全文获取类型
收费全文 | 94166篇 |
免费 | 8575篇 |
国内免费 | 5170篇 |
学科分类
工业技术 | 107911篇 |
出版年
2024年 | 137篇 |
2023年 | 1124篇 |
2022年 | 1860篇 |
2021年 | 2923篇 |
2020年 | 2393篇 |
2019年 | 2092篇 |
2018年 | 2276篇 |
2017年 | 2555篇 |
2016年 | 2493篇 |
2015年 | 3454篇 |
2014年 | 4615篇 |
2013年 | 5535篇 |
2012年 | 6562篇 |
2011年 | 7109篇 |
2010年 | 6332篇 |
2009年 | 6221篇 |
2008年 | 6244篇 |
2007年 | 6025篇 |
2006年 | 5892篇 |
2005年 | 4932篇 |
2004年 | 3887篇 |
2003年 | 3512篇 |
2002年 | 4113篇 |
2001年 | 3477篇 |
2000年 | 2516篇 |
1999年 | 1998篇 |
1998年 | 1398篇 |
1997年 | 1152篇 |
1996年 | 1061篇 |
1995年 | 929篇 |
1994年 | 748篇 |
1993年 | 524篇 |
1992年 | 411篇 |
1991年 | 312篇 |
1990年 | 260篇 |
1989年 | 175篇 |
1988年 | 150篇 |
1987年 | 109篇 |
1986年 | 57篇 |
1985年 | 57篇 |
1984年 | 53篇 |
1983年 | 41篇 |
1982年 | 34篇 |
1981年 | 27篇 |
1980年 | 27篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 19篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
61.
Siyao Li Shoulei Xu Xiangyu Wang Daini Wang Bernard A. Goodman Xing Hong Wen Deng 《Ceramics International》2021,47(3):3346-3353
Cubic zirconia single crystals stabilized with yttria and doped with Gd2O3 (0.10–5.00 mol%) were prepared by the optical floating zone method, and characterized by a combination of X-ray diffraction (XRD), and Raman, electron paramagnetic resonance (EPR), ultraviolet–visible (UV–Vis), photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopic techniques. XRD and Raman spectroscopy showed that the crystal samples were all in the cubic phase, whereas the ceramic sample consisted of a mixture of monoclinic and cubic phases. The absorption spectrum showed four peaks at 245, 273, 308, and 314 nm in the ultraviolet region, and the optical band gap differed between samples with ≤3.00 mol% and those with >3.00 mol% Gd2O3. The emission spectrum showed a weak peak at 308 nm and a strong peak at 314 nm, which are attributed to the 6P5/2 → 8S7/2 and 6P7/2 → 8S7/2 transitions of Gd3+, respectively. The intensities of the peaks in the excitation and emission spectra increased with Gd3+ concentration, reached a maximum at 2.00 mol%, then decreased with higher concentrations. This quenching is considered to be the result of the electric dipole-dipole interactions, and this interpretation is supported by the Gd3+ EPR spectra, which showed progressive broadening with increasing Gd3+ concentration throughout the concentration range investigated. 相似文献
62.
Xiaohu Ren Xilou Pu Hongfeng Yin Yun Tang Hudie Yuan Huiqing Fan 《Ceramics International》2021,47(9):12122-12129
Hexagonal barium ferries is a promising and efficient microwave (MW) absorbing material, but the low dielectric loss and poor conductivity have limited their extensive applications. In this work, a simple tactic of coating conductive polymer PANI on hexaferrite BaCo2Fe16O27 is presented, wherein the dielectric properties are customized, and more significantly, the electromagnetic loss is greatly enhanced. As displayed from structural characterizations, PANI were coated equably on the surface of hexaferrite grains by an in-situ polymerization process. The outcomes exhibit the as-prepared PANI@hexaferrite composite has remarkable electromagnetic wave absorption capacity. When the thickness is 6.0 mm, the minimal RL of ?40.4 dB was achieved at 2.9 GHz. The effective absorption bandwidth (RL < ?20 dB) of 0.65 GHz, 0.53 GHz, 0.65 GHz, 0.52 GHz, 0.46 GHz and 0.39 GHz was achieved separately when the thickness ranges from 4 to 9 mm. The highly efficient MW absorbing performance of PANI@hexaferrite composite were the consequence of multiple loss mechanisms and perfect impedance matching. It is demonstrated that the PANI@hexaferrite composite with excellent MW absorption performance is expected to be potential MW absorbers for extensive applications. 相似文献
63.
Form selection of concomitant polymorphs: A case study informed by crystallization kinetics modeling
Weiwei Tang Yufeng Quan Junbo Gong Jingkang Wang Qiuxiang Yin Tonglei Li 《American Institute of Chemical Engineers》2021,67(4):e17129
Molecular mechanisms and process kinetics of crystallizing concomitant polymorphs remain poorly understood. Solvent-mediated phase transformation and concomitant crystallization are difficult to be distinguished in practice, as multiple forms can be detected at the same time. Herein, we developed a population balance model to simulate a concomitant crystallization process of two polymorphs of tolfenamic acid. Our kinetic modeling aims to understand concomitant crystallization and help guide form selection of such a molecular system. Crystallization kinetics of ethanolic solutions were uncovered from induction time measurements, as well as seeded and unseeded crystallization experiments. Experimental and simulation results demonstrate that the stable form I crystallizes concomitantly with the metastable form II. The faster growing form II results in an intermediate decline in the composition of form I in crystallized samples, a characteristic feature of the concomitantly crystallized system. A four-quadrant scheme of attainable polymorph outcome was simulated under various crystallization conditions. 相似文献
64.
Prof. Tsung-Shing Andrew Wang Ruo-Yu Wu Yu Hong Dr. Zhe-Chong Wang Dr. Tsung-Lin Li Dr. Jiun-Jie Shie Prof. Cheng-Chih Hsu 《Chembiochem : a European journal of chemical biology》2021,22(14):2415-2419
Secondary metabolites are structurally diverse natural products (NPs) and have been widely used for medical applications. Developing new tools to enrich NPs can be a promising solution to isolate novel NPs from the native and complex samples. Here, we developed native and deuterated chemoselective labeling probes to target phenol-containing glycopeptides by the ene-type labeling used in proteomic research. The clickable azido-linker was included for further biotin functionalization to facilitate the enrichment of labeled substrates. Afterward, our chemoselective method, in conjunction with LC-MS and MSn analysis, was demonstrated in bacterial cultures. A vancomycin-related phenol-containing glycopeptide was labeled and characterized by our labeling strategy, showing its potential in glycopeptide discovery in complex environments. 相似文献
65.
Seulah Lee Yeon Ji Suh Seonguk Yang Dong Geun Hong Akihito Ishigami Hangun Kim Jae-Seoun Hur Seung-Cheol Chang Jaewon Lee 《International journal of molecular sciences》2021,22(4)
Oxidative stress, mitochondrial dysfunction, and neuroinflammation are strongly associated with the pathogenesis of Parkinson’s disease (PD), which suggests that anti-oxidative and anti-inflammatory compounds might provide an alternative treatment for PD. Here, we evaluated the neuroprotective effects of evernic aid (EA), which was screened from a lichen library provided by the Korean Lichen Research Institute at Sunchon National University. EA is a secondary metabolite generated by lichens, including Ramalina, Evernia, and Hypogymnia, and several studies have described its anticancer, antifungal, and antimicrobial effects. However, the neuroprotective effects of EA have not been studied. We found that EA protected primary cultured neurons against 1-methyl-4-phenylpyridium (MPP+)-induced cell death, mitochondrial dysfunction, and oxidative stress, and effectively reduced MPP+-induced astroglial activation by inhibiting the NF-κB pathway. In vivo, EA ameliorated MPTP-induced motor dysfunction, dopaminergic neuronal loss, and neuroinflammation in the nigrostriatal pathway in C57BL/6 mice. Taken together, our findings demonstrate that EA has neuroprotective and anti-inflammatory effects in PD models and suggest that EA is a potential therapeutic candidate for PD. 相似文献
66.
Wonjun Choi Sungjae Hong Yeonsu Jeong Yongjae Cho Hyung Gon Shin Ji Hoon Park Yeonjin Yi Seongil Im 《Advanced functional materials》2021,31(9):2009436
Among many of 2D semiconductor-based devices, type III PN junction diodes are given special attentions due to their unique function, negative differential resistance (NDR). However, it has been found uneasy to achieve well-matched type III PN junctions from 2D–2D van der Waals heterojunctions. Here, the authors present other alternatives of type III heterojunctions, using 2D p-MoTe2/organic n-type dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) and 2D p-WSe2/n-MoOx systems. Those junction diodes appear to well-demonstrate static and dynamic NDR behavior via resonant tunneling and electron–hole recombination. Extended to an inverter circuit, p-MoTe2/n-HAT-CN diode enables multilevel inverter characteristics as monolithically integrated with p-MoTe2 channel field effect transistor. The same NDR diode shows dynamic LC oscillation behavior under a constant DC voltage, connected to an external inductor. From p-WSe2/n-MoOx oxide diode, similar NDR behavior to those of p-MoTe2/n-HAT-CN is again observed along with LC oscillations. The authors attribute these visible oscillation results to high peak-to-valley current ratios of their organic or oxide/2D heterojunction diodes. 相似文献
67.
Yunxia Liu Hui Wang Daiyan Chen Lin Gao Xin Wang Xian Jian Chunhong Mu Xin Xu Yujie Zhao Liangjun Yin 《Ceramics International》2021,47(3):3244-3251
Chemical stability of phosphors is critical to the efficiency and lifetime of the white light-emitting diodes. Therefore, many strategies have been adopted to improve the stability of phosphors. However, it is still lack of report on the improvement of thermal stability and hydrolysis resistance of phosphors by a single layer coating. Due to the high transmittance and high chemical inertness of graphene, it was coated on the surface of Sr2Si5N8:Eu2+ phosphor by chemical vapor deposition, aiming to improve its thermal stability and hydrolysis resistance. The chemical composition and microstructure of the coating were characterized and analyzed. A nanoscale carbon layer was attached on the surface of Sr2Si5N8:Eu2+ phosphor particles in an amorphous state. In coated Sr2Si5N8:Eu2+ phosphor, the oxidation degree of Eu2+ to Eu3+ was significantly suppressed. At the same time, the surface of Sr2Si5N8:Eu2+ particle turned from hydrophilic to hydrophobic after carbon coating, and consequently the hydrolysis resistance of Sr2Si5N8:Eu2+ phosphor was greatly improved. After tests at 85 °C and 85% humidity for 200 h, the carbon coated Sr2Si5N8:Eu2+ phosphor still maintained about 95% of its initial luminous intensity as compared with 35% of the uncoated. By observing the in-situ microstructure evolution of coated phosphor in air-water vapor environment, remained presence of the carbon layer even at 500 °C explained the excellent chemical stability of carbon coated Sr2Si5N8:Eu2+ phosphor in complex environment. These results indicate that a nanoscale carbon layer can be used to provide superior thermal stability and hydrolysis resistance of (oxy) nitrides phosphors. 相似文献
68.
69.
The carbon vacancy in high-entropy carbides (HECs) has a significant impact on their physical and chemical properties, yet relevant studies have still been relatively few. In this study, we investigate the surface energies of HECs with variable carbon vacancies through first-principles calculations. The results show that the surface energy of the (1 0 0) surface of the stoichiometric HECs is significantly lower than that of (1 1 1) surface. With the decrease in carbon stoichiometry, the surface energies of both (1 0 0) and (1 1 1) surfaces increase gradually, which is mainly due to the weakening of covalent bonding and the decrease of metal Hirshfeld-I (HI) charges. However, the surface energy of (1 0 0) surface increases more quickly than that of (1 1 1) surface and will exceed that of (1 1 1) surface when the carbon stoichiometry decreases to a certain extent, which is primarily attributed to the greater decrease rate of metal HI charges of (1 0 0) surface. 相似文献
70.
Hua Yang Shi-Xiao Wei Han Chen Lang Chen Chak-Tong Au Ting-Liang Xie Shuang-Feng Yin 《American Institute of Chemical Engineers》2022,68(10):e17810
A high-throughput (105.5 g/h) passive four-stage asymmetric oscillating feedback microreactor using chaotic mixing mechanism was developed to prepare aggregated Barium sulfate (BaSO4) particles of high primary nanoparticle size uniformity. Three-dimensional unsteady simulations showed that chaotic mixing could be induced by three unique secondary flows (i.e., vortex, recirculation, and oscillation), and the fluid oscillation mechanism was examined in detail. Simulations and Villermaux–Dushman experiments indicate that almost complete mixing down to molecular level can be achieved and the prepared BaSO4 nanoparticles were with narrow primary particle size distribution (PSD) having geometric standard deviation, σg, less than 1.43 when the total volumetric flow rate Qtotal was larger than 10 ml/min. By selecting Qtotal and reactant concentrations, average primary particle size can be controlled from 23 to 109 nm as determined by microscopy. An average size of 26 nm with narrow primary PSD (σg = 1.22) could be achieved at Qtotal of 160 ml/min. 相似文献