全文获取类型
收费全文 | 22323篇 |
免费 | 1762篇 |
国内免费 | 874篇 |
专业分类
电工技术 | 1235篇 |
技术理论 | 2篇 |
综合类 | 1467篇 |
化学工业 | 3597篇 |
金属工艺 | 1162篇 |
机械仪表 | 1435篇 |
建筑科学 | 1892篇 |
矿业工程 | 648篇 |
能源动力 | 614篇 |
轻工业 | 1451篇 |
水利工程 | 396篇 |
石油天然气 | 1320篇 |
武器工业 | 188篇 |
无线电 | 2495篇 |
一般工业技术 | 2690篇 |
冶金工业 | 1062篇 |
原子能技术 | 202篇 |
自动化技术 | 3103篇 |
出版年
2024年 | 72篇 |
2023年 | 331篇 |
2022年 | 532篇 |
2021年 | 772篇 |
2020年 | 614篇 |
2019年 | 457篇 |
2018年 | 591篇 |
2017年 | 648篇 |
2016年 | 575篇 |
2015年 | 805篇 |
2014年 | 967篇 |
2013年 | 1254篇 |
2012年 | 1308篇 |
2011年 | 1470篇 |
2010年 | 1272篇 |
2009年 | 1189篇 |
2008年 | 1248篇 |
2007年 | 1110篇 |
2006年 | 1258篇 |
2005年 | 1204篇 |
2004年 | 766篇 |
2003年 | 726篇 |
2002年 | 719篇 |
2001年 | 626篇 |
2000年 | 592篇 |
1999年 | 740篇 |
1998年 | 551篇 |
1997年 | 525篇 |
1996年 | 430篇 |
1995年 | 351篇 |
1994年 | 313篇 |
1993年 | 206篇 |
1992年 | 189篇 |
1991年 | 136篇 |
1990年 | 114篇 |
1989年 | 91篇 |
1988年 | 76篇 |
1987年 | 36篇 |
1986年 | 26篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
隧道爆破振动速度研究 总被引:3,自引:0,他引:3
在隧道爆破开挖中,频繁反复的爆破冲击动压力对隧道设计轮廓线、施工误差和围岩的稳定性等有很大影响。依据爆炸动力学理论和弹性波动理论,分析了同时起爆和微差起爆所产生的爆炸应力场。根据爆炸波在传播过程中的叠加机理,提出了爆破后隧道围岩质点振动速度解析解。爆破振动速度解析解的提出,为隧道开挖采用合适的爆破掘进方法、减少施工误差及提高围岩的稳定性提供了理论依据。 相似文献
992.
金川二矿区深部开采稳定性分析和采矿设计优化研究 总被引:9,自引:0,他引:9
金川二矿区已进入深部开采。在采用下向胶结充填法的条件下,能不能实现无矿柱连续回采,对矿山的产量和效益影响极大。本文使用非线性有限元对预留间隔矿柱和不预留间隔矿柱两种方案的围岩应力、位移和塑性区分布以及采场的稳定性状态进行了系统的分析和比较,论证了二矿区深部实施无矿柱连续回采的合理性和可行性,为二矿区深部采矿设计优化提供了依据。 相似文献
993.
本文建立了基于弯曲流道的颗粒堆积型多孔介质内流体流动的毛细管束模型,并在低雷诺数、低空隙率范围内对颗粒层多孔介质内的渗透率、阻力特性等进行了研究,结果表明弯曲流道毛细管束模型适合于计算颗粒层多孔介质内流体流动。 相似文献
994.
995.
Liang Xu Lei Su Hongjie Wang Hongfei Gao De Lu Kang Peng Min Niu Zhixin Cai 《Journal of the American Ceramic Society》2022,105(2):1548-1557
Thermal barrier coating materials with proper thermal expansion coefficient (TEC), low thermal conductivity, and good high-temperature stability are of great significance for their applications in next-generation turbine engines. Herein, we report a new class of high-entropy (La0.2Sm0.2Er0.2Yb0.2Y0.2)2CexO3+2x with different Ce4+ contents synthesized by a solid-state reaction method. They exhibit different crystal structures at different Ce4+ content, including a bixbyite single phase without Ce4+ doping (x = 0), bixbyite-fluorite dual-phase in the RE2O3-rich region (0 < x < 2), and fluorite single phase in the stoichiometric (x = 2) and CeO2-rich region (x > 2). The high-entropy (La0.2Sm0.2Er0.2Yb0.2Y0.2)2CexO3+2x exhibit tailorable TECs at a large range of 9.04 × 10–6–13.12 × 10–6 °C–1 and engineered low thermal conductivity of 1.79–2.63 W·m–1·K–1. They also possess good sintering resistance and high-temperature phase stability. These results reveal that the high-entropy (La0.2Sm0.2Er0.2Yb0.2Y0.2)2CexO3+2x are promising candidates for thermal barrier coating materials as well as thermally insulating materials and refractories. 相似文献
996.
Chao He Bin Du Juan Ma Hao Xiong Junjie Qian Mei Cai Anze Shui 《Journal of the American Ceramic Society》2022,105(5):3177-3188
Under the condition of constant thickness, improving the low-frequency sound absorption performance of conventional sound-absorbing materials is a challenging research topic. To address this issue, a new reduced graphene oxide/polyvinyl alcohol (RGO/PVA) porous composite ceramic was fabricated using freeze-drying and optimized by redesigning the internal connecting pores of porous ceramic matrixes with a reticular microstructure using RGO and PVA. The as-prepared porous structure showed significant enhancement in the low-frequency sound absorption band compared with pristine porous ceramics. In addition, the hybrid porous ceramics exhibited low thermal conductivity. These favorable properties indicate that the hybrid sound-absorbing ceramics have potential application prospects for noise reduction in the fields of construction and electrical and mechanical devices. 相似文献
997.
Haoyi Wang Delong Cai Zhihua Yang Xiaoming Duan Bingzhu Wang Bo Wang Daxin Li Dechang Jia Yu Zhou 《Journal of the American Ceramic Society》2022,105(5):3590-3600
A type of boron nitride–magnesium aluminum silicate (BN-MAS) composite ceramics was fabricated by hot-press sintering at different sintering temperatures. The relationship between the sintering temperature and microstructure was investigated by analyzing the interaction between hexagonal boron nitride (h-BN) and the MAS phase. The main MAS phase in the composite ceramics is the α-cordierite phase at a sintering temperature of 1300°C. At temperatures above 1400°C, the inhibitory effect of h-BN on the crystallization of the MAS system is significant, and MAS mainly exists in the form of an amorphous phase. The composite sintered at 1700°C exhibited the highest bending strength of 218MPa. h-BN and MAS were co-enhanced. MAS can be used as an effective liquid-phase sintering aid to assist in the sintering of h-BN, whereas h-BN can absorb the fracture energy of the composite ceramics through the pull-out and bridging effect of the particles. 相似文献
998.
Junjie Qian Bin Du Chao He Mei Cai Xinrong Zhong Hao Xiong Shenghui Zeng Anze Shui 《Journal of the American Ceramic Society》2022,105(5):3456-3468
The hierarchical SiOC/SiCnws/CF composites (A/B/C structure) were designed via precursor infiltration and pyrolysis process. The SiOC ceramics served as the wave-transparent characteristic materials to adjust the impedance matching. Herein, the in situ growth of SiCnws not only was used for the absorber but served as the reinforcement of SiOC matrix composites. In detail, the SiOC/SiCnws/CF-1200°C-2 exhibits excellent electromagnetic absorption performance with minimum reflection loss of −46 dB at 14.4 GHz with the thickness of 1.6 mm, and its effective absorption band reaches 4.3 GHz. Its compressive strength reaches 8.69 and 16.41 MPa in z and x/y directions, separately. This contribution has a guidance for the application of carbon fiber/ceramics matrix composites in harsh environment. 相似文献
999.
Dr. Lei Chen Ying Yang Yuanliang Zhang Kecheng Li Prof. Hongmin Cai Prof. Hongwei Wang Dr. Qian Zhao 《Chembiochem : a European journal of chemical biology》2022,23(8):e202100534
Small open reading frames (sORFs) are an important class of genes with less than 100 codons. They were historically annotated as noncoding or even junk sequences. In recent years, accumulating evidence suggests that sORFs could encode a considerable number of polypeptides, many of which play important roles in both physiology and disease pathology. However, it has been technically challenging to directly detect sORF-encoded peptides (SEPs). Here, we discuss the latest advances in methodologies for identifying SEPs with mass spectrometry, as well as the progress on functional studies of SEPs. 相似文献
1000.
Silicon - In the production of multicrystalline silicon solar cell, diamond wire sawing method (DWS) is an important technique, which has already completely replaced multiwire slurry sawing (MWSS)... 相似文献