. Three-dimensional crisscross structures were fabricated at the Al2O3/glass braze interface domains, where were enhanced by crack-bridging and pull-out effect of the whiskers. Generally, ascribed to the cooperative reinforcement of the glass matrix in the seam and in-situ Al4B2O9 whiskers at Al2O3/glass braze interface domains through reactions of Al2O3 and borosilicate glass braze, strength of the as-brazed joints was promoted prominently. The shear strength of the joints reached a maximum of 61 MPa brazed at 1050 °C for 60 min. 相似文献
62.
为了研究反压压力对成型厚壁光学透镜的影响,利用自行开发的分层反压注射成型厚壁光学透镜的实验方案,通过正交实验优化设计开展了工艺参数优化实验,研究了在不同分层方式下内外层反压压力对对厚壁光学透镜光学性能的影响,从而根据正交优化参数组合成型具有优异光学性能的理想厚壁光学透镜。 正交实验研究结果表明,使用聚甲基丙烯酸甲酯(PMMA)为厚壁光学透镜的原材料进行分层反压注射成型,能够有效减少厚壁光学透镜收缩率,同时随着内外层反压压力的提高,厚壁光学透镜的透光率和折射率均不同程度的得到提高,透镜光学性能优异。 相似文献
63.
There are two major challenges faced by modern society: energy security, and lowering carbon dioxide gas emissions. Thermo-active diaphragm walls have a large potential to remedy one of these problems, since they are a renewable energy technology that uses underground infrastructure as a heat exchange medium. However, extensive research is required to determine the effects of cyclic heating and cooling on their geotechnical and structural performance. In this paper, a series of detailed finite element analyses are carried out to capture the fully coupled thermo-hydro-mechanical response of the ground and diaphragm wall. It is demonstrated that the thermal operation of the diaphragm wall causes changes in soil temperature, thermal expansion/shrinkage of pore water, and total stress applied on the diaphragm wall. These, in turn, cause displacements of the diaphragm wall and variations of the bending moments. However, these effects on the performance of diaphragm wall are not significant. The thermally induced bending strain is mainly governed by the temperature differential and uneven thermal expansion/shrinkage across the wall. 相似文献
64.
Hong Fang Lihai Wang Weijie Kuai Juan Du Guicheng Jiang Xiaoyan Lu Minglei Zhao Chunming Wang Wenbin Su Limei Zheng Chunying Wang Chunlei Wang 《Journal of the American Ceramic Society》2020,103(5):3257-3264
Domain wall motions mainly affect all kinds of properties of ferroelectric materials, such as piezoelectricity, dielectric response, and mechanical loss, and the extrinsic contributions associated with domain wall motions have always been an important issue. In this study, the reversible and irreversible extrinsic contributions to the dielectric properties of [011]C-oriented 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3:Mn single crystals have been extracted by the Rayleigh analysis. We found that in the unpoled samples, the extrinsic contributions of reversible and irreversible domain wall motions to dielectric properties significantly reduced, whereas after poling, only the irreversible extrinsic contribution decreased. The pinning effect in the 2R domain structure is much weaker than that in the 4R domain structure, leading to the low enhancement of Qm and a slight decrease in piezoelectricity caused by acceptor doping in 2R domain structure. This study explores the domain wall dynamics of acceptor-doped single crystals and mainly guides on further performance optimization in PbTiO3-based relaxor single crystals. 相似文献
65.
Degradation is an unavoidable part of a material's life making it important to both monitor and control the aging behavior of plastics. This study compares thermooxidative degraded composites of a novel bio-based and sustainable filler, Biocarbon (MBc), against that of traditional and commercially available fillers (glass fiber and talc) used in the automotive industry. The influence of thermooxidative degradation on the composites was studied under accelerated heat aging for 1000 h at 140°C. The mechanical properties of the composites were evaluated using notched Izod impact as well as both tensile and flexural tests. Morphological structure of the composites was investigated using a scanning electron microscopy. Dynamic mechanical analysis and differential scanning calorimetry were used to evaluate the physical transitions both before and after aging. The glass-filled composites displayed the best performance; while, both the talc and biocarbon composites possessed similar strength and ductility performances. Advantageously, the biocarbon composites experienced an 11% reduction in density as compared to talc-filled composites with similar weight content. After aging, all composites exhibited reduced tensile and flexural strengths ranging from 5 to 67% partly due to chain scission. Whereas, the modulus of all composites increased with a range of 1–24% due to an annealing effect. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48618. 相似文献
66.
《Ceramics International》2020,46(3):3236-3241
Chemical doping is an indispensable tool to tailor the properties of the commercial piezoelectric materials. However, a high piezoelectric coefficient with enhanced thermal stability is rarely achieved by one dopant in some high-performance ferroelectrics, e.g., the recently discovered eco-friendly (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) ceramics. In order to optimize the piezoelectric property in BCZT system by a simple way, we investigated the doping effect of Fe3+, Nb5+ and Bi3+ cations in BCZT ceramics respectively. The results indicate that only Nb5+-doped BCZT ceramics display a combination of large piezoelectric coefficient and enhanced thermal stability, compared with others. Moreover, the established phase diagrams and in-situ transmission electron microscope (TEM) observations reveal that such optimized piezoelectric properties after Nb5+ doping originates from (i) the low polarization anisotropy near the ambient tetragonal (T)-orthorhombic (O) phase transition and (ii) the easy domain wall motion of persistent miniaturized ferroelectric domains upon heating. 相似文献
67.
68.
69.
This work aims to investigate the unsteady conjugate interphase mass transfer between a stationary deformed drop and the modest extensional flow in a cross-intersected 2D channel. It is very difficult to accurately quantify the transient mass transfer rate of solute in such a geometry. Therefore, we established a mathematical model on the basic of the Stokes equation and solved it by the boundary element method, which could deal precisely with a two-phase flow system with a deformable interface; meanwhile, the convection-diffusion equation was solved by the finite difference method to calculate the unsteady conjugate interphase mass transfer. The simulation results showed that the mass transfer rate, analyzed and characterized in terms of mean concentration variation and Sherwood number Sh, was affected by capillary number Ca, Peclet number Pe, viscosity ratio λ , interior-to-exterior diffusivity ratio K, distribution coefficient m, and wall effect factor W. 相似文献