全文获取类型
收费全文 | 99948篇 |
免费 | 10222篇 |
国内免费 | 4986篇 |
专业分类
电工技术 | 7326篇 |
技术理论 | 10篇 |
综合类 | 7274篇 |
化学工业 | 15763篇 |
金属工艺 | 6027篇 |
机械仪表 | 6188篇 |
建筑科学 | 8020篇 |
矿业工程 | 3371篇 |
能源动力 | 2887篇 |
轻工业 | 6124篇 |
水利工程 | 2116篇 |
石油天然气 | 5838篇 |
武器工业 | 1019篇 |
无线电 | 11834篇 |
一般工业技术 | 11413篇 |
冶金工业 | 4348篇 |
原子能技术 | 1327篇 |
自动化技术 | 14271篇 |
出版年
2024年 | 524篇 |
2023年 | 1869篇 |
2022年 | 3678篇 |
2021年 | 4914篇 |
2020年 | 3722篇 |
2019年 | 2902篇 |
2018年 | 3377篇 |
2017年 | 3700篇 |
2016年 | 3291篇 |
2015年 | 4533篇 |
2014年 | 5545篇 |
2013年 | 6628篇 |
2012年 | 7245篇 |
2011年 | 7793篇 |
2010年 | 6639篇 |
2009年 | 6144篇 |
2008年 | 5946篇 |
2007年 | 5437篇 |
2006年 | 5366篇 |
2005年 | 4571篇 |
2004年 | 3080篇 |
2003年 | 2364篇 |
2002年 | 2167篇 |
2001年 | 1789篇 |
2000年 | 1852篇 |
1999年 | 1917篇 |
1998年 | 1468篇 |
1997年 | 1251篇 |
1996年 | 1245篇 |
1995年 | 952篇 |
1994年 | 789篇 |
1993年 | 583篇 |
1992年 | 467篇 |
1991年 | 312篇 |
1990年 | 251篇 |
1989年 | 206篇 |
1988年 | 185篇 |
1987年 | 112篇 |
1986年 | 83篇 |
1985年 | 52篇 |
1984年 | 32篇 |
1983年 | 30篇 |
1982年 | 44篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 9篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1959年 | 9篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
随着计算机技术以及并行求解技术的发展,区域分解方法越来越多地应用于计算电磁学的各个领域.针对微波管中的永磁聚焦系统仿真,该文提出一种基于有限元的非重叠区域分解方法,其引入一种新型传输条件,并采用内罚的方式推导出有限元弱形式.该区域分解法的最大优势是不需要引入多余的未知量,并且最终集成的有限元矩阵满足对称正定性,适合采用预处理共轭梯度法进行矩阵方程的求解.该文仿真了多个微波管永磁聚焦系统,并与商业软件Maxwell进行了详细的对比,结果表明所提出的区域分解方法和Maxwell精度相当,却拥有着更加优越的计算性能. 相似文献
22.
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
23.
24.
Chuncheng Wei Zhen Liu Yun Wu Yeqing Liu Heng Zhang Peng Wang Qiyan Sun Lijuan Zhou 《Ceramics International》2021,47(13):18693-18698
Laminated Si3N4/SiCw ceramics were successfully prepared by tape casting and hot-pressing. Its mechanical properties were measured and the impact resistance was discussed. The toughness of the laminated Si3N4/SiCw ceramics was 13.5 MPa m1/2, which was almost 1.6 times that of Si3N4/SiCw composite ceramics, namely 8.5 MPa m1/2. Moreover, the indentation strength of laminated Si3N4/SiCw ceramics was not sensitive to increasing indentation loads and exhibited a rising R-curve behaviour, indicating that the laminated Si3N4/SiCw ceramics had excellent impact resistance. The improved toughness and impact resistance of laminated Si3N4/SiCw ceramics was attributed to the residual stress caused by a thermal expansion coefficient mismatch between the different layers, resulting in crack deflection and bridging of SiC whiskers in the interface layer, thus consuming a large amount of fracture work. 相似文献
25.
This article proposes an active balancer, which features bidirectional charge shuttling and adaptive equalization current control, to fast counterbalance the state of charge (SOC) of cells in a lithium-ion battery (LIB) string. The power circuit consists of certain bidirectional buck-boost converters to transfer energy among the different cells back and forth. Owing to the characterization of the open-circuit voltage (OCV) vs SOC in LIB being relatively smooth near the SOC middle range, the SOC-inspected balance strategy can achieve more precise and efficient equilibrium than the voltage-based control. Accordingly, a compensated OCV-based SOC estimation is put forward to take into account the discrepancy of SOC estimation. Besides, the varied-duty-cycle (VDC) and curve-fitting modulation (CFM) methods are devised herein to tackle the problems of slow equalization rate and low balance efficacy, which arise from the diminution in balancing current as the SOC difference between the cells decreases in the later duration of equalization especially. The proposed strategies have taken the battery nonlinear characteristic and circuit parameter nonideality into account and can adaptively modulate the duty cycle with the SOC difference to keep balancing current constant throughout the balancing cycle. Simulated and experimental results are given to demonstrate the feasibility and effectiveness of the same prototype constructed. Compared with the fixed duty cycle and the VDC methods, the proposed CFM has the best balancing efficiency of 81.4%, and the balance time is shortened by 27.1% and 18.6%, respectively. 相似文献
26.
Nan Wu Xiaodong Li Mu Zhang Yi Ren Qi Zhu Haijun Peng Hongqiang Ru Xudong Sun 《Journal of the European Ceramic Society》2021,41(4):2898-2907
Refining ceramic microstructures to the nanometric range to minimize light scattering provides an interesting methodology for developing novel optical ceramic materials. In this work, we reported the fabrication and properties of a new nanocomposite optical ceramic of Gd2O3-MgO. The citric acid sol-gel combustion method was adopted to fabricate Gd2O3-MgO nanocomposites with fine-grain sizes, dense microstructures and homogeneous phase domains. Nanopowders with low agglomeration and improved sinterability can be obtained by elaborating Φ values. Further refining of the microstructure of the nanocomposites was achieved by elaborating the hot-pressing conditions. The sample sintered at 65 MPa and 1300 °C showed a quite high hardness value of 14.3 ± 0.2 GPa, a high transmittance of 80.3 %–84.7 % over the 3?6 μm wavelength range, due mainly to its extremely fine-grain size of Gd2O3 and MgO (93 and 78 nm, respectively) and high density. 相似文献
27.
Fluorescence‐Activated Cell Sorters: Standing Surface Acoustic Wave (SSAW)‐Based Fluorescence‐Activated Cell Sorter (Small 40/2018) 下载免费PDF全文
28.
29.
针对传统铁矿石磁化焙烧技术与装备存在焙烧产品质量差、产能低、能耗高和环境污染严重等问题,创造性提出了一种“预热-蓄热还原-再氧化”悬浮磁化焙烧新工艺。该工艺具有原料适应性广、焙烧产品质量均匀、回收率高、生产能耗低、无污染等特点,适合处理赤铁矿、褐铁矿、菱铁矿及其混合型难选铁矿石。通过多年的潜心基础研究与技术攻关,形成了非均质矿石颗粒悬浮态流动控制、蓄热式高效低温还原、铁物相精准调控与余热同步回收等一系列关键技术,建成了500kg/h复杂难选铁矿石悬浮磁化焙烧-高效分选半工业试验平台。 相似文献
30.