全文获取类型
收费全文 | 6676篇 |
免费 | 834篇 |
国内免费 | 856篇 |
专业分类
电工技术 | 215篇 |
技术理论 | 1篇 |
综合类 | 238篇 |
化学工业 | 1193篇 |
金属工艺 | 291篇 |
机械仪表 | 846篇 |
建筑科学 | 296篇 |
矿业工程 | 57篇 |
能源动力 | 351篇 |
轻工业 | 108篇 |
水利工程 | 49篇 |
石油天然气 | 96篇 |
武器工业 | 34篇 |
无线电 | 1682篇 |
一般工业技术 | 1077篇 |
冶金工业 | 78篇 |
原子能技术 | 98篇 |
自动化技术 | 1656篇 |
出版年
2024年 | 3篇 |
2023年 | 47篇 |
2022年 | 45篇 |
2021年 | 50篇 |
2020年 | 102篇 |
2019年 | 66篇 |
2018年 | 49篇 |
2017年 | 139篇 |
2016年 | 138篇 |
2015年 | 157篇 |
2014年 | 244篇 |
2013年 | 354篇 |
2012年 | 674篇 |
2011年 | 738篇 |
2010年 | 791篇 |
2009年 | 849篇 |
2008年 | 800篇 |
2007年 | 1176篇 |
2006年 | 1062篇 |
2005年 | 443篇 |
2004年 | 108篇 |
2003年 | 58篇 |
2002年 | 54篇 |
2001年 | 59篇 |
2000年 | 39篇 |
1999年 | 39篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1990年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有8366条查询结果,搜索用时 15 毫秒
1.
《Ceramics International》2022,48(17):24716-24724
Dielectric capacitors show great potential in superior energy storage devices. However, the energy density of these capacitors is still inadequate to meet the requirement of energy storage applications. In this study, the Bi0.5Na0.47Li0.03TiO3-xNaNbO3 (BNLT-xNN) ceramics were prepared via conventional solid-phase reaction. Results showed that NN can efficaciously enhance the breakdown strength (Eb) and the relaxation behavior of the BNLT ceramic because of the broken ferroelectric long-range order. When x = 0.3, the maximum Eb reached 350 kV/cm, at which the 0.7BNLT-0.3NN ceramic exhibited the high recoverable energy storage density (Wrec) of 4.83 J/cm3 and great efficiency (η) of 78.9%. The ceramic demonstrated good temperature stability at 20 °C-160 °C and excellent fatigue resistance. Additionally, the 0.7BNLT-0.3NN ceramic presented high power density (PD; ~77.58 MW/cm3), large current density (CD; ~861.99 A/cm2), and quite short discharge time (t0.9; ~0.090 μs). These results indicated that the 0.7BNLT-0.3NN material has excellent energy storage properties and various application prospects. 相似文献
2.
3.
4.
《中国稀土学报(英文版)》2020,38(5):571-576
The Eu(III) nitrate complex of the meso- N,N′-bis(2-pyridylmethylene)-1,2-(R,S)-cyclohexanediamine ligand was synthesized and characterized by single crystal and powder X-ray diffraction. The crystal lattice of the complex is capable of absorbing and desorbing selectively acetonitrile molecules, at 293 K upon an acetonitrile vapor pressure of ∼0.1 × 105 Pa. This process, which is partially reversible, can be easily followed by both powder X-ray diffraction (P-XRD) and Eu(III) luminescence spectroscopy. The acetonitrile molecule, located in the outer coordination sphere of the metal ion, does not affect the radiative transition probability of 5D0 level of Eu(III) and also it does not activate further non-radiative channels from this level. On the other hand, this molecule is capable of affecting the energy position and intensities of the crystal field components of the 5D0→7F2 transition. The complex in solid form can be considered a promising material for the optical sensing of acetonitrile vapors. 相似文献
5.
图像增强在提高SAR图像舰船目标检测精度方面具有十分重要的意义。由于传统算法不能很好地对SAR图像进行目标增强,提出了基于改进粗糙集理论和引力场强度的目标增强算法。通过借鉴引力场相关理论知识,将粗糙集条件属性集中的梯度属性改进为引力场强度属性,从而实现对原图像的目标增强。与其他算法进行了实验比较,结果表明提出的改进算法相比于其他算法更适用于SAR图像特性,能更好地对舰船目标像素进行针对性增强,具备一定的工程应用价值。 相似文献
6.
Yuhuan Sun Hongshuang Qin Zhengqing Yan Chuanqi Zhao Jinsong Ren Xiaogang Qu 《Advanced functional materials》2019,29(14)
Recently, quorum sensing (QS) inhibitors (QSIs) have been combined with antibiotics to enhance antibiofilm efficacy in vitro and in vivo. However, targeting QS signals alone is not enough to prevent bacterial infections. Drug resistance and recurrence of biofilms makes it difficult to eradicate. Herein, photodynamic therapy (PDT) is selected to unite QSIs and antibiotics. A synergistically antibiofilm system, which combines QSIs, antibiotics, and PDT based on hollow carbon nitride spheres (HCNSs) is envisaged. First, HCNS provides the multidrug delivering ability, enabling QSIs and antibiotics to be released in sequence. Subsequently, multistage releases sensitize bacteria effectively, potentiating the chemotherapeutic effects of the antibiotics. Finally, the integration of QSIs and PDT not only minimizes the possibility of drug resistance, but also overcomes the problem of limited mass and extension of PDT. Even after 48 h of incubation, the bacterial biofilm is obviously inhibited. And its biofilm disperse efficiency exceeds 48% (compared with QSI‐potentiated chemotherapy group) and 40% (compared with PDT group). Besides, the inhibition of the QS system influences phenotypes related to virulence factor production and surface hydrophobicity, which weaken biofilm invasion and formation. Eventually, this system is applied to disperse bacterial biofilm in vivo. Overall, PDT and QS modulation are devoted to eradicate drug resistance and recurrence of the biofilm. 相似文献
7.
《中国稀土学报(英文版)》2020,38(5):523-530
A multidisciplinary approach for the production and characterization of a series of high concentration Er~(3+)activated SrLaGa_3 O_7(abbreviated as Er:SLGO) crystal fibers is shown to have a great promise for implementation in mid-infrared laser applications.The current approach includes the design and formation of unique layered tetrahedral network structures with several kinds of rare earth(RE) ions including Er ions distributing statistically between layers,such as Er:SLGO,Er,Nd:SLGO,Er,Yb,Ho:SLGO,Er,Eu:SLGO and Er,Ho:SLGO.Five kinds of Er:SLGO crystal fibers were designed to grow via a micropulling down method.Spectroscopic analyses show that Er,Yb,Ho:SLGO and Nd,Er:SLGO crystal fibers were superiorly endowed with inhomogeneous broadening absorption and strong emission.The unique structural components design enables the generation of improved absorption and emission recombination,and the inhibition of self-termination as well.Generally,the use of structural components design may warrant high-efficiency emissions in RE-doped crystal fibers. 相似文献
8.
《International Journal of Hydrogen Energy》2020,45(11):6529-6537
MnO-MnCx coated carbon nanotubes (MnO/MnCx/CNTs) nanocomposites were prepared by a one-pot deposition method. The coating consisted of MnO, Mn5C2, Mn15C4 and Mn23C6 was formed on the surface of CNTs by heating a mixture of Mn particles and CNTs at 600 °C for 40 min under vacuum. Then after heated MnO/MnCx/CNTs in air at 350 °C for 2 h, MnO nanoparticles were partially converted to Mn3O4 nanosheets. Then Mn3O4-MnCx coated carbon nanotubes (Mn3O4/MnCx/CNTs) composed of interconnected nanosheets structure were successfully synthesized by a two-step method of one-pot deposition and heat post-treatment. The Mn3O4/MnCx/CNTs showed better oxygen reduction reaction performance in alkaline condition than MnO/MnCx/CNTs and pristine CNTs. Besides, the formed MnCx (Mn5C2 and Mn23C6) by one-pot deposition method provided a strong interface bonding between Mn3O4 and CNTs, leading to improved stability of Mn3O4/MnCx/CNTs as an electrode material. 相似文献
9.
《International Journal of Hydrogen Energy》2020,45(31):15571-15577
Here, the storage sites of hydrogen in FeCr alloy, namely (H, He)–V nano-clusters with open volume, have been investigated by first-principles calculations and positron annihilation spectroscopy. The positron lifetimes in the nano-clusters obtained by theoretical calculations and experiments were compared. These results suggest that positron is sensitive to the relative position of the gas atoms decorating the open volume; and a helium atom forms a more repulsive ion core than a hydrogen atom when it occupies the vacancy, resulting in a decrease in positron lifetime. Interpretation of the PAS data was successfully combined with theoretical calculations, and allowed us to determine the defect status in specimens after H/He irradiation with different implantation patterns. The speculated kinds of hydrogen storage sites formed after irradiation are summarized. For the He-ions pre-implanted situation, the helium-vacancy clusters or bubbles forming in advance may recombine with H atoms to form stable He–H–V complex. 相似文献
10.
We investigated the resistive switching characteristics of a polystyrene:ZnO–graphene quantum dots system and its potential application in a one diode-one resistor architecture of an organic memory cell. The log–log I–V plot and the temperature-variable I–V measurements revealed that the switching mechanism in a low-current state is closely related to thermally activated transport. The turn-on process was induced by a space-charge-limited current mechanism resulted from the ZnO–graphene quantum dots acting as charge trap sites, and charge transfer through filamentary path. The memory device with a diode presented a ∼103 ION/IOFF ratio, stable endurance cycles (102 cycles) and retention times (104 s), and uniform cell-to-cell switching. The one diode-one resistor architecture can effectively reduce cross-talk issue and realize a cross bar array as large as ∼3 kbit in the readout margin estimation. Furthermore, a specific word was encoded using the standard ASCII character code. 相似文献