全文获取类型
收费全文 | 218406篇 |
免费 | 27188篇 |
国内免费 | 6972篇 |
专业分类
电工技术 | 10319篇 |
技术理论 | 12篇 |
综合类 | 10199篇 |
化学工业 | 45936篇 |
金属工艺 | 11239篇 |
机械仪表 | 11746篇 |
建筑科学 | 12975篇 |
矿业工程 | 4492篇 |
能源动力 | 4969篇 |
轻工业 | 16983篇 |
水利工程 | 3747篇 |
石油天然气 | 10682篇 |
武器工业 | 1189篇 |
无线电 | 25711篇 |
一般工业技术 | 39223篇 |
冶金工业 | 12413篇 |
原子能技术 | 5005篇 |
自动化技术 | 25726篇 |
出版年
2024年 | 775篇 |
2023年 | 2577篇 |
2022年 | 5010篇 |
2021年 | 6980篇 |
2020年 | 6372篇 |
2019年 | 7264篇 |
2018年 | 8373篇 |
2017年 | 9119篇 |
2016年 | 9094篇 |
2015年 | 9856篇 |
2014年 | 11581篇 |
2013年 | 14320篇 |
2012年 | 12949篇 |
2011年 | 13444篇 |
2010年 | 12063篇 |
2009年 | 11789篇 |
2008年 | 11262篇 |
2007年 | 10589篇 |
2006年 | 9793篇 |
2005年 | 8381篇 |
2004年 | 6700篇 |
2003年 | 6840篇 |
2002年 | 6921篇 |
2001年 | 6234篇 |
2000年 | 5378篇 |
1999年 | 4253篇 |
1998年 | 3057篇 |
1997年 | 2626篇 |
1996年 | 2341篇 |
1995年 | 2061篇 |
1994年 | 1708篇 |
1993年 | 1443篇 |
1992年 | 1374篇 |
1991年 | 1167篇 |
1990年 | 1198篇 |
1989年 | 1114篇 |
1988年 | 962篇 |
1987年 | 872篇 |
1986年 | 797篇 |
1985年 | 736篇 |
1984年 | 715篇 |
1982年 | 679篇 |
1979年 | 737篇 |
1978年 | 779篇 |
1977年 | 740篇 |
1976年 | 757篇 |
1975年 | 713篇 |
1974年 | 719篇 |
1973年 | 723篇 |
1972年 | 705篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
31.
Lingfang Zou Zhuan Li Zonglong Gao Fu Chen Wenjie Li Yong Yu Yimin Li Peng Xiao 《Ceramics International》2021,47(14):19328-19339
Improving the piezoelectric activity of lead zirconate titanate (PZT) ceramics is of great importance for practical applications. In this study, the influence of Pr3+ doping on the ferroelectric phase composition, microstructure, and electric properties on the A-site of (Pb1-1.5xPrx)(Zr0.52Ti0.48)O3 is extensively investigated. A dense and fine microstructural sample is obtained with the introduction of Pr3+. The results show that the morphotropic phase boundary (MPB) moves to the rhombohedral phase region. The rhombohedral and tetragonal phases exhibit an ideal coexistence in the 4 mol.% Pr3+ doped (PPZT4) samples. Lead vacancy and the reduction of the potential energy barrier are considered to be the key mechanisms for donor doping, which is upheld by the Pr3+ doping. Combining the I-E hysteresis loops with the P-E hysteresis loops, it becomes apparent that both contribution maximums of the domain switching and residual polarisation are in PPZT4. Moreover, the thermal aging resistance of PZT is improved by doping, and the temperature stability is optimised from 83% in PZT to 96% in PPZT4. Hence, an appropriate amount of Pr3+ doping can effectively improve the piezoelectric activity of PZT ceramics in the MPB area and optimise the performance stability of the material under application temperatures. 相似文献
32.
Jinshuang Wang Luyao Chen Mengdi Chen Yuyang Wu Yinghui Wang Yongsheng Yu Junbin Sun Bing Liu Qiangshan Jing 《Ceramics International》2021,47(16):22965-22975
In this study, the destabilization resistance of Sc2O3 and CeO2 co-stabilized ZrO2 (SCZ) ceramics was tested in Na2SO4 + V2O5 molten salts at 750°C–1100 °C. The phase structure and microstructure evolution of the samples during the hot corrosion testing were analyzed with X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). Results showed that the destabilization of SCZ ceramics at 750 °C was the result of the chemical reaction with V2O5 to produce m-ZrO2 and CeVO4, and little ScVO4 was detected in the Sc2O3-rich SCZ ceramics. The primary corrosion products at 900 °C and 1100 °C were CeO2 and m-ZrO2 due to the mineralization effect. The Sc2O3-rich SCZ ceramics exhibited excellent degradation resistance and phase stability owing to the enhanced bond strength and the decreased size misfit between Zr4+ and Sc3+. The destabilization mechanism of SCZ ceramic under hot corrosion was also discussed. 相似文献
33.
Water Resources Management - The low impact development (LID) concept aims to control storm runoff and pollution through decentralized, small-scale source control to bring the development area as... 相似文献
34.
Dr. Qian Wang Xinli Fan Nannan Jing Han Zhao Dr. Lijia Yu Prof. Xinjing Tang 《Chembiochem : a European journal of chemical biology》2021,22(11):1901-1907
Small interfering RNA (siRNA) can effectively silence target genes through Argonate 2 (Ago2)-induced RNA interference (RNAi). It is very important to control siRNA activity in both spatial and temporal modes. Among different masking strategies, photocaging can be used to regulate gene expression through light irradiation with spatiotemporal and dose-dependent resolution. Many different caging strategies and caging groups have been reported for light-activated siRNA gene silencing. Herein, we describe a novel caging strategy that increases the blocking effect of RISC complex formation/process through host/guest (including ligand/receptor) interactions, thereby enhancing the inhibition of caged siRNA activity until light activation. This strategy can be used as a general approach to design caged siRNAs for the photomodulation of gene silencing of exogenous and endogenous genes. 相似文献
35.
36.
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
37.
Kedong Xia Shuoshuo Yu Yunling Li Huijuan Han Lingyao Duan Zhenyu Hou Xiao Liu 《Journal of the European Ceramic Society》2021,41(4):2375-2385
In this study, C/SiOC and C/SiO2 composites were prepared by using carbonaceous microspheres with different surface functional groups. Carbonaceous microspheres based on hydrothermal reaction of glucose contains hydroxyl group, while the surface carboxyl group increases after NaOH etching. The hydroxyl group increases the oxygen-enriched structural units of SiOC ceramics, and the C spheres are closely enwrapped in SiOC matrix after pyrolysis at 900 °C. However, the interfacial reaction of surface carboxyl with Si–OH results in the formation of cristobalite SiO2, and C spheres are not only encased inside the SiOC matrix, but also dispersed outside of SiOC ceramics. After removal of C via calcination at 500 °C for 5 h, C/SiOC and C/SiO2 composites are transformed into amorphous SiO2 and cristobalite SiO2, respectively. The thermogravimetric analysis indicates the oxidation resistance of SiOC is superior to that of C and SiO2. 相似文献
38.
Karolina Storesund Francine Amon Anne Steen‐Hansen Shayesteh Haghighatpanah Ida Larsson 《火与材料》2021,45(1):181-190
The aim of this exploratory study has been to investigate the fire properties and environmental aspects of different upholstery material combinations, mainly for domestic applications. An analysis of the sustainability and circularity of selected textiles, along with lifecycle assessment, is used to qualitatively evaluate materials from an environmental perspective. The cone calorimeter was the primary tool used to screen 20 different material combinations from a fire performance perspective. It was found that textile covers of conventional fibres such as wool, cotton and polyester, can be improved by blending them with fire resistant speciality fibres. A new three‐dimensional web structure has been examined as an alternative padding material, showing preliminary promising fire properties with regard to ignition time, heat release rates and smoke production. 相似文献
39.
Sijia Huo Yujin Wang Mianyi Yao Zhikun Zhang Lei Chen Hui Gu Jiahu Ouyang Yu Zhou 《Journal of the European Ceramic Society》2021,41(11):5466-5473
Novel TiC-based composites were synthesized by reactive hot-pressing at 1800 °C for 1 h with ZrB2 addition as a sintering aid for the first time. The effects of ZrB2 contents on the phase composition, microstructure evolution, and mechanical properties were reported. Based on the reaction and solid solution coupling effects between ZrB2 and TiC, the product ZrC may be partially or completely dissolved into the TiC matrix, and then phase separation within the miscibility gap is observed to form lamellar nanostructured ZrC-rich (Zr, Ti)C. The TiC-10 mol.% ZrB2 (starting batch composition) exhibits good comprehensive mechanical properties of hardness 27.7 ± 1.3 GPa, flexural strength 659 ± 48 MPa, and fracture toughness of 6.5 ± 0.6 MPa m1/2, respectively, which reach or exceed most TiC-based composites using ceramics as sintering aids in the previous reports. 相似文献
40.
Lili Hao Jiaxiang Li Peng Wang Zongliang Wang Zhenxu Wu Yu Wang Zixue Jiao Min Guo Tongfei Shi Qigang Wang Yoshihiro Ito Yen Wei Peibiao Zhang 《Advanced functional materials》2021,31(15):2009661
The degradation behavior of implants is significantly important for bone repair. However, it is still unprocurable to spatiotemporally regulate the degradation of the implants to match bone ingrowth. In this paper, a magneto-controlled biodegradation model is established to explore the degradation behavior of magnetic scaffolds in a magnetothermal microenvironment generated by an alternating magnetic field (AMF). The results demonstrate that the scaffolds can be heated by magnetic nanoparticles (NPs) under AMF, which dramatically accelerated scaffold degradation. Especially, magnetic NPs modified by oleic acid with a better interface compatibility exhibit a greater heating efficiency to further facilitate the degradation. Furthermore, the molecular dynamics simulations reveal that the enhanced motion correlation between magnetic NPs and polymer matrix can accelerate the energy transfer. As a proof-of-concept, the feasibility of magneto-controlled degradation for implants is demonstrated, and an optimizing strategy for better heating efficiency of nanomaterials is provided, which may have great instructive significance for clinical medicine. 相似文献